General Description
The DS3881 is a single-channel cold-cathode fluores-
cent lamp (CCFL) controller for automotive applications
that provides up to 300:1 dimming. It is ideal for driving
CCFLs used to backlight liquid crystal displays (LCDs)
in navigation and infotainment applications and for dri-
ving CCFLs used to backlight instrument clusters. The
DS3881 is also appropriate for use in marine and avia-
tion applications.
The DS3881 features EMI suppression functionality and
provides a lamp current overdrive mode for rapid lamp
heating in cold weather conditions. The DS3881 sup-
ports a single lamp configuration with fully independent
lamp control and minimal external components.
Multiple DS3881 controllers can be cascaded to sup-
port applications requiring more than one lamp. Control
of the DS3881, after initial programming setup, can be
completely achieved through I2C software communica-
tion. Many DS3881 functions are also pin-controllable if
software control is not desired.
Applications
Automotive LCDs
Instrument Clusters
Marine and Aviation LCDs
Features
♦Single-Channel CCFL Controller for Backlighting
LCD Panels and Instrument Clusters in
Automotive Navigation/Infotainment Applications
♦Minimal External Components Required
♦I2C Interface
♦Per-Channel Lamp-Fault Monitoring for Lamp-
Open, Lamp-Overcurrent, Failure to Strike, and
Overvoltage Conditions
♦Status Register Reports Fault Conditions
♦Accurate (±5%) Independent On-Board Oscillators
for Lamp Frequency (40kHz to 100kHz) and DPWM
Burst-Dimming Frequency (22.5Hz to 440Hz)
♦Lamp and DPWM Frequencies can be
Synchronized with External Sources to Reduce
Visual LCD Artifacts in Video Applications
♦Spread-Spectrum Lamp Clock Reduces EMI
♦Lamp Frequency can be Stepped Up or Down to
Move EMI Spurs Out of Band
♦Lamp Current Overdrive Mode with Automatic
Turn-Off Quickly Warms Lamp in Cold
Temperatures
♦Analog or Digital Brightness Control
♦300:1 Dimming Range Possible Using the Digital
Brightness Control Option
♦Programmable Soft-Start Minimizes Audible
Transformer Noise
♦On-Board Nonvolatile (NV) Memory Allows Device
Customization
♦8-Byte NV User Memory for Storage of Serial
Numbers and Date Codes
♦Low-Power Standby Mode
♦4.75V to 5.25V Single-Supply Operation
♦Temperature Range: -40°C to +105°C
♦24-Pin TSSOP Package
DS3881
Single-Channel Automotive CCFL Controller
______________________________________________
Maxim Integrated Products
1
24
23
22
1
2
3
4
5
6
7
GB1
GA1SCL
SDA
A0 FAULT
TOP VIEW
VCC
PDN
LCOBRIGHT
LOSC
21
8
GNDPSYNC
20
9
STEPPOSC
19
10
N.C.A1
18
11
OVD1GND_S
17
12
LCM1SVML
16
13
SVMH
15
14
VCC
LSYNC
TSSOP
DS3881
Pin Configuration
Rev 1; 8/07
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
+
Denotes lead-free package.
Ordering Information
Typical Operating Circuit appears at end of data sheet.
PART TEMP RANGE PIN-PACKAGE
DS3881E+ -40°C to +105°C 24 TSSOP (173 mils)
DS3881E+T&R -40°C to +105°C 24 TSSOP (173 mils)
DS3881
Single-Channel Automotive CCFL Controller
2 _____________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
RECOMMENDED OPERATING CONDITIONS
(TA= -40°C to +105°C)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Voltage Range on VCC, SDA, and
SCL Relative to Ground.....................................-0.5V to +6.0V
Voltage Range on Leads Other than VCC, SDA, and
SCL ......................-0.5V to (VCC + 0.5V), not to exceed +6.0V
Operating Temperature Range .........................-40°C to +105°C
EEPROM Programming Temperature Range .........0°C to +85°C
Storage Temperature Range .............................-55°C to +125°C
Soldering Temperature...................See J-STD-020 Specification
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Voltage VCC (Note 1) 4.75 5.25 V
Input Logic 1 VIH 2.0 VCC
+ 0.3 V
Input Logic 0 VIL -0.3 1.0 V
SVML/H Voltage Range VSVM -0.3 VCC +
0.3 V
BRIGHT Voltage Range VBRIGHT -0.3 VCC +
0.3 V
LCM Voltage Range VLCM (Note 2) -0.3 VCC +
0.3 V
OVD Voltage Range VOVD (Note 2) -0.3 VCC +
0.3 V
Gate-Driver Output Charge
Loading QG20 nC
ELECTRICAL CHARACTERISTICS
(VCC = +4.75V to +5.25V, TA= -40°C to +105°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
Supply Current ICC GA, GB loaded with 600pF 12 mA
Input Leakage (Digital Pins) IL-1.0 +1.0 µA
Power-Down Current IPDN 1mA
Output Leakage (SDA, FAULT)I
LO High impedance -1.0 +1.0 µA
Low-Level Output Voltage
(LSYNC, PSYNC) VOL IOL = 4mA 0.4 V
VOL1 IOL1 = 3mA 0.4
Low-Level Output Voltage
(SDA, FAULT)VOL2 IOL2 = 6mA 0.6 V
Low-Level Output Voltage
(GA1, GB1) VOL3 IOL3 = 4mA 0.4 V
High-Level Output Voltage
(LSYNC, PSYNC) VOH IOH = -1mA 2.4 V
DS3881
Single-Channel Automotive CCFL Controller
_____________________________________________________________________ 3
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +4.75V to +5.25V, TA= -40°C to +105°C.)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
High-Level Output Voltage
(GA, GB) VOH1 IOH1 = -1mA VCC -
0.4 V
UVLO Threshold: VCC Rising VUVLOR 4.3 V
UVLO Threshold: VCC Falling VUVLOF 3.7 V
UVLO Hysteresis VUVLOH 200 mV
SVML/H Threshold: Rising VSVMR 2.03 2.08 2.15 V
SVML/H Threshold: Falling VSVMF 1.95 2.02 2.07 V
LCM and OVD DC Bias Voltage VDCB 1.1 V
LCM and OVD Input Resistance RDCB 50 kΩ
Lamp Off Threshold VLOT (Note 3) 0.22 0.25 0.28 V
Lamp Over Current VLOC (Note 3) 2.2 2.5 2.8 V
Lamp Regulation Threshold VLRT (Notes 3, 4) 0.9 1.0 1.1 V
OVD Threshold VOVDT (Note 3) 0.9 1.0 1.1 V
Lamp Frequency Source
Frequency Range fLFS:OSC 40 100 kHz
Lamp Frequency Source
Frequency Tolerance fLFS:TOL LOSC resistor ±2% over temperature -5 +5 %
Lamp Frequency Receiver
Frequency Range fLFR:OSC 40 100 kHz
Lamp Frequency Receiver
Duty Cycle fLFR:DUTY 40 60 %
DPWM Source (Resistor)
Frequency Range fDSR:OSC 22.5 440.0 Hz
DPWM Source (Resistor)
Frequency Tolerance fDSR:TOL POSC resistor ±2% over temperature -5 +5 %
DPWM Source (Ext. Clk)
Frequency Range fDSE:OSC 22.5 440.0 Hz
DPWM Source (Ext. Clk)
Duty Cycle fDFE:DUTY 40 60 %
DPWM Receiver
Min Pulse Width tDR:MIN (Note 5) 25 µs
BRIGHT Voltage: Minimum
Brightness VBMIN 0.5 V
BRIGHT Voltage: Maximum
Brightness VBMAX 2.0 V
Gate Driver Output Rise/Fall Time tR / tFCL = 600pF 100 ns
GA1 and GB1 Duty Cycle (Note 6) 44 %
DS3881
Single-Channel Automotive CCFL Controller
4 _____________________________________________________________________
Note 1: All voltages are referenced to ground unless otherwise noted. Currents into the IC are positive, out of the IC negative.
Note 2: During fault conditions, the AC-coupled feedback values are allowed to be below the absolute max rating of the LCM1 or
OVD1 pin for up to 1 second.
