12 LVPECL/24 CMOS Output Clock
Generator with Integrated 2 GHz VCO
Data Sheet
AD9520-3
Rev. A Document Feedback
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FEATURES
Low phase noise, phase-locked loop (PLL)
On-chip VCO tunes from 1.72 GHz to 2.25 GHz
Optional external 3.3 V/5 V VCO/VCXO to 2.4 GHz
1 differential or 2 single-ended reference inputs
Accepts CMOS, LVDS, or LVPECL references to 250 MHz
Accepts 16.62 MHz to 33.3 MHz crystal for reference input
Optional reference clock doubler
Reference monitoring capability
Automatic/manual reference holdover and reference
switchover modes, with revertive switching
Glitch-free switchover between references
Automatic recovery from holdover
Digital or analog lock detect, selectable
Optional zero delay operation
Twelve 1.6 GHz LVPECL outputs divided into 4 groups
Each group of 3 outputs shares a 1-to-32 divider with
phase delay
Additive output jitter as low as 225 fs rms
Channel-to-channel skew grouped outputs < 16 ps
Each LVPECL output can be configured as 2 CMOS outputs
(for fOUT ≤ 250 MHz)
Automatic synchronization of all outputs on power-up
Manual output synchronization available
SPI- and I²C-compatible serial control port
64-lead LFCSP
Nonvolatile EEPROM stores configuration settings
APPLICATIONS
Low jitter, low phase noise clock distribution
Clock generation and translation for SONET, 10Ge, 10GFC,
Synchronous Ethernet, OTU2/3/4
Forward error correction (G.710)
Clocking high speed ADCs, DACs, DDSs, DDCs, DUCs, MxFEs
High performance wireless transceivers
ATE and high performance instrumentation
Broadband infrastructures
GENERAL DESCRIPTION
The AD9520-31 provides a multioutput clock distribution
function with subpicosecond jitter performance, along with an
on-chip PLL and VCO. The on-chip VCO tunes from 1.72 GHz
to 2.25 GHz. An external 3.3 V/5 V VCO/VCXO of up to 2.4 GHz
can also be used.
FUNCTIONAL BLOCK DIAGRAM
OPTIONAL REF1
REF2
CLK
LF
SWITCHOVER
AND MONIT OR
PLL
DIVIDER
AND MUXES
ZERO
DELAY
CP
VCO
STATUS
MONITOR
SPI/I
2
C CONT ROL
PORT AND
DIGITAL LOGIC EEPROM AD9520
OUT0
OUT1
OUT2
DIV/Φ
OUT3
OUT4
OUT5
DIV/Φ
OUT6
OUT7
OUT8
DIV/Φ
OUT9
OUT10
OUT11
DIV/Φ
LVPECL/
CMOS
REFIN
REFIN
07216-001
Figure 1.
The AD9520 serial interface supports both SPI and I²C ports.
An in-package EEPROM, which can be programmed through the
serial interface, can store user-defined register settings for
power-up and chip reset.
The AD9520 features 12 LVPECL outputs in four groups. Any
of the 1.6 GHz LVPECL outputs can be reconfigured as two
250 MHz CMOS outputs. If an application requires LVDS
drivers instead of LVPECL drivers, refer to the AD9522.
Each group of three outputs has a divider that allows both the
divide ratio (from 1 to 32) and the phase offset or coarse time
delay to be set.
The AD9520 is available in a 64-lead LFCSP and can be operated
from a single 3.3 V supply. The external VCO can have an
operating voltage of up to 5.5 V. A separate output driver power
supply can be from 2.375 V to 3.465 V.
The AD9520-3 is specified for operation over the standard
industrial range of −40°C to +85°C.
1 AD9520 is used throughout this data sheet to refer to all the members of the AD9520 family. However, when AD9520-3 is used, it refers to that specific member of the
AD9520 family.
AD9520-3 Data Sheet
Rev. A | Page 2 of 80
TABLE OF CONTENTS
Features .............................................................................................. 1
Applications ....................................................................................... 1
General Description ......................................................................... 1
Functional Block Diagram .............................................................. 1
Revision History ............................................................................... 3
Specifications ..................................................................................... 4
Power Supply Requirements ....................................................... 4
PLL Characteristics ...................................................................... 4
Clock Inputs .................................................................................. 7
Clock Outputs ............................................................................... 7
Timing Characteristics ................................................................ 8
Clock Output Additive Phase Noise (Distribution Only;
VCO Divider Not Used) ............................................................ 10
Clock Output Absolute Phase Noise (Internal VCO Used) .. 11
Clock Output Absolute Time Jitter (Clock Generation
Using Internal VCO) .................................................................. 11
Clock Output Absolute Time Jitter (Clock Cleanup
Using Internal VCO) .................................................................. 11
Clock Output Absolute Time Jitter (Clock Generation
Using External VCXO) .............................................................. 12
Clock Output Additive Time Jitter (VCO Divider
Not Used) ..................................................................................... 12
Clock Output Additive Time Jitter (VCO Divider Used) ..... 12
Serial Control Port—SPI Mode ................................................ 13
Serial Control Port—IC Mode ................................................ 14
PD, EEPROM, RESET, and SYNC Pins .................................. 15
Serial Port Setup Pins—SP1, SP0 ............................................. 15
LD, STATUS, and REFMON Pins ............................................ 15
Power Dissipation ....................................................................... 16
Absolute Maximum Ratings .......................................................... 17
Thermal Resistance .................................................................... 17
ESD Caution ................................................................................ 17
Pin Configuration and Function Descriptions ........................... 18
Typical Performance Characteristics ........................................... 21
Terminology .................................................................................... 26
Detailed Block Diagram ................................................................ 27
Theory of Operation ...................................................................... 28
Operational Configurations ...................................................... 28
Zero Delay Operation ................................................................ 42
Clock Distribution ..................................................................... 43
Reset Modes ................................................................................ 49
Power-Down Modes .................................................................. 50
Serial Control Port ......................................................................... 51
SPI/IC Port Selection ................................................................ 51
IC Serial Port Operation .......................................................... 51
SPI Serial Port Operation .......................................................... 54
SPI Instruction Word (16 Bits) ................................................. 55
SPI MSB/LSB First Transfers .................................................... 55
EEPROM Operations ..................................................................... 58
Writing to the EEPROM ........................................................... 58
Reading from the EEPROM ..................................................... 58
Programming the EEPROM Buffer Segment ......................... 59
Thermal Performance .................................................................... 60
Register Map ................................................................................... 61
Register Map Descriptions ............................................................ 64
Applications Information .............................................................. 77
Frequency Planning Using the AD9520 .................................. 77
Using the AD9520 Outputs for ADC Clock Applications .... 77
CMOS Clock Distribution ........................................................ 78
Outline Dimensions ....................................................................... 80
Ordering Guide .......................................................................... 80
Data Sheet AD9520-3
Rev. A | Page 3 of 80
REVISION HISTORY
8/13—Rev. 0 to Rev. A
Changes to Features Section, Applications Section, and
General Description Section ............................................................ 1
Changes to Table 2 ............................................................................ 4
Changes to Input Frequency Parameter; Change to Input
Sensitivity, Differential Parameter Test Conditions/Comments,
Table 3 ................................................................................................. 7
Change to Output Differential Voltage, VOD Parameter Test
Conditions/Comments; Added Source Current and Sink
Current Parameters, Table 4 ............................................................ 7
Change to Output Skew, LVPECL Outputs Parameter, Test
Conditions/Comments, Table 5 ...................................................... 8
Reordered Figure 2 to Figure 4 ........................................................ 9
Change to Reset Timing, Pulse Width Low Parameter, Table 15 ... 15
Change to Maximum Power, Full Operation Parameter,
Internal VCO Value in Test Conditions/Comments, Table 18 . 16
Change to Junction Temperature, Table 19; Reformatted
Table 19 ............................................................................................. 17
Change to Table 21 .......................................................................... 18
Deleted Figure 13, Renumbered Sequentially ............................. 22
Reordered Figure 31 and Figure 32; Moved Figure 34 and
Figure 35 to PLL External Loop Filter Section, Page 35; Added
Figure 33, Renumbered Sequentially ............................................ 25
Change to Mode 0—Internal VCO and Clock Distribution
Section .............................................................................................. 28
Change to Configuration of the PLL Section; Changes to
Charge Pump (CP) Section ............................................................ 34
Changes to On-Chip VCO Section and PLL External Loop
Filter Section; Added Figure 40; Moved Figure 41 and Figure 42
from Typical Performance Characteristics Section to PLL
External Loop Filter Section; Changes to PLL Reference
Inputs Section .................................................................................. 35
Changes to Reference Switchover Section ................................... 36
Change to Prescaler Section and A and B Counters Section;
Changes to Table 29 ........................................................................ 37
Changes to Current Source Digital Lock Detect (CSDLD)
Section .............................................................................................. 38
Changes to Frequency Status Monitors Section and VCO
Calibration Section ......................................................................... 41
Added Table 31, Renumbered Sequentially; Change to
Internal Zero Delay Mode Section ................................................ 42
Change to External Zero Delay Mode Section ............................ 43
Change to Clock Frequency Division Section; Added Channel
Divider Maximum Frequency Section ......................................... 45
Reformatted Table 36 to Table 39 .................................................. 46
Change to Phase Offset or Coarse Time Delay Section ............. 47
Change to LVPECL Output Drivers Section; Changes to CMOS
Output Drivers Section; Change to Power-On Reset Section ... 49
Changes to Soft Reset via the Serial Port Section and Soft
Reset to Settings in EEPROM When EEPROM Pin = 0b
via the Serial Port Section .............................................................. 50
Change to Pin Descriptions Section, SPI Mode Operation
Section, and Write Section ............................................................. 54
Changes to SPI Instruction Word (16 Bits) Section ................... 55
Changes to EEPROM Operations Section, Writing to the
EEPROM Section, and Reading from the EEPROM Section ... 58
Changes to Programming the EEPROM Buffer Segment
Section and Register Section Definition Group Section;
Added Operational Codes Section Heading ............................... 59
Changes to Table 50 ........................................................................ 61
Added Unused Bits to Register Map Descriptions Section;
Changes to Address 0x000, Bit 5, and Added Address 0x003,
Table 51; Changes to Address 0x000, Bit 5, and Added
Address 0x003, Table 52 ................................................................. 64
Changes to Address 0x017, Table 54 ............................................ 66
Changes to Address 0x018, Bit 4 and Bits[2:1], Table 54 ........... 67
Change to Address 0x1A, Bit 6, Table 54 .....................................68
Changes to Address 0x01B, Bits[4:0], Table 54 ........................... 69
Changes to Address 0x191, Bit 5, and Address 0x194, Bit 5,
Table 56 ............................................................................................. 72
Changes to Address 0x197, Bit 5, Table 56 .................................. 73
Changes to Address 0x19A, Bit 5, Table 56 ................................. 74
Changes to Table 60 ........................................................................ 75
Changes to Address 0xB02, Bit 0, and Address 0xB03, Bit 0,
Table 61 ............................................................................................. 76
Change to Frequency Planning Using the AD9520 Section ..... 77
Added LVPECL Y-Termination and Far-End Thevenin
Termination Headings; Changes to CMOS Clock Distribution
Section .............................................................................................. 78
9/08—Revision 0: Initial Version
AD9520-3 Data Sheet
Rev. A | Page 4 of 80
SPECIFICATIONS
Typical is given for VS = VS_DRV = 3.3 V ± 5%; VS ≤ VCP ≤ 5.25 V; TA = 25°C; RSET = 4.12 kΩ; CPRSET = 5.1 kΩ, unless otherwise noted. Minimum
and maximum values are given over full VS and TA (−40°C to +85°C) variation.
POWER SUPPLY REQUIREMENTS
Table 1.
Parameter Min Typ Max Unit Test Conditions/Comments
POWER PINS
VS 3.135 3.3 3.465 V 3.3 V ± 5%
VS_DRV 2.375 VS V Nominally 2.5 V to 3.3 V ± 5%
VCP VS 5.25 V Nominally 3.3 V to 5.0 V ± 5%
CURRENT SET RESISTORS
RSET Pin Resistor 4.12 kΩ Sets internal biasing currents; connect to ground
CPRSET Pin Resistor 5.1 kΩ Sets internal CP current range, nominally 4.8 mA
(CP_lsb = 600 µA); actual current can be calculated by
CP_lsb = 3.06/CPRSET; connect to ground
BYPASS PIN CAPACITOR 220 nF Bypass for internal LDO regulator; necessary for LDO
stability; connect to ground
PLL CHARACTERISTICS
Table 2.
Parameter Min Typ Max Unit Test Conditions/Comments
VCO (ON CHIP)
Frequency Range 1720 2250 MHz
VCO Gain (K
VCO
)
47
MHz/V
See Figure 8
Tuning Voltage (VT) 0.5 VCP − 0.5 V VT ≤ VS when using internal VCO
Frequency Pushing (Open-Loop) 1 MHz/V
Phase Noise at 1 kHz Offset −55 dBc/Hz f = 2000 MHz
Phase Noise at 100 kHz Offset −110 dBc/Hz f = 2000 MHz
Phase Noise at 1 MHz Offset −129 dBc/Hz f = 2000 MHz
REFERENCE INPUTS
Differential Mode (REFIN, REFIN) Differential mode (can accommodate single-ended
input by ac grounding undriven input)
Input Frequency 0 250 MHz Frequencies below about 1 MHz should be dc-coupled;
be careful to match VCM (self-bias voltage)
Input Sensitivity 280 mV p-p PLL figure of merit (FOM) increases with increasing slew
rate (see Figure 12); the input sensitivity is sufficient for
ac-coupled LVDS and LVPECL signals
Self-Bias Voltage, REFIN 1.35 1.60 1.75 V Self-bias voltage of REFIN1
Self-Bias Voltage, REFIN 1.30 1.50 1.60 V Self-bias voltage of REFIN1
Input Resistance, REFIN 4.0 4.8 5.9 kΩ Self-biased1
Input Resistance, REFIN
4.4
5.3
kΩ
Self-biased1
Dual Single-Ended Mode (REF1, REF2) Two single-ended CMOS-compatible inputs
Input Frequency (AC-Coupled) with DC
Offset Off)
10 250 MHz Slew rate must be >50 V/µs
Input Frequency (AC-Coupled with
DC Offset On)
250 MHz Slew rate must be >50 V/µs, and input amplitude
sensitivity specification must be met; see the input
sensitivity parameter
Input Frequency (DC-Coupled) 0 250 MHz Slew rate > 50 V/µs; CMOS levels
Input Sensitivity (AC-Coupled with
DC Offset Off)
0.55 3.28 V p-p VIH should not exceed VS
Input Sensitivity (AC-Coupled with
DC Offset On)
1.5 2.78 V p-p VIH should not exceed VS
Input Logic High, DC Offset Off 2.0 V
Input Logic Low, DC Offset Off 0.8 V
Input Current −100 +100 µA
Input Capacitance 2 pF Each pin, REFIN (REF1)/REFIN (REF2)
Data Sheet AD9520-3
Rev. A | Page 5 of 80
Parameter Min Typ Max Unit Test Conditions/Comments
Pulse Width High/Low 1.8 ns The amount of time that a square wave is high/low;
determines the allowable input duty cycle
Crystal Oscillator
Crystal Resonator Frequency Range 16.62 33.33 MHz
Maximum Crystal Motional Resistance 30 Ω
PHASE/FREQUENCY DETECTOR (PFD)
PFD Input Frequency 100 MHz Antibacklash pulse width = 1.3 ns
45 MHz Antibacklash pulse width = 2.9 ns
Reference Input Clock Doubler Frequency 0.004 50 MHz
Antibacklash Pulse Width 1.3 ns Register 0x017[1:0] = 01b
2.9 ns Register 0x017[1:0] = 00b; Register 0x017[1:0] = 11b
6.0 ns Register 0x017[1:0] = 10b
CHARGE PUMP (CP)
CP
V
is the CP pin voltage; V
CP
is the charge pump power
supply voltage (VCP pin)
ICP Sink/Source Programmable
High Value 4.8 mA With CPRSET = 5.1 kΩ; higher ICP is possible by changing
CPRSET
Low Value 0.60 mA With CPRSET = 5.1 kΩ; lower ICP is possible by changing
CPRSET
Absolute Accuracy 2.5 % CPV = VCP/2
CPRSET Range 2.7 10 kΩ
ICP High Impedance Mode Leakage 1 nA
Sink-and-Source Current Matching 1 % 0.5 V < CPV < VCP − 0.5 V; CPV is the CP pin voltage;
VCP is the charge pump power supply voltage (VCP pin)
ICP vs. VCP 1.5 % 0.5 V < CPV < VCP − 0.5 V
I
CP
vs. Temperature
2
%
CP
V
= V
CP
/2
PRESCALER (PART OF N DIVIDER)
Prescaler Input Frequency
P = 1 FD 300 MHz
P = 2 FD
MHz
P = 3 FD 900 MHz
P = 2 DM (2/3) 200 MHz
P = 4 DM (4/5) 1000 MHz
P = 8 DM (8/9) 2400 MHz
P = 16 DM (16/17)
MHz
P = 32 DM (32/33) 3000 MHz
Prescaler Output Frequency 300 MHz A, B counter input frequency (prescaler input
frequency divided by P)
PLL N DIVIDER DELAY Register 0x019[2:0]; see Table 54
000 Off
001 385 ps
010 486 ps
011 623 ps
100
730
ps
101 852 ps
110 976 ps
111 1101 ps
PLL R DIVIDER DELAY
Register 0x019[5:3]; see Table 54
000 Off
001 365 ps
010 486 ps
011 608 ps
100 730 ps
101 852 ps
110 976 ps
111 1101 ps
AD9520-3 Data Sheet
Rev. A | Page 6 of 80
Parameter Min Typ Max Unit Test Conditions/Comments
PHASE OFFSET IN ZERO DELAY REF refers to REFIN (REF1)/REFIN (REF2)
Phase Offset (REF-to-LVPECL Clock Output
Pins) in Internal Zero Delay Mode
560 1060 1310 ps When N delay and R delay are bypassed
Phase Offset (REF-to-LVPECL Clock Output
Pins) in Internal Zero Delay Mode
−320 +50 +240 ps When N delay setting = 110b, and R delay is bypassed
Phase Offset (REF-to-CLK Input Pins) in
External Zero Delay Mode
140 630 870 ps When N delay and R delay are bypassed
Phase Offset (REF-to-CLK Input Pins) in
External Zero Delay Mode
−460
−20
ps
When N delay setting = 011b, and R delay is bypassed
NOISE CHARACTERISTICS
In-Band Phase Noise of the Charge Pump/
Phase Frequency Detector 2
The PLL in-band phase noise floor is estimated by
measuring the in-band phase noise at the output of the
VCO and subtracting 20 log(N) (where N is the value of
the N divider).
500 kHz PFD Frequency −165 dBc/Hz
1 MHz PFD Frequency −162 dBc/Hz
10 MHz PFD Frequency −152 dBc/Hz
50 MHz PFD Frequency −144 dBc/Hz
PLL Figure of Merit (FOM) −222 dBc/Hz Reference slew rate > 0.5 V/ns; FOM + 10 log(fPFD) is an
approximation of the PFD/CP in-band phase noise (in the
flat region) inside the PLL loop bandwidth; when
running closed-loop, the phase noise, as observed at the
VCO output, is increased by 20 log(N); PLL figure of merit
decreases with decreasing slew rate; see Figure 12
PLL DIGITAL LOCK DETECT WINDOW3 Signal available at the LD, STATUS, and REFMON pins
when selected by appropriate register settings; the lock
detect threshold varies linearly with the value of the
CPRSET resistor
Lock Threshold (Coincidence of Edges) Selected by Register 0x017[1:0] and Register 0x018[4]
(this is the threshold to go from unlock to lock)
Low Range (ABP 1.3 ns, 2.9 ns) 3.5 ns Register 0x017[1:0] = 00b, 01b,11b;
Register 0x018[4] = 1b
High Range (ABP 1.3 ns, 2.9 ns) 7.5 ns Register 0x017[1:0] = 00b, 01b, 11b;
Register 0x018[4] = 0b
High Range (ABP 6.0 ns) 3.5 ns Register 0x017[1:0] = 10b; Register 0x018[4] = 0b
Unlock Threshold (Hysteresis)3 Selected by Register 0x017[1:0] and Register 0x018[4] (this
is the threshold to go from lock to unlock)
Low Range (ABP 1.3 ns, 2.9 ns) 7 ns Register 0x017[1:0] = 00b, 01b, 11b;
Register 0x018[4] = 1b
High Range (ABP 1.3 ns, 2.9 ns) 15 ns Register 0x017[1:0] = 00b, 01b, 11b;
Register 0x018[4] = 0b
High Range (ABP 6.0 ns) 11 ns Register 0x017[1:0] = 10b; Register 0x018[4] = 0b
1 The REFIN and REFIN self-bias points are offset slightly to avoid chatter on an open input condition.
2 In-band means within the LBW of the PLL.
3 For reliable operation of the digital lock detect, the period of the PFD frequency must be greater than the unlock-after-lock time.
Data Sheet AD9520-3
Rev. A | Page 7 of 80
CLOCK INPUTS
Table 3.
Parameter Min Typ Max Unit Test Conditions/Comments
CLOCK INPUTS (CLK, CLK) Differential input
Input Frequency
01
2.4
GHz
High frequency distribution (VCO divider)
01 2.0 GHz Distribution only (VCO divider bypassed); this is the
frequency range supported by the channel divider for
all divide ratios except divide-by-17 and divide-by-3
01 1.6 GHz Distribution only (VCO divider bypassed); this is the
frequency range supported by all channel divider ratios
Input Sensitivity, Differential 150 mV p-p Measured at 2.4 GHz; jitter performance is improved
with slew rates > 1 V/ns; the input sensitivity is
sufficient for ac-coupled LVDS and LVPECL signals
Input Level, Differential 2 V p-p Larger voltage swings can turn on the protection
diodes and can degrade jitter performance
Input Common-Mode Voltage, VCM 1.3 1.57 1.8 V Self-biased; enables ac coupling
Input Common-Mode Range, VCMR 1.3 1.8 V With 200 mV p-p signal applied; dc-coupled
Input Sensitivity, Single-Ended
150
mV p-p
CLK ac-coupled; CLK ac-bypassed to RF ground
Input Resistance 3.9 4.7 5.7 kΩ Self-biased
Input Capacitance 2 pF
1 Below about 1 MHz, the input should be dc-coupled. Care should be taken to match VCM.
CLOCK OUTPUTS
Table 4.
Parameter Min Typ Max Unit Test Conditions/Comments
LVPECL CLOCK OUTPUTS Termination = 50 Ω to VS_DRV − 2 V
OUT0, OUT1, OUT2, OUT3, OUT4,
OUT5, OUT6, OUT7, OUT8,
OUT9, OUT10, OUT11
Differential (OUT, OUT)
Output Frequency, Maximum 2400 MHz Using direct to output (see Figure 20); higher
frequencies are possible, but the resulting amplitude
does not meet the VOD specification; the maximum
output frequency is limited by either the maximum VCO
frequency or the frequency at the CLK inputs,
depending on the AD9520 configuration
Output High Voltage, V
OH
V
S_DRV
− 1.07
V
S_DRV
− 0.96
V
S_DRV
− 0.84
V
Output Low Voltage, VOL VS_DRV − 1.95 VS_DRV − 1.79 VS_DRV − 1.64 V
Output Differential Voltage, VOD 660 820 950 mV VOH − VOL for each leg of a differential pair for default
amplitude setting with the driver not toggling; the
peak-to-peak amplitude measured using a differential
probe across the differential pair with the driver
toggling is roughly 2× these values (see Figure 20 for
variation over frequency)
CMOS CLOCK OUTPUTS
OUT0A, OUT0B, OUT1A, OUT1B,
OUT2A, OUT2B, OUT3A, OUT3B,
OUT4A, OUT4B, OUT5A, OUT5B,
OUT6A, OUT6B, OUT7A, OUT7B,
OUT8A, OUT8B, OUT9A, OUT9B,
OUT10A, OUT10B, OUT11A,
OUT11B
Single-ended; termination = 10 pF
Output Frequency
250
MHz
See Figure 21
Output Voltage High, VOH VS − 0.1 V 1 mA load, VS_DRV = 3.3 V/2.5 V
Output Voltage Low, VOL 0.1 V 1 mA load, VS_DRV = 3.3 V/2.5 V
Output Voltage High, VOH 2.7 V 10 mA load VS_DRV = 3.3 V
Output Voltage Low, VOL 0.5 V 10 mA load, VS_DRV = 3.3 V
Output Voltage High, VOH 1.8 V 10 mA load, VS_DRV = 2.5 V
Output Voltage Low, V
OL
0.6
V
10 mA load, V
S_DRV
= 2.5 V
AD9520-3 Data Sheet
Rev. A | Page 8 of 80
Parameter Min Typ Max Unit Test Conditions/Comments
Source Current Damage to the part can result if values are exceeded
Static 20 mA
Dynamic 16 mA
Sink Current Damage to the part can result if values are exceeded
Static 8 mA
Dynamic 16 mA
TIMING CHARACTERISTICS
Table 5.
Parameter
Min
Typ
Max
Unit
Test Conditions/Comments
LVPECL OUTPUT RISE/FALL TIMES Termination = 50 Ω to VS_DRV − 2 V
Output Rise Time, t
RP
130
170
ps
20% to 80%, measured differentially (rise/fall times
are independent of VS and are valid for VS_DRV = 3.3 V
and 2.5 V)
Output Fall Time, tFP 130 170 ps 80% to 20%, measured differentially (rise/fall times
are independent of VS and are valid for VS_DRV = 3.3 V
and 2.5 V)
PROPAGATION DELAY, tPECL,
CLK-TO-LVPECL OUTPUT
For All Divide Values 850 1050 1280 ps High frequency clock distribution configuration
800
970
1180
ps
Clock distribution configuration
Variation with Temperature 1.0 ps/°C
OUTPUT SKEW, LVPECL OUTPUTS1 Termination = 50 Ω to VS_DRV – 2 V
LVPECL Outputs Sharing the Same
Divider
5 16 ps VS_DRV = 3.3 V
5 20 ps VS_DRV = 2.5 V
LVPECL Outputs on Different
Dividers
5 45 ps VS_DRV = 3.3 V
5 60 ps VS_DRV = 2.5 V
All LVPECL Outputs Across
Multiple Parts
190
ps
V
S_DRV
= 3.3 V and 2.5 V
CMOS OUTPUT RISE/FALL TIMES Termination = open
Output Rise Time, tRC 750 960 ps 20% to 80%; CLOAD = 10 pF; VS_DRV = 3.3 V
Output Fall Time, tFC 715 890 ps 80% to 20%; CLOAD = 10 pF; VS_DRV = 3.3 V
Output Rise Time, tRC 965 1280 ps 20% to 80%; CLOAD = 10 pF; VS_DRV = 2.5 V
Output Fall Time, tFC 890 1100 ps 80% to 20%; CLOAD = 10 pF; VS_DRV = 2.5 V
PROPAGATION DELAY, tCMOS, CLK-TO-
CMOS OUTPUT
Clock distribution configuration
For All Divide Values 2.1 2.75 3.55 ns VS_DRV = 3.3 V
3.35 ns VS_DRV = 2.5 V
Variation with Temperature 2 ps/°C VS_DRV = 3.3 V and 2.5 V
OUTPUT SKEW, CMOS OUTPUTS1
CMOS Outputs Sharing the Same
Divider
7 85 ps VS_DRV = 3.3 V
10 105 ps VS_DRV = 2.5 V
All CMOS Outputs on Different
Dividers
10 240 ps VS_DRV = 3.3 V
10 285 ps VS_DRV = 2.5 V
All CMOS Outputs Across Multiple
Parts
600 ps VS_DRV = 3.3 V
620 ps VS_DRV = 2.5 V
OUTPUT SKEW, LVPECL-TO-CMOS
OUTPUTS1
All settings identical; different logic type
Outputs Sharing the Same Divider 1.18 1.76 2.48 ns LVPECL to CMOS on same part
Outputs on Different Dividers 1.20 1.78 2.50 ns LVPECL to CMOS on same part
1 The output skew is the difference between any two similar delay paths while operating at the same voltage and temperature.
Data Sheet AD9520-3
Rev. A | Page 9 of 80
Timing Diagrams
DIFFERENTIAL
LVPECL
80%
20%
t
RP
t
FP
07216-061
Figure 2. LVPECL Timing, Differential
CLK
tCMOS
tCLK
tPECL
07216-060
Figure 3. CLK/CLK to Clock Output Timing, DIV = 1
SINGLE-ENDED
CMOS
10pF LOAD
80%
20%
tRC tFC
07216-063
Figure 4. CMOS Timing, Single-Ended, 10 pF Load
AD9520-3 Data Sheet
Rev. A | Page 10 of 80
CLOCK OUTPUT ADDITIVE PHASE NOISE (DISTRIBUTION ONLY; VCO DIVIDER NOT USED)
Table 6.
Parameter Min Typ Max Unit Test Conditions/Comments
CLK-TO-LVPECL ADDITIVE PHASE NOISE
Distribution section only; does not include PLL and VCO
CLK = 1 GHz, Output = 1 GHz Input slew rate > 1 V/ns
Divider = 1
10 Hz Offset −107 dBc/Hz
100 Hz Offset −117 dBc/Hz
1 kHz Offset −127 dBc/Hz
10 kHz Offset −135 dBc/Hz
100 kHz Offset −142 dBc/Hz
1 MHz Offset −145 dBc/Hz
10 MHz Offset −147 dBc/Hz
100 MHz Offset −150 dBc/Hz
CLK = 1 GHz, Output = 200 MHz Input slew rate > 1 V/ns
Divider = 5
10 Hz Offset −122 dBc/Hz
100 Hz Offset −132 dBc/Hz
1 kHz Offset −143 dBc/Hz
10 kHz Offset −150 dBc/Hz
100 kHz Offset
−156
dBc/Hz
1 MHz Offset −157 dBc/Hz
>10 MHz Offset −157 dBc/Hz
CLK-TO-CMOS ADDITIVE PHASE NOISE Distribution section only; does not include PLL and VCO
CLK = 1 GHz, Output = 250 MHz Input slew rate > 1 V/ns
Divider = 4
10 Hz Offset −107 dBc/Hz
100 Hz Offset −119 dBc/Hz
1 kHz Offset −125 dBc/Hz
10 kHz Offset −134 dBc/Hz
100 kHz Offset −144 dBc/Hz
1 MHz Offset −148 dBc/Hz
>10 MHz Offset −154 dBc/Hz
CLK = 1 GHz, Output = 50 MHz Input slew rate > 1 V/ns
Divider = 20
10 Hz Offset −126 dBc/Hz
100 Hz Offset −133 dBc/Hz
1 kHz Offset −140 dBc/Hz
10 kHz Offset −148 dBc/Hz
100 kHz Offset
−157
dBc/Hz
1 MHz Offset −160 dBc/Hz
>10 MHz Offset −163 dBc/Hz
Data Sheet AD9520-3
Rev. A | Page 11 of 80
CLOCK OUTPUT ABSOLUTE PHASE NOISE (INTERNAL VCO USED)
Table 7.