Note 3: Voltage with respect to VDCB.
Note 4: Lamp overdrive and analog dimming (based on reduction of lamp current) are disabled.
Note 5: This is the minimum pulse width guaranteed to generate an output burst, which will generate the DS3881’s minimum burst
duty cycle. This duty cycle may be greater than the duty cycle of the PSYNC input. Once the duty cycle of the PSYNC input
is greater than the DS3881’s minimum duty cycle, the output’s duty cycle will track the PSYNC’s duty cycle. Leaving
PSYNC low (0% duty cycle) disables the GA1 and GB1 outputs in DPWM receiver mode.
Note 6: This is the maximum lamp frequency duty cycle that will be generated at GA1 or GB1 outputs with spread-spectrum modu-
lation disabled.
Note 7: I2C interface timing shown is for fast-mode (400kHz) operation. This device is also backward compatible with I2C standard-
mode timing.
Note 8: After this period, the first clock pulse can be generated.
Note 9: CB—total capacitance allowed on one bus line in picofarads.
Note 10: EEPROM write time applies to all the EEPROM memory. EEPROM write begins after a stop condition occurs.
Note 11: Guaranteed by design.
I2C AC ELECTRICAL CHARACTERISTICS (See Figure 9)
(VCC = +4.75V to +5.25V, TA= -40°C to +105°C, timing referenced to VIL(MAX) and VIH(MIN).)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
SCL Clock Frequency fSCL (Note 7) 0 400 kHz
Bus Free Time Between Stop and
Start Conditions tBUF 1.3 µs
Hold Time (Repeated) Start
Condition tHD:STA (Note 8) 0.6 µs
Low Period of SCL tLOW 1.3 µs
High Period of SCL tHIGH 0.6 µs
Data Hold Time tHD:DAT 0 0.9 µs
Data Setup Time tSU:DAT 100 ns
Start Setup Time tSU:STA 0.6 µs
SDA and SCL Rise Time tR(Note 9) 20+
0.1CB300 ns
SDA and SCL Fall Time tF(Note 9) 20+
0.1CB300 ns
Stop Setup Time tSU:STO 0.6 µs
SDA and SCL Capacitive
Loading CB(Note 9) 400 pF
EEPROM Write Time tW(Note 10) 20 30 ms
NONVOLATILE MEMORY CHARACTERISTICS
(VCC = +4.75V to +5.25V)
PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS
EEPROM Write Cycles +85°C (Note 11) 30,000
DS3881
Single-Channel Automotive CCFL Controller
_____________________________________________________________________
5
ACTIVE SUPPLY CURRENT
vs. SUPPLY VOLTAGE
DS3881 toc01
SUPPLY VOLTAGE (V)
SUPPLY CURRENT (mA)
5.205.154.80 4.85 4.90 5.00 5.054.95 5.10
4.5
5.0
5.5
6.0
6.5
7.0
4.0
4.75 5.25
DPWM = 10% DPWM = 50%
DPWM = 100%
SVML< 2V
fLF:OSC = 64kHz
GATE QC = 3.5nC
ACTIVE SUPPLY CURRENT
vs. TEMPERATURE
DS3881 toc02
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
32.5
5.5
6.0
6.5
7.0
5.0
-40.0 105
VCC = 4.75V
VCC = 5.0V
VCC = 5.25V
DPWM = 100%
fLF:OSC = 64kHz
GATE QC = 3.5nC
INTERNAL FREQUENCY CHANGE
vs. TEMPERATURE
DS3881 toc03
TEMPERATURE (°C)
FREQUENCY CHANGE (%)
32.5
-0.8
-0.6
-0.4
-0.2
0
0.2
0.4
0.6
0.8
1.0
-1.0
-40.0 105
DPWM FREQUENCY
LAMP FREQUENCY
TYPICAL OPERATION AT 11V
DS3881 toc04
10μs
5.0V
GA
10μs
5.0V
GB
10μs
2.00V LCM
10μs
2.00V OVD
TYPICAL OPERATION AT 13V
DS3881 toc05
10μs
5.0V
GA
10μs
5.0V
GB
10μs
2.00V LCM
10μs
2.00V OVD
TYPICAL OPERATION AT 16V
DS3881 toc06
10μs
5.0V
GA
10μs
5.0V
GB
10μs
2.00V LCM
10μs
2.00V OVD
TYPICAL STARTUP WITH SVM
DS3881 toc07
2ms
5.0V SVML
2ms
5.0V
GB
2ms
2.00V LCM
2ms
2.00V OVD
BURST DIMMING AT 150Hz AND 10%
DS3881 toc08
1ms
5.0V
GA
1ms
5.0V
GB
1ms
2.00V LCM
1ms
2.00V OVD
BURST DIMMING AT 150Hz AND 50%
DS3881 toc09
1ms
5.0V
GA
1ms
5.0V
GB
1ms
2.00V LCM
1ms
2.00V OVD
Typical Operating Characteristics
(VCC = 5.0V, TA = +25°C, unless otherwise noted.)
DS3881
Single-Channel Automotive CCFL Controller
6 _____________________________________________________________________
Typical Operating Characteristics (continued)
(VCC = 5.0V, TA = +25°C, unless otherwise noted.)
SOFT-START AT VINV = 16V
DS3881 toc10
50μs
5.0V
GA
50μs
5.0V
GB
50μs
2.00V LCM
50μs
2.00V OVD
LAMP STRIKE—EXPANDED VIEW
DS3881 toc11
1ms
5.0V
GA
1ms
5.0V
GB
1ms
2.00V LCM
1ms
2.00V OVD
LAMP STRIKE WITH OPEN LAMP,
AUTO RETRY DISABLED
DS3881 toc12
0.5s
5.0V
GA
0.5s
5.0V
GB
0.5s
2.00V LCM
0.5s
2.00 OVD
LAMP OUT (LAMP OPENED),
AUTO-RETRY DISABLED
DS3881 toc13
0.1s
5.0V
GA
0.1s
5.0V
GB
0.1s
2.00V LCM
0.1s
2.00V OVD
LAMP OPENED
DS3881
Single-Channel Automotive CCFL Controller
_____________________________________________________________________ 7
Pin Description
PIN NAME FUNCTION
1, 9
A0, A1
Address Select Input. Determines I2C slave address.
2 SDA S er i al D ata Inp ut / O utp ut. I2C b i d i r ecti onal d ata p i n, w hi ch r eq ui r es a p ul l up r esi stor to r eal i ze hi g h l og i c l evel s.
3 SCL Serial Clock Input. I2C clock input.
4
LSYNC
Lamp Frequency Input/Output. This pin is the input for an externally sourced lamp frequency
when the DS3881 is configured as a lamp frequency receiver. If the DS3881 is configured as a lamp
frequency source (i.e., the lamp frequency is generated internally), the frequency is output on this pin for
use by other lamp frequency receiver DS3881s.
5 LOSC Lam p Osci l l ator Resi stor Ad j ust. A r esi stor to g r ound on thi s l ead sets the fr eq uency of the i nter nal l am p osci l l ator .
6
BRIGHT
Analog Brightness Control Input. Used to control the DPWM dimming feature. Ground if unused.
7
PSYNC
D P W M Inp ut/Outp ut. Thi s p i n i s the i np ut for an exter nal l y g ener ated D P WM si g nal w hen the D S 3881 i s
confi g ur ed as a D P WM r ecei ver . If the D S 3881 i s confi g ur ed as a D P WM sour ce ( i .e., the D P WM si g nal i s
g ener ated i nter nal l y) , the D P WM si g nal i s outp ut on thi s p i n for use b y other D P WM r ecei ver D S 3881s.
8 POSC
DPWM Oscillator Resistor Adjust. A resistor to ground on this lead sets the frequency of the DPWM
oscillator. This lead can optionally accept a 22.5Hz to 440Hz clock that will become the source timing of
the internal DPWM signal.
10
GND_S
I2C Interface Ground Connection. GND_S must be at the same potential as GND.
11 SVML Low-Supply Voltage Monitor Input. Used to monitor the inverter voltage for undervoltage conditions.
12 SVMH High-Supply Voltage Monitor Input. Used to monitor the inverter voltage for overvoltage conditions.
13, 21 VCC Power Supply Connections. Both pins must be connected.
14 LCM1 Lamp Current Monitor Input. Lamp current is monitored by a resistor placed in series with the low voltage
side of the lamp.
15 OVD1 Overvoltage Detection. Lamp voltage is monitored by a capacitor divider placed on the high voltage side
of the transformer.
16 N.C. No Connection. Do not connect any signal to this pin.
17 STEP
Lamp Frequency Step Input. This active-high digital input moves the lamp oscillator frequency up or down
by either 1%, 2%, 3%, or 4% as configured in the EMIC register. This pin is logically ORed with the STEPE
bit in the EMIC register.
18 GND Ground Connection
19 LCO
Lamp Current Overdrive Enable Input. A high digital level at this input enables the lamp current overdrive
circuit. The amount of overdrive current is configured by the LCOC register. When this input is low, the
lamp current is set to its nominal level. This pin is logically ORed with the LCOE bit in the LCOC register.
20 PDN
Lamp On/Off Control Input. A low digital level at this input turns the lamp on. A high digital level clears the
fault logic, turns the lamp off, and places the device into the power-down mode. This pin is logically ORed
with the PDNE bit in the CR2 register.
22, 23
GA1, GB1
MOSFET A and B Gate Drive. Connect directly to logic-level mode n-channel MOSFET.
24
FAULT
Active-Low Fault Output. This open-drain pin requires external pullup resistor to realize high-logic levels.
DS3881
Single-Channel Automotive CCFL Controller
8 _____________________________________________________________________
Functional Diagrams
GA1 MOSFET
GATE
DRIVERS
GB1
OVD1
OVERVOLTAGE
DETECTION
LAMP FREQUENCY
INPUT/OUTPUT [20.48MHz ~ 51.20MHz]
I2C DEVICE
CONFIGURATION AND
CONTROL PORT
22.5Hz TO 440Hz
EXTERNAL RESISTOR
LAMP FREQUENCY SET
GND
SINGLE
CCFL
CONTROLLER
EXTERNAL RESISTOR
DPWM FREQUENCY
SET/DPWM CLOCK INPUT
DPWM SIGNAL
INPUT/OUTPUT
ANALOG BRIGHTNESS
CONTROL
SVMH
SUPPLY VOLTAGE
MONITOR—HIGH
[40kHz ~ 100kHz]
System
Enable /
POR
EEPROM
8 BYTE USER MEMORY
CONTROL REGISTERS
FAULT
CHANNEL FAULT
CHANNEL ENABLE
SDA
SCL
LSYNC
LOSC
PSYNC
BRIGHT
DPWM
SIGNAL
2.0V
STATUS REGISTERS
PDN
LCO
2.0V
SVML
SUPPLY VOLTAGE
MONITOR—LOW
STEP
STEP LAMP FREQUENCY
UP OR DOWN
40kHz TO 100kHz
OSCILLATOR (±5%)
LCM1
LAMP CURRENT
MONITOR
VCC
[4.75V TO 5.25V]
x512
PLL
I2C
INTERFACE
SYSTEM
ENABLE/
POR
FAULT
HANDLING
22.5Hz TO
440Hz
OSCILLATOR
(±5%)
POSC
A0/A1
GND_S
DPSS BIT
AT CR1.3
LFSS BIT
AT CR1.2
UVLO
VREF
MUX
POSCS BIT
AT CR1.1
MUX
RGSO BIT
AT CR1.4
MUX
DPSS BIT
AT CR1.3
RAMP
GENERATOR
DS3881
Figure 1. Functional Diagram
DS3881
Single-Channel Automotive CCFL Controller
_____________________________________________________________________ 9
Detailed Description
The DS3881 uses a push-pull drive scheme to convert
a DC voltage (8V to 16V) to the high-voltage (300VRMS
to 1000VRMS) AC waveform that is required to power
the CCFL. The push-pull drive scheme uses a minimal
number of external components, which reduces assem-
bly cost and makes the printed circuit board design
easy to implement. The push-pull drive scheme also
provides an efficient DC-to-AC conversion and pro-
duces near-sinusoidal waveforms.
Each DS3881 drives two logic-level n-channel
MOSFETs that are connected between the ends of a
step-up transformer and ground (see the
Typical
Operating Circuit
). The transformer has a center tap on
the primary side that is connected to a DC voltage sup-
ply. The DS3881 alternately turns on the two MOSFETs
to create the high-voltage AC waveform on the sec-
ondary side. By varying the duration of the MOSFET
turn-on times, the CCFL current is able to be accurately
controlled.
A resistor in series with the CCFL’s ground connection
enables current monitoring. The voltage across this
resistor is fed to the lamp current monitor (LCM) input
and compared to an internal reference voltage to deter-
mine the duty cycle for the MOSFET gates. The CCFL
receives current monitoring and control, which maxi-
mizes the lamp’s brightness and lifetime.
Block diagrams of the DS3881 are shown in Figures 1
and 2. More operating details of the DS3881 are dis-
cussed on the following pages of this data sheet.
Memory Registers and
I2C-Compatible Serial Interface
The DS3881 uses an I2C-compatible serial interface for
communication with the on-board EEPROM and SRAM
configuration/status registers as well as user memory.
The configuration registers, which are a mixture of
shadowed EEPROM and SRAM, allow the user to cus-
tomize many DS3881 parameters such as the soft-start
ramp rate, the lamp and dimming frequency sources,
brightness of the lamps, fault-monitoring options, chan-
nel enabling/disabling, EMI control, and lamp current
overdrive control. The eight bytes of NV user memory
can be used to store manufacturing data such as date
codes, serial numbers, or product identification num-
bers. The device is shipped from the factory with the
configuration registers programmed to a set of default
configuration parameters. To inquire about custom pro-
gramming, contact the factory.
GATE
DRIVERS
MOSFET
GATE
DRIVERS
GA1
GB1
DIGITAL
CCFL
CONTROLLER
CHANNEL FAULT
512 x LAMP FREQUENCY
[20.48MHz ~ 51.20MHz]
LAMP FREQUENCY
[40kHz ~ 80kHz]
DIMMING PWM SIGNAL
CHANNEL ENABLE
VLRT (1.0V NOMINAL)
LCM1
LAMP CURRENT
MONITOR
300mV
2.5V
LAMP OVERCURRENT
LAMP STRIKE AND REGULATION
LOCE BIT IN CR1.0
LAMP OUT
1.0V
OVD1
OVERVOLTAGE DETECTOR
LAMP MAXIMUM VOLTAGE REGULATION
64 LAMP CYCLE
INTEGRATOR
OVERVOLTAGE
Figure 2. Per Channel Logic Diagram
Functional Diagrams (continued)
DS3881
Single-Channel Automotive CCFL Controller
10 ____________________________________________________________________
Shadowed EEPROM
The DS3881 incorporates SRAM-shadowed EEPROM
memory locations for all memory that needs to be
retained during power cycling. At power-up, SEEB (bit 7
of the BLC register) is low, which causes the shadowed
locations to act as ordinary EEPROM. Setting SEEB
high disables the EEPROM write function and causes
the shadowed locations to function as ordinary SRAM
cells. This allows an infinite number of write cycles with-
out causing EEPROM damage and also eliminates the
EEPROM write time, tWfrom the write cycle. Because
memory changes made when SEEB is set high are not
written to EEPROM, these changes are not retained
through power cycles, and the power-up EEPROM values
are the last values written with SEEB low.
Lamp Dimming Control
The DS3881 provides two independent methods of
lamp dimming that can be combined to achieve a dim-
ming ratio of 300:1 or greater. The first method is
“burst” dimming, which uses a digital pulse-width-mod-
ulated (DPWM) signal (22.5Hz to 440Hz) to control the
lamp brightness. The second is “analog” dimming,
which is accomplished by adjusting the lamp current.
Burst dimming provides 128 linearly spaced brightness
steps. Analog dimming provides smaller substeps that
allow incremental brightness changes between burst
dimming steps. This ability is especially useful for low-
brightness dimming changes, where using burst dim-
ming alone would cause visible brightness step
changes. Analog dimming also allows the brightness to
be reduced below the minimum burst dimming level,
which provides for the maximum dimming range.