Parameter Min Typ Max Unit Test Conditions/Comments
LVPECL ABSOLUTE PHASE NOISE
Internal VCO; direct-to-LVPECL output and
for loop bandwidths < 1 kHz
VCO = 2.25 GHz; Output = 2.25 GHz
1 kHz Offset −50 dBc/Hz
10 kHz Offset −82 dBc/Hz
100 kHz Offset −107 dBc/Hz
1 MHz Offset −126 dBc/Hz
10 MHz Offset −140 dBc/Hz
40 MHz Offset −146 dBc/Hz
VCO = 2 GHz; Output = 2 GHz
1 kHz Offset −55 dBc/Hz
10 kHz Offset
−85
dBc/Hz
100 kHz Offset −110 dBc/Hz
1 MHz Offset −129 dBc/Hz
10 MHz Offset −142 dBc/Hz
40 MHz Offset −147 dBc/Hz
VCO = 1.75 GHz; Output = 1.75 GHz
1 kHz Offset −59 dBc/Hz
10 kHz Offset −89 dBc/Hz
100 kHz Offset −114 dBc/Hz
1 MHz Offset −132 dBc/Hz
10 MHz Offset −143 dBc/Hz
40 MHz Offset −147 dBc/Hz
CLOCK OUTPUT ABSOLUTE TIME JITTER (CLOCK GENERATION USING INTERNAL VCO)
Table 8.
Parameter Min Typ Max Unit Test Conditions/Comments
LVPECL OUTPUT ABSOLUTE TIME JITTER Application example based on a typical
setup where the reference source is
clean, so a wider PLL loop bandwidth is
used; reference = 15.36 MHz; R divider = 1
VCO = 1.966 GHz; LVPECL = 245.76 MHz; PLL LBW = 55 kHz 135 fs rms Integration BW = 200 kHz to 10 MHz
308 fs rms Integration BW = 12 kHz to 20 MHz
VCO = 1.966 GHz; LVPECL = 122.88 MHz; PLL LBW = 55 kHz 129 fs rms Integration BW = 200 kHz to 10 MHz
293 fs rms Integration BW = 12 kHz to 20 MHz
VCO = 1.966 GHz; LVPECL = 61.44 MHz; PLL LBW = 55 kHz 163 fs rms Integration BW = 200 kHz to 10 MHz
323 fs rms Integration BW = 12 kHz to 20 MHz
CLOCK OUTPUT ABSOLUTE TIME JITTER (CLOCK CLEANUP USING INTERNAL VCO)
Table 9.
Parameter Min Typ Max Unit Test Conditions/Comments
LVPECL OUTPUT ABSOLUTE TIME JITTER Application example based on a typical
setup where the reference source is jittery,
so a narrower PLL loop bandwidth is used;
reference = 19.44 MHz; R divider = 162
VCO = 1.866 GHz; LVPECL = 155.52 MHz; PLL LBW = 1.9 kHz
377
fs rms
Integration BW = 12 kHz to 20 MHz
VCO = 1.966 GHz; LVPECL = 122.88 MHz; PLL LBW = 2.2 kHz 386 fs rms Integration BW = 12 kHz to 20 MHz
AD9520-3 Data Sheet
Rev. A | Page 12 of 80
CLOCK OUTPUT ABSOLUTE TIME JITTER (CLOCK GENERATION USING EXTERNAL VCXO)
Table 10.
Parameter Min Typ Max Unit Test Conditions/Comments
LVPECL OUTPUT ABSOLUTE TIME JITTER
Application example based on a typical setup
using an external 245.76 MHz VCXO (Toyocom
TCO-2112); reference = 15.36 MHz; R divider = 1
LVPECL = 245.76 MHz; PLL LBW = 125 Hz 54 fs rms Integration BW = 200 kHz to 5 MHz
77 fs rms Integration BW = 200 kHz to 10 MHz
109 fs rms Integration BW = 12 kHz to 20 MHz
LVPECL = 122.88 MHz; PLL LBW = 125 Hz 79 fs rms Integration BW = 200 kHz to 5 MHz
114 fs rms Integration BW = 200 kHz to 10 MHz
163 fs rms Integration BW = 12 kHz to 20 MHz
LVPECL = 61.44 MHz; PLL LBW = 125 Hz 124 fs rms Integration BW = 200 kHz to 5 MHz
176 fs rms Integration BW = 200 kHz to 10 MHz
259 fs rms Integration BW = 12 kHz to 20 MHz
CLOCK OUTPUT ADDITIVE TIME JITTER (VCO DIVIDER NOT USED)
Table 11.
Parameter Min Typ Max Unit Test Conditions/Comments
LVPECL OUTPUT ADDITIVE TIME JITTER Distribution section only; does not include PLL
and VCO; measured at rising edge of clock
signal
CLK = 622.08 MHz 46 fs rms Integration bandwidth = 12 kHz to 20 MHz
Any LVPECL Output = 622.08 MHz
Divide Ratio = 1
CLK = 622.08 MHz 64 fs rms Integration bandwidth = 12 kHz to 20 MHz
Any LVPECL Output = 155.52 MHz
Divide Ratio = 4
CLK = 1000 MHz 223 fs rms Calculated from SNR of ADC method
Any LVPECL Output = 100 MHz Broadband jitter
Divide Ratio = 10
CLK = 500 MHz 209 fs rms Calculated from SNR of ADC method
Any LVPECL Output = 100 MHz Broadband jitter
Divide Ratio = 5
CMOS OUTPUT ADDITIVE TIME JITTER Distribution section only; does not include PLL
and VCO
CLK = 200 MHz 325 fs rms Calculated from SNR of ADC method
Any CMOS Output Pair = 100 MHz Broadband jitter
Divide Ratio = 2
CLOCK OUTPUT ADDITIVE TIME JITTER (VCO DIVIDER USED)
Table 12.
Parameter Min Typ Max Unit Test Conditions/Comments
LVPECL OUTPUT ADDITIVE TIME JITTER Distribution section only; does not include PLL
and VCO; uses rising edge of clock signal
CLK = 1.0 GHz; VCO DIV = 5; LVPECL = 100 MHz;
Channel Divider = 2; Duty-Cycle Correction = Off
230 fs rms Calculated from SNR of ADC method
(broadband jitter)
CLK = 500 MHz; VCO DIV = 5; LVPECL = 100 MHz;
Bypass Channel Divider; Duty-Cycle Correction = On
215 fs rms Calculated from SNR of ADC method
(broadband jitter)
CMOS OUTPUT ADDITIVE TIME JITTER Distribution section only; does not include PLL
and VCO; uses rising edge of clock signal
CLK = 200 MHz; VCO DIV = 2; CMOS = 100 MHz;
Bypass Channel Divider; Duty-Cycle Correction = Off
326 fs rms Calculated from SNR of ADC method
(broadband jitter)
CLK = 1600 MHz; VCO DIV = 2; CMOS = 100 MHz;
Channel Divider = 8; Duty-Cycle Correction = Off
362 fs rms Calculated from SNR of ADC method
(broadband jitter)
Data Sheet AD9520-3
Rev. A | Page 13 of 80
SERIAL CONTROL PORT—SPI MODE
Table 13.
Parameter Min Typ Max Unit Test Conditions/Comments
CS
(INPUT)
CS
has an internal 30 kΩ pull-up resistor
Input Logic 1 Voltage 2.0 V
Input Logic 0 Voltage 0.8 V
Input Logic 1 Current 3 µA
Input Logic 0 Current −110 µA The minus sign indicates that current is flowing
out of the AD9520, which is due to the internal
pull-up resistor
Input Capacitance 2 pF
SCLK (INPUT IN SPI MODE) SCLK has an internal 30 kΩ pull-down resistor in
SPI mode but not in I2C mode
Input Logic 1 Voltage 2.0 V
Input Logic 0 Voltage 0.8 V
Input Logic 1 Current 110 µA
Input Logic 0 Current
1
µA
Input Capacitance 2 pF
SDIO (INPUT IN BIDIRECTIONAL MODE)
Input Logic 1 Voltage 2.0 V
Input Logic 0 Voltage 0.8 V
Input Logic 1 Current 1 µA
Input Logic 0 Current 1 µA
Input Capacitance 2 pF
SDIO, SDO (OUTPUTS)
Output Logic 1 Voltage 2.7 V
Output Logic 0 Voltage 0.4 V
TIMING
Clock Rate (SCLK, 1/tSCLK) 25 MHz
Pulse Width High, tHIGH 16 ns
Pulse Width Low, tLOW 16 ns
SDIO to SCLK Setup, tDS 4 ns
SCLK to SDIO Hold, tDH 0 ns
SCLK to Valid SDIO and SDO, tDV 11 ns
CS to SCLK Setup and Hold, tS, tC 2 ns
CS Minimum Pulse Width High, tPWH 3 ns
AD9520-3 Data Sheet
Rev. A | Page 14 of 80
SERIAL CONTROL PORT—I²C MODE
Table 14.
Parameter Min Typ Max Unit Test Conditions/Comments
SDA, SCL (WHEN INPUTTING DATA)
Input Logic 1 Voltage 0.7 × VS V
Input Logic 0 Voltage 0.3 × VS V
Input Current with an Input Voltage Between
0.1 × VS and 0.9 × VS
−10 +10 µA
Hysteresis of Schmitt Trigger Inputs 0.015 × VS V
Pulse Width of Spikes That Must Be Suppressed by
the Input Filter, tSPIKE
50 ns
SDA (WHEN OUTPUTTING DATA)
Output Logic 0 Voltage at 3 mA Sink Current 0.4 V
Output Fall Time from VIHMIN to VILMAX with a Bus
Capacitance from 10 pF to 400 pF
20 + 0.1 Cb 250 ns Cb = capacitance of one bus line in pF
TIMING Note that all I2C timing values are
referred to VIHMIN (0.3 × VS) and VILMAX
levels (0.7 × VS)
Clock Rate (SCL, fI2C) 400 kHz
Bus Free Time Between a Stop and Start Condition, tIDLE 1.3 µs
Setup Time for a Repeated Start Condition, t
SET; STR
0.6
µs
Hold Time (Repeated) Start Condition, tHLD; STR 0.6 µs After this period, the first clock pulse
is generated
Setup Time for Stop Condition, tSET; STP 0.6 µs
Low Period of the SCL Clock, tLOW 1.3 µs
High Period of the SCL Clock, tHIGH 0.6 µs
SCL, SDA Rise Time, tRISE 20 + 0.1 Cb 300 ns
SCL, SDA Fall Time, tFALL 20 + 0.1 Cb 300 ns
Data Setup Time, tSET; DAT 120 ns This is a minor deviation from the
original I²C specification of 100 ns
minimum
Data Hold Time, tHLD; DAT 140 880 ns This is a minor deviation from the
original I²C specification of 0 ns
minimum1
Capacitive Load for Each Bus Line, Cb 400 pF
1 According to the original I2C specification, an I2C master must also provide a minimum hold time of 300 ns for the SDA signal to bridge the undefined region of the SCL
falling edge.
Data Sheet AD9520-3
Rev. A | Page 15 of 80
PD, EEPROM, RESET, AND SYNC PINS
Table 15.
Parameter Min Typ Max Unit Test Conditions/Comments
INPUT CHARACTERISTICS
Each pin has a 30 kΩ internal pull-up resistor
Logic 1 Voltage 2.0 V
Logic 0 Voltage 0.8 V
Logic 1 Current 1 µA
Logic 0 Current −110 µA The minus sign indicates that current is flowing out of
the AD9520, which is due to the internal pull-up resistor
Capacitance
2
pF
RESET TIMING
Pulse Width Low
500
ns
RESET Inactive to Start of Register
Programming
100 ns
SYNC
TIMING
Pulse Width Low 1.3 ns High speed clock is CLK input signal
SERIAL PORT SETUP PINS—SP1, SP0
Table 16.
Parameter Min Typ Max Unit Test Conditions/Comments
SP1, SP0
These pins do not have internal pull-up/pull-down
resistors
Logic Level 0 0.25 × VS V VS is the voltage on the VS pin
Logic Level ½ 0.4 × VS 0.65 × VS V These pins can be floated to obtain Logic Level ½; if
floating the pin, connect a capacitor to ground
Logic Level 1 0.8 × VS V
LD, STATUS, AND REFMON PINS
Table 17.
Parameter
Min
Typ
Max
Unit
Test Conditions/Comments
OUTPUT CHARACTERISTICS When selected as a digital output (CMOS); there are
other modes in which these pins are not CMOS digital
outputs; see Table 54, Register 0x017, Register 0x01A,
and Register 0x01B
Output Voltage High, VOH 2.7 V
Output Voltage Low, VOL 0.4 V
MAXIMUM TOGGLE RATE 100 MHz Applies when mux is set to any divider or counter output
or PFD up/down pulse; also applies in analog lock detect
mode; usually debug mode only; beware that spurs can
couple to output when any pin is toggling
ANALOG LOCK DETECT
Capacitance 3 pF On-chip capacitance; used to calculate RC time constant
for analog lock detect readback; use a pull-up resistor
REF1, REF2, AND VCO FREQUENCY
STATUS MONITOR
Normal Range
1.02
MHz
Frequency above which the monitor indicates the
presence of the reference
Extended Range 8 kHz Frequency above which the monitor indicates the
presence of the reference
LD PIN COMPARATOR
Trip Point 1.6 V
Hysteresis 260 mV
AD9520-3 Data Sheet
Rev. A | Page 16 of 80
POWER DISSIPATION
Table 18.
Parameter Min Typ Max Unit Test Conditions/Comments
POWER DISSIPATION, CHIP
Does not include power dissipated in external resistors; all
LVPECL outputs terminated with 50 Ω to VCC − 2 V; all CMOS
outputs have 10 pF capacitive loading; VS_DRV = 3.3 V
Power-On Default 1.32 1.5 W No clock; no programming; default register values
PLL Locked; One LVPECL Output Enabled 0.55 0.64 W fREF = 25 MHz; fOUT = 250 MHz; VCO = 2 GHz; VCO divider = 2;
one LVPECL output and output divider enabled; zero delay off;
ICP = 4.8 mA
PLL Locked; One CMOS Output Enabled 0.52 0.62 W fREF = 25 MHz; fOUT = 62.5 MHz; VCO = 2 GHz; VCO divider = 2;
one CMOS output and output divider enabled; zero delay off;
ICP = 4.8 mA
Distribution Only Mode; VCO Divider On;
One LVPECL Output Enabled
0.39 0.46 W fCLK = 2.4 GHz; fOUT = 200 MHz; VCO divider = 2; one LVPECL
output and output divider enabled; zero delay off
Distribution Only Mode; VCO Divider Off;
One LVPECL Output Enabled
0.36 0.42 W fCLK = 2 GHz; fOUT = 200 MHz; VCO divider bypassed; one
LVPECL output and output divider enabled; zero delay off
Maximum Power, Full Operation 1.5 1.7 W PLL on; internal VCO = 2000 MHz; VCO divider = 2; all channel
dividers on; 12 LVPECL outputs at 125 MHz; zero delay on
PD Power-Down 60 80 mW PD pin pulled low; does not include power dissipated in
termination resistors
PD Power-Down, Maximum Sleep 24 33 mW PD pin pulled low; PLL power-down, Register 0x010[1:0] = 01b;
power-down SYNC, Register 0x230[2] = 1b; power-down
distribution reference, Register 0x230[1] = 1b
VCP Supply 4 4.8 mW PLL operating; typical closed-loop configuration
POWER DELTAS, INDIVIDUAL FUNCTIONS Power delta when a function is enabled/disabled
VCO Divider On/Off 32 40 mW VCO divider not used
REFIN (Differential) Off 25 30 mW Delta between reference input off and differential reference
input mode
REF1, REF2 (Single-Ended) On/Off 15 20 mW Delta between reference inputs off and one singled-ended
reference enabled; double this number if both REF1 and REF2
are powered up
VCO On/Off 67 104 mW Internal VCO disabled; CLK input selected
PLL Dividers and Phase Detector On/Off 51 63 mW PLL off to PLL on, normal operation; no reference enabled
LVPECL Channel 121 144 mW No LVPECL output on to one LVPECL output on; channel divider
is set to 1
LVPECL Driver 51 73 mW Second LVPECL output turned on, same channel
CMOS Channel 145 180 mW No CMOS output on to one CMOS output on; channel divider
is set to 1; fOUT = 62.5 MHz and 10 pF of capacitive loading
CMOS Driver On/Off 11 24 mW Additional CMOS outputs within the same channel turned on
Channel Divider Enabled 40 57 mW Delta between divider bypassed (divide-by-1) and divide-by-2
to divide-by-32
Zero Delay Block On/Off 30 34 mW
Data Sheet AD9520-3
Rev. A | Page 17 of 80
ABSOLUTE MAXIMUM RATINGS
Table 19.
Parameter Rating
VS to GND −0.3 V to +3.6 V
VCP, CP to GND
−0.3 V to +5.8 V
VS_DRV to GND −0.3 V to +3.6 V
REFIN, REFIN to GND −0.3 V to VS + 0.3 V
RSET, LF, BYPASS to GND −0.3 V to VS + 0.3 V
CPRSET to GND −0.3 V to VS + 0.3 V
CLK, CLK to GND −0.3 V to VS + 0.3 V
CLK to
CLK
−1.2 V to +1.2 V
SCLK/SCL, SDIO/SDA, SDO, CS to GND −0.3 V to VS + 0.3 V
OUT0, OUT0, OUT1, OUT1,
OUT2, OUT2, OUT3, OUT3,
OUT4, OUT4, OUT5, OUT5,
OUT6, OUT6, OUT7, OUT7,
OUT8, OUT8, OUT9, OUT9,
OUT10, OUT10, OUT11, OUT11 to GND
−0.3 V to VS + 0.3 V
SYNC, RESET, PD to GND −0.3 V to VS + 0.3 V
REFMON, STATUS, LD to GND −0.3 V to VS + 0.3 V
SP0, SP1, EEPROM to GND −0.3 V to VS + 0.3 V
Junction Temperature1 125°C
Storage Temperature Range −65°C to +150°C
Lead Temperature (10 sec) 300°C
1 See Table 20 for θJA.
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
THERMAL RESISTANCE
Thermal impedance measurements were taken on a JEDEC
JESD51-5 2S2P test board in still air in accordance with JEDEC
JESD51-2. See the Thermal Performance section for more
details.
Table 20.
Package Type
θ
JA
Unit
64-Lead LFCSP (CP-64-4) 22 °C/W
ESD CAUTION
AD9520-3 Data Sheet
Rev. A | Page 18 of 80
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
07216-003
NOTES
1. E X P OSED DIE PAD M US T BE CO NNE CTED T O G ND.
PIN 1
INDICATOR
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
SDIO/SDA
SDO
GND
SP1
SP0
EEPROM
RESET
PD
OUT9 (O UT9A)
OUT9 (O UT9B)
VS_DRV
OUT10 (O UT10A)
OUT10 (O UT10B)
OUT11 (O UT11A)
OUT11 (O UT11B)
VS
64
63
62
61
60
59
58
57
56
55
54
53
52
51
50
49
REF IN (REF1)
REF IN (REF2)
CPRSET
VS
VS
GND
RSET
VS
OUT0 (O UT0A)
OUT0 (O UT0B)
VS_DRV
OUT1 (O UT1A)
OUT1 (O UT1B)
OUT2 (O UT2A)
OUT2 (O UT2B)
VS
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
VS
REFMON
LD
VCP
CP
STATUS
REF_SEL
SYNC
LF
BYPASS
VS
VS
CLK
CLK
CS
SCLK/SCL
OUT3 (O UT3A)
OUT3 (O UT3B)
VS_DRV
OUT4 (O UT4A)
OUT4 (O UT4B)
OUT5 (O UT5A)
OUT5 (O UT5B)
VS
VS
OUT8 (O UT8B)
OUT8 (O UT8A)
OUT7 (O UT7B)
OUT7 (O UT7A)
VS_DRV
OUT6 (O UT6B)
OUT6 (O UT6A)
48
47
46
45
44
43
42
41
40
39
38
37
36
35
34
33
AD9520
TOP VI EW
(No t t o Scal e)
Figure 5. Pin Configuration
Table 21. Pin Function Descriptions
Pin No.
Input/
Output
Pin
Type Mnemonic Description
1, 11, 12,
32, 40, 41,
49, 57, 60,
61
I Power VS 3.3 V Power Pins.
2 O 3.3 V CMOS REFMON Reference Monitor (Output). This pin has multiple selectable outputs.
3 O 3.3 V CMOS LD Lock Detect (Output). This pin has multiple selectable outputs.
4 I Power VCP Power Supply for Charge Pump (CP); VS ≤ VCP ≤ 5.25 V. VCP must still be connected
to 3.3 V if the PLL is not used.
5 O Loop filter CP Charge Pump (Output). This pin connects to an external loop filter; it can be left
unconnected if the PLL is not used.
6
O
3.3 V CMOS
STATUS
Programmable Status Output.
7 I 3.3 V CMOS REF_SEL Reference Select. This pin selects REF1 (low) or REF2 (high) and has an internal 30 kΩ
pull-down resistor.
8 I 3.3 V CMOS SYNC Manual Synchronization and Manual Holdover. This pin initiates a manual
synchronization and is used for manual holdover. Active low. This pin has an
internal 30 kΩ pull-up resistor.
9 I Loop filter LF Loop Filter (Input). This pin connects internally to the VCO control voltage node.
10 O Loop filter BYPASS This pin is for bypassing the LDO to ground with a 220 nF capacitor. It can be left
unconnected if the PLL is not used.
13 I Differential
clock input
CLK Along with CLK, this pin is the differential input for the clock distribution section.
14
I
Differential
clock input
CLK
Along with CLK, this pin is the differential input for the clock distribution section.
If a single-ended input is connected to the CLK pin, connect a 0.1 µF bypass capacitor
from this pin to ground.
Data Sheet AD9520-3
Rev. A | Page 19 of 80
Pin No.
Input/
Output
Pin
Type Mnemonic Description
15 I 3.3 V CMOS CS Serial Control Port Chip Select; Active Low. This pin has an internal 30 kΩ
pull-up resistor.
16 I 3.3 V CMOS SCLK/SCL Serial Control Port Clock Signal. This pin has an internal 30 kΩ pull-down resistor
in SPI mode but is high impedance in I²C mode.
17 I/O 3.3 V CMOS SDIO/SDA Serial Control Port Bidirectional Serial Data In/Out.
18 O 3.3 V CMOS SDO Serial Control Port Unidirectional Serial Data Out.
19, 59 I GND GND Ground Pins.
20 I Three-level
logic
SP1 Select SPI or I²C as the serial interface port and select the I²C slave address in I²C
mode. Three-level logic. This pin is internally biased for the open logic level.
21 I Three-level
logic
SP0 Select SPI or I²C as the serial interface port and select the I²C slave address in I²C
mode. Three-level logic. This pin is internally biased for the open logic level.
22 I 3.3 V CMOS EEPROM Setting this pin high selects the register values stored in the internal EEPROM to be
loaded at reset and/or power-up. Setting this pin low causes the AD9520 to load the
hard-coded default register values at power-up/reset (unless Register 0xB02[1] is
used. See the Soft Reset via the Serial Port section). This pin has an internal 30 kΩ
pull-down resistor. Note that, to guarantee proper loading of the EEPROM during
startup, a high-low-high pulse on the RESET pin should occur after the power supply
has stabilized.
23 I 3.3 V CMOS RESET Chip Reset, Active Low. This pin has an internal 30 kΩ pull-up resistor.
24 I 3.3 V CMOS PD Chip Power Down, Active Low. This pin has an internal 30 kΩ pull-up resistor.
25 O LVPECL or
CMOS
OUT9 (OUT9A) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
26 O LVPECL or
CMOS
OUT9 (OUT9B) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
27, 35,
46, 54
I Power VS_DRV Output Driver Power Supply Pins. As a group, these pins can be set to either
2.5 V or 3.3 V. All four pins must be set to the same voltage.
28 O LVPECL or
CMOS
OUT10 (OUT10A) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
29 O LVPECL or
CMOS
OUT10 (OUT10B) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
30
O
LVPECL or
CMOS
OUT11 (OUT11A)
Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
31 O LVPECL or
CMOS
OUT11 (OUT11B) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
33 O LVPECL or
CMOS
OUT6 (OUT6A) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
34 O LVPECL or
CMOS
OUT6 (OUT6B) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
36 O LVPECL or
CMOS
OUT7 (OUT7A) Clock Output. This pin can be configured as one side of a differential LVPECL
output, or as a single-ended CMOS output.
37 O LVPECL or
CMOS
OUT7 (OUT7B) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
38 O LVPECL or
CMOS
OUT8 (OUT8A) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
39 O LVPECL or
CMOS
OUT8 (OUT8B) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
42 O LVPECL or
CMOS
OUT5 (OUT5B) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
43 O LVPECL or
CMOS
OUT5 (OUT5A) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
44 O LVPECL or
CMOS
OUT4 (OUT4B) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
45 O LVPECL or
CMOS
OUT4 (OUT4A) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
AD9520-3 Data Sheet
Rev. A | Page 20 of 80
Pin No.
Input/
Output
Pin
Type Mnemonic Description
47 O LVPECL or
CMOS
OUT3 (OUT3B) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
48 O LVPECL or
CMOS
OUT3 (OUT3A) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
50 O LVPECL or
CMOS
OUT2 (OUT2B) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
51 O LVPECL or
CMOS
OUT2 (OUT2A) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
52 O LVPECL or
CMOS
OUT1 (OUT1B) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
53 O LVPECL or
CMOS
OUT1 (OUT1A) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
55 O LVPECL or
CMOS
OUT0 (OUT0B) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
56 O LVPECL or
CMOS
OUT0 (OUT0A) Clock Output. This pin can be configured as one side of a differential LVPECL
output or as a single-ended CMOS output.
58 O Current set
resistor
RSET Clock Distribution Current Set Resistor. Connect a 4.12 kΩ resistor from this pin
to GND.
62 O Current set
resistor
CPRSET Charge Pump Current Set Resistor. Connect a 5.1 kΩ resistor from this pin to GND.
This resistor can be omitted if the PLL is not used.
63 I Reference
input
REFIN (REF2) Along with REFIN, this is the differential input for the PLL reference. Alternatively,
this pin is a single-ended input for REF2.
64 I Reference
input
REFIN (REF1) Along with REFIN, this is the differential input for the PLL reference. Alternatively,
this pin is a single-ended input for REF1.
EPAD GND GND The exposed die pad must be connected to GND.