Burst dimming can be controlled using a user-supplied
analog voltage on the BRIGHT pin or through the I2C
interface. Analog dimming can only be controlled
through the I2C interface. Therefore, for applications that
require the complete dimming range and resolution capa-
bility of the DS3881, I2C dimming control must be used.
Burst Dimming
Burst dimming increases/decreases the brightness by
adjusting (i.e., modulating) the duty cycle of the DPWM
signal. During the high period of the DPWM cycle, the
lamps are driven at the selected lamp frequency
(40kHz to 100kHz) as shown in Figure 6. This part of
the cycle is called the “burst” period because of the
lamp frequency burst that occurs during this time.
During the low period of the DPWM cycle, the controller
disables the MOSFET gate drivers so the lamps are not
driven. This causes the current to stop flowing in the
lamps, but the time is short enough to keep the lamps
from de-ionizing.
The DS3881 can generate its own DPWM signal inter-
nally (set DPSS = 0 in CR1), which can then be
sourced to other DS3881s if required, or the DPWM sig-
nal can be supplied from an external source (set DPSS
= 1 in CR1). To generate the DPWM signal internally,
the DS3881 requires a clock (referred to as the dim-
ming clock) to set the DPWM frequency. The user can
supply the dimming clock by setting POSCS = 1 in CR1
and applying an external 22.5Hz to 440Hz signal at the
POSC pin, or the dimming clock can be generated by
the DS3881’s internal oscillator (set POSCS = 0 in
CR1), in which case the frequency is set by an external
resistor at the POSC pin. These two dimming clock
options are shown in Figure 3. Regardless of whether
the dimming clock is generated internally or sourced
externally, the POSCR0 and POSCR1 bits in CR2 must
be set to match the desired dimming clock frequency.
The internally generated DPWM signal can be provided
at the PSYNC I/O pin (set RGSO = 0 in CR1) for sourc-
ing to other DS3881s, if any, in the circuit. This allows
all DS3881s in the system to be synchronized to the
same DPWM signal. A DS3881 that is generating the
DPWM signal for other DS3881s in the system is
referred to as the DPWM source. When bringing in an
externally generated DPWM signal, either from another
DS3881 acting as a DPWM source or from some other
user-provided source, it is input into the PSYNC I/O pin
of the DS3881, and the receiving DS3881 is referred to
a DPWM receiver. In this mode, the BRIGHT and POSC
inputs are disabled and should be grounded (see
Figure 5).
When the DPWM signal is generated internally, its duty
cycle (and, thus, the lamp brightness) is controlled
either by a user-supplied analog voltage at the BRIGHT
input or through the I2C interface by varying the 7-bit
PWM code in the BPWM register. When using the
BRIGHT pin to control burst dimming, a voltage of less
than 0.5V causes the DS3881 to operate with the mini-
mum burst duty cycle, providing the lowest brightness
setting, while any voltage greater than 2.0V causes a
100% burst duty cycle (i.e., lamps always being dri-
ven), which provides the maximum brightness. For volt-
ages between 0.5V and 2V, the duty cycle varies
linearly between the minimum and 100%. Writing a non-
zero PWM code to the BPWM register disables the
BRIGHT pin and enables I2C burst dimming control.
Setting the 7-bit PWM code to 0000001b causes the
DS3881 to operate with the minimum burst duty cycle,
while a setting of 1111111b causes a 100% burst duty
cycle. For settings between these two codes, the duty
cycle varies linearly between the minimum and 100%.
DS3881
Single-Channel Automotive CCFL Controller
____________________________________________________________________ 11
Analog Dimming
Analog dimming changes the brightness by increasing
or decreasing the lamp current. The DS3881 accom-
plishes this by making small shifts to the lamp regula-
tion voltage, VLRT (see Figure 2). Analog dimming is
only possible by software communication with the lower
five bits (LC4–LC0) in the BLC register. This function is
not pin controllable. The default power-on state of the
LC bits is 00000b, which corresponds to 100% of the
nominal current level. Therefore on power-up, analog
dimming does not interfere with burst dimming func-
tionality if it is not desired. Setting the LC bits to 11111b
reduces the lamp current to 35% of its nominal level. For
LC values between 11111b and 00000b, the lamp cur-
rent varies linearly between 35% and 100% of nominal.
Lamp Frequency Configuration
The DS3881 can generate its own lamp frequency
clock internally (set LFSS = 0 in CR1), which can then
be sourced to other DS3881s if required, or the lamp
clock can be supplied from an external source (set
LFSS = 1 in CR1). When the lamp clock is internally
generated, the frequency (40kHz to 100kHz) is set by
an external resistor at the LOSC. In this case, the
DS3881 can act as a lamp frequency source because
the lamp clock is output at the LSYNC I/O pin for syn-
chronizing any other DS3881s configured as lamp fre-
quency receivers. While DS3881 is sourcing lamp
frequency to other DS3881’s and spread-spectrum
modulation or frequency step features are enabled, the
LSYNC output is not affected by either EMI suppression
features. The DS3881 acts as a lamp frequency receiv-
er when the lamp clock is supplied externally. In this
case, a 40kHz to 100kHz clock must be supplied at the
LSYNC I/O. The external clock can originate from the
LSYNC I/O of a DS3881 configured as a lamp frequen-
cy source or from some other source.
Configuring Systems
with Multiple DS3881s
The source and receiver options for the lamp frequency
clock and DPWM signal allow multiple DS3881s to be
synchronized in systems requiring more than 1 lamp.
The lamp and dimming clocks can either be generated
on board the DS3881 using external resistors to set the
frequency, or they can be sourced by the host system
to synchronize the DS3881 to other system resources.
Figure 5 shows various multiple DS3881 configurations
that allow both lamp and/or DPWM synchronization for
all DS3881s in the system.
BRIGHT
PSYNC
POSC
2.0V
0.5V
22.5Hz TO 440Hz 22.5Hz TO 440Hz
EXTERNAL RESISTOR
SETS DPWM RATE
DPWM
SIGNAL
ANALOG DIMMING
CONTROL VOLTAGE
RESISTOR-SET DIMMING CLOCK
BRIGHT
PSYNC
POSC
2.0V
0.5V
22.5Hz TO 440Hz
DPWM
SIGNAL
EXTERNAL
DPWM CLOCK
ANALOG DIMMING
CONTROL VOLTAGE
EXTERNAL DIMMING CLOCK
Figure 3. DPWM Source Configuration Options
BRIGHT
PSYNC
POSC
22.5Hz TO 440Hz
DPWM
SIGNAL
DPWM RECEIVER
Figure 4. DPWM Receiver Configuration
DS3881
Single-Channel Automotive CCFL Controller
12 ____________________________________________________________________
2.0V BRIGHT
LAMP FREQUENCY SOURCE
DPWM SOURCE
PSYNC
LSYNC
POSC
LOSC
0.5V
RESISTOR-SET
DIMMING
FREQUENCY
RESISTOR-SET
LAMP FREQUENCY
DS3881
BRIGHT
LAMP FREQUENCY RECEIVER
DPWM RECEIVER
PSYNC
LSYNC
POSC
LOSC
DS3881
2.0V BRIGHT
LAMP FREQUENCY SOURCE
DPWM SOURCE
PSYNC
LSYNC
POSC
LOSC
0.5V
ANALOG
BRIGHTNESS
ANALOG
BRIGHTNESS
RESISTOR-SET
LAMP FREQUENCY
DIMMING CLOCK
(22.5Hz TO 440Hz)
DPWM SIGNAL
(22.5Hz TO 440Hz)
DS3881
BRIGHT
LAMP FREQUENCY RECEIVER
DPWM RECEIVER
PSYNC
LSYNC
POSC
LOSC
DS3881
BRIGHT
LAMP FREQUENCY SOURCE
DPWM RECEIVER
PSYNC
LSYNC
POSC
LOSC
RESISTOR-SET
LAMP FREQUENCY
DS3881
BRIGHT
LAMP FREQUENCY RECEIVER
DPWM RECEIVER
PSYNC
LSYNC
POSC
LOSC
DS3881
2.0V BRIGHT
LAMP FREQUENCY RECEIVER
DPWM SOURCE
PSYNC
LSYNC
POSC
LOSCN.C.
N.C.
N.C.
N.C.
N.C.
N.C.
N.C.
N.C.
N.C.
N.C.
N.C.
N.C.
N.C.
N.C.
N.C.
N.C.
N.C.
0.5V
RESISTOR-SET
DIMMING FREQUENCY
DS3881
BRIGHT
LAMP FREQUENCY RECEIVER
DPWM RECEIVER
PSYNC
LSYNC
POSC
LOSC
DS3881
2.0V BRIGHT
LAMP FREQUENCY RECEIVER
DPWM SOURCE
PSYNC
LSYNC
POSC
LOSC
0.5V
ANALOG
BRIGHTNESS
ANALOG
BRIGHTNESS
LAMP CLOCK
(40kHz TO 100kHz)
DIMMING CLOCK
(22.5Hz TO 440Hz)
LAMP CLOCK
(40kHz TO 100kHz)
DPWM SIGNAL
(22.5Hz TO 440Hz)
LAMP CLOCK
(40kHz TO 100kHz)
DS3881
BRIGHT
LAMP FREQUENCY RECEIVER
DPWM RECEIVER
PSYNC
LSYNC
POSC
LOSC
DS3881
BRIGHT
LAMP FREQUENCY RECEIVER
DPWM RECEIVER
PSYNC
LSYNC
POSC
LOSC
DS3881
BRIGHT
LAMP FREQUENCY RECEIVER
DPWM RECEIVER
PSYNC
LSYNC
POSC
LOSC
DS3881
Figure 5. Frequency Configuration Options for Designs Using Multiple DS3881s
DS3881
Single-Channel Automotive CCFL Controller
____________________________________________________________________ 13
DPWM Soft-Start
At the beginning of each lamp burst, the DS3881 pro-
vides a soft-start that slowly increases the MOSFET
gate-driver duty cycle (see Figure 6). This minimizes
the possibility of audible transformer noise that could
result from current surges in the transformer primary.
The soft-start length is fixed at 16 lamp cycles, but the
soft-start ramp profile is programmable through the
four soft-start profile registers (SSP1/2/3/4) and can
be adjusted to match the application. There are seven
different driver duty cycles to select from to customize
the soft-start ramp (see Tables 4a and 4b). The avail-
able duty cycles range from 0% to 19% in ~3% incre-
ments. In addition, the MOSFET duty cycle from the
last lamp cycle of the previous burst can be used as
part of the soft-start ramp by using the most recent
value duty cycle code. Each programmed MOSFET
gate duty cycle repeats twice to make up the 16 soft-
start lamp cycles.
1615141312111098765432
SSP1. 0-3
LAMP CURRENT
SOFT-START PROFILE REGISTER
SOFT-START
SOFT-START (EXPANDED)
22.5Hz TO 440Hz
DPWM SIGNAL
LAMP CURRENT
LAMP CYCLE
GA1/GB1
MOSFET GATE DRIVERS
PROGRAMMABLE SOFT-START PROFILE WITH INCREASING MOSFET PULSE WIDTHS OVER
A 16 LAMP CYCLE PERIOD RESULTS IN A LINEAR RAMP IN LAMP CURRENT.
SSP1. 4-7 SSP2. 0-3 SSP2. 4-7 SSP3. 0-3 SSP3. 4-7 SSP4. 0-3 SSP4. 4-7
1
Figure 6. Digital PWM Dimming and Soft-Start
DS3881
Single-Channel Automotive CCFL Controller
14 ____________________________________________________________________
Setting the Lamp and Dimming
Clock (DPWM) Frequencies
Using External Resistors
Both the lamp and dimming clock frequencies can be
set using external resistors. The resistance required for
either frequency can be determined using the following
formula:
where K = 1600kΩ•kHz for lamp frequency calculations.
When calculating the resistor value for the dimming clock
frequency, K will be one of four values as determined by
the desired frequency and the POSCR0 and POSCR1 bit
settings as shown in the Control Register 2 (CR2) Table 6
in the
Detailed Register Descriptions
section.
Example: Selecting the resistor values to configure a
DS3881 to have a 50kHz lamp frequency and a 160Hz
dimming clock frequency: For this configuration,
POSCR0 and POSCR1 must be programmed to 1 and
0, respectively, to select 90Hz to 220Hz as the dimming
clock frequency range. This sets K for the dimming
clock resistor (RPOSC) calculation to 4kΩ•kHz. For the
lamp frequency resistor (RLOSC) calculation, K =
1600kΩ•kHz, which sets the lamp frequency K value
regardless of the frequency. The formula above can
now be used to calculate the resistor values for RLOSC
and RPOSC as follows:
Supply Monitoring
The DS3881 has supply voltage monitors (SVMs) for
both the inverter’s transformer DC supply (VINV) and its
own VCC supply to ensure that both voltage levels are
adequate for proper operation. The transformer supply
is monitored for overvoltage conditions at the SVMH pin
and undervoltage conditions at the SVML pin. External
resistor-dividers at each SVM input feed into two com-
parators (see Figure 7), both having 2V thresholds.
Using the equation below to determine the resistor val-
ues, the SVMH and SVML trip points (VTRIP) can be
customized to shut off the inverter when the trans-
former’s supply voltage rises above or drops below
specified values. Operating with the transformer’s sup-
ply at too low of a level can prevent the inverter from
reaching the strike voltage and could potentially cause
numerous other problems. Operating with the trans-
former voltage at too high of a level can be damaging
to the inverter components. Proper use of the SVMs
can prevent these problems. If desired, the high and/or
low SVMs can be disabled by connecting the SVMH
pin to GND and the SVML pin to VCC.
The VCC monitor is used as a 5V supply undervoltage
lockout (UVLO) that prevents operation when the
DS3881 does not have adequate voltage for its analog
circuitry to operate or to drive the external MOSFETs.
The VCC monitor features hysteresis to prevent VCC
noise from causing spurious operation when VCC is
near the trip point. This monitor cannot be disabled by
any means.
Fault Monitoring
The DS3881 provides extensive fault monitoring. It can
detect open-lamp, lamp overcurrent, failure to strike,
and overvoltage conditions. The DS3881 can be con-
figured to disable the output if the channel enters a
fault state. Once a fault state has been entered, the
FAULT output is asserted and the channel remains dis-
abled until it is reset by a user or host control event.
See
Step 4, Fault Handling
for more detail. The DS3881
can also be configured to automatically attempt to clear
a detected fault (except lamp overcurrent) by re-strik-
ing the lamp. Configuration bits for the fault monitoring
options are located in CR1 and CR2. The DS3881 also
has real-time status indicator bits located in the SR1
and SR2 register (SRAM) that assert whenever a corre-
sponding fault occurs.
VRR
R
TRIP .
=⎛
⎝
⎜⎞
⎠
⎟
+
20 12
1
Rk kHz
kHz k
Rk kHz
kHz k
LOSC
POSC
.
. .
=•=
=•=
1600
50 32 0
4
0 160 25 0
ΩΩ
ΩΩ
RK
f
OSC OSC
=
SVML
R2
R12.0V
VINV
SVMH
R2
VTRIP
VTRIP
R1
2.0V
VINV
DS3881
Figure 7. Setting the SVM Threshold Voltage
DS3881
Single-Channel Automotive CCFL Controller
____________________________________________________________________ 15
Figure 8 shows a flowchart of how the DS3881 controls
and monitors each lamp. The steps are as follows:
1) Supply Check—The lamps do not turn on unless the
DS3881 supply voltage is above 4.3V and the volt-
age at the supply voltage monitors, SVML and SVMH,
are respectively above 2.0V and below 2.0V.
2) Strike Lamp—When both the DS3881 and the DC
inverter supplies are at acceptable levels, the
DS3881 attempts to strike the lamp. The DS3881
slowly ramps up the MOSFET gate duty cycle until
the lamp strikes. The controller detects that the lamp
has struck by detecting current flow in the lamp,
detected by the LCM1 pin. If during the strike ramp,
the maximum allowable voltage is reached on the
OVD1 pin, the controller stops increasing the MOS-
FET gate duty cycle to keep from overstressing the
system. The DS3881 goes into a fault handling state
(step 4) if the lamp has not struck after the timeout
period as defined by the LST0 and LST1 control bits
in the SSP1 register. If an overvoltage event is detect-
ed during the strike attempt, the DS3881 disables the
MOSFET gate drivers and go into the fault handling
state.