Data Sheet AD9520-3
Rev. A | Page 21 of 80
TYPICAL PERFORMANCE CHARACTERISTICS
350
300
250
200
150
100 0500 1000 1500 2000 2500 3000
CURRENT ( mA)
FREQUENCY (MHz)
3 CHANNEL S — 6 LVPE CL
3 CHANNEL S — 3 LVPE CL
2 CHANNEL S — 2 LVPE CL
1 CHANNEL — 1 LVPE CL
07216-108
Figure 6. Total Current vs. Frequency, CLK-to-Output (PLL Off),
LVPECL Outputs Terminated 50 Ω to VS_DRV − 2 V
240
220
200
180
160
140
120
100
80 050 100 150 200 250
CURRENT ( mA)
FREQUENCY (MHz)
3 CHANNEL S — 6 CM OS
3 CHANNEL S — 3 CM OS
2 CHANNEL S — 2 CM OS
1 CHANNEL — 1 CM OS
07216-109
Figure 7. Total Current vs. Frequency, CLK-to-Output (PLL Off),
CMOS Outputs with 10 pF Load
70
65
60
55
50
45
40
35
30
251.7 1.8 1.9 2.0 2.1 2.2 2.3
KVCO (MHz/V)
VCO FREQ UE NCY ( GHz)
07216-010
Figure 8. KVCO vs. VCO Frequency
5
4
3
2
1
003.53.02.52.01.51.00.5
CURRENT FROM CP P IN (mA)
VOLT AGE O N CP PIN (V)
PUMP UPPUMP DOWN
07216-111
Figure 9. Charge Pump Characteristics at CPV = 3.3 V
5
4
3
2
1
005.04.03.0 4.53.52.52.01.51.00.5
CURRENT FROM CP P IN (mA)
VOLT AGE O N CP PIN (V)
PUMP DOWN PUMP UP
07216-112
Figure 10. Charge Pump Characteristics at CPV = 5.0 V
–140
–145
–150
–155
–160
–165
–1700.1 110010
PF D P HAS E NOIS E RE FERRED TO P FD INP UT
(dBc/Hz)
PFD FREQUENCY (MHz)
07216-013
Figure 11. PFD Phase Noise Referred to PFD Input vs. PFD Frequency
AD9520-3 Data Sheet
Rev. A | Page 22 of 80
–208
–210
–212
–214
–216
–218
–220
–222
–224 00.4 0.8 1.20.2 0.6 1.0 1.4
PLL FIGURE OF MERIT (dBc/Hz)
INPUT SLEW RATE (V/n s)
DIFFERENTIAL INPUT
SI NGLE - E NDE D INPUT
07216-114
Figure 12. PLL Figure of Merit (FOM) vs. Slew Rate at REFIN/REFIN
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
PO WER (dBm)
100 145140135130125120115110105 FREQUENCY (MHz)
07216-116
Figure 13. PFD/CP Spurs; 122.88 MHz; PFD = 15.36 MHz;
LBW = 127 kHz; ICP = 3.0 mA; fVCO = 1966.08 MHz
0
–10
–20
–30
–40
–50
–60
–70
–80
–90
–100
PO WER (dBm)
122.38 122.58 122.78 122.98 123.18 123.38
FREQUENCY (MHz)
07216-117
Figure 14. Output Spectrum, LVPECL; 122.88 MHz; PFD = 15.36 MHz;
LBW = 127 kHz; ICP = 3.0 mA; fVCO = 1966.08 MHz
3.5
0
0.5
1.0
1.5
2.0
2.5
3.0
VOH (V)
10k 1k 100
RESISTIVE LOAD (Ω)
VS_DRV = 3.135V
VS_DRV = 2.35V
VS_DRV = 3.3V
VS_DRV = 2.5V
07216-118
Figure 15. CMOS Output VOH (Static) vs. RLOAD (to Ground)
1.2
0.8
0.4
0
–0.4
–0.8
–1.2 024222018161412108642
DIFFERENTIAL OUTPUT (V)
TIME (n s)
07216-014
Figure 16. LVPECL Output (Differential) at 100 MHz
1.0
0.6
0.2
–0.2
–0.6
–1.0 01.50.5 1.0
DIFFERENTIAL SWING (V p-p)
TIME (n s)
07216-015
Figure 17. LVPECL Differential Voltage Swing at 1600 MHz
Data Sheet AD9520-3
Rev. A | Page 23 of 80
3.2
2.8
2.4
2.0
1.6
1.2
0.8
0.4
008060 1004020 7050 903010
AMPLITUDE (V)
TIME (n s)
07216-018
Figure 18. CMOS Output with 10 pF Load at 25 MHz
3.2
2.8
2.4
2.0
1.6
1.2
0.8
0.4
0010987654321
AMPLITUDE (V)
TIME (n s)
2pF LOAD
10pF
LOAD
07216-019
Figure 19. CMOS Output with 2 pF and 10 pF Load at 250 MHz
2.0
1.8
1.6
1.4
1.2
1.0 03.01.5 2.0 2.51.00.5
DIFFERENTIAL SWING (V p-p)
FRE QUENCY ( GHz)
07216-123
Figure 20. LVPECL Differential Voltage Swing vs. Frequency
4.0
3.5
3.0
2.5
2.0
1.5
1.0
0.5
00700
2pF
10pF
20pF
600500400300200100
AMPLITUDE (V)
FREQUENCY (MHz)
07216-124
Figure 21. CMOS Output Swing vs. Frequency and Capacitive Load
–40
–150
–140
–130
–120
–110
–100
–90
–80
–70
–60
–50
1k 100M1M 10M100k10k
PHASE NOISE (d Bc/Hz)
FRE QUENCY ( Hz )
07216-023
Figure 22. Internal VCO Phase Noise (Absolute), Direct-to-LVPECL at 1750 MHz
–40
–150
–140
–130
–120
–110
–100
–90
–80
–70
–60
–50
1k 100M1M 10M100k10k
PHASE NOISE (d Bc/Hz)
FRE QUENCY ( Hz )
07216-024
Figure 23. Internal VCO Phase Noise (Absolute), Direct-to-LVPECL at 2000 MHz
AD9520-3 Data Sheet
Rev. A | Page 24 of 80
–40
–150
–140
–130
–120
–110
–100
–90
–80
–70
–60
–50
1k 100M1M 10M100k10k
PHASE NOISE (d Bc/Hz)
FRE QUENCY ( Hz )
07216-025
Figure 24. Internal VCO Phase Noise (Absolute), Direct-to-LVPECL at 2250 MHz
–100
–110
–120
–130
–140
–150
–16010 1k100 100M1M 10M100k10k
PHASE NOISE (d Bc/Hz)
FRE QUENCY ( Hz )
07216-128
Figure 25. Additive (Residual) Phase Noise, CLK-to-LVPECL at
245.76 MHz, Divide-by-1
–100
–110
–120
–130
–140
–150
–16010 1k100 100M1M 10M100k10k
PHASE NOISE (d Bc/Hz)
FRE QUENCY ( Hz )
07216-129
Figure 26. Additive (Residual) Phase Noise, CLK-to-LVPECL at
200 MHz, Divide-by-5
–100
–110
–120
–130
–140
–150
–16010 1k100 100M1M 10M100k10k
PHASE NOISE (d Bc/Hz)
FRE QUENCY ( Hz )
07216-130
Figure 27. Additive (Residual) Phase Noise, CLK-to-LVPECL at
1600 MHz, Divide-by-1
–110
–120
–130
–140
–150
–170
–160
10 1k100 100M1M 10M100k10k
PHASE NOISE (d Bc/Hz)
FRE QUENCY ( Hz )
07216-131
Figure 28. Additive (Residual) Phase Noise, CLK-to-CMOS at
50 MHz, Divide-by-20
–100
–110
–120
–130
–140
–150
–16010 1k100 100M1M 10M100k10k
PHASE NOISE (d Bc/Hz)
FRE QUENCY ( Hz )
07216-132
Figure 29. Additive (Residual) Phase Noise, CLK-to-CMOS at
250 MHz, Divide-by-4
Data Sheet AD9520-3
Rev. A | Page 25 of 80
–100
–160
–150
–140
–130
–120
–110
1k 100M1M 10M100k10k
PHASE NOISE (d Bc/Hz)
FREQUENCY (Hz)
07216-033
NOTES
1. THE LOOP FILTER USED TO GENERATE THIS PLOT IS SHOWN IN FIGURE 41.
Figure 30. Phase Noise (Absolute) Clock Generation; Internal VCO at
1.966 GHz; PFD = 15.36 MHz; LBW = 40 kHz; LVPECL Output = 122.88 MHz
1k 100M1M 10M100k10k
PHASE NOISE (d Bc/Hz)
FRE QUENCY ( Hz )
–120
–160
–150
–140
–130
07216-135
Figure 31. Phase Noise (Absolute), External VCXO (Toyocom TCO-2112)
at 245.76 MHz; PFD = 15.36 MHz; LBW = 250 Hz; LVPECL Output = 245.76 MHz
–80
–90
–100
–110
–120
–130
–140
–150
–1601k 100M1M 10M100k10k
PHASE NOISE (d Bc/Hz)
FREQUENCY (Hz)
INTEGRATED RM S JITTER (12kHz TO 20MHz) : 377fs
07216-034
NOTES
1. THE LOOP FILTER USED TO GENERATE THIS PLOT IS SHOWN IN FIGURE 42.
Figure 32. Phase Noise (Absolute) Clock Cleanup; Internal VCO at 1.866 GHz;
PFD = 120 kHz; LBW = 1.84 kHz; LVPECL Output = 155.52 MHz
1000
100
10
1
0.1
0.01 0.1
110 100 1000
JITTER FREQUENCY (kHz)
OC-48 OBJECTIV E M AS K
AD9520
fOBJ
07216-134
NOT E : 375UI MAX AT 10Hz OFFSET IS THE
MAXIMUM JITTER THAT CAN BE
GENERATED BY THE TEST EQ UIPMENT.
FAILURE POINT IS GREATER THAN 375UI.
INPUT JITTERAMPLITUDE (UI p-p)
Figure 33. Telcordia GR-253 Jitter Tolerance Plot
AD9520-3 Data Sheet
Rev. A | Page 26 of 80
TERMINOLOGY
Phase Jitter and Phase Noise
An ideal sine wave can be thought of as having a continuous
and even progression of phase with time from 0° to 360° for
each cycle. Actual signals, however, display a certain amount
of variation from ideal phase progression over time. This
phenomenon is called phase jitter. Although many causes can
contribute to phase jitter, one major cause is random noise,
which is characterized statistically as being Gaussian (normal)
in distribution.
This phase jitter leads to a spreading out of the energy of the
sine wave in the frequency domain, producing a continuous
power spectrum. This power spectrum is usually reported as a
series of values whose units are dBc/Hz at a given offset in
frequency from the sine wave (carrier). The value is a ratio
(expressed in decibels) of the power contained within a 1 Hz
bandwidth with respect to the power at the carrier frequency.
For each measurement, the offset from the carrier frequency is
also given.
It is meaningful to integrate the total power contained within
some interval of offset frequencies (for example, 10 kHz to
10 MHz). This is called the integrated phase noise over that
frequency offset interval and can be readily related to the time
jitter due to the phase noise within that offset frequency interval.
Phase noise has a detrimental effect on the performance of ADCs,
DACs, and RF mixers. It lowers the achievable dynamic range of
the converters and mixers, although they are affected in somewhat
different ways.
Time Jitter
Phase noise is a frequency domain phenomenon. In the time
domain, the same effect is exhibited as time jitter. When observing
a sine wave, the time of successive zero crossings varies. In a square
wave, the time jitter is a displacement of the edges from their
ideal (regular) times of occurrence. In both cases, the variations in
timing from the ideal are the time jitter. Because these variations
are random in nature, the time jitter is specified in seconds root
mean square (rms) or 1 sigma of the Gaussian distribution.
Time jitter that occurs on a sampling clock for a DAC or an
ADC decreases the signal-to-noise ratio (SNR) and dynamic
range of the converter. A sampling clock with the lowest possible
jitter provides the highest performance from a given converter.
Additive Phase Noise
Additive phase noise is the amount of phase noise that can be
attributed to the device or subsystem being measured. The phase
noise of any external oscillators or clock sources is subtracted.
This makes it possible to predict the degree to which the device
impacts the total system phase noise when used in conjunction
with the various oscillators and clock sources, each of which
contributes its own phase noise to the total. In many cases, the
phase noise of one element dominates the system phase noise.
When there are multiple contributors to phase noise, the total is
the square root of the sum of squares of the individual contributors.
Additive Time Jitter
Additive time jitter is the amount of time jitter that can be
attributed to the device or subsystem being measured. The time
jitter of any external oscillators or clock sources is subtracted.
This makes it possible to predict the degree to which the device
impacts the total system time jitter when used in conjunction
with the various oscillators and clock sources, each of which
contributes its own time jitter to the total. In many cases, the
time jitter of the external oscillators and clock sources
dominates the system time jitter.
Data Sheet AD9520-3
Rev. A | Page 27 of 80
DETAILED BLOCK DIAGRAM
PROGRAMMABLE
N DEL AY
REFIN
CLK
CLK
REF1
REF2
BUF
AMP
AD9520
STATUS
STATUS
R
DIVIDER
CLOCK
DOUBLER
STATUS
PROGRAMMABLE
R DEL AY
REFERENCE
SWITCHOVER
REF_SEL CPRSET VCP
VS GND
RSET
DISTRIBUTION
REFERENCE
REFMON
CP
VS_DRV
STATUS
LD
P, P + 1
PRESCALER A/B
COUNTERS
N DIV IDER
BYPASS
LF
LOW DROPOUT
REGULATOR (LDO) PHASE
FREQUENCY
DETECTOR
LOCK
DETECT
CHARGE
PUMP
PLL
REFERENCE
HOLD
01
DIV IDE BY 1,
2, 3, 4, 5, OR 6
PD
SYNC
REFIN
RESET
EEPROM
DIGITAL
LOGIC EEPROM
DIV IDE BY
1 TO 32
OUT0
OUT0
OUT1
OUT1
OUT2
OUT2
DIV IDE BY
1 TO 32
OUT3
OUT3
OUT4
OUT4
OUT5
OUT5
DIV IDE BY
1 TO 32
OUT6
OUT6
OUT7
OUT7
OUT8
OUT8
DIV IDE BY
1 TO 32
OUT9
OUT9
OUT10
OUT10
OUT11
OUT11
ZE RO DEL AY BLOCK
LVPECL/CMOS O UTPUT
SP1
SP0
SPI
INTERFACE I
2
C
INTERFACE
SCLK/SCL
SDIO/SDA
SDO
CS
SERIAL
PORT
DECODE
OPTIONAL
07216-028
Figure 34.
AD9520-3 Data Sheet
Rev. A | Page 28 of 80
THEORY OF OPERATION
OPERATIONAL CONFIGURATIONS
The AD9520 can be configured in several ways. These
configurations must be set up by loading the control registers
(see Table 50 to Table 61). Each section or function must be
individually programmed by setting the appropriate bits in the
corresponding control register or registers. After the desired
configuration is programmed, the user can store these values in
the on-board EEPROM to allow the part to power up in the desired
configuration without user intervention.
Mode 0—Internal VCO and Clock Distribution
When the internal VCO and PLL are used, the VCO divider must
also be used, in most cases, to ensure that the frequency presented
to the channel dividers does not exceed its specified maximum
frequency (see Table 3). The exceptions to this are the VCO direct
mode and cases where the VCO frequency is ≤1600 MHz. The
internal PLL uses an external loop filter to set the loop bandwidth.
The external loop filter is also crucial to the loop stability.
When the internal VCO is used, the VCO must be calibrated
(Register 0x018[0] = 1b) to ensure optimal performance.
For internal VCO and clock distribution applications, use the
register settings shown in Table 22.
Table 22. Settings When Using Internal VCO
Register Description
0x010[1:0] = 00b PLL normal operation (PLL on)
0x010 to 0x01E PLL settings; select and enable a reference
input; set R, N (P, A, B), PFD polarity, and ICP
according to the intended loop configuration
0x1E1[1] = 1b Select VCO as the source
0x01C[2:0] Enable reference inputs
0x1E0[2:0] Set VCO divider
0x1E1[0] = 0b Use the VCO divider as the source for the
distribution section
0x018[0] = 0b,
0x232[0] = 1b
Clear previous VCO calibration and issue
IO_UPDATE (not necessary the first time
after power-up, but must be done
subsequently)
0x018[0] = 1b,
0x232[0] = 1b
Initiate VCO calibration, issue IO_UPDATE
Data Sheet AD9520-3
Rev. A | Page 29 of 80
PROGRAMMABLE
N DEL AY
REFIN
CLK
CLK
REF1
REF2
BUF
AMP
AD9520
R
DIVIDER
CLOCK
DOUBLER
STATUS
PROGRAMMABLE
R DEL AY
REFERENCE
SWITCHOVER
REF_SEL CPRSET VCPVS GND RSET
DISTRIBUTION
REFERENCE
REFMON
CP
STATUS
LD
P, P + 1
PRESCALER A/B
COUNTERS
N DIV IDER
BYPASS
LF
LOW DROPOUT
REGULATOR (LDO) PHASE
FREQUENCY
DETECTOR
LOCK
DETECT
CHARGE
PUMP
PLL
REFERENCE
HOLD
01
DIV IDE BY 1,
2, 3, 4, 5, OR 6
PD
SYNC
REFIN
RESET
EEPROM
DIGITAL
LOGIC EEPROM
DIV IDE BY
1 TO 32
OUT0
OUT0
OUT1
OUT1
OUT2
OUT2
DIV IDE BY
1 TO 32
OUT3
OUT3
OUT4
OUT4
OUT5
OUT5
DIV IDE BY
1 TO 32
OUT6
OUT6
OUT7
OUT7
OUT8
OUT8
DIV IDE BY
1 TO 32
OUT9
OUT9
OUT10
OUT10
OUT11
OUT11
ZE RO DEL AY BLOCK
LVPECL/CMOS O UTPUT
STATUS
STATUS
SP1
SP0
SPI
INTERFACE I
2
C
INTERFACE
SCLK/SCL
SDIO/SDA
SDO
CS
SERIAL
PORT
DECODE
VS_DRV
OPTIONAL
07216-030
Figure 35. Internal VCO and Clock Distribution (Mode 0)
AD9520-3 Data Sheet
Rev. A | Page 30 of 80
Mode 1—Clock Distribution or External VCO < 1600 MHz
When the external clock source to be distributed or the external
VCO/VCXO is <1600 MHz, a configuration that bypasses the
VCO divider can be used. This is the only difference from Mode 2.
Bypassing the VCO divider limits the frequency of the clock
source to <1600 MHz (due to the maximum input frequency
allowed at the channel dividers).
Configuration and Register Settings
For clock distribution applications where the external clock is
<1600 MHz, use the register settings shown in Table 23.
Table 23. Settings for Clock Distribution < 1600 MHz
Register Description
0x010[1:0] = 01b PLL asynchronous power-down (PLL off)
0x1E1[0] = 1b Bypass the VCO divider as the source for
the distribution section
0x1E1[1] = 0b Select CLK as the source
When the internal PLL is used with an external VCO < 1600 MHz,
the PLL must be turned on.
Table 24. Settings for Using Internal PLL with External VCO <
1600 MHz
Register Description
0x1E1[0] = 1b Bypass the VCO divider as the source for the
distribution section
0x010[1:0] = 00b PLL normal operation (PLL on) along with
other appropriate PLL settings in Register
0x010 to Register 0x01E
An external VCO/VCXO requires an external loop filter that
must be connected between the CP pin and the tuning pin of
the VCO/VCXO. This loop filter determines the loop bandwidth
and stability of the PLL. Make sure to select the proper PFD
polarity for the VCO/VCXO being used.
Table 25. Setting the PFD Polarity
Register Description
0x010[7] = 0b PFD polarity positive (higher control voltage
produces higher frequency)
0x010[7] = 1b PFD polarity negative (higher control
voltage
produces lower frequency)
Data Sheet AD9520-3
Rev. A | Page 31 of 80
PROGRAMMABLE
N DEL AY
REFIN
CLK
CLK
REF1
REF2
BUF
AMP
AD9520
R
DIVIDER
CLOCK
DOUBLER
STATUS
PROGRAMMABLE
R DEL AY
REFERENCE
SWITCHOVER
REF_SEL CPRSET VCPVS GND RSET
DISTRIBUTION
REFERENCE
REFMON
CP
STATUS
LD
P, P + 1
PRESCALER A/B
COUNTERS
N DIV IDER
BYPASS
LF
PHASE
FREQUENCY
DETECTOR
LOCK
DETECT
CHARGE
PUMP
PLL
REFERENCE
HOLD
01
DIV IDE BY 1,
2, 3, 4, 5, OR 6
PD
SYNC
REFIN
RESET
EEPROM
DIGITAL
LOGIC EEPROM
DIV IDE BY
1 TO 32
OUT0
OUT0
OUT1
OUT1
OUT2
OUT2
DIV IDE BY
1 TO 32
OUT3
OUT3
OUT4
OUT4
OUT5
OUT5
DIV IDE BY
1 TO 32
OUT6
OUT6
OUT7
OUT7
OUT8
OUT8
DIV IDE BY
1 TO 32
OUT9
OUT9
OUT10
OUT10
OUT11
OUT11
ZE RO DEL AY BLOCK
LVPECL/CMOS O UTPUT
STATUS
STATUS
SP1
SP0
SPI
INTERFACE I
2
C
INTERFACE
SCLK/SCL
SDIO/SDA
SDO
CS
SERIAL
PORT
DECODE
VS_DRV
OPTIONAL
07216-031
LOW DROPOUT
REGULATOR (LDO)
Figure 36. Clock Distribution or External VCO < 1600 MHz (Mode 1)
AD9520-3 Data Sheet
Rev. A | Page 32 of 80
Mode 2—High Frequency Clock Distribution; CLK or
External VCO > 1600 MHz
The AD9520 power-up default configuration has the PLL
powered off and the routing of the input set so that the CLK/
CLK input is connected to the distribution section through the
VCO divider (divide-by-1/divide-by-2/divide-by-3/ divide-by-4/
divide-by-5/divide-by-6). This is a distribution only mode that
allows for an external input up to 2400 MHz (see Table 3). The
maximum frequency that can be applied to the channel dividers
is 1600 MHz; therefore, higher input frequencies must be divided
down before reaching the channel dividers.
When the PLL is enabled, this routing also allows the use of the
PLL with an external VCO or VCXO with a frequency of less than
2400 MHz. In this configuration, the internal VCO is not used and
is powered off. The external VCO/VCXO feeds directly into the
prescaler.
The register settings shown in Table 26 are the default values of
these registers at power-up or after a reset operation.
Table 26. Default Register Settings for Clock Distribution
Mode
Register Description
0x010[1:0] = 01b PLL asynchronous power-down (PLL off)
0x1E0[2:0] = 000b Set VCO divider = 2
0x1E1[0] = 0b Use the VCO divider
0x1E1[1] = 0b Select CLK as the source
When the internal PLL is used with an external VCO, the PLL
must be turned on.
Table 27. Settings When Using an External VCO
Register Description
0x010[1:0] = 00b PLL normal operation (PLL on)
0x010 to 0x01E PLL settings; select and enable a
reference input; set R, N (P, A, B), PFD
polarity, and ICP according to the intended
loop configuration
0x1E1[1] = 0b Select CLK as the source
An external VCO requires an external loop filter that must be
connected between CP and the tuning pin of the VCO. This
loop filter determines the loop bandwidth and stability of the
PLL. Make sure to select the proper PFD polarity for the VCO
being used.
Table 28. Setting the PFD Polarity
Register Description
0x010[7] = 0b PFD polarity positive (higher control
voltage produces higher frequency)
0x010[7] = 1b PFD polarity negative (higher control
voltage produces lower frequency)
Data Sheet AD9520-3
Rev. A | Page 33 of 80
PROGRAMMABLE
N DEL AY
REFIN
CLK
CLK
REF1
REF2
BUF
AMP
AD9520
R
DIVIDER
CLOCK
DOUBLER
STATUS
PROGRAMMABLE
R DELAY
REFERENCE
SWITCHOVER
REF_SEL CPRSET VCP
VS GND RSET
DISTRIBUTION
REFERENCE
REFMON
CP
STATUS
LD
P, P + 1
PRESCALER A/B
COUNTERS
N DIV IDER
BYPASS
LF
LOW DROPOUT
REGULATOR (LDO) PHASE
FREQUENCY
DETECTOR
LOCK
DETECT
CHARGE
PUMP
PLL
REFERENCE
HOLD
01
DIV IDE BY 1,
2, 3, 4, 5, OR 6
PD
SYNC
REFIN
RESET
EEPROM
DIGITAL
LOGIC EEPROM
DIV IDE BY
1 TO 32
OUT0
OUT0
OUT1
OUT1
OUT2
OUT2
DIV IDE BY
1 TO 32
OUT3
OUT3
OUT4
OUT4
OUT5
OUT5
DIV IDE BY
1 TO 32
OUT6
OUT6
OUT7
OUT7
OUT8
OUT8
DIV IDE BY
1 TO 32
OUT9
OUT9
OUT10
OUT10
OUT11
OUT11
ZE RO DEL AY BLOCK
LVPECL/CMOS OUTPUT
STATUS
STATUS
SP1
SP0
SPI
INTERFACE I
2
C
INTERFACE
SCLK/SCL
SDIO/SDA
SDO
CS
SERIAL
PORT
DECODE
VS_DRV
OPTIONAL
07216-029
Figure 37. High Frequency Clock Distribution or External VCO > 1600 MHz (Mode 2)
AD9520-3 Data Sheet
Rev. A | Page 34 of 80
Phase-Locked Loop (PLL)
PROGRAMMABLE
N DELAY
REFIN
CLK
CLK
REF1
REF2
BUF
STATUS
STATUS
R
DIVIDER
CLOCK
DOUBLER
STATUS
PROGRAMMABLE
R DELAY
REFERENCE
SWITCHOVER
REF_SEL CPRSET VCPVS GND RSET
DISTRIBUTION
REFERENCE
REFMON
CP
STATUS
LD
P, P + 1
PRESCALER A/B
COUNTERS
N DIVIDER
BYPASS
LF
LOW DROPOUT
REGULATOR (LDO) PHASE
FREQUENCY
DETECTOR
LOCK
DETECT
CHARGE
PUMP
PLL
REFERENCE
HOLD
01
DIVIDE BY 1,
2, 3, 4, 5, O R 6
ZERO DELAY BLOCK
FRO M CHANNE L
DIVIDER 0
VS_DRV
OPTIONAL
REFIN
07216-064
Figure 38. PLL Functional Block Diagram
The AD9520 includes an on-chip PLL with an on-chip VCO.
The PLL blocks can be used either with the on-chip VCO to
create a complete phase-locked loop or with an external VCO
or VCXO. The PLL requires an external loop filter, which
usually consists of a small number of capacitors and resistors.
The configuration and components of the loop filter help to
establish the loop bandwidth and stability of the operating PLL.
The AD9520 PLL is useful for generating clock frequencies
from a supplied reference frequency. This includes conversion
of reference frequencies to much higher frequencies for subsequent
division and distribution. In addition, the PLL can be used to
clean up jitter and phase noise on a noisy reference. The exact
choice of PLL parameters and loop dynamics is application
specific. The flexibility and depth of the AD9520 PLL allow the
part to be tailored to function in many different applications
and signal environments.
Configuration of the PLL
The AD9520 allows flexible configuration of the PLL, which
accommodates various reference frequencies, PFD comparison
frequencies, VCO frequencies, internal or external VCO/VCXO,
and loop dynamics. This is accomplished by the various settings
for the R divider, N divider, PFD polarity (applicable only to the
external VCO/VCXO), antibacklash pulse width, charge pump
current, selection of internal VCO or external VCO/ VCXO, and
the loop bandwidth. These are managed through programmable
register settings (see Table 50 and Table 54) and by the design of
the external loop filter. Successful PLL operation and satisfactory
PLL loop performance are highly dependent upon proper
configuration of the PLL settings, and the design of the external
loop filter is crucial to the proper operation of the PLL.
ADIsimCLK™ is a free program that can help with the design
and exploration of the capabilities and features of the AD9520,
including the design of the PLL loop filter.
Phase Frequency Detector (PFD)
The PFD takes inputs from the R divider and the N divider and
produces an output proportional to the phase and frequency
difference between them. The PFD includes a programmable
delay element that controls the width of the antibacklash pulse.
This pulse ensures that there is no dead zone in the PFD
transfer function and minimizes phase noise and reference
spurs. The antibacklash pulse width is set by Register
0x017[1:0].
An important limit to keep in mind is the maximum frequency
allowed into the PFD. The maximum input frequency into the
PFD is a function of the antibacklash pulse setting, as specified
in the phase/frequency detector (PFD) parameter in Table 2.
Charge Pump (CP)
The charge pump is controlled by the PFD. The PFD monitors
the phase and frequency relationship between its two inputs and
tells the CP to pump up or pump down to charge or discharge the
integrating node (part of the loop filter). The integrated and
filtered CP current is transformed into a voltage that drives the
tuning node of the internal VCO through the LF pin (or the
tuning pin of an external VCO) to move the VCO frequency up
or down.
The CP can be set (Register 0x010[3:2]) for high impedance
(allows holdover operation), for normal operation (attempts to
lock the PLL loop), or for pump-up or pump-down (test modes).
The CP current is programmable in eight steps from (nominally)
0.6 mA to 4.8 mA. The CP current LSB is set by the CPRSET
resistor, which is nominally 5.1 kΩ. The exact value of the CP
current can be calculated with the following equation:
ICP (A) =
)(
06.3
Ω
RSET
CP
Data Sheet AD9520-3
Rev. A | Page 35 of 80
On-Chip VCO
The AD9520 includes an on-chip VCO covering the frequency
range shown in Table 2. The calibration procedure ensures that
the VCO operating voltage is centered for the desired VCO
frequency. The VCO must be calibrated when the VCO loop
is first set up, as well as any time the nominal VCO frequency
changes. However, once the VCO is calibrated, the VCO has
sufficient operating range to stay locked over temperature and
voltage extremes without needing additional calibration. See
the VCO Calibration section for additional information.
The on-chip VCO is powered by an on-chip, low dropout (LDO),
linear voltage regulator. The LDO provides some isolation of
the VCO from variations in the power supply voltage level. The
BYPASS pin should be connected to ground by a 220 nF capacitor
to ensure stability. This LDO employs the same technology that
is used in the anyCAP® line of regulators from Analog Devices, Inc.,
making it insensitive to the type of capacitor used. Driving an
external load from the BYPASS pin is not supported.
PLL External Loop Filter
When using the internal VCO, reference the external loop filter
to the BYPASS pin for optimal noise and spurious performance.
Figure 39 shows an example of an external loop filter for the PLL.
This third-order design usually offers the best performance. A loop
filter must be calculated for each desired PLL configuration. The
component values depend upon the VCO frequency, the KVCO, the
PFD frequency, the CP current, the desired loop bandwidth, and
the desired phase margin. The loop filter affects the phase noise,
loop settling time, and loop stability. A knowledge of PLL theory
is necessary for understanding loop filter design. Available tools,
such as ADIsimCLK, can help with the calculation of a loop
filter according to the application requirements.
LF
VCO
CHARGE
PUMP
CP
BYPASS C1 C2 C3
R1
31pF
R2
C
BP
= 220nF
AD9520
07216-142
Figure 39. Example of External Loop Filter for a PLL Using the Internal VCO
When using an external VCO, ensure that the external loop filter
is referenced to ground. See Figure 40for an example of an
external loop filter for a PLL using an external VCO.
CLK/CLK
EXTERNAL
VCO/VCXO
CHARGE
PUMP
CP
C1 C2 C3
R1
R2
AD9520
07216-143
Figure 40. Example of External Loop Filter for a PLL Using an External VCO
Figure 41 and Figure 42 show the typical PLL loop filters that
are used to generate the plots in Figure 30 and Figure 32,
respectively.
07216-234
C1
62pF
C3
33pF
C2
240nF
C12
220nF
BYPASS
CAPACITOR
FOR LDO
R1
820Ω
R2
390Ω
LFCP
BYPASS
Figure 41. Typical PLL Loop Filter Used for Clock Generation
07216-235
C1
1.5nF
C3
2.2nF
C2
4.7µF
C12
220nF
BYPASS
CAPACITOR
FOR LDO
R1
2.1kΩ
R2
3kΩ
LFCP
BYPASS
Figure 42. Typical PLL Loop Filter Used for Clock Cleanup
PLL Reference Inputs
The AD9520 features a flexible PLL reference input circuit that
allows a fully differential input, two separate single-ended inputs,
or a 16.67 MHz to 33.33 MHz crystal oscillator with an on-chip
maintaining amplifier. An optional reference clock doubler
can be used to double the PLL reference frequency. The input
frequency range for the reference inputs is specified in Table 2.
Both the differential and the single-ended inputs are self-biased,
allowing for easy ac coupling of input signals.
Either a differential or a single-ended reference must be specifically
enabled. All PLL reference inputs are off by default.
The differential input and the single-ended inputs share two pins,
REFIN and REFIN (REF1 and REF2, respectively). The desired
reference input type is selected and controlled by Register 0x01C
(see Table 50 and Table 54).
When the differential reference input is selected, the self-bias
level of the two sides is offset slightly (~100 mV, see Table 2) to
prevent chattering of the input buffer when the reference is slow
or missing. This increases the voltage swing that is required of
the driver and overcomes the offset. The differential reference
input can be driven by either ac-coupled LVDS or ac-coupled
LVPECL signals.
The single-ended inputs can be driven by either a dc-coupled
CMOS level signal or an ac-coupled sine wave or square wave.
To avoid input buffer chatter when a single-ended, ac-coupled
input signal stops toggling, the user can set Register 0x018[7]
to 1b. This shifts the dc offset bias point down 140 mV. To increase
isolation and reduce power, each single-ended input can be
independently powered down.
AD9520-3 Data Sheet
Rev. A | Page 36 of 80
The differential reference input receiver is powered down when
the differential reference input is not selected or when the PLL
is powered down. The single-ended buffers power down when
the PLL is powered down or when their respective individual
power-down registers are set. When the differential mode is
selected, the single-ended inputs are powered down.
In differential mode, the reference input pins are internally self-
biased so that they can be ac-coupled via capacitors. It is possible to
dc couple to these inputs. If the differential REFIN is driven by
a single-ended signal, the unused side (REFIN) should be
decoupled via a suitable capacitor to a quiet ground. Figure 43
shows the equivalent circuit of REFIN.
VS
REF1
REF2
REFIN
150Ω
150Ω
10kΩ 12kΩ
10kΩ 10kΩ
REFIN
85kΩ
VS
85kΩ
VS
07216-066
Figure 43. REFIN Equivalent Circuit for Non-XTAL Mode
Crystal mode is nearly identical to differential mode. The user
enables a maintaining amplifier by setting the enable XTAL
OSC bit, and putting a series resonant, AT fundamental cut
crystal across the REFIN and REFIN pins.
Reference Switchover
The AD9520 supports dual single-ended CMOS inputs, as well
as a single differential reference input. In the dual single-ended
reference mode, the AD9520 supports automatic revertive and
manual PLL reference clock switching between REF1 (on Pin
REFIN) and REF2 (on Pin REFIN). This feature supports
networking and other applications that require smooth switching
of redundant references. When used in conjunction with the
automatic holdover function, the AD9520 can achieve a worst-
case reference input switchover with an output frequency
disturbance as low as 10 ppm.
The AD9520 features a dc offset option in single-ended mode.
This option is designed to eliminate the risk of the reference
inputs chattering when they are ac-coupled and the reference
clock disappears. When using the reference switchover, the single-
ended reference inputs should be dc-coupled CMOS levels (with
the AD9520 dc offset feature disabled). Alternatively, the inputs
can be ac-coupled and dc offset feature enabled.
Keep in mind, however, that the minimum input amplitude for
the reference inputs is greater when the dc offset is turned on.
Reference switchover can be performed manually or automatically.
Manual switchover is performed either through Register 0x01C
or by using the REF_SEL pin. Manual switchover requires the
presence of a clock on the reference input that is being switched
to; otherwise, the deglitching feature must be disabled in Bit 7
of Register 0x01C. The reference switching logic fails if this
condition is not met, and the PLL does not reacquire.
Automatic revertive switchover relies on the REFMON pin to
indicate when REF1 disappears. By programming Register 0x01B =
0xF7 and Register 0x01C = 0x26, the REFMON pin is programmed
to be high when REF1 is invalid, which commands the switch to
REF2. When REF1 is valid again, the REFMON pin goes low, and
the part again locks to REF1. The STATUS pin can also be used
for this function, and REF2 can be used as the preferred
reference.
A switchover deglitch feature ensures that the PLL does not
receive rising edges that are far out of alignment with the newly
selected reference. For the switchover deglitch feature to work
correctly, the presence of a clock is required on the reference input
that is being switched to. The deglitching feature can also be
disabled (Register 0x01C[7]).
Automatic nonrevertive switching is not supported.
Reference Divider R
The reference inputs are routed to the reference divider, R. R is
a 14-bit counter that can be set to any value from 0 to 16,383 by
writing to Register 0x011 and Register 0x012 (both R = 0 and R = 1
give divide-by-1.) The output of the R divider goes to one of the
PFD inputs to be compared with the VCO frequency divided by
the N divider. The frequency applied to the PFD must not exceed
the maximum allowable frequency, which depends on the
antibacklash pulse setting (see Table 2).
The R divider has its own reset. The R divider can be reset using
the shared reset bit of the R, A, and B counters. It can also be
reset by a SYNC operation.
VCO/VCXO Feedback Divider N—P, A, and B
The N divider is a combination of a prescaler, P, and two counters,
A and B. The total divider value is
N = (P × B) + A
where P can be 2, 4, 8, 16, or 32.
Data Sheet AD9520-3
Rev. A | Page 37 of 80
Prescaler
The prescaler of the AD9520 allows for two modes of operation:
a fixed divide (FD) mode of 1, 2, or 3, and a dual modulus (DM)
mode where the prescaler divides by P and (P + 1) {2 and 3, 4
and 5, 8 and 9, 16 and 17, or 32 and 33}. The prescaler modes of
operation are given in Table 54, Register 0x016[2:0]. Not all
modes are available at all frequencies (see Table 2).
When operating the AD9520 in dual modulus mode, P/(P + 1),
the equation used to relate the input reference frequency to the
VCO output frequency is
fVCO = (fREF/R) × (P × B + A) = fREF × N/R
However, when operating the prescaler in FD Mode 1, FD Mode 2,
or FD Mode 3, the A counter is not used (A = 0; the divide is a
fixed divide of P = 2, 4, 8, 16, or 32) and the equation simplifies to
fVCO = (fREF/R) × (P × B) = fREF × N/R
By using combinations of DM and FD modes, the AD9520 can
achieve values of N from 1 to 262,175.
Table 29 shows how a 10 MHz reference input can be locked to
any integer multiple of N.
Note that the same value of N can be derived in different ways,
as illustrated by the case of N = 12. The user can choose a fixed
divide mode of P = 2 with B = 6; use the dual modulus mode of
2/3 with A = 0, B = 6; or use the dual modulus mode of 4/5 with
A = 0, B = 3.
A and B Counters
The B counter must be ≥3 or bypassed, and unlike the R counter,
A = 0 is actually zero.
When the prescaler is in dual modulus mode, the A counter
must be equal to or less than the B counter.
The maximum input frequency to the A/B counter is reflected
in the maximum prescaler output frequency (~300 MHz) that is
specified in Table 2. This is the prescaler input frequency (VCO or
CLK) divided by P. For example, a dual modulus mode of P = 8/9
is not allowed if the VCO frequency is greater than 2400 MHz
because the frequency going to the A/B counter is too high.
When the AD9520 B counter is bypassed (B = 1), the A counter
should be set to zero, and the overall resulting divide is equal to
the prescaler setting, P. The possible divide ratios in this mode
are 1, 2, 3, 4, 8, 16, and 32. This mode is useful only when an
external VCO/VCXO is used because the frequency range of the
internal VCO requires an overall feedback divider greater than 32.
Although manual reset is not normally required, the A/B counters
have their own reset bit. Alternatively, the A and B counters can be
reset using the shared reset bit of the R, A, and B counters. Note
that these reset bits are not self-clearing.
R, A, and B Counters—SYNC Pin Reset
The R, A, and B counters can be reset simultaneously through the
SYNC pin. This function is controlled by Register 0x019[7:6] (see
Table 54). The SYNC pin reset is disabled by default.
R and N Divider Delays
Both the R and N dividers feature a programmable delay cell.
These delays can be enabled to allow adjustment of the phase
relationship between the PLL reference clock and the VCO or
CLK. Each delay is controlled by three bits. The total delay
range is about 1 ns. See Register 0x019 in Table 2 and Table 54.
Table 29. How a 10 MHz Reference Input Can Be Locked to Any Integer Multiple of N
f
REF
(MHz)
R
P
A
B
N
f
VCO
(MHz)
Mode
Description
10 1 1 X1 1 1 10 FD P = 1, B = 1 (A and B counters are bypassed).
10
1
2
X
1
1
2
20
FD
P = 2, B = 1 (A and B counters are bypassed).
10 1 1 X1 3 3 30 FD A counter is bypassed.
10 1 1 X1 4 4 40 FD A counter is bypassed.
10 1 1 X1 5 5 50 FD A counter is bypassed.
10 1 2 X1 3 6 60 FD A counter is bypassed.
10 1 2 0 3 6 60 DM
10 1 2 1 3 7 70 DM Maximum frequency into prescaler in P = 2/3 mode is 200 MHz.
If N = 7 or N = 11 is desired for prescaler input frequency of 200 MHz
to 300 MHz, use P = 1 and N = 7 or 11, respectively.
10 1 2 2 3 8 80 DM
10 1 2 1 4 9 90 DM
10 1 8 6 18 150 1500 DM
10 1 8 7 18 151 1510 DM
10 1 16 7 9 151 1510 DM
10 10 32 6 47 1510 1510 DM
10 1 8 0 25 200 2000 DM
10 1 16 0 15 240 2400 DM
10
10
32
0
75
2400
2400
DM
1 X = don’t care.
AD9520-3 Data Sheet
Rev. A | Page 38 of 80
Digital Lock Detect (DLD)
By selecting the proper output through the mux on each pin, the
DLD function is available at the LD, STATUS, and REFMON pins.
The digital lock detect circuit indicates a lock when the time
difference of the rising edges at the PFD inputs is less than a
specified value (the lock threshold). The loss of a lock is indicated
when the time difference exceeds a specified value (the unlock
threshold). Note that the unlock threshold is wider than the
lock threshold, which allows some phase error in excess of the
lock window to occur without chattering on the lock indicator.
The lock detect window timing depends on the value of the
CPRSET resistor, as well as three settings: the digital lock detect
window bit (Register 0x018[4]), the antibacklash pulse width
bit (Register 0x017[1:0], see Table 2), and the lock detect
counter (Register 0x018[6:5]). The lock and unlock detection
values listed in Table 2 are for the nominal value of CPRSET =
5.11 kΩ. Doubling the CPRSET value to 10 kΩ doubles the values
in Table 2.
A lock is not indicated until there is a programmable number of
consecutive PFD cycles with a time difference that is less than the
lock detect threshold. The lock detect circuit continues to indicate
a lock until a time difference that is greater than the unlock
threshold occurs on a single subsequent cycle. For the lock detect
to work properly, the period of the PFD frequency must be greater
than the unlock threshold. The number of consecutive PFD cycles
required for lock is programmable (Register 0x018[6:5]).
Note that, in certain low (<500 Hz) loop bandwidth, high phase
margin cases, the DLD may chatter during acquisition, which
can cause the AD9520 to automatically enter and exit holdover.
To avoid this problem, it is recommended that the user provide
for a capacitor to ground on the LD pin such that current source
digital lock detect (CSDLD) mode can be used.
Analog Lock Detect (ALD)
The AD9520 provides an ALD function that can be selected for
use at the LD pin. There are two operating modes for ALD:
• N-channel open-drain lock detect. This signal requires
a pull-up resistor to the positive supply, VS. The output is
normally high with short, low going pulses. Lock is indicated
by the minimum duty cycle of the low-going pulses.
• P-channel open-drain lock detect. This signal requires a
pull-down resistor to GND. The output is normally low with
short, high going pulses. Lock is indicated by the minimum
duty cycle of the high-going pulses.
AD9520
ALD
LD R1
C
V
OUT
R2
V
S
= 3.3V
07216-067
Figure 44. Example of Analog Lock Detect Filter Using
N-Channel Open-Drain Driver
The analog lock detect function requires an RC filter to provide a
logic level indicating lock/unlock. The ADIsimCLK tool can be
used to help the user select the right passive component values
for ALD to ensure its correct operation.
Current Source Digital Lock Detect (CSDLD)
During the PLL locking sequence, it is normal for the DLD
signal to toggle a number of times before remaining steady
when the PLL is completely locked and stable. There may be
applications where it is desirable to have DLD asserted only
after the PLL is solidly locked. This is possible by using the
current source digital lock detect function.
AD9520
LD
REFMON
OR
STATUS
C
V
OUT
110µA
DLD
LD PIN
COMPARATOR
07216-068
Figure 45. Current Source Digital Lock Detect
The current source lock detect provides a current of 110 µA when
DLD is true and shorts to ground when DLD is false. If a capacitor
is connected to the LD pin, it charges at a rate determined by the
current source during the DLD true time but is discharged nearly
instantly when DLD is false. By monitoring the voltage at the
LD pin (top of the capacitor), LD = high happens only after the
DLD is true for a sufficiently long time. Any momentary DLD
false resets the charging. By selecting a properly sized capacitor,
it is possible to delay a lock detect indication until the PLL is
stably locked and the lock detect does not chatter.
To use current source digital lock detect, do the following:
• Place a capacitor to ground on the LD pin.
• Set Register 0x01A[5:0] = 0x04.
• Enable the LD pin comparator (Register 0x01D[3] = 1b).
The LD pin comparator senses the voltage on the LD pin, and
the comparator output can be made available at the REFMON
pin control (Register 0x01B[4:0]) or the STATUS pin control
(Register 0x017[7:2]). The internal LD pin comparator trip point
and hysteresis are given in Table 17. The voltage on the capacitor
can also be sensed by an external comparator that is connected
to the LD pin. In this case, enabling the on-board LD pin
comparator is not necessary.
The user can asynchronously enable individual clock outputs
only when CSDLD is high. To enable this feature, set the
appropriate bits in the enable output on the CSDLD registers
(Register 0x0FC and Register 0x0FD).
Data Sheet AD9520-3
Rev. A | Page 39 of 80
External VCXO/VCO Clock Input (CLK/CLK)
This differential input is used to drive the AD9520 clock
distribution section. This input can receive up to 2.4 GHz.
The pins are internally self-biased, and the input signal should
be ac-coupled via capacitors.
VS
CLO CK INPUT
STAGE
CLK
CLK
5kΩ
5kΩ
2.5kΩ 2.5kΩ
07216-032
Figure 46. CLK Equivalent Input Circuit
The CLK/CLK input can be used either as a distribution only
input (with the PLL off) or as a feedback input for an external
VCO/VCXO using the internal PLL when the internal VCO is
not used. These inputs are also used as a feedback path for the
external zero delay mode.
Holdover Mode
The AD9520 PLL has a holdover function. Holdover mode
allows the VCO to maintain a relatively constant frequency
even though there is no reference clock. This function is useful
when the PLL reference clock is lost. Holdover is implemented
by placing the charge pump in a high impedance state. Without
this function, the charge pump is placed into a constant pump-up
or pump-down state, resulting in a massive VCO frequency
shift. Because the charge pump is placed in a high impedance
state, any leakage that occurs at the charge pump output or the
VCO tuning node causes a drift of the VCO frequency. This
drift can be mitigated by using a loop filter that contains a large
capacitive component because this drift is limited by the current
leakage-induced slew rate (ILEAK/C) of the VCO control voltage.
Both a manual holdover mode, using the SYNC pin, and an
automatic holdover mode are provided. To use either function, the
holdover function must be enabled (Register 0x01D[0]).
Manual/External Holdover Mode
A manual holdover mode can be enabled that allows the user to
place the charge pump into a high impedance state when the
SYNC pin is asserted low. This operation is edge sensitive, not
level sensitive. The charge pump enters a high impedance state
immediately. To take the charge pump out of a high impedance
state, take the SYNC pin high. The charge pump then leaves the
high impedance state synchronously with the next PFD rising
edge from the reference clock. This prevents extraneous charge
pump events from occurring during the time between SYNC
going high and the next PFD event. This also means that the
charge pump stays in a high impedance state if no reference
clock is present.
The B counter (in the N divider) is reset synchronously with the
charge pump, leaving the high impedance state on the reference
path PFD event. This helps align the edges out of the R and N
dividers for faster settling of the PLL. Because the prescaler is
not reset, this feature works best when the B and R numbers are
close, resulting in a smaller phase difference for the loop to
settle out.
When using this mode, set the channel dividers to ignore the
SYNC pin (at least after an initial SYNC event). If the dividers are
not set to ignore the SYNC pin, the distribution outputs turn off
when SYNC is taken low to put the part into holdover mode. The
channel divider ignore SYNC function is programmed in Bit 6 of
Register 0x191, Register 0x194, Register 0x197, and Register 0x19A
for Channel Divider 0, Channel Divider 1, Channel Divider 2, and
Channel Divider 3, respectively.
Automatic/Internal Holdover Mode
When enabled, this function automatically places the charge
pump into a high impedance state when the loop loses lock.
The assumption is that the only reason the loop loses lock is due
to the PLL losing the reference clock; therefore, the holdover
function puts the charge pump into a high impedance state to
maintain the VCO frequency as close as possible to the original
frequency before the reference clock disappeared.
The holdover function senses the logic level of the LD pin as a
condition to enter holdover. The signal at LD can be from the
DLD, ALD, or current source LD mode. The LD comparator
can be disabled (Register 0x01D[3]), which causes the holdover
function to always sense LD as being high. If DLD is used, it is
possible for the DLD signal to chatter while the PLL is reacquiring
lock. The holdover function may retrigger, thereby preventing
the holdover mode from terminating. Use of the current source
lock detect mode is recommended to avoid this situation (see the
Current Source Digital Lock Detect (CSDLD) section).
When in holdover mode, the charge pump stays in a high
impedance state as long as there is no reference clock present.
As in the external holdover mode, the B counter (in the N divider)
is reset synchronously with the charge pump leaving the high
impedance state on the reference path PFD event. This helps
align the edges out of the R and N dividers for faster settling of
the PLL and reduces frequency errors during settling. Because
the prescaler is not reset, this feature works best when the B and
R numbers are close because this results in a smaller phase
difference for the loop to settle out.
After leaving holdover, the loop then reacquires lock, and the
LD pin must go high (if Register 0x01D[3] = 1b) before it can
reenter holdover (CP high impedance).
The holdover function always responds to the state of the currently
selected reference (Register 0x01C). If the loop loses lock during
a reference switchover (see the Reference Switchover section),
holdover is triggered briefly until the next reference clock edge
at the PFD.
AD9520-3 Data Sheet
Rev. A | Page 40 of 80
A flowchart of the automatic/internal holdover function
operation is shown in Figure 47.
NO
NO
NO
NO
YES
YES
YES
YES
YES
PLL ENABLED
DLD == LOW
WAS
LD PIN == HIGH
WHE N DLD WE NT
LOW?
HIGH IM P E DANCE
CHARGE P UMP
REF E RE NCE
EDGE AT PFD?
RELEASE
CHARGE P UMP
HIGH IM P E DANCE
DLD == HIG H
YES
07216-069
LOOP OUT OF LOCK. DIGITAL LOCK
DETECT SIGNAL GOES LOW WHEN THE
LOOP LEAVES LOCK, AS DETERMINED
BY THE PHAS E DIFFERE NCE AT THE
INPUT OF THE PFD.
REG 0x01D[ 3] : LD PI N COM PARATOR ENABLE.
0b = DISABLE; 1b = ENABLE. WHEN DISABL E D,
THE HOLDOVER FUNCTIONALWAYS SENSES
THE LD PINAS HIG H.
CHARGE P UMP IS M ADE HIG H IMPE DANCE .
PLL COUNTE RS CONTINUE
OPERAT ING NORMALLY.
CHARGE P UMP REMAINS HIGH IMPE DANCE
UNTIL THE REFERE NCE RE TURNS.
TAKE CHARGE P UMP OUT OF
HIGH IM P E DANCE . PLL CAN NO W RESE TTLE.
WAIT FOR DLD TO GO HIGH. THISTAKES
5 TO 255 CYCL E S ( P ROGRAM M ING OF
THE DLD DELAY CO UNTER) WI TH THE
REFERENCE AND F E E DBACK CLOCKS
INS IDE T HE LOCK WINDOW AT THE PFD.
THIS ENSURES THAT THE HOLDOVER
FUNCTION WAITS FOR THE PLL TO SETTLE
AND LOCK BEF ORE T HE HOLDOVER
FUNCTION CAN BE RETRIGGE RE D.
Figure 47. Flowchart of Automatic/Internal Holdover Mode
The following registers affect the automatic/internal holdover
function:
• Register 0x018[6:5]—lock detect counter. This changes
how many consecutive PFD cycles with edges inside the
lock detect window are required for the DLD indicator to
indicate lock. This impacts the time required before the LD
pin can begin to charge as well as the delay from the end of
a holdover event until the holdover function can be reengaged.
• Register 0x018[3]—disable digital lock detect. This bit must
be set to 0b to enable the DLD circuit. Automatic/internal
holdover does not operate correctly without the DLD function
enabled.
• Register 0x01A[5:0]—lock detect pin control. Set these bits
to 000100b to program the current source lock detect
mode if using the LD pin comparator. Load the LD pin
with a capacitor of an appropriate value.
• Register 0x01D[3]—LD pin comparator enable. 1b = enable;
0b = disable. When disabled, the holdover function always
senses the LD pin as high.
• Register 0x01D[1]—external holdover control.
• Register 0x01D[0]—holdover enable. If holdover is disabled,
both external and automatic/internal holdover are disabled.
In the following example, automatic holdover is configured with
• Automatic reference switchover, prefer REF1.
• Digital lock detect: five PFD cycles, high range window.
• Automatic holdover using the LD pin comparator.
The following registers are set (in addition to the normal PLL
registers):
• Register 0x018[6:5] = 00b; lock detect counter = five cycles.
• Register 0x018[4] = 0b; digital lock detect window = high
range.
• Register 0x018[3] = 1b; disable DLD normal operation.
• Register 0x01A[5:0] = 000100b; program LD pin control to
current source lock detect mode.
• Register 0x01C[4] = 1b; enable automatic switchover.
• Register 0x01C[3] = 0b; prefer REF1.
• Register 0x01C[2:1] = 11b; enable REF1 and REF2 input
buffers.
• Register 0x01D[3] = 1b; enable LD pin comparator.
• Register 0x01D[1] = 0b; disable external holdover mode and
use automatic/internal holdover mode.
• Register 0x01D[0] = 1b; enable holdover.
Data Sheet AD9520-3
Rev. A | Page 41 of 80
PROGRAMMABLE
N DEL AY
CLK
CLK
REF1
REF2
BUF
STATUS
STATUS
R
DIVIDER
CLOCK
DOUBLER
VCO S TATUS
PROGRAMMABLE
R DEL AY
REFERENCE
SWITCHOVER
REF_SEL CPRSET VCP
VS GND RSET
DISTRIBUTION
REFERENCE
REFMON
CP
STATUS
LD
P, P + 1
PRESCALER A/B
COUNTERS
N DIV IDER
BYPASS
LF
LOW DROPOUT
REGULATOR (LDO) PHASE
FREQUENCY
DETECTOR
LOCK
DETECT
CHARGE
PUMP
PLL
REFERENCE
HOLD
01
DIV IDE BY 1,
2, 3, 4, 5, OR 6
ZE RO DEL AY BLOCK
FROM CHANNEL
DIV IDER 0
VS_DRV
REFIN
OPTIONAL
REFIN
07216-070
Figure 48. Reference and VCO/CLK Frequency Status Monitors
Frequency Status Monitors
The AD9520 contains three frequency status monitors that are
used to indicate if the PLL reference (or references, in the case of
single-ended mode) and the VCO/CLK input have fallen below
a threshold frequency. Note that the VCO frequency monitor
becomes a CLK input frequency monitor if the CLK input is
selected instead of the internal VCO. Figure 48 shows the
location of the frequency status monitors in the PLL.
The PLL reference monitors have two threshold frequencies:
normal and extended (see Table 17). The reference frequency
monitor thresholds are set in Register 0x01A[6].
VCO Calibration
The AD9520 on-chip VCO must be calibrated to ensure proper
operation over process and temperature. The VCO calibration
is controlled by a calibration controller running off a divided
REFIN clock. The calibration requires that the PLL be set up
properly to lock the PLL loop and that the REFIN clock be
present. The REFIN clock must come from a stable source
external to the AD9520.
VCO calibration can be performed two ways: automatically at
power-up and manually. Automatic VCO calibration occurs when
the EEPROM is set to automatically load the preprogrammed
values in the EEPROM, and then automatically calibrate the VCO.
For the automatic calibration to complete, a valid reference
must be provided at power-up. If no valid reference is provided,
the user must calibrate the VCO manually.
During the first initialization after a power-up or a reset of the
AD9520, a manual VCO calibration sequence is initiated by
setting Register 0x018[0] = 1b. This can be done as part of the
initial setup before executing an update all registers operation
(IO_UPDATE, Register 0x232[0] = 1b).
Subsequent to the initial setup, a VCO calibration sequence is
initiated by resetting Register 0x018[0] = 0b, executing an
IO_UPDATE, setting Register 0x018[0] = 1b, and executing
another IO_UPDATE. A readback bit (Register 0x01F[6])
indicates when VCO calibration is finished by returning a logic
true (that is, 1b).
The sequence of operations for the VCO calibration follows:
1. Program the PLL registers to the proper values for the PLL
loop. Note that the VCO divider (Register 0x1E0[2:0])
must not be set to static during VCO calibration.
2. Ensure that the input reference signal is present.
3. For initial setting of the registers after a power-up or reset,
initiate a VCO calibration by setting Register 0x018[0] = 1b.
4. Subsequently, whenever a calibration is desired, set
Register 0x018[0] = 0b, update registers; and then set
Register 0x018[0] = 1b, update registers.
5. A SYNC operation is initiated internally, causing the
outputs to go to a static state determined by normal SYNC
function operation.
6. VCO is calibrated to the desired setting for the requested
VCO frequency.
7. Internally, the SYNC signal is released, allowing outputs to
continue clocking.
8. The PLL loop is closed.
9. The PLL locks.
A SYNC is executed during the VCO calibration; therefore,
the outputs of the AD9520 are held static during the calibration,
which prevents unwanted frequencies from being produced.
However, at the end of a VCO calibration, the outputs may
resume clocking before the PLL loop is completely settled.
AD9520-3 Data Sheet
Rev. A | Page 42 of 80
The VCO calibration clock divider is set as shown in Table 54
(Register 0x018[2:1]). The calibration divider divides the PFD
frequency (reference frequency divided by R) down to the
calibration clock. The calibration occurs at the PFD frequency
divided by the calibration divider setting. Lower VCO calibration
clock frequencies result in longer times for a calibration to be done.
The VCO calibration clock frequency is given by
fCAL_CLOCK = fREFIN/(R × cal_div)
where:
fREFIN is the frequency of the REFIN signal.
R is the value of the R counter.
cal_div is the division set for the VCO calibration divider
(Register 0x018[2:1]).
Choose a calibration divider such that the calibration frequency
is less than 6.25 MHz. Table 30 shows the appropriate value for
the calibration divider.
Table 30. VCO Calibration Divider Values for Different
Phase Detector Frequencies
PFD Rate (MHz) Recommended VCO Calibration Divider
<12 Any
12 to 25 4, 8, 16
25 to 50
8, 16
50 to 100 16
The VCO calibration takes 4400 calibration clock cycles. Therefore,
the VCO calibration time in PLL reference clock cycles is given by
Time to Calibrate VCO =
4400 × R × cal_div PLL Reference Clock Cycles
Table 31. Example Time to Complete a VCO Calibration
with Different fREFIN Frequencies
fREFIN (MHz) R Divider PFD Time to Calibrate VCO
100 1 100 MHz 88 µs
10 10 1 MHz 8.8 ms
10 100 100 kHz 88 ms
A VCO calibration must be manually initiated, which allows for
flexibility in deciding what order to program registers and when
to initiate a calibration, instead of having it occur every time the
values of certain PLL registers change. For example, this allows
for the VCO frequency to be changed by small amounts without
having an automatic calibration occur each time; this should be
done with caution and only when the user knows the VCO control
voltage will not exceed the nominal best performance limits. For
example, a few 100 kHz steps are fine, but a few MHz may not be.
In addition, because the calibration procedure results in rapid
changes in the VCO frequency, the distribution section is
automatically placed in SYNC until the calibration is finished.
Therefore, this temporary loss of outputs must be expected.
A VCO calibration should be initiated in the following conditions:
• After changing any of the PLL R, P, B, and A divider
settings, or after a change in the PLL reference clock
frequency. This, in effect, means any time a PLL register or
reference clock is changed such that a different VCO
frequency results.
• When system calibration is desired. The VCO is designed
to operate properly over extremes of temperature even
when it is first calibrated at the opposite extreme. However,
a VCO calibration can be initiated at any time, if desired.
ZERO DELAY OPERATION
Zero delay operation aligns the phase of the output clocks with
the phase of the external PLL reference input. There are two
zero delay modes on the AD9520: internal and external.
Internal Zero Delay Mode
The internal zero delay function of the AD9520 is achieved by
feeding the output of Channel Divider 0 back to the PLL N
divider. In Figure 49, the change in signal routing for internal
zero delay mode is shown in blue.
Set Register 0x01E[2:1] = 01b to select internal zero delay mode.
In the default internal zero delay mode, the output of Channel
Divider 0 is routed back to the PLL (N divider) through MUX3
and MUX1 (feedback path shown in blue in Figure 49). The PLL
synchronizes the phase/edge of the output of Channel Divider 0
with the phase/edge of the reference input. External zero delay
mode must be used if Channel Divider 1, Channel Divider 2, or
Channel Divider 3 is to be used for zero delay feedback. This is
accomplished by changing the value in Register 0x01E[4:3].
Because the channel dividers are synchronized to each other,
the outputs of the channel divider are synchronous with the
reference input. Both the R delay and the N delay inside the
PLL can be programmed to compensate for the propagation
delay from the output drivers and PLL components to minimize
the phase offset between the clock output and the reference
input to achieve zero delay.
Data Sheet AD9520-3
Rev. A | Page 43 of 80
DIVIDE BY 1,
2, 3, 4, 5, OR 6
LF
CLK/CLK
R
DIVIDER R
DELAY
N
DIVIDER N
DELAY
PFD CP LOOP
FILTER
MUX1 REG 0x01E[ 1] = 1
01
REFIN/
REFIN
MUX3
REG 0x01E [ 2] ZERO DEL AY
INT E RNAL F E E DBACK P ATH
EXT E RNAL F E E DBACK P ATH
ZERO DELAY F E E DBACK CLOCK
CHANNEL DIVIDER 0
CHANNEL DIVIDER 1
CHANNEL DIVIDER 2
CHANNEL DIVIDER 3
OUT0 TO OUT2
OUT3 TO OUT5
OUT6 TO OUT8
OUT9 TO OUT11
AD9520
07216-053
Figure 49. Zero Delay Function
External Zero Delay Mode
The external zero delay function of the AD9520 is achieved by
feeding one clock output back to the CLK input and ultimately
back to the PLL N divider. In Figure 49, the change in signal
routing for external zero delay mode is shown in red.
Set Register 0x01E[2:1] = 11b to select external zero delay mode.
In external zero delay mode, one of the twelve output clocks
(OUT0 to OUT11) can be routed back to the PLL (N divider)
through the CLK/CLK pins and through MUX3 and MUX1.
This feedback path is shown in red in Figure 49.
For VCO calibration to work correctly, the user must specify which
channel divider is used for external zero delay mode. Channel
Divider 0 is the default. Change the value in Register 0x01E[4:3]
to select Channel Divider 1, Channel Divider 2, or Channel
Divider 3 for zero delay feedback.
The PLL synchronizes the phase/edge of the feedback output clock
with the phase/edge of the reference input. Because the channel
dividers are synchronized to each other, the clock outputs are
synchronous with the reference input. Both the R delay and the
N delay inside the PLL can be programmed to compensate for
the propagation delay from the PLL components to minimize the
phase offset between the feedback clock and the reference input.
CLOCK DISTRIBUTION
A clock channel consists of three LVPECL clock outputs or six
CMOS clock outputs that share a common divider. A clock
output consists of the drivers that connect to the output pins.
The clock outputs have either LVPECL or CMOS at the pins.
The AD9520 has four clock channels. Each channel has its own
programmable divider that divides the clock frequency applied
to its input. The channel dividers can divide by any integer from
1 to 32.
The AD9520 features a VCO divider that divides the VCO output
by 1, 2, 3, 4, 5, or 6 before going to the individual channel dividers.
The VCO divider has two purposes. The first is to limit the
maximum input frequency of the channel dividers to 1.6 GHz.
The other is to allow the AD9520 to generate even lower
frequencies than would be possible with only a simple post divider.
External clock signals connected to the CLK input can also use
the VCO divider.
The channel dividers allow for a selection of various duty cycles,
depending on the currently set division. That is, for any specific
division, D, the output of the divider can be set to high for N + 1
input clock cycles and low for M + 1 input clock cycles (where
D = N + M + 2). For example, a divide-by-5 can be high for one
divider input cycle and low for four cycles, or a divide-by-5 can
be high for three divider input cycles and low for two cycles.
Other combinations are also possible.
The channel dividers include a duty-cycle correction function
that can be disabled. In contrast to the selectable duty cycle
just described, this function can correct a non-50% duty cycle
caused by an odd division. However, this requires that the
division be set by M = N + 1.
AD9520-3 Data Sheet
Rev. A | Page 44 of 80
In addition, the channel dividers allow a coarse phase offset or
delay to be set. Depending on the division selected, the output
can be delayed by up to 15 input clock cycles. For example, if
the frequency at the input of the channel divider is 1 GHz, the
channel divider output can be delayed by up to 15 ns. The
divider outputs can also be set to start high or to start low.
Operation Modes
There are three clock distribution operating modes, and these
are shown in Figure 50. One of these modes uses the internal
VCO, whereas the other two modes bypass the internal VCO
and use the signal provided on the CLK/CLK pins.