3) Run Lamp—Once the lamp is struck, the DS3881
adjusts the MOSFET gate duty cycle to optimize the
lamp current. The gate duty cycle is always con-
strained to keep the system from exceeding the
maximum allowable lamp voltage. The lamp current
sampling rate is user-selectable using the LSR0 and
LSR1 bits in CR2. If lamp current ever drops below the
lamp out reference point for the period as defined by
the LST0 and LST1 control bits in the SSP1 register,
then the lamp is considered extinguished. In this case,
the MOSFET gate drivers are disabled and the device
moves to the fault handling stage.
4) Fault Handling—During fault handling, the DS3881
performs an optional (user-selectable) automatic
retry to attempt to clear all faults except a lamp over-
current. The automatic retry makes 14 additional
attempts to rectify the fault before declaring the
channel in a fault state and permanently disabling
the channel. Between each of the 14 attempts, the
controller waits 1024 lamp cycles. In the case of a
lamp overcurrent, the DS3881 instantaneously
declares the channel to be in a fault state and per-
manently disables the channel. Once a fault state is
entered, the channel remains in that state until one of
the following occurs:
•VCC drops below the UVLO threshold.
•The SVML or SVMH thresholds are crossed.
•The PDN pin goes high.
•The PDNE software bit is written to a logic 1.
•The channel is disabled by the CH1D control bit.
DS3881
Single-Channel Automotive CCFL Controller
16 ____________________________________________________________________
MOSFET GATE DRIVERS ENABLED
DEVICE AND
INVERTER SUPPLIES
AT PROPER LEVELS?
STRIKE LAMP
[RAMP AND REGULATE TO
OVD THRESHOLD]
FAULT WAIT
[1024 LAMP CYCLES]
LAMP STRIKE TIMEOUT
[SEE REGISTER SSP1]
RUN LAMP
[REGULATE LAMP
CURRENT BOUNDED BY
LAMP VOLTAGE]
LAMP OUT TIMEOUT
[SEE REGISTER SSP1]
INCREMENT FAULT
COUNTER / SET
FAULT_RT STATUS BIT
FAULT COUNTER = 15?
FAULT STATE
[ACTIVATE FAULT OUTPUT]
LAMP OVERCURRENT
[INSTANTANEOUS IF
ENABLED BY THE
LOCE BIT AT CR1.0]
NO
YES
AUTORETRY ENABLED?
[ARD BIT AT CR1.5]
NO YES
YES
OVERVOLTAGE
[64 LAMP CYCLES]
SET LOUT_L
STATUS BIT
SET OV_L
STATUS BIT
SET STO_L
STATUS BIT
SET LOC_L
STATUS BIT
CLEAR
FAULT_RT
STATUS BIT
IF LAMP REGULATION
THRESHOLD IS MET
RESET FAULT COUNTER
AND FAULT OUTPUT
SET FAULT_L
AND FAULT_RT
STATUS BITS
Figure 8. Fault-Handling Flowchart
DS3881
Single-Channel Automotive CCFL Controller
____________________________________________________________________ 17
EMI Suppression Functionality
The DS3881 contains two electromagnetic interference
suppression features: spread-spectrum modulation and
lamp oscillator frequency stepping. The first is the abili-
ty to spread the spectrum of the lamp frequency. By
setting either SS0 and/or SS1 in EMIC register, the con-
troller can be configured to dither the lamp frequency
by ±1.5%, ±3%, or ±6%. By setting a non-zero value in
SS0/1, spread-spectrum modulation is enabled and
oscillator frequency stepping is disabled. In spread-
spectrum modulation mode the dither modulation rate
is also selectable by setting FS0/1/2, and has either a
triangular (SSM = 0) or a pseudorandom profile (SSM =
1). Users have the flexibility to choosing the best modu-
lation rate (through FS0/1/2) for the application.
The second EMI suppression scheme is the ability to
move the lamp frequency up or down by 1%, 2%, 3%,
or 4%. In this scheme, the actual radiated EMI is not
reduced but it is moved out of a sensitive frequency
region. STEPE bit and/or STEP pin is used to enable
lamp frequency stepping (SS0/1 must be 0). Once
enabled, the FS0/1/2 value controls the lamp oscillator
frequency shift. For example, if the lamp frequency cre-
ates EMI disturbing an audio radio station, it can be
moved up or down slightly to slide the spurious interfer-
er out of band.
Lamp Current Overdrive Functionality
Another feature the DS3881 offers is the ability to over-
drive the lamps to allow them to heat up quickly in cold
environments. After setting the LCO0/1/2 bits in the
LCOC register and enabling the LCOE bit or LCO pin,
the DS3881 overdrives the nominal current settings in
12.5% steps from 112.5% up to 200%. The DS3881
accomplishes this by automatically shifting the lamp
regulation threshold, VLRT, upward to allow more cur-
rent to flow in the lamps (Figure 2). This multilevel
adjustment makes it possible to slowly decrease the
current overdrive (through I2C) after the lamps have
warmed up, so the end user does not see any change
in brightness when the overdrive is no longer needed.
The DS3881 also features an optional timer capable of
automatically turning off the current overdrive. This
timer is adjustable from approximately 1.5 minutes to
21 minutes (if a 50kHz lamp frequency is used).
Detailed Register Descriptions
The DS3881’s register map is shown in Table 1.
Detailed register and bit descriptions follow in the sub-
sequent tables.
Table 1. Register Map
BYTE
ADDRESS
BYTE
NAME
FACTORY
DEFAULT BIT 7 BIT 6 BIT 5 BIT 4 BIT 3 BIT 2 BIT 1 BIT 0
E0h SR1 00h SVMH_RT SVML_RT LOC_L1 LOUT_L1 OV_L1 STO_L1 FAULT_L1 FAULT_RT1
E1h RSVD 00h RSVD RSVD RSVD RSVD RSVD RSVD RSVD RSVD
E2h BPWM 00h RSVD PWM6 PWM5 PWM4 PWM3 PWM2 PWM1 PWM0
E3h BLC 1Fh SEEB RSVD CH1D LC4 LC3 LC2 LC1 LC0
F0h SSP1 21h LST1 MDC code for soft-start lamp
cycles 3, 4 LST0 M D C cod e for soft- star t l am p cycl es 1, 2
F1h SSP2 43h MDC code for soft-start lamp cycles 7, 8 MDC code for soft-start lamp cycles 5, 6
F2h SSP3 65h MDC code for soft-start lamp cycles 11, 12 MDC code for soft-start lamp cycles 9, 10
F3h SSP4 77h MDC code for soft-start lamp cycles 15, 16 MDC code for soft-start lamp cycles 13, 14
F4h CR1 00h DPD RSVD ARD RGSO DPSS LFSS POSCS LOCE
F5h CR2 08h PDNE RSVD RSVD LSR1 LSR0 POSCR1 POSCR0 UMWP
F6h EMIC 00h FS2 FS1 FS0 STEPE RSVD SSM SS1 SS0
F7h LCOC 00h TO3 TO2 TO1 TO0 LCOE LCO2 LCO1 LCO0
F8h–FFh USER 00h EE EE EE EE EE EE EE EE
Note 1: E0h–E3h are SRAM locations, and F0h–FFh are SRAM-shadowed EEPROM.
Note 2: Altering the DS3881 configuration during active CCFL operation can cause serious adverse effects.
DS3881
Single-Channel Automotive CCFL Controller
18 ____________________________________________________________________
Table 2. Status Register 1 (SR1) [SRAM, E0h]
BIT R/W POWER-UP
DEFAULT NAME FUNCTION
0 R 0 FAULT_RT
Fault Condition—Real Time. A real-time bit that indicates the current operating status of
channel 1.
0 = Normal condition
1 = Fault condition
1 R 0 FAULT_L Fault Condition—Latched. A latched bit that is set when the channel enters a fault
condition. This bit is cleared when read, regardless of the current state of fault.