In Mode 0 (internal VCO mode), there are two signal paths
available. In the first path, the VCO signal is sent to the VCO
divider and then to the individual channel dividers. In the
second path, the user bypasses the VCO and channel dividers
and sends the VCO signal directly to the drivers.
When CLK is selected as the source, it is not necessary to use the
VCO divider if the CLK frequency is less than the maximum
channel divider input frequency (1600 MHz); otherwise, the
VCO divider must be used to reduce the frequency going to the
channel dividers.
Table 32 shows how the VCO, CLK, and VCO divider are selected.
Register 0x1E1[1:0] selects the channel divider source and
determines whether the VCO divider is used. It is not possible
to select the VCO without using the VCO divider.
Table 32. Operation Modes
Mode
Register 0x1E1
Channel Divider Source VCO Divider Bit 1 Bit 0
2 0 0 CLK Used
1 0 1 CLK Not used
0 1 0 VCO Used
1 1 Not allowed Not allowed
CLK or VCO Direct-to-LVPECL Outputs
It is possible to connect either the internal VCO or the CLK
(whichever is selected as the input to the VCO divider) directly
to the LVPECL outputs. This configuration can pass frequencies
up to the maximum frequency of the VCO directly to the LVPECL
outputs. However, the LVPECL outputs may not be able to meet
the VOD specification in Table 4 at the highest frequencies.
Either the internal VCO or the CLK can be selected as the
source for the direct-to-output signal routing. To connect the
LVPECL outputs directly to the internal VCO or CLK, the VCO
divider must be selected as the source to the distribution section,
even if no channel uses it.
Table 33. Routing VCO Divider Input Directly to the Outputs
Register Setting Selection
0x1E1[1:0] = 00b CLK is the source; VCO divider selected
0x1E1[1:0] = 10b VCO is the source; VCO divider selected
0x192[1] = 1b Direct-to-output OUT0, OUT1, OUT2
0x195[1] = 1b Direct-to-output OUT3, OUT4, OUT5
0x198[1] = 1b Direct-to-output OUT6, OUT7, OUT8
0x19B[1] = 1b Direct-to-output OUT9, OUT10, OUT11
Clock Frequency Division
The total frequency division is a combination of the VCO
divider (when used) and the channel divider. When the VCO
divider is used, the total division from the VCO or CLK to the
output is the product of the VCO divider (1, 2, 3, 4, 5, and 6)
and the division of the channel divider. Table 34 shows how the
frequency division for a channel is set.
Table 34. Frequency Division
CLK or VCO
Selected
VCO
Divider
Setting1
Channel
Divider
Setting
Direct-to-
Output
Setting
Resulting
Frequency
Division
CLK or VCO
input
1 to 6 Don’t care Enable 1
CLK or VCO
input
1 to 6 2 to 32 Disable (1 to 6) ×
(2 to 32)
CLK or VCO
input
2 to 6 Bypass Disable (2 to 6) × (1)
CLK or VCO
input
1 Bypass Disable Output static
(illegal state)
CLK (internal
VCO off)
VCO
divider
bypassed
Bypass Don’t care 1
CLK (internal
VCO off)
VCO
divider
bypassed
2 to 32 Don’t care 2 to 32
1 The bypass VCO divider (Register 0x1E1[0] = 1b) is not the same as VCO
divider = 1 (divide-by-1).
MODE 0 (INTE RNAL VCO MODE)
CLK
CLK
LF
01
DIVIDE BY 1,
2, 3, 4, 5, OR 6
CLOCK
DISTRI-
BUTION
PLL
DISTRIBUTION
CLOCK
MODE 1 (CLOCK DI STRIBUTI ON MODE )
DISTRIBUTION
CLOCK
MODE 2 (HF CLOCK DI STRIBUTION MODE)
CLK
CLK
LF
01
DIVIDE BY 1,
2, 3, 4, 5, OR 6
CLOCK
DISTRI-
BUTION
PLL
CLK
CLK
LF
01
DIVIDE BY 1,
2, 3, 4, 5, OR 6
CLOCK
DISTRI-
BUTION
PLL
DISTRIBUTION
CLOCK
07216-054
Figure 50. Simplified Diagram of the Three Clock Distribution Operation Modes
Data Sheet AD9520-3
Rev. A | Page 45 of 80
The channel dividers feeding the output drivers contain one 2-to-
32 frequency divider. This divider provides for division-by-1 to
division-by-32. Division-by-1 is accomplished by bypassing the
divider. The dividers also provide for a programmable duty cycle,
with optional duty-cycle correction when the divide ratio is odd.
A phase offset or delay in increments of the input clock cycle is
selectable. The channel dividers operate with a signal of up to
1600 MHz at their inputs across all channel divider ratios. The
features and settings of the dividers are selected by programming
the appropriate setup and control registers (see Table 50 through
Table 61).
VCO Divider
The VCO divider provides frequency division between the
internal VCO or the external CLK input and the clock
distribution channel dividers. The VCO divider can be set
to divide by 1, 2, 3, 4, 5, or 6 (see Table 57, Register 0x1E0[2:0]).
However, when the VCO divider is set to 1, none of the channel
output dividers can be bypassed.
The VCO divider can also be set to static, which is useful for
applications where the only desired output frequency is the
VCO frequency. Making the VCO divider static increases the
wide band spurious-free dynamic range (SFDR). If the VCO
divider is static during VCO calibration, there is no output
signal. Therefore, it is important to calibrate the VCO with the
VCO divider set to a nonstatic value during VCO calibration,
and then set the VCO divider to static when VCO calibration is
complete.
The recommended alternative to achieving the same SFDR
performance is to set the VCO divider to 1 and enable VCO direct
mode. This allows the user to program the EEPROM with the
desired values and does not require further action after the VCO
calibration is complete.
Channel Dividers
A channel divider drives each group of three LVPECL outputs.
There are four channel dividers (0, 1, 2, and 3) driving 12 LVPECL
outputs (OUT0 to OUT11). Table 35 lists the bit locations used
for setting the division and other functions of these dividers. The
division is set by the M and N values. The divider can be
bypassed (equivalent to divide-by-1, divider circuit is powered
down) by setting the bypass bit. The duty-cycle correction can
be enabled or disabled according to the setting of the disable
Divider x DCC bits.
Table 35. Setting DX for the Output Dividers
Divider
Low Cycles,
M Value Bits
High Cycles,
N Value Bits
Bypass
Bits
Disable
Divider x
DCC Bits
0
0x190[7:4]
0x190[3:0]
0x191[7]
0x192[0]
1 0x193[7:4] 0x193[3:0] 0x194[7] 0x195[0]
2 0x196[7:4] 0x196[3:0] 0x197[7] 0x198[0]
3 0x199[7:4] 0x199[3:0] 0x19A[7] 0x19B[0]
Channel Divider Maximum Frequency
The maximum frequency at which all features of the channel
divider are guaranteed to work is 1.6 GHz; this is the number that
appears elsewhere in the datasheet. The maximum frequency at
which all features of the channel divider are guaranteed to work
is 1.6 GHz; this is the number that appears elsewhere in the data
sheet. However, if the divide-by-3 and divide-by-17 settings are
avoided, the maximum channel divider input frequency is 2 GHz.
Channel Frequency Division (0, 1, 2, or 3)
For each channel (where the channel number (x) is 0, 1, 2, or 3),
the frequency division, DX, is set by the values of M and N
(four bits each, representing Decimal 0 to Decimal 15), where
Number of Low Cycles = M + 1
Number of High Cycles = N + 1
The high and low cycles are the cycles of the clock signal that
are currently routed to the input of the channel dividers (VCO
divider out or CLK).
When a divider is bypassed, DX = 1.
Otherwise, DX = (N + 1) + (M + 1) = N + M + 2. This allows
each channel divider to divide by any integer from 2 to 32.
Duty Cycle and Duty-Cycle Correction
The duty cycle of the clock signal at the output of a channel is
a result of some or all of the following conditions:
• M and N values for the channel
• DCC enabled/disabled
• VCO divider enabled/bypassed
• CLK input duty cycle (note that the internal VCO has
a 50% duty cycle)
The DCC function is enabled, by default, for each channel divider.
However, the DCC function can be disabled individually for
each channel divider by setting the disable Divider x DCC bit
for that channel.
Certain M and N values for a channel divider result in a non-
50% duty cycle. A non-50% duty cycle can also result in an
even division, if M ≠ N. The duty-cycle correction function
automatically corrects non-50% duty cycles at the channel
divider output to 50% duty cycle.
Duty-cycle correction requires the following channel divider
conditions:
• An even division must be set as M = N
• An odd division must be set as M = N + 1
When not bypassed or corrected by the DCC function, the duty
cycle of each channel divider output is the numerical value of
(N + 1)/(N + M + 2), expressed as a percent.
AD9520-3 Data Sheet
Rev. A | Page 46 of 80
Table 36 to Table 39 show the output duty cycle for various configurations of the channel divider and VCO divider.
Table 36. Channel Divider Output Duty Cycle with VCO Divider ≠ 1; Input Duty Cycle Is 50%
VCO Divider
DX Output Duty Cycle
N + M + 2 Disable Divider x DCC = 1b Disable Divider x DCC = 0b
Even Channel divider bypassed 50% 50%
Odd = 3 Channel divider bypassed 33.3% 50%
Odd = 5 Channel divider bypassed 40% 50%
Even, odd Even (N + 1)/(N + M + 2) 50%, requires M = N
Even, odd Odd (N + 1)/(N + M + 2) 50%, requires M = N + 1
Table 37. Channel Divider Output Duty Cycle with VCO Divider ≠ 1; Input Duty Cycle Is X%
VCO Divider
DX Output Duty Cycle
N + M + 2 Disable Divider x DCC = 1b Disable Divider x DCC = 0b
Even Channel divider bypassed 50% 50%
Odd = 3 Channel divider bypassed 33.3% (1 + X%)/3
Odd = 5 Channel divider bypassed 40% (2 + X%)/5
Even Even (N + 1)/(N + M + 2) 50%, requires M = N
Even Odd (N + 1)/(N + M + 2) 50%, requires M = N + 1
Odd = 3 Even (N + 1)/(N + M + 2) 50%, requires M = N
Odd = 3 Odd (N + 1)/(N + M + 2) (3N + 4 + X%)/(6N + 9), requires M = N + 1
Odd = 5 Even (N + 1)/(N + M + 2) 50%, requires M = N
Odd = 5 Odd (N + 1)/(N + M + 2) (5N + 7 + X%)/(10N + 15), requires M = N + 1
Table 38. Channel Divider Output Duty Cycle When the VCO Divider Is Enabled and Set to 1
Input Clock
Duty Cycle
DX Output Duty Cycle
N + M + 2 Disable Divider x DCC = 1b Disable Divider x DCC = 0b
Any Even (N + 1)/(M + N + 2) 50%, requires M = N
50% Odd (N + 1)/(M + N + 2) 50%, requires M = N + 1
X% Odd (N + 1)/(M + N + 2) (N + 1 + X%)/(2 × N + 3), requires M = N + 1
The channel divider must be enabled when the VCO divider = 1.
Table 39. Channel Divider Output Duty Cycle When the VCO Divider Is Bypassed
Input Clock
Duty Cycle
DX Output Duty Cycle
N + M + 2 Disable Divider x DCC = 1b Disable Divider x DCC = 0b
Any Channel divider bypassed Same as input duty cycle Same as input duty cycle
Any
Even
(N + 1)/(M + N + 2)
50%, requires M = N
50% Odd (N + 1)/(M + N + 2) 50%, requires M = N + 1
X% Odd (N + 1)/(M + N + 2) (N + 1 + X%)/(2 × N + 3), requires M = N + 1
The internal VCO has a duty cycle of 50%. Therefore, when the
VCO is connected directly to the output, the duty cycle is 50%.
If the CLK input is routed directly to the output, the duty cycle of
the output is the same as the CLK input.
Phase Offset or Coarse Time Delay
Each channel divider allows for a phase offset or a coarse time
delay to be programmed by setting register bits (see Table 40).
These settings determine the number of cycles (successive rising
edges) of the channel divider input frequency by which to offset, or
delay, the rising edge of the output of the divider. This delay is
with respect to a nondelayed output (that is, with a phase offset
of zero). The amount of the delay is set by five bits loaded into
the phase offset (PO) register plus the start high (SH) bit for
each channel divider.
When the start high bit is set, the delay is also affected by the
number of low cycles (M) programmed for the divider.
The SYNC function must be used to make phase offsets effective
(see the Synchronizing the Outputs—SYNC Function section).
Table 40. Setting Phase Offset and Division
Divider
Start
High
(SH) Bits
Phase
Offset
(PO) Bits
Low Cycles,
M Value Bits
High Cycles,
N Value Bits
0 0x191[4] 0x191[3:0] 0x190[7:4] 0x190[3:0]
1 0x194[4] 0x194[3:0] 0x193[7:4] 0x193[3:0]
2 0x197[4] 0x197[3:0] 0x196[7:4] 0x196[3:0]
3 0x19A[4] 0x19A[3:0] 0x199[7:4] 0x199[3:0]
Data Sheet AD9520-3
Rev. A | Page 47 of 80
Note that the value stored in the register equals the number of
cycles minus one. For example, Register 0x190[7:4] = 0001b
equals two low cycles (M = 2) for Divider 0.
Let
Δt = delay (in seconds).
Δc = delay (in cycles of clock signal at input to DX).
TX = period of the clock signal at the input of the divider, DX (in
seconds).
Φ =
16 × SH[4] + 8 × PO[3] + 4 × PO[2] + 2 × PO[1] + 1 × PO[0].
The channel divide by is set as N = high cycles and M = low
cycles.
Case 1
For Φ ≤ 15,
Δt = Φ × TX
Δc = Δt/TX = Φ
Case 2
For Φ ≥ 16,
Δt = (Φ − 16 + M + 1) × TX
Δc = Δt/TX
By giving each divider a different phase offset, output-to-output
delays can be set in increments of the channel divider input
clock cycle. Figure 51 shows the results of setting such a coarse
offset between outputs.
012345678910 11 12 13 14 15
Tx
DIVIDER 0
DIVIDER 1
DIVIDER 2
CHANNEL
DIVIDER INPUT
SH = 0
PO = 0
SH = 0
PO = 1
SH = 0
PO = 2 1 × T x
2 × Tx
CHANNEL DIVIDER O UTPUT S
DIV = 4, DUT Y = 50%
07216-071
Figure 51. Effect of Coarse Phase Offset (or Delay)
Synchronizing the Outputs—SYNC Function
The AD9520 clock outputs can be synchronized to each other.
Outputs can be individually excluded from synchronization.
Synchronization consists of setting the nonexcluded outputs to a
preset set of static conditions. These conditions include the divider
ratio and phase offsets for a given channel divider. This allows
the user to specify different divide ratios and phase offsets for each
of the four channel dividers. Releasing the SYNC pin allows the
outputs to continue clocking with the preset conditions applied.
Synchronization of the outputs is executed in the following ways:
• The SYNC pin is forced low and then released (manual sync).
• By setting and then resetting any one of the following three
bits: the soft SYNC bit (Register 0x230[0]), the soft reset bit
(Register 0x000[5] [mirrored]), and the power-down
distribution reference bit (Register 0x230[1]).
• Synchronization of the outputs can be executed as part of
the chip power-up sequence.
• The RESET pin is forced low and then released (chip reset).
• The PD pin is forced low, then released (chip power-down).
• When a VCO calibration is completed, an internal SYNC
signal is automatically asserted at the beginning and
released upon the completion of a VCO calibration.
The most common way to execute the SYNC function is to use
the SYNC pin to perform a manual synchronization of the outputs.
This requires a low going signal on the SYNC pin, which is held
low and then released when synchronization is desired. The
timing of the SYNC operation is shown in Figure 52 (using the
VCO divider) and in Figure 53 (the VCO divider is not used).
There is an uncertainty of up to one cycle of the clock at the input
to the channel divider due to the asynchronous nature of the
SYNC signal with respect to the clock edges inside the AD9520.
The pipeline delay from the SYNC rising edge to the beginning
of the synchronized output clocking is between 14 cycles and
15 cycles of clock at the channel divider input, plus either one
cycle of the VCO divider input (see Figure 52), or one cycle of
the channel divider input (see Figure 53), depending on whether
the VCO divider is used. Cycles are counted from the rising
edge of the signal. In addition, there is an additional 1.2 ns (typical)
delay from the SYNC signal to the internal synchronization logic,
as well as the propagation delay of the output driver. The driver
propagation delay is approximately 100 ps for the LVPECL
driver and approximately 1.5 ns for the CMOS driver.
Another common way to execute the SYNC function is by
setting and resetting the soft SYNC bit at Register 0x230[0]. Both
setting and resetting of the soft SYNC bit require an update all
registers (Register 0x232[0] = 1b) operation to take effect.
A SYNC operation brings all outputs that have not been excluded
(by the ignore SYNC bit) to a preset condition before allowing
the outputs to begin clocking in synchronicity. The preset condition
takes into account the settings in each of the channel’s start high
bit and its phase offset. These settings govern both the static state
of each output when the SYNC operation is happening and the
state and relative phase of the outputs when they begin clocking
again upon completion of the SYNC operation. Between outputs
and after synchronization, this allows for the setting of phase offsets.
The AD9520 differential LVPECL outputs are four groups of
three, sharing a channel divider per triplet. In the case of CMOS,
each LVPECL differential pair can be configured as two single-
ended CMOS outputs. The synchronization conditions apply to
all of the drivers that belong to that channel divider.
Each channel (a divider and its outputs) can be excluded from
any SYNC operation by setting the ignore SYNC bit of the channel.
Channels that are set to ignore SYNC (excluded channels) do
not set their outputs static during a SYNC operation, and their
outputs are not synchronized with those of the included channels.
AD9520-3 Data Sheet
Rev. A | Page 48 of 80
1 2 3 4 5 6 7 8910
INPUT TO VCO DIVIDER
INP UT TO CHANNEL DIVI DE R
OUTPUT OF
CHANNEL DIVI DE R
SYNC PIN
1
11 12 13 14
14 TO 15 CYCL E S AT CHANNEL DIVI DE R INPUT + 1 CY CLE AT VCO DIVI DE R INPUT
CHANNEL DIVI DE R OUTP UT ST ATIC CHANNEL DIVI DE R
OUTPUT CLOCKING
CHANNEL DIVI DE R
OUTPUT CLOCKING
07216-073
Figure 52. SYNC Timing Pipeline Delay When the VCO Divider Is Used—CLK or VCO Is Input
INPUT TO CLK
INP UT TO CHANNEL DIVI DE R
OUTPUT OF
CHANNEL DIVI DE R
SYNC PIN
14 TO 15 CYCL E S AT CHANNEL DIVI DE R INPUT + 1 CY CLE AT CLK INPUT
1 2 3 4 5 6 7 8910 11 12 13 14
1
CHANNEL DIVI DE R OUTP UT ST ATIC CHANNEL DIVI DE R
OUTPUT CLOCKING
CHANNEL DIVI DE R
OUTPUT CLOCKING
07216-074
Figure 53. SYNC Timing Pipeline Delay When the VCO Divider Is Not Used—CLK Input Only
Data Sheet AD9520-3
Rev. A | Page 49 of 80
LVPECL Output Drivers
The LVPECL differential voltage (VOD) is selectable (from
~400 mV to 960 mV, see Bit 1 and Bit 2 in Register 0x0F0 to
Register 0x0FB). The LVPECL outputs have dedicated pins for
power supply (VS_DRV), allowing a separate power supply to
be used. VS_DRV can be set to either 2.5 V or 3.3 V.
The LVPECL output polarity can be set as noninverting or
inverting, which allows for the adjustment of the relative
polarity of outputs within an application without requiring a
board layout change. Each LVPECL output can be powered
down or powered up as needed. Because of the architecture of
the LVPECL output stages, there is the possibility of electrical
overstress and breakdown under certain power-down conditions.
For this reason, the LVPECL outputs have two power-down
modes: total power-down and safe power-down.
R2
200Ω R1
200Ω
SW1B SW1A
SW2
QN2
QN1
N2
N1
OUT
OUT
4.4mA
07216-058
Figure 54. LVPECL Output Simplified Equivalent Circuit
In total power-down mode, all output drivers are shut off
simultaneously. This mode must not be used if there is an
external voltage bias network (such as Thevenin equivalent
termination) on the output pins that causes a dc voltage to
appear at the powered down outputs. However, total power-
down mode is allowed when the LVPECL drivers are terminated
using only pull-down resistors. The total power-down mode is
activated by setting Register 0x230[1].
The primary power-down mode is the safe power-down mode.
This mode continues to protect the output devices while powered
down. There are three ways to activate safe power-down mode:
individually set the power-down bit for each driver, power down
an individual output channel (all of the drivers associated with
that channel are powered down automatically), and activate
sleep mode.
CMOS Output Drivers
The user can also individually configure each LVPECL output as a
pair of CMOS outputs, which provides up to 24 CMOS outputs.
When an output is configured as CMOS, CMOS Output A and
CMOS Output B are automatically turned on. For any given
differential pair, either CMOS Output A or CMOS Output B
can be turned on or off independently.
The user can also select the relative polarity of the CMOS outputs
for any combination of inverting and noninverting (refer to
Register 0x0F0 to Register 0x0FB).
OUT1/
OUT1
VS_DRV
07216-035
Figure 55. CMOS Equivalent Output Circuit
Each CMOS output can be powered down, as needed, to save
power. The CMOS output power-down is individually controlled
by the enable CMOS output bits, Bits[6:5] in Register 0x0F0 to
Register 0x0FB. The CMOS driver is in tristate when it is
powered down.
Note that activating a CMOS driver in the same output channel
group as the LVPECL drivers may cause the LVPECL driver
performance to degrade. In applications where jitter
performance is critical, the user should test the desired
configuration using an evaluation board, and special steps may
need to be taken to ensure the desired performance.
RESET MODES
The AD9520 has a power-on reset (POR) and several other
ways to apply a reset condition to the chip.
Power-On Reset
During chip power-up, a power-on reset pulse is issued when VS
reaches ~2.6 V (<2.8 V) and restores the chip either to the setting
that is stored in the EEPROM (with the EEPROM pin = 1b) or
to the on-chip setting (with the EEPROM pin = 0b). At power-
on, the AD9520 also executes a SYNC operation approximately
50 ms after the supply reaches ~2.4 V, which brings the outputs
into phase alignment according to the default settings. It takes
~70 ms for the outputs to begin toggling after the power-on
reset pulse signal is internally generated.
AD9520-3 Data Sheet
Rev. A | Page 50 of 80
Hardware Reset via the RESET Pin
RESET, a hard reset (an asynchronous hard reset is executed by
briefly pulling RESET low), restores the chip either to the setting
stored in the EEPROM (the EEPROM pin = 1b) or to the on-chip
setting (the EEPROM pin = 0b). A hard reset also executes
a SYNC operation, bringing the outputs into phase alignment
according to the default settings. When the EEPROM is inactive
(the EEPROM pin = 0b), it takes ~2 µs for the outputs to begin
toggling after RESET is issued. When the EEPROM is active
(the EEPROM pin = 1b), it takes ~20 ms for the outputs to toggle
after RESET is brought high.
Soft Reset via the Serial Port
The serial port control register allows for a soft reset by setting
Bit 2 and Bit 5 in Register 0x000. The function of this register is
determined by the state of the EEPROM pin.
When Bit 2 and Bit 5 are set and the EEPROM pin is high, the chip
is restored to the settings saved in the EEPROM. When Bit 2 and
Bit 5 are set and the EEPROM pin is low, the chip is restored to
the on-chip defaults.
Except for the self-clearing bits, Bit 2 and Bit 5, Register 0x000
retains its previous value prior to reset. During the internal reset,
the outputs hold static. However, the self-clearing operation does
not complete until an additional serial port SCLK cycle occurs,
and the AD9520 is held in reset until that happens.
Soft Reset to Settings in EEPROM when EEPROM Pin = 0b
via the Serial Port
If the EEPROM pin is low, the serial port control register allows
the chip to be reset to settings in EEPROM via Register 0xB02[1].
(Bit 1 is self-clearing.) This bit does not have any effect when the
EEPROM pin is high. It takes ~20 ms for the outputs to begin
toggling after the SOFT_EEPROM register is cleared.
POWER-DOWN MODES
Chip Power-Down via PD
The AD9520 can be put into a power-down condition by pulling
the PD pin low. Power-down turns off most of the functions and
currents inside the AD9520. The chip remains in this power-down
state until PD is brought back to logic high. When taken out of
power-down mode, the AD9520 returns to the settings
programmed into its registers prior to the power-down, unless
the registers are changed by new programming while the PD
pin is held low.
Powering down the chip shuts down the currents on the chip,
except for the bias current necessary to maintain the LVPECL
outputs in a safe shutdown mode. The LVPECL bias currents are
needed to protect the LVPECL output circuitry from damage that
can be caused by certain termination and load configurations
when tristated. Because this is not a complete power-down, it
can be called sleep mode. The AD9520 contains special circuitry to
prevent runt pulses on the outputs when the chip is entering or
exiting sleep mode.
When the AD9520 is in a PD power-down, the chip is in the
following state:
• The PLL is off (asynchronous power-down).
• The VCO is off.
• The CLK input buffer is off, but the CLK input dc bias
circuit is on.
• In differential mode, the reference input buffer is off, but
the dc bias circuit is still on.
• In singled-ended mode, the reference input buffer is off,
and the dc bias circuit is off.
• All dividers are off.
• All CMOS outputs are tristated.
• All LVPECL outputs are in safe off mode.
• The serial control port is active, and the chip responds to
commands.
PLL Power-Down
The PLL section of the AD9520 can be selectively powered
down. There are two PLL power-down modes set by
Register 0x010[1:0]: asynchronous and synchronous.
In asynchronous power-down mode, the device powers down as
soon as the registers are updated. In synchronous power-down
mode, the PLL power-down is gated by the charge pump to
prevent unwanted frequency jumps. The device goes into power-
down on the occurrence of the next charge pump event after the
registers are updated.
Distribution Power-Down
The distribution section can be powered down by writing
Register 0x230[1] = 1b, which turns off the bias to the distribution
section. If the LVPECL power-down mode is in normal operation
(Register 0x230[1] = 0b), it is possible for a low impedance load
on that LVPECL output to draw significant current during this
power-down. If the LVPECL power-down mode is set to 1b, the
LVPECL output is not protected from reverse bias and can be
damaged under certain termination conditions.
Individual Clock Output Power-Down
Any of the clock distribution outputs can be powered down
into safe power-down mode by individually writing to the
appropriate registers. The register map details the individual
power-down settings for each output. These settings are found
in Bit 0 of Register 0x0F0 to Register 0x0FB.
Individual Clock Channel Power-Down
Any of the clock distribution channels can be powered down
individually by writing to the appropriate registers. Powering
down a clock channel is similar to powering down an individual
driver, but it saves more power because the dividers are also
powered down. Powering down a clock channel also automatically
powers down the drivers connected to it. The register map
details the individual power-down settings for each output
channel. These settings are found in Bit 2 of Register 0x192,
Register 0x195, Register 0x198, and Register 0x19B.
Data Sheet AD9520-3
Rev. A | Page 51 of 80
SERIAL CONTROL PORT
The AD9520 serial control port is a flexible, synchronous serial
communications port that allows an easy interface with many
industry-standard microcontrollers and microprocessors. The
AD9520 serial control port is compatible with most synchronous
transfer formats, including Philips I²C, Motorola® SPI®, and
Intel® SSR protocols. The AD9520 I²C implementation deviates
from the classic I²C specification on two specifications, and
these deviations are documented in Table 14. The serial control
port allows read/write access to all registers that configure the
AD9520.
SPI/I²C PORT SELECTION
The AD9520 has two serial interfaces, SPI and I²C. Users can
select either SPI or I²C depending on the states of the three- level
(high, open, low) logic input pins, SP1 and SP0. When both SP1
and SP0 are high, the SPI interface is active. Otherwise, I²C is active
with eight different I²C slave address (seven bits wide) settings
(see Table 41). The four MSBs of the slave address are hardware
coded as 1011b; the three LSBs are programmed by SP1 and SP0.
Table 41. Serial Port Mode Selection
SP1 SP0 Address
Low Low I²C, 1011000b
Low Open I²C, 1011001b
Low
High
I²C, 1011010b
Open Low I²C, 1011011b
Open Open I²C, 1011100b
Open High I²C, 1011101b
High Low I²C, 1011110b
High Open I²C, 1011111b
High
High
SPI
I²C SERIAL PORT OPERATION
The AD9520 I²C port is based on the I²C fast mode standard.
The AD9520 supports both I²C protocols: standard mode
(100 kHz) and fast mode (400 kHz).
The AD9520 I²C port has a 2-wire interface consisting of a serial
data line (SDA) and a serial clock line (SCL). In an I²C bus system,
the AD9520 is connected to the serial bus (data bus SDA and clock
bus SCL) as a slave device, meaning that no clock is generated by
the AD9520. The AD9520 uses direct 16-bit (two bytes) memory
addressing instead of traditional 8-bit (one byte) memory
addressing.
I2C Bus Characteristics
Table 42. I2C Bus Definitions
Abbreviation Definition
S Start
Sr Repeated start
P Stop
A Acknowledge
A No acknowledge
W
Write
R Read
One pulse on the SCL clock line is generated for each data bit
transferred.
The data on the SDA line must not change during the high period
of the clock. The state of the data line can change only when the
clock on the SCL line is low.
SDA
SCL
DATA L INE
STABLE;
DATA VALID
CHANGE
OF DATA
ALLOWED
07216-160
Figure 56. Valid Bit Transfer
A start condition is a transition from high to low on the SDA
line while SCL is high. The start condition is always generated
by the master to initialize the data transfer.
A stop condition is a transition from low to high on the SDA
line while SCL is high. The stop condition is always generated
by the master to end the data transfer.
START
CONDITION
S
STOP
CONDITION
P
SDA
SCL
07216-161
Figure 57. Start and Stop Conditions
A byte on the SDA line is always eight bits long. An acknowledge
bit must follow every byte. Bytes are sent MSB first.
The acknowledge bit is the ninth bit attached to any 8-bit data
byte. An acknowledge bit is always generated by the receiving
device (receiver) to inform the transmitter that the byte has
been received. It is accomplished by pulling the SDA line low
during the ninth clock pulse after each 8-bit data byte.
The no acknowledge bit is the ninth bit attached to any 8-bit
data byte. A no acknowledge bit is always generated by the
receiving device (receiver) to inform the transmitter that the
byte has not been received. It is accomplished by leaving the SDA
line high during the ninth clock pulse after each 8-bit data byte.
AD9520-3 Data Sheet
Rev. A | Page 52 of 80
SDA MSB
ACKNOW LEDGE F ROM
SLAVE-RECEIVER ACKNOWLEDGE F ROM
SLAVE-RECEIVER
SCL SP
12 8 9128
3 TO 7
3 TO 7 910
07216-162
Figure 58. Acknowledge Bit
SDA MSB = 0
ACKNOW LEDGE F ROM
SLAVE-RECEIVER ACKNOWLEDGE F ROM
SLAVE-RECEIVER
SCL SP
1 2 89 1 2 83 TO 73 TO 7 910
07216-163
Figure 59. Data Transfer Process (Master Write Mode, 2-Byte Transfer Used for Illustration)
SDA
ACKNOW LEDGE F ROM
MASTER-RECEIVER NO ACKNOW LEDGE
FROM
SLAVE-RECEIVER
SCL SP
1 2 8 9 1 2 8
3 TO 7
3 TO 7 910
MSB = 1
07216-164
Figure 60. Data Transfer Process (Master Read Mode, 2-Byte Transfer Used for Illustration)
Data Transfer Process
The master initiates data transfer by asserting a start condition.
This indicates that a data stream follows. All I²C slave devices
connected to the serial bus respond to the start condition.
The master then sends an 8-bit address byte over the SDA line,
consisting of a 7-bit slave address (MSB first) plus an R/W bit.
This bit determines the direction of the data transfer, that is,
whether data is written to or read from the slave device
(0b = write, 1b = read).
The peripheral whose address corresponds to the transmitted
address responds by sending an acknowledge bit. All other
devices on the bus remain idle while the selected device waits
for data to be read from or written to it. If the R/W bit is 0b, the
master (transmitter) writes to the slave device (receiver). If the
R/W bit is 1b, the master (receiver) reads from the slave device
(transmitter).
The format for these commands is described in the Data
Transfer Format section.
Data is then sent over the serial bus in the format of nine clock
pulses, one data byte (8-bit) from either master (write mode)
or slave (read mode), followed by an acknowledge bit from the
receiving device. The number of bytes that can be transmitted per
transfer is unrestricted. In write mode, the first two data bytes
immediately after the slave address byte are the internal memory
(control registers) address bytes with the high address byte first.
This addressing scheme gives a memory address up to 216 − 1 =
65,535. The data bytes after these two memory address bytes are
register data written into the control registers. In read mode, the
data bytes after the slave address byte are register data read from
the control registers.
When all data bytes are read or written, stop conditions are
established. In write mode, the master (transmitter) asserts a
stop condition to end data transfer during the (10th) clock
pulse following the acknowledge bit for the last data byte from
the slave device (receiver). In read mode, the master device
(receiver) receives the last data byte from the slave device
(transmitter) but does not pull it low during the ninth clock
pulse. This is known as a no acknowledge bit. By receiving the no
acknowledge bit, the slave device knows that the data transfer is
finished and releases the SDA line. The master then takes the
data line low during the low period before the 10th clock pulse,
and high during the 10th clock pulse to assert a stop condition.
A repeated start (Sr) condition can be used in place of a stop
condition. Furthermore, a start or stop condition can occur at
any time and partially transferred bytes are discarded.
Data Sheet AD9520-3
Rev. A | Page 53 of 80
Data Transfer Format
Send byte format—the send byte protocol is used to set up the register address for subsequent commands.
S Slave Address W A RAM Address High Byte A RAM Address Low Byte A P
Write byte format—the write byte protocol is used to write a register address to the RAM starting from the specified RAM address.
S Slave Address W A
RAM Address
High Byte A
RAM Address
Low Byte A RAM Data 0 A RAM Data 1 A RAM Data 2 A P
Receive byte format—the receive byte protocol is used to read the data byte(s) from RAM starting from the current address.
S Slave Address R A RAM Data 0 A RAM Data 1 A RAM Data 2 A P
Read byte format—the combined format of the send byte and the receive byte.
S
Slave
Address W A
RAM Address
High Byte A
RAM Address
Low Byte A Sr
Slave
Address R A
RAM
Data 0 A
RAM
Data 1 A
RAM
Data 2 A P
I²C Serial Port Timing
07216-165
SDA
SCL
S Sr P S
t
FALL
t
SET; DAT
t
LOW
t
RISE
t
HLD; S TR
t
HLD; DAT
t
HIGH
t
FALL
t
SET; STR
t
HLD; S TR
t
SPIKE
t
SET; STP
t
RISE
t
IDLE
Figure 61. I²C Serial Port Timing
Table 43. I²C Timing Definitions
Parameter Description
fI2C I²C clock frequency
tIDLE Bus idle time between stop and start conditions
tHLD; STR Hold time for repeated start condition
tSET; STR Setup time for repeated start condition
tSET; STP Setup time for stop condition
t
HLD; DAT
Hold time for data
tSET; DAT Setup time for data
tLOW Duration of SCL clock low
tHIGH Duration of SCL clock high
tRISE SCL/SDA rise time
t
FALL
SCL/SDA fall time
tSPIKE Voltage spike pulse width that must be suppressed by the input filter
AD9520-3 Data Sheet
Rev. A | Page 54 of 80
SPI SERIAL PORT OPERATION
Pin Descriptions
SCLK (serial clock) is the serial shift clock. This pin is an input.
SCLK is used to synchronize serial control port reads and writes.
Write data bits are registered on the rising edge of this clock,
and the read data bits transition on the falling edge of SCLK.
This pin is internally pulled down by a 30 kΩ resistor to
ground.
SDIO (serial data input/output) is a dual-purpose pin and acts
either as an input only (unidirectional mode) or as both an input
and an output (bidirectional mode). The AD9520 defaults to
the bidirectional I/O mode (Register 0x000[7] = 0b).
SDO (serial data out) is used only in the unidirectional I/O
mode (Register 0x000[7]) as a separate output pin for reading back
data.
CS (chip select bar) is an active low control that gates the read
and write cycles. When CS is high, SDO and SDIO are in a high
impedance state. This pin is internally pulled up by a 30 kΩ
resistor to VS.
AD9520
SERIAL
CONTROL
PORT
SCLK/SCL 16
SDO 18
SDIO/SDA 17
CS 15
07216-036
Figure 62. Serial Control Port
SPI Mode Operation
In SPI mode, single or multiple byte transfers are supported, as
well as MSB first or LSB first transfer formats. The AD9520
serial control port can be configured for a single bidirectional
I/O pin (SDIO only) or for two unidirectional I/O pins (SDIO/
SDO). By default, the AD9520 is in bidirectional mode. Short
instruction mode (8-bit instructions) is not supported. Only
long (16-bit) instruction mode is supported. It is possible that
the serial activity on the SDIO/SDO pins may induce jitter on
the PLL while data is being transmitted.
A write or a read operation to the AD9520 is initiated by pulling
CS low.
The CS stalled high mode is supported in data transfers where
three or fewer bytes of data (plus instruction data) are transferred
(see Table 44). In this mode, the CS pin can temporarily return
high on any byte boundary, allowing time for the system controller
to process the next byte. CS can go high on byte boundaries only
and can go high during either part (instruction or data) of the
transfer.
During this period, the serial control port state machine enters
a wait state until all data is sent. If the system controller decides
to abort the transfer before all of the data is sent, the state machine
must be reset by either completing the remaining transfers or by
returning CS low for at least one complete SCLK cycle (but fewer
than eight SCLK cycles). Raising the CS pin on a nonbyte boundary
terminates the serial transfer and flushes the buffer.
In the streaming mode (see Table 44), any number of data bytes
can be transferred in a continuous stream. The register address
is automatically incremented or decremented (see the SPI
MSB/LSB First Transfers section). CS must be raised at the end
of the last byte to be transferred, thereby ending streaming mode.
Communication Cycle—Instruction Plus Data
There are two parts to a communication cycle with the AD9520.
The first part writes a 16-bit instruction word into the AD9520,
coincident with the first 16 SCLK rising edges. The instruction
word provides the AD9520 serial control port with information
regarding the data transfer, which is the second part of the
communication cycle. The instruction word defines whether
the upcoming data transfer is a read or a write, the number of
bytes in the data transfer, and the starting register address for
the first byte of the data transfer.
Write
If the instruction word is for a write operation, the second part
is the transfer of data into the serial control port buffer of the
AD9520. Data bits are registered on the rising edge of SCLK.
The length of the transfer (one, two, or three bytes, or streaming
mode) is indicated by two bits (W1:W0) in the instruction byte.
When the transfer is one, two, or three bytes, but not streaming,
CS can be raised after each sequence of eight bits to stall the bus
(except after the last byte, where it ends the cycle). When the bus
is stalled, the serial transfer resumes when CS is lowered. Raising
the CS pin on a nonbyte boundary resets the serial control port.
During a write, streaming mode does not skip over reserved or
blank registers, and the user can write 0x00 to the reserved
register addresses.
Because data is written into a serial control port buffer area, not
directly into the actual control registers of the AD9520, an
additional operation is needed to transfer the serial control port
buffer contents to the actual control registers of the AD9520,
thereby causing them to become active. The update registers
operation consists of setting Register 0x232[0] = 1b (this bit is
self-clearing). Any number of bytes of data can be changed
before executing an update registers. The update registers
simultaneously actuates all register changes that have been
written to the buffer since any previous update.
Read
The AD9520 supports only the long instruction mode. If the
instruction word is for a read operation, the next N × 8 SCLK
cycles clock out the data from the address specified in the
instruction word, where N is 1 to 3 as determined by Bits[W1:W0].
If N = 4, the read operation is in streaming mode, continuing
until CS is raised. Streaming mode does not skip over reserved
or blank registers. The readback data is valid on the falling edge
of SCLK.
Data Sheet AD9520-3
Rev. A | Page 55 of 80
The default mode of the AD9520 serial control port is the
bidirectional mode. In bidirectional mode, both the sent data
and the readback data appear on the SDIO pin. It is also possible to
set the AD9520 to unidirectional mode (Register 0x000[7] = 1b
and Register 0x000[0] = 1b). In unidirectional mode, the
readback data appears on the SDO pin.
A readback request reads the data in the serial control port buffer
area or the data in the active registers (see Figure 63). Readback of
the buffer or active registers is controlled by Register 0x004[0].
The AD9520 uses Register 0x000 to Register 0xB03.
SERIAL
CONTROL
PORT
BUFFER REGIS TERS
UPDATE
REGISTERS
WRI TE RE GIS TER 0x232 = 0x001
TO UPDATE REGISTERS
ACTIVE REGISTERS
SCLK/SCL
SDO
SDIO/SDA
CS
07216-037
Figure 63. Relationship Between Serial Control Port Buffer Registers and
Active Registers of the AD9520
SPI INSTRUCTION WORD (16 BITS)
The MSB of the instruction word is R/W, which indicates
whether the instruction is a read or a write. The next two bits
(W1:W0) indicate the length of the transfer in bytes. The final
13 bits are the address (A12:A0) at which to begin the read or
write operation.
For a write, the instruction word is followed by the number of
bytes of data indicated by Bits [W1:W0], see Table 44.
Table 44. Byte Transfer Count
W1 W0 Bytes to Transfer
0 0 1
0 1 2
1
0
3
1 1 Streaming mode
Bits[A12:A0] select the address within the register map that is
written to or read from during the data transfer portion of the
communications cycle. For multibyte transfers, this address is
the starting byte address. In MSB first mode, subsequent bytes
decrement the address.
SPI MSB/LSB FIRST TRANSFERS
The AD9520 instruction word and byte data can be MSB first
or LSB first. Any data written to Register 0x000 must be mirrored;
the upper four bits (Bits[7:4]) must mirror the lower four bits
(Bits[3:0]). This makes it irrelevant whether LSB first or MSB
first is in effect. As an example of this mirroring, see the default
setting for Register 0x000, which mirrors Bit 4 and Bit 3. This
sets the long instruction mode, which is the default and the only
mode that is supported.
The default for the AD9520 is MSB first.
When LSB first is set by Register 0x000[1] and Register 0x000[6],
it takes effect immediately because it affects only the operation
of the serial control port and does not require that an update be
executed.
When MSB first mode is active, the instruction and data bytes
must be written from MSB to LSB. Multibyte data transfers in
MSB first format start with an instruction byte that includes the
register address of the most significant data byte. Subsequent
data bytes must follow in order from the high address to the
low address. In MSB first mode, the serial control port internal
address generator decrements for each data byte of the multibyte
transfer cycle.
When LSB first is active, the instruction and data bytes must be
written from LSB to MSB. Multibyte data transfers in LSB first
format start with an instruction byte that includes the register
address of the least significant data byte followed by multiple
data bytes. In a multibyte transfer cycle, the internal byte
address generator of the serial port increments for each byte.
The AD9520 serial control port register address decrements
from the register address just written toward Register 0x000 for
multibyte I/O operations if the MSB first mode is active
(default). If the LSB first mode is active, the register address of
the serial control port increments from the address just written
toward Register 0x232 for multibyte I/O operations.
Streaming mode always terminates when it reaches Register
0x232. Note that unused addresses are not skipped during
multibyte I/O operations.
Table 45. Streaming Mode (No Addresses Are Skipped)
Write Mode
Address
Direction Stop Sequence
LSB first Increment Register 0x230, Register 0x231,
Register 0x232, stop
MSB first Decrement Register 0x001, Register 0x000,
Register 0x232, stop
Table 46. Serial Control Port, 16-Bit Instruction Word, MSB First
MSB LSB
I15 I14 I13 I12 I11 I10 I9 I8 I7 I6 I5 I4 I3 I2 I1 I0
R/W W1 W0 A12 = 0 A11 = 0 A10 = 0 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0
AD9520-3 Data Sheet
Rev. A | Page 56 of 80
CS
SCLK
DON'T CARE
SDIO A12W0W1R/W A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0 D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0 DON' T CARE
DON'T CARE
DON' T CARE
16-BIT INS TRUCTION HE ADE R REGIST E R ( N) DATA REGIST E R ( N – 1) DATA
07216-038
Figure 64. Serial Control Port Write—MSB First, 16-Bit Instruction, Two Bytes of Data
CS
SCLK
SDIO
SDO
REGIST E R ( N) DATA16-BIT INS TRUCTION HE ADE R REGIST E R ( N – 1) DATA REG IST E R ( N – 2) DATA REGIST E R ( N – 3) DATA
A12W0W1R/W A11 A10 A9 A8 A7 A6 A5 A4 A3 A2 A1 A0
DON'T CARE
DON' T CARE
DON' T CARE
DON'T
CARE
D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0 D7 D6 D5 D4 D3 D2 D1 D0
07216-039
Figure 65. Serial Control Port Read—MSB First, 16-Bit Instruction, Four Bytes of Data
07216-040
tS
DON' T CARE
DON' T CARE W1 W0 A12 A11 A10 A9 A8 A7 A6 A5 D4 D3 D2 D1 D0
DON' T CARE
DON' T CARE
R/W
tDS
tDH
tHIGH
tLOW
tCLK tC
CS
SCLK
SDIO
Figure 66. Serial Control Port Write—MSB First, 16-Bit Instruction, Timing Measurements
DATA BIT N–1DATA BIT N
CS
SCLK
SDIO
SDO
tDV
07216-041
Figure 67. Timing Diagram for Serial Control Port Register Read
CS
SCLK
DON'T CARE
DON' T CARE
16-BIT INS TRUCTION HE ADE R REGIST E R ( N) DATA REGI S TER (N + 1) DATA
SDIO DON'T CARE
DON'T CARE
A0 A1 A2 A3 A4 A5 A6 A7 A8 A9 A10 A11 A12 D1D0R/WW1W0 D2 D3 D4 D5 D6 D7 D0 D1 D2 D3 D4 D5 D6 D7
07216-042
Figure 68. Serial Control Port Write—LSB First, 16-Bit Instruction, Two Bytes of Data
Data Sheet AD9520-3
Rev. A | Page 57 of 80
CS
SCLK
SDIO
tHIGH tLOW
tCLK
tS
tDS
tDH
tC
BIT N BIT N + 1
07216-043
Figure 69. Serial Control Port Timing—Write
Table 47. Serial Control Port Timing
Parameter Description
tDS Setup time between data and rising edge of SCLK
t
DH
Hold time between data and rising edge of SCLK
tCLK Period of the clock
tS Setup time between the CS falling edge and the SCLK rising edge (start of communication cycle)
tC Setup time between the SCLK rising edge and the CS rising edge (end of communication cycle)
tHIGH Minimum period that SCLK should be in a logic high state
tLOW Minimum period that SCLK should be in a logic low state
tDV SCLK to valid SDIO and SDO (see Figure 67)
AD9520-3 Data Sheet
Rev. A | Page 58 of 80
EEPROM OPERATIONS
The AD9520 contains an internal EEPROM (nonvolatile memory).
The EEPROM can be programmed by users to create and store
a user-defined register setting file when the power is off. This
setting file can be used for power-up and chip reset as a default
setting. The EEPROM size is 512 bytes.
Note that, to guarantee proper loading of the EEPROM during
startup, a high-low-high pulse on the RESET pin should occur
after the power supply has stabilized.
During the data transfer process, the write and read registers via
the serial port are generally not available except for one readback
register, STATUS_EEPROM.
To determine the data transfer state through the serial port
in SPI mode, users can read the value of STATUS_EEPROM
(1b = in process; 0b = completed).
In I²C mode, the user can address the AD9520 slave port with
the external I²C master (send an address byte to the AD9520).
If the AD9520 responds with a no acknowledge bit, the data
transfer process does not take place. If the AD9520 responds with
an acknowledge bit, the data transfer process is completed. The
user can monitor the STATUS_EEPROM register or program
the STATUS pin to monitor the status of the data transfer.
WRITING TO THE EEPROM
The EEPROM cannot be programmed directly through the serial
port interface. To program the EEPROM and store a register
setting file, do the following:
1. Program the AD9520 registers to the desired circuit state.
If the user wants the PLL to lock automatically after power-up,
the VCO calibration now bit (Register 0x018[0]) must be
set to 1b. This allows VCO calibration to start automatically
after register loading. Note that a valid input reference signal
must be present during VCO calibration.
2. Program the EEPROM buffer registers, if necessary (see
the Programming the EEPROM Buffer Segment section).
This step is necessary only if the user wants to use the
EEPROM to control the default setting of some (but not
all) of the AD9520 registers or to control the register
setting update sequence during power-up or chip reset.
3. Set the enable EEPROM write bit (Register 0xB02[0]) to 1b
to enable the EEPROM.
4. Set the REG2EEPROM bit (Register 0xB03[0]) to 1b.
5. Set the IO_UPDATE bit (Register 0x232[0]) to 1b, which
starts the process of writing data into the EEPROM to create
the EEPROM setting file. This enables the AD9520 EEPROM
controller to transfer the current register values, as well as
the memory address and instruction bytes from the EEPROM
buffer segment, into the EEPROM. After the write process
is completed, the internal controller sets Register 0xB03[0]
(REG2EEPROM) back to 0b.
The STATUS_EEPROM bit in the readback register
(Register 0xB00[0]) is used to indicate the data transfer
status between the EEPROM and the control registers
(0b = complete/inactive; 1b = in process/active). At the start
of the data transfer, STATUS_EEPROM is set to 1b by the
EEPROM controller and cleared to 0b at the end of the data
transfer. The STATUS_EEPROM bit can be accessed through
the STATUS pin when the STATUS pin is programmed to
monitor the STATUS_EEPROM bit. Alternatively, the user
can monitor the STATUS_EEPROM bit directly by reading
the register.
6. When the data transfer process is done (Register 0xB00[0] =
0b), set the enable EEPROM write bit (Register 0xB02[0])
to 0b to disable writing to the EEPROM.
To verify that the data transfer has completed correctly, ensure
that Register 0xB01[0] = 0b. A value of 1b in this register indicates
a data transfer error. When an EEPROM save/load transfer is
complete, wait a minimum of 10 µs before starting the next
EEPROM save/load transfer.
READING FROM THE EEPROM
The following reset-related events can start the process of
restoring the settings stored in EEPROM to control registers.
When the EEPROM pin is set high, do any of the following:
• Power up the AD9520.
• Perform a hardware chip reset by pulling the RESET pin
low and then releasing RESET.
• Set the self-clearing soft reset bit (Register 0x000[5]) to 1b.
When the EEPROM pin is set low, set the self-clearing
SOFT_EEPROM bit (Register 0xB02[1]) to 1b. The AD9520
then starts to read the EEPROM and loads the values into the
active registers.
If the EEPROM pin is low during reset or power-up, the
EEPROM is not active, and the AD9520 default values are
loaded instead.
Note that, when using the EEPROM to automatically load the
AD9520 register values and lock the PLL, the VCO calibration
now bit (Register 0x018[0]) must be set to 1b when the register
values are written to the EEPROM. This allows VCO calibration
to start automatically after register loading. A valid input
reference signal must be present during VCO calibration.
To verify that the data transfer has completed correctly, verify
that Register 0xB01[0] = 0b. A value of 1b in this register indicates
a data transfer error. When an EEPROM save/load transfer is
complete, wait a minimum of 10 µs before starting the next
EEPROM save/load transfer.
Data Sheet AD9520-3
Rev. A | Page 59 of 80
PROGRAMMING THE EEPROM BUFFER SEGMENT
The EEPROM buffer segment is a register space on the AD9520.
The user can specify which groups of registers are stored to the
EEPROM during EEPROM programming. Note that programming
this register space is optional. The default power-up values for the
EEPROM buffer segment allow storage of all the AD9520 register
values from Register 0x000 to Register 0x231 to the EEPROM.
As an example, a user might want to load only the output driver
settings from the EEPROM without disturbing the PLL register
settings currently stored in the AD9520. The user can alter the
EEPROM buffer segment to include only the registers that apply
to the output drivers and exclude the registers that apply to the
PLL configuration.
There are two parts to the EEPROM buffer segment: register
section definition groups and operational codes. Table 48 shows
an example of the EEPROM buffer segment.
Register Section Definition Group
Note that the AD9520 register map is noncontiguous, and the
EEPROM is only 512 bytes long. The register section definition
group tells the EEPROM controller how the AD9520 register map
is segmented. Each register section definition group contains the
starting address and number of bytes to be written to EEPROM.
The register section definition group defines a continuous register
section for the EEPROM profile. It consists of three bytes. The first
byte defines how many continuous register bytes are in this
group. If the user writes 0x000 to the first byte, it means that
there is only one byte in this group. If the user writes 0x001, it
means that there are two bytes in this group. The maximum
number of registers in one group is 128. The next two bytes are
the low byte and high byte, respectively, of the 16-bit memory
address of the first register in this group.
Operational Codes
There are three operational codes: IO_UPDATE, end-of-data, and
pseudo-end-of-data. It is important that the EEPROM buffer
segment always have either an end-of-data or a pseudo-end-of-
data operational code and that an IO_UPDATE operational code
appear at least once before the end-of-data operational code.
IO_UPDATE (Operational Code 0x80)
The EEPROM controller uses this operational code to generate
an IO_UPDATE signal to update the active control register
bank from the buffer register bank during the download process.
At a minimum, there should be at least one IO_UPDATE
operational code after the end of the final register section definition
group. This code is needed so that at least one IO_UPDATE occurs
after all of the AD9520 registers are loaded when the EEPROM
is read. If this operational code is absent during a write to the
EEPROM, the register values loaded from the EEPROM are not
transferred to the active register space, and these values do not
take effect after they are loaded from the EEPROM to the AD9520.
End-of-Data (Operational Code 0xFF)
The EEPROM controller uses this operational code to terminate
the data transfer process between EEPROM and the control
register during the upload and download process. The last item
appearing in the EEPROM buffer segment should be either this
operational code or the pseudo-end-of-data operational code.
Pseudo-End-of-Data (Operational Code 0xFE)
The AD9520 EEPROM buffer segment has 23 bytes that can
contain up to seven register section definition groups. If the user
wants to define more than seven register section definition groups,
the pseudo-end-of-data operational code can be used. During
the upload process, when the EEPROM controller receives the
pseudo-end-of-data operational code, it halts the data transfer
process, clears the REG2EEPROM bit, and enables the AD9520
serial port. The user can then program the EEPROM buffer
segment again and reinitiate the data transfer process by setting
the REG2EEPROM bit (Register 0xB03[0]) to 1b and the
IO_UPDATE bit (Register 0x232[0]) to 1b. The internal I²C master
then begins writing to the EEPROM starting from the EEPROM
address held from the last writing.
This sequence provides the user with more discrete instructions
that can be written to the EEPROM than would otherwise be
possible due to the limited size of the EEPROM buffer segment.
It also allows for the same register to be written multiple times
with a different value each time.
Table 48. Example of the EEPROM Buffer Segment
Reg Addr (Hex) Bit 7 (MSB) Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 (LSB)
Start EEPROM Buffer Segment
0xA00 0 Number of bytes [6:0] of the first group of registers
0xA01 Address [15:8] of the first group of registers
0xA02 Address [7:0] of the first group of registers
0xA03 0 Number of bytes [6:0] of the second group of registers
0xA04 Address [15:8] of the second group of registers
0xA05 Address [7:0] of the second group of registers
0xA06 0 Number of bytes [6:0] of the third group of registers
0xA07 Address [15:8] of the third group of registers
0xA08 Address [7:0] of the third group of registers
0xA09 IO_UPDATE operational code (0x80)
0xA0A End-of-data operational code (0xFF)
AD9520-3 Data Sheet
Rev. A | Page 60 of 80
THERMAL PERFORMANCE
Table 49. Thermal Parameters for 64-Lead LFCSP
Symbol Thermal Characteristic Using a JEDEC JESD51-7 Plus JEDEC JESD51-5 2S2P Test Board Value (°C/W)
θJA Junction-to-ambient thermal resistance, 0.0 m/sec airflow per JEDEC JESD51-2 (still air) 22.0
θJMA Junction-to-ambient thermal resistance, 1.0 m/sec airflow per JEDEC JESD51-6 (moving air) 19.2
θJMA Junction-to-ambient thermal resistance, 2.0 m/sec airflow per JEDEC JESD51-6 (moving air) 17.2
ΨJB Junction-to-board characterization parameter, 1.0 m/sec airflow per JEDEC JESD51-6 (moving air)
and JEDEC JESD51-8
11.6
θJC Junction-to-case thermal resistance (die-to-heat sink) per MIL-Std 883, Method 1012.1 1.3
Ψ
JT
Junction-to-top-of-package characterization parameter, 0 m/sec airflow per JEDEC JESD51-2 (still air)
0.1
The AD9520 is specified for a case temperature (TCASE). To ensure
that TCASE is not exceeded, an airflow source can be used.
Use the following equation to determine the junction
temperature on the application PCB:
TJ = TCASE + (ΨJT × PD)
where:
TJ is the junction temperature (°C).
TCASE is the case temperature (°C) measured by the user at the
top center of the package.
ΨJT is the value from Table 49.
PD is the power dissipation (see the total power dissipation in
Table 18).
Values of θJA are provided for package comparison and PCB
design considerations. θJA can be used for a first-order
approximation of TJ by the equation
TJ = TA + (θJA × PD)
where TA is the ambient temperature (°C).
Values of θJC are provided for package comparison and PCB
design considerations when an external heat sink is required.
Values of ΨJB are provided for package comparison and PCB
design considerations.
Data Sheet AD9520-3
Rev. A | Page 61 of 80
REGISTER MAP
Register addresses that are not listed in Table 50 are not used, and writing to those registers has no effect. Writing to register addresses
that are marked as unused also has no effect.