2 R 0 STO_L Lamp Strike Timeout—Latched. A latched bit that is set when the lamp fails to strike.
This bit is cleared when read.
3 R 0 OV_L Overvoltage—Latched. A latched bit that is set when a lamp overvoltage is present for
at least 64 lamp cycles. This bit is cleared when read.
4 R 0 LOUT_L Lamp Out—Latched. A latched bit that is set when a lamp out is detected. This bit is
cleared when read.
5 R 0 LOC_L Lamp Overcurrent—Latched. A latched bit that is set when a lamp overcurrent is
detected. This bit is cleared when read.
6 R 0 SVML_RT Supply Voltage Monitor Low—Real Time. A real-time bit that reports the comparator
output of the SVML pin.
7 R 0 SVMH_RT Supply Voltage Monitor High—Real Time. A real-time bit that reports the comparator
output of the SVMH pin.
Note 1: Writing to this register has no effect on it.
Note 2: See Figure 8 for more details on how the status bits are set.
Note 3: SR1 is cleared when only the following occurs:
•VCC drops below the UVLO threshold.
•The SVML or SVMH thresholds are crossed.
•The PDN hardware pin goes high.
•The PDNE software bit is written to a logic 1.
•The channel is disabled by the CH1D control bit.
Table 3. Brightness Lamp Current Register (BLC) [SRAM, E3h]
BIT R/W FACTORY
DEFAULT NAME FUNCTION
0 R/W 0 LC0
1 R/W 0 LC1
2 R/W 0 LC2
3 R/W 0 LC3
4 R/W 0 LC4
These five control bits determine the target value for the lamp current. 11111b is
35% of the nominal level and 00000b is 100% of the nominal level. These control
bits are used for fine adjustment of the lamp brightness.
5 R/W 0 CH1D
Channel 1 Disable
0 = Channel 1 enabled
1 = Channel 1 disabled
6 R/W 0 RSVD Reserved. Should be set to 0.
7 R/W 0 SEEB
SRAM-Shadowed EEPROM Write Control
0 = Enables writes to EEPROM
1 = Disables writes to EEPROM
DS3881
Single-Channel Automotive CCFL Controller
____________________________________________________________________ 19
Table 4a. Soft-Start Protocol Registers (SSPx) [Shadowed-EEPROM, F0h, F1h, F2h, F3h]
MSB LSB
SSP# ADDR FACTORY
DEFAULT 7 654 3 2 1 0
SSP1 F0h 21h LST1 Lamp Cycles 3 and 4 LST0 Lamp Cycles 1 and 2
SSP2 F1h 43h RSVD Lamp Cycles 7 and 8 RSVD Lamp Cycles 5 and 6
SSP3 F2h 65h RSVD Lamp Cycles 11 and 12 RSVD Lamp Cycles 9 and 10
SSP4 F3h 77h RSVD Lamp Cycles 15 and 16 RSVD Lamp Cycles 13 and 14
Table 4b. MOSFET Duty Cycle (MDC)⎯Codes for Soft-Start Settings
BIT R/W NAME FUNCTION
0 R/W MDC0
MDC0/1/2/3: These bits determine a MOSFET duty cycle that repeats twice in the
16 lamp cycle soft-start.
1 R/W MDC1
MDC CODE MOSFET DUTY CYCLE MDC CODE MOSFET DUTY CYCLE
0h Fixed at 0% 4h Fixed at 13%
2 R/W MDC2 1h Fixed at 3% 5h Fixed at 16%
2h Fixed at 6% 6h Fixed at 19%
3h Fixed at 9% 7h Most Recent Value
3 R/W LST0 / RSVD
4 R/W MDC0 LST0/1: These bits select strike and lamp out timeout. LST0 and LST1
control fault behavior for all lamps.
5 R/W MDC1 LST1 LST0 STRIKE AND LAMP OUT TIMEOUT
(LAMP FREQUENCY CYCLES)
EXAMPLE TIMEOUT IF
LAMP FREQUENCY IS 50kHz
0 0 32,768 0.66 seconds
6 R/W MDC2 0 1 65,536 1.31 seconds
1 0 98,304 1.97 seconds
7 R/W LST1 / RSVD 1 1 Reserved —
DS3881
Single-Channel Automotive CCFL Controller
20 ____________________________________________________________________
Table 5. Control Register 1 (CR1) [Shadowed-EEPROM, F4h]
BIT R/W FACTORY
DEFAULT NAME FUNCTION
0 R/W 0 LOCE
Lamp Overcurrent Enable
0 = Lamp overcurrent detection disabled.
1 = Lamp overcurrent detection enabled.
1 R/W 0 POSCS
POSC Select. See POSCR0 and POSCR1 control bits in Control Register 2 to select
the oscillator range.
0 = POSC input is connected with a resistor to ground to set the frequency of the
internal PWM oscillator.
1 = POSC input is a 22.5Hz to 440Hz clock.
2 R/W 0 LFSS
Lamp Frequency Source Select
0 = Lamp frequency generated internally and sourced from the LSYNC output.
1 = Lamp frequency generated externally and supplied to the LSYNC input.
3 R/W 0 DPSS
DPWM Signal Source Select
0 = DPWM signal generated internally and sourced from the PSYNC output.
1 = DPWM signal generated externally and supplied to the PSYNC input.
4 R/W 0 RGSO
Ramp Generator Source Option
0 = Source DPWM at the PSYNC output.
1 = Source internal ramp generator at the PSYNC output.
5 R/W 0 ARD
Autoretry Disable
0 = Autoretry function enabled.
1 = Autoretry function disabled.
6 R/W 0 RSVD Reserved. Should be set to 0.
7 R/W 0 DPD
DPWM Disable
0 = DPWM function enabled.
1 = DPWM function disabled.
DS3881
Single-Channel Automotive CCFL Controller
____________________________________________________________________ 21
Table 6. Control Register 2 (CR2) [Shadowed-EEPROM, F5h]
BIT R/W DEFAULT NAME FUNCTION
0 R/W 0 UMWP
User Memory Write Protect
0 = Write access blocked.
1 = Write access permitted.
1 R/W 0 POSCR0
DPWM Oscillator Range Select. When using an external source for the dimming clock,
these bits must be set to match the external oscillator’s frequency. When using a
resistor to set the dimming frequency, these bits plus the external resistor control the
frequency.
POSCR1 POSCR0 DIMMING CLOCK (DPWM)
FREQUENCY RANGE (Hz) k (kΩ • kHz)
0 0 22.5 to 55.0 1
0 1 45 to 110 2
1 0 90 to 220 4
2 R/W 0 POSCR1
1 1 180 to 440 8
Lamp Sample Rate Select. Determines the feedback sample rate of the LCM inputs.
LSR1 LSR0 SELECTED LAMP SAMPLE
RATE
EXAMPLE SAMPLE RATE
IF LAMP FREQUENCY IS
50kHz
3 R/W 1 LSR0
0 0 4 Lamp Frequency Cycles 12,500Hz
0 1 8 Lamp Frequency Cycles 6250Hz
1 0 16 Lamp Frequency Cycles 3125Hz
4 R/W 0 LSR1
1 1 32 Lamp Frequency Cycles 1563Hz
5 — 0 RSVD Reserved. This bit should be set to zero.
6 — 0 RSVD Reserved. This bit should be set to zero.
7 R/W 0 PDNE
Power-Down. Logically ORed with the PDN pin. Setting this bit high resets the controller,
clears the fault logic, and places the part in power-down mode. 0 = Normal. All circuitry is
off, except I2C interface.
DS3881
Single-Channel Automotive CCFL Controller
22 ____________________________________________________________________
Table 7. EMI Control Register (EMIC) [Shadowed-EEPROM, F6h]
BIT R/W FACTORY
DEFAULT NAME FUNCTION
LAMP OSCILLATOR SPREAD-SPECTRUM MODULATION SELECT
SS1 SS0 SELECTED LAMP FREQUENCY SPREAD
0 R/W 0 SS0
0 0 SPREAD-SPECTRUM DISABLED
0 1 ±1.5%
1 0 ±3.0%
1 R/W 0 SS1
1 1 ±6.0%
2 R/W 0 SSM
Lamp Oscillator Spread-Spectrum Modulation Select
0 = Triangular modulation.