Table 50. Register Map Overview
Addr
(Hex) Parameter Bit 7 (MSB) Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 (LSB)
Default
Value
(Hex)
Serial Port Configuration
0x000 Serial port config
(SPI mode)
SDO active LSB first/
addr incr
Soft reset
(self-clear)
Unused Unused Soft reset
(self-clear)
LSB first/
addr incr
SDO active 0x00
Serial port config
(I²C mode)
Unused Soft reset
(self-clear)
Unused Unused Soft reset
(self-clear)
Unused 0x00
0x001 Unused Unused N/A
0x002 Reserved Reserved N/A
0x003 Part ID Part ID (read only) 0x20
0x004 Readback control Unused Read back
active regs
0x00
EEPROM ID
0x005 EEPROM customer
version ID
EEPROM customer version ID (LSB) 0x00
0x006 EEPROM customer version ID (MSB) 0x00
0x007
to
0x00F
Unused Unused 0x00
PLL
0x010
PFD charge pump
PFD polarity
Charge pump current
Charge pump mode
PLL power-down
0x7D
0x011
R counter
14-bit R counter, Bits[7:0] (LSB)
0x01
0x012
Unused
14-bit R counter, Bits[13:8] (MSB)
0x00
0x013 A counter Unused 6-bit A counter 0x00
0x014
B counter
13-bit B counter, Bits[7:0] (LSB)
0x03
0x015 Unused 13-bit B counter, Bits[12:8] (MSB) 0x00
0x016 PLL_CTRL_1 Set CP pin
to VCP/2
Reset
R counter
Reset
A and B
counters
Reset all
counters
B counter
bypass
Prescaler P 0x06
0x017 PLL_CTRL_2 STATUS pin control Antibacklash pulse width 0x00
0x018 PLL_CTRL_3 Enable CMOS
reference input
dc offset
Lock detect counter Digital
lock detect
window
Disable
digital
lock detect
VCO calibration divider VCO
calibration
now
0x06
0x019
PLL_CTRL_4
R, A, and B counters
SYNC pin reset
R path delay
N path delay
0x00
0x01A PLL_CTRL_5 Enable STATUS
pin divider
Ref freq
monitor
threshold
LD pin control 0x00
0x01B PLL_CTRL_6 Enable VCO
frequency
monitor
Enable
REF2
(REFIN)
frequency
monitor
Enable
REF1
(REFIN)
frequency
monitor
REFMON pin control 0x00
0x01C PLL_CTRL_7 Disable
switchover
deglitch
Select
REF2
Use
REF_SEL
pin
Enable
automatic
reference
switchover
Stay on REF2 Enable
REF2
Enable
REF1
Enable
differential
reference
0x00
0x01D PLL_CTRL_8 Enable
STATUS_EEPROM
at STATUS pin
Enable
XTAL OSC
Enable
clock
doubler
Disable PLL
status
register
Enable LD pin
comparator
Unused Enable external
holdover
Enable
holdover
0x80
0x01E PLL_CTRL_9 Unused External zero delay feedback
channel divider select
Enable
external
zero delay
Enable
zero delay
Unused 0x00
0x01F PLL_Readback
(read only)
Unused VCO cal
finished
Holdover
active
REF2
selected
VCO freq >
threshold
REF2
freq >
threshold
REF1 freq >
threshold
Digital lock
detect
N/A
AD9520-3 Data Sheet
Rev. A | Page 62 of 80
Addr
(Hex) Parameter Bit 7 (MSB) Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 (LSB)
Default
Value
(Hex)
Output Driver Control
0x0F0 OUT0 control OUT0 format OUT0 CMOS
configuration
OUT0 polarity OUT0 LVPECL
differential voltage
OUT0 LVPECL
power-down
0x64
0x0F1 OUT1 control OUT1 format OUT1 CMOS
configuration
OUT1 polarity OUT1 LVPECL
differential voltage
OUT1 LVPECL
power-down
0x64
0x0F2 OUT2 control OUT2 format OUT2 CMOS
configuration
OUT2 polarity OUT2 LVPECL
differential voltage
OUT2 LVPECL
power-down
0x64
0x0F3 OUT3 control OUT3 format OUT3 CMOS
configuration
OUT3 polarity OUT3 LVPECL
differential voltage
OUT3 LVPECL
power-down
0x64
0x0F4 OUT4 control OUT4 format OUT4 CMOS
configuration
OUT4 polarity OUT4 LVPECL
differential voltage
OUT4 LVPECL
power-down
0x64
0x0F5 OUT5 control OUT5 format OUT5 CMOS
configuration
OUT5 polarity OUT5 LVPECL
differential voltage
OUT5 LVPECL
power-down
0x64
0x0F6 OUT6 control OUT6 format OUT6 CMOS
configuration
OUT6 polarity OUT6 LVPECL
differential voltage
OUT6 LVPECL
power-down
0x64
0x0F7 OUT7 control OUT7 format OUT7 CMOS
configuration
OUT7 polarity OUT7 LVPECL
differential voltage
OUT7 LVPECL
power-down
0x64
0x0F8 OUT8 control OUT8 format OUT8 CMOS
configuration
OUT8 polarity OUT8 LVPECL
differential voltage
OUT8 LVPECL
power-down
0x64
0x0F9 OUT9 control OUT9 format OUT9 CMOS
configuration
OUT9 polarity OUT9 LVPECL
differential voltage
OUT9 LVPECL
power-down
0x64
0x0FA OUT10 control OUT10 format OUT10 CMOS
configuration
OUT10 polarity OUT10 LVPECL
differential voltage
OUT10 LVPECL
power-down
0x64
0x0FB OUT11 control OUT11 format OUT11 CMOS
configuration
OUT11 polarity OUT11 LVPECL
differential voltage
OUT11 LVPECL
power-down
0x64
0x0FC
Enable output
on CSDLD
CSDLD en
OUT7
CSDLD en
OUT6
CSDLD en
OUT4
CSDLD en
OUT3
CSDLD en
OUT2
CSDLD en
OUT1
CSDLD en
OUT0
0x00
0x0FD Unused Unused Unused Unused CSDLD en
OUT11
CSDLD en
OUT10
CSDLD en
OUT9
CSDLD en
OUT8
0x00
0x0FE
to
0x18F
Unused
Unused
0x00
LVPECL Channel Dividers
0x190 Divider 0 (PECL) Divider 0 low cycles Divider 0 high cycles 0x77
0x191 Divider 0 bypass Divider 0
ignore
SYNC
Divider 0
force high
Divider 0
start high
Divider 0
phase offset
0x00
0x192 Unused Unused Channel 0
power-
down
Channel 0
direct-to-
output
Disable
Divider 0
DCC
0x00
0x193 Divider 1 (PECL) Divider 1 low cycles Divider 1 high cycles 0x33
0x194 Divider 1 bypass Divider 1
ignore
SYNC
Divider 1
force high
Divider 1
start high
Divider 1
phase offset
0x00
0x195 Unused Unused Channel 1
power-
down
Channel 1
direct-to-
output
Disable
Divider 1
DCC
0x00
0x196 Divider 2 (PECL) Divider 2 low cycles Divider 2 high cycles 0x11
0x197 Divider 2 bypass Divider 2
ignore
SYNC
Divider 2
force high
Divider 2
start high
Divider 2
phase offset
0x00
0x198 Unused Unused Channel 2
power-
down
Channel 2
direct-to-
output
Disable
Divider 2
DCC
0x00
0x199 Divider 3 (PECL) Divider 3 low cycles Divider 3 high cycles 0x00
0x19A Divider 3 bypass Divider 3
ignore
SYNC
Divider 3
force high
Divider 3
start high
Divider 3
phase offset
0x00
0x19B Unused Unused Channel 3
power-
down
Channel 3
direct-to-
output
Disable
Divider 3
DCC
0x00
0x19C
to
0x1DF
Unused Unused 0x00
Data Sheet AD9520-3
Rev. A | Page 63 of 80
Addr
(Hex) Parameter Bit 7 (MSB) Bit 6 Bit 5 Bit 4 Bit 3 Bit 2 Bit 1 Bit 0 (LSB)
Default
Value
(Hex)
VCO Divider and CLK Input
0x1E0 VCO divider Unused Unused VCO divider 0x00
0x1E1 Input CLKs Unused Unused
(default = 01b)
Power
down clock
input
section
Power down
VCO clock
interface
Power
down
VCO and
CLK
Select VCO or
CLK
Bypass VCO
divider
0x20
0x1E2
to
0x22A
Unused Unused 0x00
System
0x230 Power-down
and SYNC
Unused Disable
power on
SYNC
Power
down
SYNC
Power down
distribution
reference
Soft SYNC 0x00
0x231 Unused Unused Unused 0x00
Update All Registers
0x232 IO_UPDATE Unused IO_UPDATE
(self-clearing)
0x00
0x233
to
0x9FF
Unused
Unused
0x00
EEPROM Buffer Segment
0xA00 Serial port
configuration
Data transfer: one byte 0x00
0xA01 Starting address: Address 0x000 0x00
0xA02 0x00
0xA03 EEPROM customer
version ID
Data transfer: three bytes 0x02
0xA04 Starting address: Address 0x004 0x00
0xA05 0x04
0xA06 PLL settings Data transfer: 16 bytes 0x0E
0xA07 Starting address: Address 0x010 0x00
0xA08 0x10
0xA09 Output driver
control
Data transfer: 16 bytes 0x0E
0xA0A Starting address: Address 0x0F0 0x00
0xA0B 0xF0
0xA0C LVPECL channel
dividers
Data transfer: 12 bytes 0x0B
0xA0D Starting address: Address 0x190 0x01
0xA0E 0x90
0xA0F VCO divider and
CLK input
Data transfer: two bytes 0x01
0xA10 Starting address: Address 0x1E0 0x01
0xA11 0xE0
0xA12 Power-down and
SYNC
Data transfer: two bytes 0x01
0xA13 Starting address: Address 0x230 0x02
0xA14 0x30
0xA15 I/O update Action: IO_UPDATE 0x80
0xA16 End of data Action: end of data 0xFF
0xA17
to
0xAFF
Unused Unused
(available for additional EEPROM instructions)
0x00
EEPROM Control
0xB00 EEPROM status
(read only)
Unused Unused STATUS_
EEPROM
0x00
0xB01 EEPROM
error checking
(read only)
Unused Unused EEPROM
data error
0x00
0xB02 EEPROM Control 1 Unused SOFT_EEPROM
(self-clearing)
Enable
EEPROM write
0x00
0xB03 EEPROM Control 2 Unused Unused REG2EEPROM
(self-clearing)
0x00
AD9520-3 Data Sheet
Rev. A | Page 64 of 80
REGISTER MAP DESCRIPTIONS
Table 51 to Table 61 provide a detailed description of each of the control register functions.
Table 51. SPI Mode Serial Port Configuration
Reg.
Addr.
(Hex) Bits Name Description
0x000 7 SDO active Selects unidirectional or bidirectional data transfer mode.
0: SDIO pin is used for write and read; SDO pin is high impedance (default).
1: SDO pin is used for read; SDIO pin is used for write; unidirectional mode.
6 LSB first/addr incr SPI MSB or LSB data orientation. (This bit is ignored in I2C mode.)
0: data-oriented MSB first; the addressing decrements (default).
1: data-oriented LSB first; the addressing increments.
5 Soft reset Soft reset.
1 (self-clearing): if the EEPROM pin is high, soft reset loads the register values from the EEPROM. If the
EEPROM pin is low, soft reset loads the register values to the on-chip defaults.
4
Unused
Unused.
[3:0] Mirror[7:4] Bits[3:0] should always mirror Bits[7:4] so that it does not matter whether the part is in MSB or LSB first mode
(see Register 0x000[6]). Set the bits as follows:
Bit 0 = Bit 7
Bit 1 = Bit 6
Bit 2 = Bit 5
Bit 3 = Bit 4
0x003 [7:0] Part ID (read only) Uniquely identifies the dash version (AD9520-0 to AD9520-5) of the AD9520, as follows:
AD9520-0: 0x20
AD9520-1: 0x60
AD9520-2: 0xA0
AD9520-3: 0x61
AD9520-4: 0xE1
AD9520-5: 0xE0
0x004 [7:1] Unused Unused.
0 Read back active
registers
Selects register bank used for a readback.
0: reads back buffer registers (default).
1: reads back active registers.
Table 52. I2C Mode Serial Port Configuration
Reg.
Addr.
(Hex) Bits Name Description
0x000 [7:6] Unused Unused.
5
Soft reset
Soft reset.
1 (self-clearing): if the EEPROM pin is high, soft reset loads the register values from the EEPROM. If the
EEPROM pin is low, soft reset loads the register values to the on chip defaults.
4 Unused Unused.
[3:0] Mirror[7:4] Bits[3:0] should always mirror Bits[7:4] so that it does not matter whether the part is in MSB or LSB first mode.
See Table 51, Register 0x000, Bits[3:0].
0x003 [7:0] Part ID (read only) Uniquely identifies the dash version (AD9520-0 to AD9520-5) of the AD9520. See Table 51, Register 0x003.
0x004 [7:1] Unused Unused.
0 Read back active
registers
Selects register bank used for a readback.
0: reads back buffer registers (default).
1: reads back active registers.
Table 53. EEPROM Customer Version ID
Reg.
Addr.
(Hex) Bits Name Description
0x005 [7:0] EEPROM
customer version
ID (LSB)
16-bit EEPROM ID[7:0]. This register, along with Register 0x006, allows the user to store a unique ID
to identify which version of the AD9520 register settings is stored in the EEPROM. It does not affect
AD9520 operation in any way (default: 0x00).
0x006 [7:0] EEPROM
customer version
ID (MSB)
16-bit EEPROM ID[15:8]. This register, along with Register 0x005, allows the user to store a unique ID
to identify which version of the AD9520 register settings is stored in the EEPROM. It does not affect
AD9520 operation in any way (default: 0x00).
Data Sheet AD9520-3
Rev. A | Page 65 of 80
Table 54. PLL
Reg.
Addr.
(Hex) Bits Name Description
0x010 7 PFD polarity Sets the PFD polarity. Negative polarity is for use (if needed) with external VCO/VCXO only.
The on-chip VCO requires positive polarity; Bit 7 = 0b.
0: positive (higher control voltage produces higher frequency) (default).
1: negative (higher control voltage produces lower frequency).
[6:4] CP current Charge pump current (with CPRSET = 5.1 kΩ).
Bit 6 Bit 5 Bit 4 ICP (mA)
0 0 0 0.6
0 0 1 1.2
0 1 0 1.8
0 1 1 2.4
1 0 0 3.0
1 0 1 3.6
1 1 0 4.2
1 1 1 4.8 (default)
[3:2] CP mode Charge pump operating mode.
Bit 3 Bit 2 Charge Pump Mode
0 0 High impedance state.
0 1 Forces source current (pump up).
1 0 Forces sink current (pump down).
1 1 Normal operation (default).
[1:0] PLL power-down PLL operating mode.
Bit 1
Bit 0
Mode
0 0 Normal operation; this mode must be selected to use the PLL.
0 1 Asynchronous power-down (default).
1 0 Unused.
1 1 Synchronous power-down.
0x011 [7:0] 14-bit R counter,
Bits[7:0] (LSB)
Reference divider LSBs—lower eight bits. The reference divider (also called the R divider or R counter) is 14 bits long.
The lower eight bits are in this register (default: 0x01).
0x012 [7:6] Unused Unused.
[5:0] 14-bit R counter,
Bits[13:8] (MSB)
Reference divider MSBs—upper six bits. The reference divider (also called the R divider or R counter) is 14 bits long.
The upper six bits are in this register (default: 0x00).
0x013 [7:6] Unused Unused.
[5:0] 6-bit A counter A counter (part of N divider). The N divider is also called the feedback divider (default: 0x00).
0x014 [7:0]
13-bit B counter,
Bits[7:0] (LSB)
B counter (part of N divider)—lower eight bits. The N divider is also called the feedback divider (default: 0x03).
0x015 [7:5] Unused Unused.
[4:0]
13-bit B counter,
Bits[12:8] (MSB)
B counter (part of N divider)—upper five bits. The N divider is also called the feedback divider (default: 0x00).
0x016 7 Set CP pin to VCP/2 Sets the CP pin to one-half of the VCP supply voltage.
0: CP normal operation (default).
1: CP pin set to VCP/2.
6 Reset R counter Resets R counter (R divider).
0: normal (default).
1: holds R counter in reset.
5
Reset A and B
counters
Resets A and B counters (part of N divider).
0: normal (default).
1: holds A and B counters in reset.
4 Reset all counters Resets R, A, and B counters.
0: normal (default).
1: holds R, A, and B counters in reset.
3 B counter bypass B counter bypass. This is valid only when operating the prescaler in FD mode.
0: normal (default).
1: B counter is set to divide-by-1. This allows the prescaler setting to determine the divide for the N divider.
AD9520-3 Data Sheet
Rev. A | Page 66 of 80
Reg.
Addr.
(Hex) Bits Name Description
[2:0] Prescaler P Prescaler: DM = dual modulus; FD = fixed divide. Prescaler P is part of the feedback divider. See the VCO/VCXO Feedback Divider
N—P, A, and B section of the datasheet for details.
Bit
2
Bit
1
Bit
0 Mode Prescaler
0
0
0
FD
Divide-by-1.
0
0
1
FD
Divide-by-2.
0
1
0
DM
Divide-by-2 and divide-by-3 when A ≠ 0; divide-by-2 when A = 0.
0 1 1 DM Divide-by-4 and divide-by-5 when A ≠ 0; divide-by-4 when A = 0.
1 0 0 DM Divide-by-8 and divide-by-9 when A ≠ 0; divide-by-8 when A = 0.
1 0 1 DM Divide-by-16 and divide-by-17 when A ≠ 0; divide-by-16 when A = 0.
1 1 0 DM Divide-by-32 and divide-by-33 when A ≠ 0; divide-by-32 when A = 0 (default).
1 1 1 FD Divide-by-3.
0x017 [7:2] STATUS
pin control
Selects the signal that appears at the STATUS pin. Register 0x01D[7] must be 0b to reprogram the STATUS pin.
Bit
7
Bit
6
Bit
5
Bit
4
Bit
3
Bit
2
Level or
Dynamic
Signal Signal at STATUS Pin
0 0 0 0 0 0 LVL Ground (dc) (default).
0 0 0 0 0 1 DYN N divider output (after the delay).
0 0 0 0 1 0 DYN R divider output (after the delay).
0 0 0 0 1 1 DYN A divider output.
0 0 0 1 0 0 DYN Prescaler output.
0 0 0 1 0 1 DYN PFD up pulse.
0 0 0 1 1 0 DYN PFD down pulse.
0 X X X X X LVL Ground (dc). Used for all settings of these bits that are not otherwise specified in this table.
The selections that follow are also used for REFMON and LD pin control.
1 0 0 0 0 0 LVL Ground (dc).
1 0 0 0 0 1 DYN REF1 clock (differential reference when in differential mode).
1
0
0
0
1
0
DYN
REF2 clock (N/A in differential mode).
1
0
0
0
1
1
DYN
Selected reference to PLL (differential reference when in differential mode).
1 0 0 1 0 0 DYN Unselected reference to PLL (not available in differential mode).
1 0 0 1 0 1 LVL Status of selected reference (status of differential reference); active high.
1 0 0 1 1 0 LVL Status of unselected reference (not available in differential mode); active high.
1 0 0 1 1 1 LVL Status of REF1 frequency; active high.
1 0 1 0 0 0 LVL Status of REF2 frequency; active high.
1 0 1 0 0 1 LVL (Status of REF1 frequency) AND (status of REF2 frequency).
1 0 1 0 1 0 LVL (DLD) AND (status of selected reference) AND (status of VCO).
1 0 1 0 1 1 LVL Status of VCO frequency; active high.
1 0 1 1 0 0 LVL Selected reference (low = REF1, high = REF2).
1 0 1 1 0 1 LVL DLD; active high.
1
0
1
1
1
0
LVL
Holdover active; active high.
1
0
1
1
1
1
LVL
N/A. Do not use.
1 1 0 0 0 0 LVL VS (PLL power supply).
1 1 0 0 0 1 DYN REF1 clock (differential reference when in differential mode).
1 1 0 0 1 0 DYN REF2 clock (not available in differential mode).
1 1 0 0 1 1 DYN Selected reference to PLL (differential reference when in differential mode).
1 1 0 1 0 0 DYN Unselected reference to PLL (not available when in differential mode).
1 1 0 1 0 1 LVL Status of selected reference (status of differential reference); active low.
1 1 0 1 1 0 LVL Status of unselected reference (not available in differential mode); active low.
1 1 0 1 1 1 LVL Status of REF1 frequency; active low.
1 1 1 0 0 0 LVL Status of REF2 frequency; active low.
1 1 1 0 0 1 LVL (Status of REF1 frequency) AND (status of REF2 frequency).
1 1 1 0 1 0 LVL (DLD) AND (status of selected reference) AND (status of VCO).
1 1 1 0 1 1 LVL Status of VCO frequency; active low.
1 1 1 1 0 0 LVL Selected reference (low = REF2, high = REF1).
1 1 1 1 0 1 LVL DLD; active low.
1
1
1
1
1
0
LVL
Holdover active; active low.
1 1 1 1 1 1 LVL N/A. Do not use.
Data Sheet AD9520-3
Rev. A | Page 67 of 80
Reg.
Addr.
(Hex) Bits Name Description
[1:0] Antibacklash
pulse width
Bit 1 Bit 0 Antibacklash Pulse Width (ns)
0 0 2.9 (default)
0 1 1.3
1 0 6.0
1 1 2.9
0x018 7 Enable CMOS
reference input
dc offset
Enables dc offset in single-ended CMOS input mode to prevent chattering when ac-coupled and input is lost.
0: disables dc offset (default).
1: enables dc offset.
[6:5] Lock detect
counter
Required consecutive number of PFD cycles with edges inside lock detect window before the DLD indicates a locked condition.
Bit 6
Bit 5
PFD Cycles to Determine Lock
0 0 5 (default)
0 1 16
1 0 64
1 1 255
4
Digital lock
detect window
If the time difference of the rising edges at the inputs to the PFD is less than the lock detect window time, the digital lock detect
flag is set. The flag remains set until the time difference is greater than the loss-of-lock threshold.
0: high range (default). The default setting is 3.5 ns.
1: low range.
3 Disable digital
lock detect
Digital lock detect operation.
0: normal lock detect operation (default).
1: disables lock detect.
[2:1] VCO calibration
divider
Divider used to generate the VCO calibration clock from the PLL reference clock (see the VCO Calibration section for the
recommended setting of the VCO calibration divider based on the PFD rate).
Bit 2
Bit 1
VCO Calibration Clock Divider
0 0 2. This setting is fine for PFD frequencies < 12.5 MHz. The PFD frequency is fREF/R.
0 1 4. This setting is fine for PFD frequencies < 12.5 MHz. The PFD frequency is fREF/R.
1 0 8. This setting is fine for PFD frequencies < 50 MHz.
1 1 16 (default). This setting is fine for any PFD frequency, but it also results in the longest VCO calibration time.
0 VCO calibration
now
Initiates VCO calibration. This bit must be toggled from 0b to 1b in the active registers. The sequence to initiate a calibration is
as follows: program to 0b, followed by an IO_UPDATE (Register 0x232[0]); then program to 1b, followed by another IO_UPDATE
(Register 0x232[0]). This sequence gives complete control over when the VCO calibration occurs relative to the programming of
other registers that can impact the calibration (default = 0b). Note that the VCO divider (Register 0x1E0[2:0]) must not be static
during VCO calibration.
0x019 [7:6] R, A, B counters
SYNC pin reset
Bit 7 Bit 6 Action
0 0 Does nothing on SYNC (default).
0 1 Asynchronous reset.
1 0 Synchronous reset.
1 1 Does nothing on SYNC.
[5:3] R path delay R path delay, see Table 2 (default: 0x0).
[2:0] N path delay N path delay, see Table 2 (default: 0x0).
0x01A 7
Enable STATUS
pin divider
Enables a divide-by-4 on the STATUS pin. This makes it easier to look at low duty-cycle signals out of the R and N dividers.
0: divide-by-4 disabled on STATUS pin (default).
1: divide-by-4 enabled on STATUS pin.
6 Ref freq monitor
threshold
Sets the reference (REF1/REF2) frequency monitor’s detection threshold frequency. This does not affect the VCO frequency monitor’s
detection threshold (see Table 17: REF1, REF2, and VCO frequency status monitor parameter).
0: frequency valid if frequency is above 1.02 MHz (default).
1: frequency valid if frequency is above 6 kHz.
AD9520-3 Data Sheet
Rev. A | Page 68 of 80
Reg.
Addr.
(Hex) Bits Name Description
[5:0] LD pin control Selects the signal that is connected to the LD pin.
Bit
5
Bit
4
Bit
3
Bit
2
Bit
1
Bit
0
Level or
Dynamic
Signal Signal at LD Pin
0 0 0 0 0 0 LVL Digital lock detect (high = lock; low = unlock, default).
0 0 0 0 0 1 DYN P-channel, open-drain lock detect (analog lock detect).
0 0 0 0 1 0 DYN N-channel, open-drain lock detect (analog lock detect).
0 0 0 0 1 1 HIZ Tristate (high-Z) LD pin.
0 0 0 1 0 0 CUR Current source lock detect (110 µA when DLD is true).
0 X X X X X LVL Ground (dc). Used for all settings of these bits that are not otherwise specified in this table.
The selections that follow are also used for REFMON and STATUS pin control.
1 0 0 0 0 0 LVL Ground (dc).
1
0
0
0
0
1
DYN
REF1 clock (differential reference when in differential mode).
1
0
0
0
1
0
DYN
REF2 clock (N/A in differential mode).
1 0 0 0 1 1 DYN Selected reference to PLL (differential reference when in differential mode).
1 0 0 1 0 0 DYN Unselected reference to PLL (not available in differential mode).
1 0 0 1 0 1 LVL Status of selected reference (status of differential reference); active high.
1 0 0 1 1 0 LVL Status of unselected reference (not available in differential mode); active high.
1 0 0 1 1 1 LVL Status of REF1 frequency; active high.
1 0 1 0 0 0 LVL Status of REF2 frequency; active high.
1 0 1 0 0 1 LVL (Status of REF1 frequency) AND (status of REF2 frequency).
1 0 1 0 1 0 LVL (DLD) AND (status of selected reference) AND (status of VCO).
1 0 1 0 1 1 LVL Status of VCO frequency; active high.
1 0 1 1 0 0 LVL Selected reference (low = REF1, high = REF2).
1 0 1 1 0 1 LVL DLD; active high.
1 0 1 1 1 0 LVL Holdover active; active high.
1 0 1 1 1 1 LVL N/A. Do not use.
1 1 0 0 0 0 LVL VS (PLL power supply).
1 1 0 0 0 1 DYN REF1 clock (differential reference when in differential mode).
1 1 0 0 1 0 DYN REF2 clock (not available in differential mode).
1 1 0 0 1 1 DYN Selected reference to PLL (differential reference when in differential mode).
1 1 0 1 0 0 DYN Unselected reference to PLL (not available when in differential mode).
1 1 0 1 0 1 LVL Status of selected reference (status of differential reference); active low.
1 1 0 1 1 0 LVL Status of unselected reference (not available in differential mode); active low.
1 1 0 1 1 1 LVL Status of REF1 frequency; active low.
1 1 1 0 0 0 LVL Status of REF2 frequency; active low.
1 1 1 0 0 1 LVL (Status of REF1 frequency) AND (status of REF2 frequency).
1 1 1 0 1 0 LVL (DLD) AND (status of selected reference) AND (status of VCO).
1 1 1 0 1 1 LVL Status of VCO frequency; active low.
1 1 1 1 0 0 LVL Selected reference (low = REF2, high = REF1).
1 1 1 1 0 1 LVL DLD; active low.
1 1 1 1 1 0 LVL Holdover active; active low.
1 1 1 1 1 1 LVL N/A. Do not use.
0x01B 7
Enable VCO
frequency
monitor
Enables or disables the VCO frequency monitor.
0: disables the VCO frequency monitor (default).
1: enables the VCO frequency monitor.
6 Enable REF2
(REFIN) frequency
monitor
Enables or disables the REF2 frequency monitor.
0: disables the REF2 frequency monitor (default).
1: enables the REF2 frequency monitor.
5 Enable REF1
(REFIN) frequency
monitor
REF1 (REFIN) frequency monitor enabled; this is for both REF1 (single-ended) and REFIN (differential) inputs (as selected by
differential reference mode).
0: disables the REF1 (REFIN) frequency monitor (default).
1: enables the REF1 (REFIN) frequency monitor.
Data Sheet AD9520-3
Rev. A | Page 69 of 80
Reg.
Addr.
(Hex) Bits Name Description
[4:0] REFMON pin
control
Selects the signal that is connected to the REFMON pin.
Bit
4
Bit
3
Bit
2
Bit
1
Bit
0
Level or
Dynamic
Signal Signal at REFMON Pin
0 0 0 0 0 LVL Ground, dc (default).
0 0 0 0 1 DYN REF1 clock (differential reference when in differential mode).
0 0 0 1 0 DYN REF2 clock (N/A in differential mode).
0 0 0 1 1 DYN Selected reference to PLL (differential reference when in differential mode).
0 0 1 0 0 DYN Unselected reference to PLL (not available in differential mode).
0 0 1 0 1 LVL Status of selected reference (status of differential reference); active high.
0 0 1 1 0 LVL Status of unselected reference (not available in differential mode); active high.
0 0 1 1 1 LVL Status of REF1 frequency; active high.
0 1 0 0 0 LVL Status of REF2 frequency; active high.
0 1 0 0 1 LVL (Status of REF1 frequency) AND (status of REF2 frequency).
0 1 0 1 0 LVL (DLD) AND (status of selected reference) AND (status of VCO).
0 1 0 1 1 LVL Status of VCO frequency; active high.
0 1 1 0 0 LVL Selected reference (low = REF1, high = REF2).
0 1 1 0 1 LVL DLD; active high.
0 1 1 1 0 LVL Holdover active; active high.
0 1 1 1 1 LVL N/A. Do not use.
1 0 0 0 0 LVL VS (PLL power supply).
1 0 0 0 1 DYN REF1 clock (differential reference when in differential mode).
1 0 0 1 0 DYN REF2 clock (not available in differential mode).
1 0 0 1 1 DYN Selected reference to PLL (differential reference when in differential mode).
1 0 1 0 0 DYN Unselected reference to PLL (not available when in differential mode).
1 0 1 0 1 LVL Status of selected reference (status of differential reference); active low.
1 0 1 1 0 LVL Status of unselected reference (not available in differential mode); active low.
1 0 1 1 1 LVL Status of REF1 frequency; active low.
1 1 0 0 0 LVL Status of REF2 frequency; active low.
1 1 0 0 1 LVL (Status of REF1 frequency) AND (status of REF2 frequency).
1 1 0 1 0 LVL (DLD) AND (status of selected reference) AND (status of VCO).
1 1 0 1 1 LVL Status of VCO frequency; active low.
1 1 1 0 0 LVL Selected reference (low = REF2, high = REF1).
1 1 1 0 1 LVL DLD; active low.
1 1 1 1 0 LVL Holdover active; active low.
1 1 1 1 1 LVL N/A. Do not use.
0x01C 7 Disable
switchover
deglitch
Disables or enables the switchover deglitch circuit.
0: enables the switchover deglitch circuit (default).
1: disables the switchover deglitch circuit.
6 Select REF2 If Register 0x01C[5] = 0b, selects the reference for PLL when in manual; register selected reference control.
0: selects REF1 (default).
1: selects REF2.
5
Use REF_SEL pin
If Register 0x01C[4] = 0b (manual), sets the method of PLL reference selection.
0: uses Register 0x01C[6] (default).
1: uses REF_SEL pin.
4 Enable automatic
reference
switchover
Automatic or manual reference switchover. Single-ended reference mode must be selected by Register 0x01C[0] = 0b.
0: manual reference switchover (default).
1: automatic reference switchover. Setting this bit also powers on REF1 and REF2 and overrides the settings in Register 0x01C[2:1].
3 Stay on REF2 Stays on REF2 after switchover.
0: returns to REF1 automatically when REF1 status is good again (default).
1: stays on REF2 after switchover. Does not automatically return to REF1.
2 Enable REF2 This bit turns the REF2 power on. This bit is overridden when automatic reference switchover is enabled.
0: REF2 power off (default).
1: REF2 power on.
1 Enable REF1 This bit turns the REF1 power on. This bit is overridden when automatic reference switchover is enabled.
0: REF1 power off (default).
1: REF1 power on.
0 Enable differential
reference
Selects the PLL reference mode, differential or single-ended. Register 0x01C[2:1] should be cleared when this bit is set.
0: single-ended reference mode (default); 1: differential reference mode.
AD9520-3 Data Sheet
Rev. A | Page 70 of 80
Reg.
Addr.
(Hex) Bits Name Description
0x01D 7 Enable
STATUS_EEPROM
at STATUS pin
Enables the Status_EEPROM signal at the STATUS pin.
0: the STATUS pin is controlled by Register 0x017[7:2] selection.
1: select STATUS_EEPROM signal at STATUS pin. This bit overrides Register 0x017[7:2] (default).
6
Enable
XTAL OSC
Enables the maintaining amplifier needed by a crystal oscillator at the PLL reference input.
0: crystal oscillator maintaining amplifier disabled (default).
1: crystal oscillator maintaining amplifier enabled.
5 Enable
clock doubler
Enables PLL reference input clock doubler.
0: doubler disabled (default).
1: doubler enabled.
4 Disable PLL status
register
Disables the PLL status register readback.
0: PLL status register enabled (default).
1: PLL status register disabled. If this bit is set, Register 01F is not automatically updated.
3 Enable LD pin
comparator
Enables the LD pin voltage comparator. Used with the LD pin current source lock detect mode. When the AD9520 is in internal
(automatic) holdover mode, this bit enables the use of the voltage on the LD pin to determine if the PLL was previously in
a locked state (see Figure 47). Otherwise, this setting can be used with the REFMON and STATUS pins to monitor the voltage
on the LD pin.
0: disables LD pin comparator and ignore the LD pin voltage; internal/automatic holdover controller treats the LD pin as true
(high, default).
1: enables LD pin comparator (use LD pin voltage to determine if the PLL was previously locked).
2 Unused Unused.
1 Enable external
holdover Enables the external hold control through the SYNC pin. (This disables the internal holdover mode.)
0: automatic holdover mode, holdover controlled by automatic holdover circuit (default).
1: external holdover mode, holdover controlled by SYNC pin.
0
Enable holdover
Enables the internally controlled holdover function.
0: holdover disabled (default).
1: holdover enabled.
0x01E [7:5] Unused Unused.
[4:3] External
zero delay
feedback
channel divider
select
Bit 4 Bit 3 Selection of Channel Divider for Use in the External Zero-Delay Path
0 0 Selects Channel Divider 0 (default).
0 1 Selects Channel Divider 1.
1
0
Selects Channel Divider 2.
1 1 Selects Channel Divider 3
2
Enable external
zero delay
Selects which zero delay mode to use.
0: enables internal zero delay mode if Register 0x01E[1] = 1 (default).
1: enables external zero delay mode if Register 0x01E[1] = 1.
1 Enable zero delay Enables zero delay function.
0: disables zero delay function (default).
1: enables zero delay function.
0 Unused Unused.
0x01F 7 Unused Unused.
6 VCO calibration
finished
(read only)
Readback register. Indicates the status of the VCO calibration.
0: VCO calibration not finished.
1: VCO calibration finished.
5
Holdover active
(read only)
Readback register. Indicates if the part is in the holdover state (see Figure 47). Note that this is not the same as holdover enabled.
0: not in holdover state.
1: holdover state active.
4 REF2 selected
(read only)
Readback register. Indicates which PLL reference is selected as the input to the PLL.
0: REF1 selected (or differential reference if in differential mode).
1: REF2 selected.
3 VCO frequency >
threshold
(read only)
Readback register. Indicates if the VCO frequency is greater than the threshold (see Table 17: REF1, REF2, and VCO frequency
status monitor parameter).
0: VCO frequency is less than the threshold.
1: VCO frequency is greater than the threshold.
2
REF2 frequency >
threshold
(read only)
Readback register. Indicates if the frequency of the signal at REF2 is greater than the threshold frequency set by Register 0x01A[6].
0: REF2 frequency is less than the threshold frequency.
1: REF2 frequency is greater than the threshold frequency.
1 REF1 frequency >
threshold
(read only)
Readback register. Indicates if the frequency of the signal at REF1 is greater t
han the threshold frequency set by Register 0x01A[6].
0: REF1 frequency is less than the threshold frequency.
1: REF1 frequency is greater than the threshold frequency.
0 Digital lock detect
(read only)
Readback register. Digital lock detect.
0: PLL is not locked.
1: PLL is locked.
Data Sheet AD9520-3
Rev. A | Page 71 of 80
Table 55. Output Driver Control
Reg.
Addr.
(Hex) Bits Name Description
0x0F0 7 OUT0 format Selects the output type for OUT0.
0: LVPECL (default).
1: CMOS.
[6:5] OUT0 CMOS
configuration
Sets the CMOS output configuration for OUT0 when Register 0x0F0[7] = 1b.
Bits[6:5]
OUT0A
OUT0B
00
01
10
11 (default)
Tristate
On
Tristate
On
Tristate
Tristate
On
On
[4:3] OUT0 polarity Sets the output polarity for OUT0.
Bit 7 Bit 4 Bit 3 Output Type OUT0A OUT0B
0 (default)
0
1
1
1
1
X
X
0 (default)
0
1
1
0 (default)
1
0
1
0
1
LVPECL
LVPECL
CMOS
CMOS
CMOS
CMOS
Noninverting
Inverting
Noninverting
Inverting
Noninverting
Inverting
Inverting
Noninverting Noninverting
Inverting
Inverting
Noninverting
[2:1]
OUT0 LVPECL
differential
voltage
Sets the LVPECL output differential voltage (VOD).
Bit 2 Bit 1 VOD (mV)
0
0
1 (default)
1
0
1
0 (default)
1
400
600
780
960
0 OUT0 LVPECL
power-down
LVPECL power-down.
0: normal operation (default).
1: safe power-down.
0x0F1 [7:0] OUT1 control This register controls OUT1, and the bit assignments for this register are identical to Register 0x0F0.
0x0F2 [7:0] OUT2 control This register controls OUT2, and the bit assignments for this register are identical to Register 0x0F0.
0x0F3 [7:0] OUT3 control This register controls OUT3, and the bit assignments for this register are identical to Register 0x0F0.
0x0F4 [7:0] OUT4 control This register controls OUT4, and the bit assignments for this register are identical to Register 0x0F0.
0x0F5 [7:0] OUT5 control This register controls OUT5, and the bit assignments for this register are identical to Register 0x0F0.
0x0F6
[7:0]
OUT6 control
This register controls OUT6, and the bit assignments for this register are identical to Register 0x0F0.
0x0F7 [7:0] OUT7 control This register controls OUT7, and the bit assignments for this register are identical to Register 0x0F0.
0x0F8
[7:0]
OUT8 control
This register controls OUT8, and the bit assignments for this register are identical to Register 0x0F0.
0x0F9 [7:0] OUT9 control This register controls OUT9, and the bit assignments for this register are identical to Register 0x0F0.
0x0FA [7:0] OUT10 control This register controls OUT10, and the bit assignments for this register are identical to Register 0x0F0.
0x0FB [7:0] OUT11 control This register controls OUT11, and the bit assignments for this register are identical to Register 0x0F0.
0x0FC 7 CSDLD en OUT7 OUT7 is enabled only if the CSDLD signal is high.
Bit 7
CSDLD
Signal OUT7 Enable Status
0
1
1
0
0
1
Not affected by CSDLD signal (default).
Asynchronous power-down.
Asynchronously enables OUT7 if not powered down by other settings. For this feature, use current
source digital lock detect and set the enable LD pin comparator bit (Register 0x01D[3]).
6 CSDLD en OUT6 OUT6 is enabled only if CSDLD is high. Setting is identical to Register 0x0FC[7].
5 CSDLD en OUT5 OUT5 is enabled only if CSDLD is high. Setting is identical to Register 0x0FC[7].
4 CSDLD en OUT4 OUT4 is enabled only if CSDLD is high. Setting is identical to Register 0x0FC[7].
3 CSDLD en OUT3 OUT3 is enabled only if CSDLD is high. Setting is identical to Register 0x0FC[7].
2 CSDLD en OUT2 OUT2 is enabled only if CSDLD is high. Setting is identical to Register 0x0FC[7].
1 CSDLD en OUT1 OUT1 is enabled only if CSDLD is high. Setting is identical to Register 0x0FC[7].
0 CSDLD en OUT0 OUT0 is enabled only if CSDLD is high. Setting is identical to Register 0x0FC[7].
0x0FD [7:4] Unused Unused.
3 CSDLD en OUT11 OUT11 is enabled only if CSDLD is high. Setting is identical to Register 0x0FC[7].
2 CSDLD en OUT10 OUT10 is enabled only if CSDLD is high. Setting is identical to Register 0x0FC[7].
1 CSDLD en OUT9 OUT9 is enabled only if CSDLD is high. Setting is identical to Register 0x0FC[7].
0 CSDLD en OUT8 OUT8 is enabled only if CSDLD is high. Setting is identical to Register 0x0FC[7].
AD9520-3 Data Sheet
Rev. A | Page 72 of 80
Table 56. LVPECL Channel Dividers
Reg.
Addr.
(Hex) Bits Name Description
0x190 [7:4] Divider 0 low cycles Number of clock cycles (minus 1) of the divider input during which the divider output stays low.
A value of 0x7 means that the divider is low for eight input clock cycles (default: 0x7).
[3:0]
Divider 0 high cycles
Number of clock cycles (minus 1) of the divider input during which the divider output stays high.
A value of 0x7 means that the divider is high for eight input clock cycles (default: 0x7).
0x191 7 Divider 0 bypass Bypasses and powers down the divider; routes input to divider output.
0: uses divider (default).
1: bypasses divider.
6 Divider 0 ignore SYNC Ignores SYNC.
0: obeys chip-level SYNC signal (default).
1: ignores chip-level SYNC signal.
5 Divider 0 force high Forces divider output to a specific state. This requires that ignore SYNC also be set. Note that this bit
has no effect if the channel divider is bypassed, but the driver polarity can still be reversed.
0: divider output is forced to low (default).
1: divider output is forced to the setting stored in Bit 4 of this register.
4 Divider 0 start high Selects clock output to start high or start low.
0: starts low (default).
1: starts high.
[3:0] Divider 0 phase offset Phase offset (default: 0x0).
0x192 [7:3] Unused Unused.
2 Channel 0 power-down Channel 0 powers down.
0: normal operation (default).
1: powered down. (Setting this bit puts OUT0/OUT0, OUT1/OUT1, and OUT2/OUT2 into safe power-
down mode.)
1 Channel 0 direct-to-output Connects OUT0, OUT1, and OUT2 to Divider 0 or directly to VCO or CLK.
0: OUT0, OUT1, and OUT2 are connected to Divider 0 (default).
1: If Register 0x1E1[1:0] = 10b, the VCO is routed directly to OUT0, OUT1, and OUT2.
If Register 0x1E1[1:0] = 00b, the CLK is routed directly to OUT0, OUT1, and OUT2.
If Register 0x1E1[1:0] = 01b, there is no effect.
0 Disable Divider 0 DCC Duty-cycle correction function.
0: enables duty-cycle correction (default).
1: disables duty-cycle correction.
0x193 [7:4] Divider 1 low cycles Number of clock cycles (minus 1) of the divider input during which the divider output stays low.
A value of 0x3 means that the divider is low for four input clock cycles (default: 0x3).
[3:0] Divider 1 high cycles Number of clock cycles (minus 1) of the divider input during which the divider output stays high.
A value of 0x3 means that the divider is high for four input clock cycles (default: 0x3).
0x194 7 Divider 1 bypass Bypasses and powers down the divider; routes input to divider output.
0: uses divider (default).
1: bypasses divider.
6 Divider 1 ignore SYNC Ignores SYNC.
0: obeys chip-level SYNC signal (default).
1: ignores chip-level SYNC signal.
5 Divider 1 force high Forces divider output to a specific state. This requires that ignore SYNC also be set. Note that this bit
has no effect if the channel divider is bypassed, but the driver polarity can still be reversed.
0: divider output is forced to low (default).
1: divider output is forced to the setting stored in Bit 4 of this register.
4 Divider 1 start high Selects clock output to start high or start low.
0: starts low (default).
1: starts high.
[3:0] Divider 1 phase offset Phase offset (default: 0x0).
Data Sheet AD9520-3
Rev. A | Page 73 of 80
Reg.
Addr.
(Hex) Bits Name Description
0x195 [7:3] Unused Unused.
2 Channel 1 power-down Channel 1 powers down.
0: normal operation (default).
1: powered down. (Setting this bit puts OUT3/OUT3, OUT4/OUT4, and OUT5/OUT5 into safe power-
down mode.)
1 Channel 1 direct-to-output Connects OUT3, OUT4, and OUT5 to Divider 1 or directly to VCO or CLK.
0: OUT3, OUT4, and OUT5 are connected to Divider 1 (default).
1: If Register 0x1E1[1:0] = 10b, the VCO is routed directly to OUT3, OUT4, and OUT5.
If Register 0x1E1[1:0] = 00b, the CLK is routed directly to OUT3, OUT4, and OUT5.
If Register 0x1E1[1:0] = 01b, there is no effect.
0 Disable Divider 1 DCC Duty-cycle correction function.
0: enables duty-cycle correction (default).
1: disables duty-cycle correction.
0x196 [7:4] Divider 2 low cycles Number of clock cycles (minus 1) of the divider input during which the divider output stays low.
A value of 0x1 means that the divider is low for two input clock cycles (default: 0x1).
[3:0] Divider 2 high cycles Number of clock cycles (minus 1) of the divider input during which the divider output stays high.
A value of 0x1 means that the divider is high for two input clock cycles (default: 0x1).
0x197 7 Divider 2 bypass Bypasses and powers down the divider; routes input to divider output.
0: uses divider (default).
1: bypasses divider.
6
Divider 2 ignore SYNC
Ignores SYNC.
0: obeys chip-level SYNC signal (default).
1: ignores chip-level SYNC signal.
5 Divider 2 force high Forces divider output to a specific state. This requires that ignore SYNC also be set. Note that this bit
has no effect if the channel divider is bypassed, but the driver polarity can still be reversed.
0: divider output is forced to low (default).
1: divider output is forced to the setting stored in Bit 4 of this register.
4 Divider 2 start high Selects clock output to start high or start low.
0: starts low (default).
1: starts high.
[3:0] Divider 2 phase offset Phase offset (default: 0x0).
0x198 [7:3] Unused Unused.
2 Channel 2 power-down Channel 2 powers down.
0: normal operation (default).
1: powered down. (Setting this bit puts OUT6/OUT6, OUT7/OUT7, and OUT8/OUT8 into safe power-
down mode.)
1 Channel 2 direct-to-output Connects OUT6, OUT7, and OUT8 to Divider 2 or directly to VCO or CLK.
0: OUT6, OUT7, and OUT8 are connected to Divider 2 (default).
1: If Register 0x1E1[1:0] = 10b, the VCO is routed directly to OUT6, OUT7, and OUT8.
If Register 0x1E1[1:0] = 00b, the CLK is routed directly to OUT6, OUT7, and OUT8.
If Register 0x1E1[1:0] = 01b, there is no effect.
0 Disable Divider 2 DCC Duty-cycle correction function.
0: enables duty-cycle correction (default).
1: disables duty-cycle correction.
0x199 [7:4] Divider 3 low cycles Number of clock cycles (minus 1) of the divider input during which the divider output stays low.
A value of 0x0 means that the divider is low for one input clock cycle (default: 0x0).
[3:0] Divider 3 high cycles Number of clock cycles (minus 1) of the divider input during which the divider output stays high.
A value of 0x0 means that the divider is high for one input clock cycle (default: 0x0).
AD9520-3 Data Sheet
Rev. A | Page 74 of 80
Reg.
Addr.
(Hex) Bits Name Description
0x19A 7 Divider 3 bypass Bypasses and powers down the divider; routes input to divider output.
0: uses divider (default).
1: bypasses divider.
6 Divider 3 ignore SYNC Ignores SYNC.
0: obeys chip-level SYNC signal (default).
1: ignores chip-level SYNC signal.
5 Divider 3 force high Forces divider output to a specific state. This requires that ignore SYNC also be set. Note that this bit
has no effect if the channel divider is bypassed, but the driver polarity can still be reversed.
0: divider output is forced to low (default).
1: divider output is forced to the setting stored in Bit 4 of this register.
4 Divider 3 start high Selects clock output to start high or start low.
0: starts low (default).
1: starts high.
[3:0] Divider 3 phase offset Phase offset (default: 0x0).
0x19B [7:3] Unused Unused.
2 Channel 3 power-down Channel 3 powers down.
0: normal operation (default).
1: powered down. (Setting this bit puts OUT9/OUT9, OUT10/OUT10, and OUT11/OUT11 into safe
power-down mode.)
1 Channel 3 direct to output Connects OUT9, OUT10, and OUT11 to Divider 3 or directly to VCO or CLK.
0: OUT9, OUT10, and OUT11 are connected to Divider 3 (default).
1: If Register 0x1E1[1:0] = 10b, the VCO is routed directly to OUT9, OUT10, and OUT11.
If Register 0x1E1[1:0] = 00b, the CLK is routed directly to OUT9, OUT10, and OUT11.
If Register 0x1E1[1:0] = 01b, there is no effect.
0 Disable Divider 3 DCC Duty-cycle correction function.
0: enables duty-cycle correction (default).
1: disables duty-cycle correction.
Table 57. VCO Divider and CLK Input
Reg.
Addr.
(Hex) Bits Name Description
0x1E0 [2:0] VCO divider Bit 2 Bit 1 Bit 0 Divide
0 0 0 2 (default)
0 0 1 3
0 1 0 4
0 1 1 5
1 0 0 6
1 0 1 Output static
1 1 0 1 (bypass)
1 1 1 Output static
0x1E1 [7:5] Unused Unused.
4 Power down
clock input section
Powers down the clock input section (including CLK buffer, VCO divider, and CLK tree).
0: normal operation (default).
1: power-down.
3 Power down
VCO clock interface
Powers down the interface block between VCO and clock distribution.
0: normal operation (default).
1: power-down.
2 Power down VCO and CLK Powers down both the VCO and the CLK input.
0: normal operation (default).
1: power-down.
1 Select VCO or CLK Selects either the VCO or the CLK as the input to VCO divider.
0: selects external CLK as input to VCO divider (default).
1: selects VCO as input to VCO divider; VCO divider cannot be bypassed when this bit is set. This bit
must be set to use the PLL with the internal VCO.
0 Bypass VCO divider Bypasses or uses the VCO divider.
0: uses VCO divider (default).
1: bypasses VCO divider; VCO cannot be selected as input when this bit is set.
Data Sheet AD9520-3
Rev. A | Page 75 of 80
Table 58. System
Reg.
Addr.
(Hex) Bits Name Description
0x230
[7:4]
Unused
Unused.
3 Disable power on SYNC Powers on SYNC mode. Used to disable the antiruntpulse circuitry.
0: enables the antiruntpulse circuitry (default).
1: disables the antiruntpulse circuitry.
2 Power down SYNC Powers down the SYNC function.
0: normal operation of the SYNC function (default).
1: powers down SYNC circuitry.
1 Power down distribution
reference
Powers down the reference for the distribution section.
0: normal operation of the reference for the distribution section (default).
1: powers down the reference for the distribution section.
0 Soft SYNC The soft SYNC bit works in the same way as the SYNC pin, except that the polarity of the bit is
reversed. That is, a high level forces selected channels into a predetermined static state, and a 1b-
to-0b transition triggers a SYNC.
0: same as SYNC pin high.
1: same as SYNC pin low.
Table 59. Update All Registers
Reg.
Addr.
(Hex) Bits Name Description
0x232
[7:1] Unused Unused.
0 IO_UPDATE This bit must be set to 1b to transfer the contents of the buffer registers into the active registers.
This transfer occurs on the next SCLK rising edge. This bit is self-clearing; that is, it does not have to be set
back to 0b.
1 (self-clearing): updates all active registers to the contents of the buffer registers.
Table 60. EEPROM Buffer Segment
Reg
Addr
(Hex) Bits Name Description
0xA00
to
0xAFF
EEPROM buffer segment The EEPROM buffer segment section stores the starting address and number of bytes that are to be
stored and then read back to and from the EEPROM. Because the AD9520 register space is
noncontiguous, the EEPROM controller uses the starting address and number of bytes in the
AD9520 register space to store and retrieve from the EEPROM.
There are two types of entries in the EEPROM buffer segment: data transfers and operational codes.
For a data transfer, Bit 7 of the command byte is set to 0b. The remaining seven bits are the size of
the transfer, minus 1 (that is, 0x01 indicates a 2-byte transfer). The starting address (MSB first) of the
transfer is contained in the two bytes of the EEPROM buffer segment that immediately follow the
data transfer command.
For an operational code, Bit 7 of the command byte is set to 1b and is a special instruction for the
EE
PROM controller. There are two operational codes: IO_UPDATE and end of data. The IO_UPDATE
operational code instructs the EEPROM controller to transfer the AD9520 register values into the
active register space (and is functionally equivalent to writing 0x01 to Register 0x232). The end-of-
data operational code informs the EEPROM controller that the end of data has been reached and to
terminate the transfer. The last byte of the EEPROM buffer segment must contain an end-of-data
operational code.
Using the on-chip default setting of the EEPROM buffer segment registers, the EEPROM controller
transfers all register values to/from the EEPROM, and an IO_UPDATE is issued after transfer.
Therefore, the user does not normally need to alter the EEPROM buffer segment.
See the Programming the EEPROM Buffer Segment section for more information.
AD9520-3 Data Sheet
Rev. A | Page 76 of 80
Table 61. EEPROM Control
Reg
Addr
(Hex) Bits Name Description
0xB00
[7:1]
Unused
Unused.
0
STATUS_EEPROM
(read only)
This read-only register indicates the status of the data transfer between the EEPROM and the buffer
register bank during the writing and reading of the EEPROM. This signal is also available at the STATUS pin
when Register 0x01D[7] is set.
0: data transfer is complete.
1: data transfer is not complete.
0xB01
[7:1] Unused Unused.
0 EEPROM
data error
(read only)
This read-only register indicates an error during the data transfer between the EEPROM and the buffer.
0: no error. Data is correct.
1: incorrect data detected.
0xB02
[7:2] Unused Unused.
1 SOFT_EEPROM When the EEPROM pin is tied low, setting SOFT_EEPROM resets the AD9520 using the settings saved in the
EEPROM.
1: soft reset with EEPROM settings (self-clearing).
0 Enable EEPROM
write
Enables the user to write to the EEPROM.
0: EEPROM write protection is enabled. User cannot write to the EEPROM (default).
1: EEPROM write protection is disabled. User can write to the EEPROM.
Once an EEPROM save/load transfer is
complete, the user must wait a minimum of 10 µs before starting the next EEPROM save/load transfer.
0xB03
[7:1] Unused Unused.
0 REG2EEPROM Transfers data from the buffer register to the EEPROM (self-clearing).
1: setting this bit initiates the data transfer from the buffer register to the EEPROM (writing process); it is
reset by the I²C master after the data transfer is complete. Once an EEPROM save/load transfer is complete,
the user must wait a minimum of 10 µs before starting the next EEPROM save/load transfer.
Data Sheet AD9520-3
Rev. A | Page 77 of 80
APPLICATIONS INFORMATION
FREQUENCY PLANNING USING THE AD9520
The AD9520 is a highly flexible PLL. When choosing the PLL
settings and version of the AD9520, keep in mind the following
guidelines.
The AD9520 has four frequency dividers: the reference (or R)
divider, the feedback (or N) divider, the VCO divider, and the
channel divider. When trying to achieve a particularly difficult
frequency divide ratio requiring a large amount of frequency
division, some of the frequency division can be done by either
the VCO divider or the channel divider, thus allowing a higher
phase detector frequency and more flexibility in choosing the
loop bandwidth.
Within the AD9520 family, lower VCO frequencies generally
result in slightly better jitter. The difference in integrated jitter
(from 12 kHz to 20 MHz offset) for the same output frequency is
usually less than 150 fs over the entire VCO frequency range
(1.4 GHz to 2.95 GHz) of the AD9520 family. If the desired
frequency plan can be achieved with a version of the AD9520
that has a lower VCO frequency, choosing the lower frequency
part results in the best phase noise and the lowest jitter. However,
choosing a higher VCO frequency can result in more flexibility
in frequency planning.
When determining a starting point, choosing a nominal charge
pump current in the middle of the allowable range allows the
designer to increase or decrease the charge pump current and,
thus, allows fine-tuning of the PLL loop bandwidth in either
direction.
Analog Devices has an AD9520 configuration tool that can
determine the best PLL configuration, based on the user’s input
and output frequencies. It can also design the loop filter based
on user requirements.
In addition to the configuration tool, ADIsimCLK is a powerful
PLL modeling tool and a very accurate tool for determining the
optimal loop filter for a given application.
USING THE AD9520 OUTPUTS FOR ADC CLOCK
APPLICATIONS
Any high speed ADC is extremely sensitive to the quality of the
AD9520 sampling clock. An ADC can be thought of as a sampling
mixer; and any noise, distortion, or time jitter on the clock is
combined with the desired signal at the analog-to-digital output.
Clock integrity requirements scale with the analog input frequency
and resolution, with higher analog input frequency applications
at ≥14-bit resolution being the most stringent. The theoretical SNR
of an ADC is limited by the ADC resolution and the jitter on the
sampling clock.
Considering an ideal ADC of infinite resolution where the step
size and quantization error can be ignored, the available SNR
can be expressed, approximately, by the following equation:
π
=
J
A
tf
SNR 2
1
20log(dB)
where:
fA is the highest analog frequency being digitized.
tJ is the rms jitter on the sampling clock.
Figure 70 shows the required sampling clock jitter as a function
of the analog frequency and effective number of bits (ENOB).
f
A
(MHz)
SNR (dB)
ENOB
10 1k100
30
40
50
60
70
80
90
100
110
6
8
10
12
14
16
18
t
J
= 100fs
t
J
= 200fs
t
J
= 400fs
t
J
= 1ps
t
J
= 2ps
t
J
= 10ps
SNR = 20l og 1
2πf
A
t
J
07216-044
Figure 70. SNR and ENOB vs. Analog Input Frequency
For more information, see the AN-756 Application Note,
Sampled Systems and the Effects of Clock Phase Noise and Jitter;
and the AN-501 Application Note, Aperture Uncertainty and
ADC System Performance.
Many high performance ADCs feature differential clock inputs
to simplify the task of providing the required low jitter clock on
a noisy PCB. Distributing a single-ended clock on a noisy PCB
can result in coupled noise on the sampling clock. Differential
distribution has inherent common-mode rejection that can
provide superior clock performance in a noisy environment.
The differential LVPECL outputs of the AD9520 enable clock
solutions that maximize converter SNR performance.
The input requirements of the ADC (differential or single-
ended, logic level termination) should be considered when
selecting the best clocking/converter solution.
AD9520-3 Data Sheet
Rev. A | Page 78 of 80
LVPECL Clock Distribution
The LVPECL outputs of the AD9520 provide the lowest jitter
clock signals available from the AD9520. The LVPECL outputs
(because they are open emitter) require a dc termination to bias
the output transistors. The simplified equivalent circuit in
Figure 54 shows the LVPECL output stage.
In most applications, an LVPECL far-end Thevenin termination
(see Figure 71) or Y-termination (see Figure 72) is recommended.
In both cases, VS of the receiving buffer should match VS_DRV. If it
does not, ac coupling is recommended (see Figure 73).
VS_DRV
LVPECL
50Ω
50Ω
SINGLE-ENDED
(NOT CO UP LED)
VS
VS_DRV
LVPECL
127Ω127Ω
83Ω83Ω
07216-045
Figure 71. DC-Coupled 3.3 V LVPECL Far-End Thevenin Termination
V
S_DRV
LVPECL
Z
0
= 50Ω
V
S
= V
S_DRV
LVPECL
50Ω
50Ω 50Ω
Z
0
= 50Ω
07216-047
Figure 72. DC-Coupled 3.3 V LVPECL Y-Termination
VS_DRV
LVPECL 100Ω DIFFERENTIAL
(COUPLED)
TRANSMISSION LINE
VS
LVPECL
100Ω
0.1nF
0.1nF
200Ω 200Ω
07216-046
Figure 73. AC-Coupled LVPECL with Parallel Transmission Line
LVPECL Y-Termination
LVPECL Y-termination is an elegant termination scheme that
uses the fewest components and offers both odd- and even-mode
impedance matching. Even-mode impedance matching is an
important consideration for closely coupled transmission lines
at high frequencies. Its main drawback is that it offers limited
flexibility for varying the drive strength of the emitter-follower
LVPECL driver. This can be an important consideration when
driving long trace lengths but is usually not an issue. In the case
where VS_DRV = 2.5 V, the 50 Ω termination resistor connected to
ground in Figure 72 should be changed to 19 Ω.
Far-End Thevenin Termination
Far-end Thevenin termination uses a resistor network to provide
50 Ω termination to a dc voltage that is below VOL of the LVPECL
driver. In this case, VS_DRV on the AD9520 should equal VS of the
receiving buffer. Although the resistor combination shown results
in a dc bias point of VS_DRV − 2 V, the actual common-mode voltage
is VS_DRV − 1.3 V because there is additional current flowing from
the AD9520 LVPECL driver through the pull-down resistor.
The circuit is identical for the case where VS_DRV = 2.5 V, except that
the pull-down resistor is 62.5 Ω and the pull-up resistor is 250 Ω.
CMOS CLOCK DISTRIBUTION
The output drivers of the AD9520 can be configured as CMOS
drivers. When selected as a CMOS driver, each output becomes
a pair of CMOS outputs, each of which can be individually
turned on or off and set as inverting or noninverting. These
outputs are 3.3 V or 2.5 V CMOS compatible. However, every
output driver (including the LVPECL drivers) must be run at
either 2.5 V or 3.3 V. The user cannot mix and match 2.5 V and
3.3 V outputs.
When using single-ended CMOS clocking, consider the
following guidelines:
• Using the CMOS drivers in the same output channel group
as the LVPECL drivers may result in performance degradation
of the LVPECL drivers. Where possible, program the two
CMOS drivers that form the same output of a differential
pair to be out of phase such that one driver is high while
the other is low. It is recommended that the evaluation
board be used to verify the performance of the AD9520 in
demanding applications where both CMOS and LVPECL
drivers are in the same group, and the very best jitter
performance is required.
• If possible, design point-to-point connections such that
each driver has only one receiver. Connecting outputs in
this manner allows for simple termination schemes and
minimizes ringing due to possible mismatched impedances
on the output trace. Series termination at the source is
generally required to provide transmission line matching
and/or to reduce current transients at the driver.
• The value of the resistor is dependent on the board design
and timing requirements (typically 10 Ω to 100 Ω is used).
CMOS outputs are also limited in terms of the capacitive
load or trace length that they can drive. Typically, trace
lengths of less than 3 inches are recommended to preserve
signal rise/fall times and signal integrity.
CMOS CMOS
10Ω
60.4Ω
(1.0 INCH)
MICROSTRIP
07216-076
Figure 74. Series Termination of CMOS Output
Data Sheet AD9520-3
Rev. A | Page 79 of 80
Termination at the far end of the PCB trace is a second option.
The CMOS outputs of the AD9520 do not supply enough current
to provide a full voltage swing with a low impedance resistive, far-
end termination, as shown in Figure 75. The far-end termination
network should match the PCB trace impedance and provide the
desired switching point. The reduced signal swing may still meet
receiver input requirements in some applications. This can be
useful when driving long trace lengths on less critical nets.
CMOS CMOS
10Ω 50Ω
100Ω
100Ω
VS
07216-077
Figure 75. CMOS Output with Far-End Termination
Because of the limitations of single-ended CMOS clocking,
consider using differential outputs when driving high speed
signals over long traces. The AD9520 offers LVPECL outputs
that are better suited for driving long traces where the inherent
noise immunity of differential signaling provides superior
performance for clocking converters.
AD9520-3 Data Sheet
Rev. A | Page 80 of 80
OUTLINE DIMENSIONS
COM P LIANT TO JEDEC S TANDARDS M O-220-V M M D- 4
0.25 M IN
1
64
16
17
49
48
32
33
0.50
0.40
0.30
0.50
BSC
0.20 RE F
12° M AX 0.80 MAX
0.65 TYP
1.00
0.85
0.80
7.50 RE F
0.05 M AX
0.02 NOM
0.60 M AX
0.60
MAX
SEATING
PLANE
PI N 1
INDICATOR
6.35
6.20 S Q
6.05
PIN 1
INDICATOR
0.30
0.25
0.18
FOR PRO P E R CONNECT ION OF
THE EXPOSED PAD, REFER TO
THE P IN CONFIGURATIO N AND
FUNCTION DESCRIPT IO NS
SECTION OF THIS DATA SHEET.
TOP VIEW
EXPOSED
PAD
BOTTOM VIEW
9.10
9.00 S Q
8.90
8.85
8.75 S Q
8.65
06-12-2012-B
Figure 76. 64-Lead Lead Frame Chip Scale Package [LFCSP_VQ]
9 mm × 9 mm Body, Very Thin Quad
CP-64-4
Dimensions shown in millimeters
ORDERING GUIDE
Model1 Temperature Range Package Description Package Option
AD9520-3BCPZ −40°C to +85°C 64-Lead Lead Frame Chip Scale Package (LFCSP_VQ) CP-64-4
AD9520-3BCPZ-REEL7 −40°C to +85°C 64-Lead Lead Frame Chip Scale Package (LFCSP_VQ) CP-64-4
AD9520-3/PCBZ Evaluation Board
1 Z = RoHS Compliant Part.
I2C refers to a communications protocol originally developed by Philips Semiconductors (now NXP Semiconductors).
©2008–2013 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
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