1 = Pseudorandom modulation.
3⎯⎯RSVD Reserved. This bit should be set to zero.
4 R/W 0 STEPE
Lamp Frequency Step Enable. Logically ORed with the step invoked.
0 = Lamp operates at nominal frequency.
1 = Frequency step invoked.
LAMP OSCILLATOR FREQUENCY STEP SELECT
FS2 FS1 FS0
SELECTED LAMP
FREQUENCY STEP
(SS0 = 0 AND SS1= 0)
SPREAD-SPECTRUM
MODULATION RATE
(SS0 AND/OR SS1 = 1)
5 R/W 0 FS0
0 0 0 Step Up 1% Lamp Frequency x4
0 0 1 Step Up 2% Lamp Frequency x2
0 1 0 Step Up 3% Lamp Frequency x1
0 1 1 Step Up 4% Lamp Frequency x1/2
6 R/W 0 FS1
1 0 0 Step Down 1% Lamp Frequency x1/4
1 0 1 Step Down 2% Lamp Frequency x1/8
1 1 0 Step Down 3% Lamp Frequency x1/16
7 R/W 0 FS2
1 1 1 Step Down 4% Lamp Frequency x1/32
DS3881
Single-Channel Automotive CCFL Controller
____________________________________________________________________ 23
Table 8. Lamp Current Overdrive Control Register (LCOC) [Shadowed-EEPROM, F7h]
BIT R/W FACTORY
DEFAULT NAME FUNCTION
LAMP CURRENT OVERDRIVE SELECT
LCO2 LCO1 LCO0 SELECTED LAMP CURRENT OVERDRIVE
0 0 0 Nominal Current + 12.50%
0 R/W 0 LCO0
0 0 1 Nominal Current + 25.00%
0 1 0 Nominal Current + 37.50%
0 1 1 Nominal Current + 50.00%
1 R/W 0 LCO1
1 0 0 Nominal Current + 62.50%
1 0 1 Nominal Current + 75.00%
1 1 0 Nominal Current + 87.50%2 R/W 0 LCO2
1 1 1 Nominal Current + 100.00%
3 R/W 0 LCOE
Lamp Current Overdrive Enable. Logically ORed with the LCO pin.
0 = Lamp operated with nominal current setting.
1 = Lamp overdrive invoked.
AUTOMATIC LAMP CURRENT OVERDRIVE TIMEOUT SELECT
TO3 TO2 TO1 TO0
SELECTED TIMEOUT
IN LAMP FREQUENCY
CYCLES
EXAMPLE TIMEOUT IF
LAMP FREQUENCY IS
50kHz
4 R/W 0 TO0
0 0 0 0 Disabled —
0001 1 x 2
22 1.4 min
0010 2 x 2
22 2.8 min
0011 3 x 2
22 4.2 min
0100 4 x 2
22 5.6 min
5 R/W 0 TO1
0101 5 x 2
22 7.0 min
0110 6 x 2
22 8.4 min
0111 7 x 2
22 9.8 min
1000 8 x 2
22 11.2 min
1001 9 x 2
22 12.6 min
6 R/W 0 TO2
1 0 1 0 10 x 222 14.0 min
1 0 1 1 11 x 222 15.4 min
1 1 0 0 12 x 222 16.8 min
1 1 0 1 13 x 222 18.2 min
1 1 1 0 14 x 222 19.6 min
7 R/W 0 TO3
1 1 1 1 15 x 222 21.0 min
DS3881
Single-Channel Automotive CCFL Controller
24 ____________________________________________________________________
I2C Definitions
The following terminology is commonly used to
describe I2C data transfers:
Master Device: The master device controls the slave
devices on the bus. The master device generates SCL
clock pulses, start, and stop conditions.
Slave Devices: Slave devices send and receive data
at the master’s request.
Bus Idle or Not Busy: Time between stop and start
conditions when both SDA and SCL are inactive and in
their logic-high states.
Start Condition: A start condition is generated by the
master to initiate a new data transfer with a slave.
Transitioning SDA from high to low while SCL remains
high generates a start condition. See the timing dia-
gram for applicable timing.
Stop Condition: A stop condition is generated by the
master to end a data transfer with a slave. Transitioning
SDA from low to high while SCL remains high gener-
ates a stop condition. See the timing diagram for
applicable timing.
Repeated Start Condition: The master can use a
repeated start condition at the end of one data transfer
to indicate that it will immediately initiate a new data
transfer following the current one. Repeated starts are
commonly used during read operations to identify a
specific memory address to begin a data transfer. A
repeated start condition is issued identically to a nor-
mal start condition. See the timing diagram for applica-
ble timing.
Bit Write: Transitions of SDA must occur during the low
state of SCL. The data on SDA must remain valid and
unchanged during the entire high pulse of SCL plus the
setup and hold time requirements (see Figure 9). Data is
shifted into the device during the rising edge of the SCL.
Bit Read: At the end of a write operation, the master
must release the SDA bus line for the proper amount of
setup time (see Figure 9) before the next rising edge of
SCL during a bit read. The device shifts out each bit of
data on SDA at the falling edge of the previous SCL
pulse and the data bit is valid at the rising edge of the
current SCL pulse. Remember that the master gener-
ates all SCL clock pulses including when it is reading
bits from the slave.
Acknowledgement (ACK and NACK): An acknowl-
edgement (ACK) or not acknowledge (NACK) is always
the 9th bit transmitted during a byte transfer. The
device receiving data (the master during a read or the
slave during a write operation) performs an ACK by
transmitting a zero during the 9th bit. A device per-
forms a NACK by transmitting a one during the 9th bit.
Timing (Figure 9) for the ACK and NACK is identical to
all other bit writes. An ACK is the acknowledgment that
the device is properly receiving data. A NACK is used
to terminate a read sequence or as an indication that
the device is not receiving data.
Byte Write: A byte write consists of 8 bits of informa-
tion transferred from the master to the slave (most sig-
nificant bit first) plus a 1-bit acknowledgement from the
slave to the master. The 8 bits transmitted by the mas-
ter are done according to the bit-write definition and the
acknowledgement is read using the bit-read definition.
SDA
SCL
tHD:STA
tLOW
tHIGH
tRtF
tBUF
tHD:DAT
tSU:DAT REPEATED
START
tSU:STA
tHD:STA
tSU:STO
tSP
STOP
NOTE: TIMING IS REFERENCE TO VIL(MAX) AND VIH(MIN).
START
Figure 9. I2C Timing Diagram
DS3881
Single-Channel Automotive CCFL Controller
____________________________________________________________________ 25
Byte Read: A byte read is an 8-bit information transfer
from the slave to the master plus a 1-bit ACK or NACK
from the master to the slave. The 8 bits of information
that are transferred (most significant bit first) from the
slave to the master are read by the master using the bit
read definition above, and the master transmits an ACK
using the bit write definition to receive additional data
bytes. The master must NACK the last byte read to ter-
minate communication so the slave will return control of
SDA to the master.
Slave Address Byte: Each slave on the I2C bus
responds to a slave addressing byte sent immediately
following a start condition. The slave address byte
(Figure 10) contains the slave address in the most sig-
nificant seven bits and the R/Wbit in the least signifi-
cant bit. The DS3881’s slave address is 10100A1A00
(binary), where A0and A1are the values of the address
pins (A0 and A1). The address pin allows the device to
respond to one of four possible slave addresses. By
writing the correct slave address with R/W= 0, the
master indicates it will write data to the slave. If R/W=
1, the master will read data from the slave. If an incor-
rect slave address is written, the DS3881 will assume
the master is communicating with another I2C device
and ignore the communications until the next start con-
dition is sent.
Memory Address: During an I2C write operation, the
master must transmit a memory address to identify the
memory location where the slave is to store the data.
The memory address is always the second byte trans-
mitted during a write operation following the slave
address byte.
I
2
C Communication
Writing a Data Byte to a Slave: The master must gen-
erate a start condition, write the slave address byte
(R/W= 0), write the memory address, write the byte of
data, and generate a stop condition. Remember the
master must read the slave’s acknowledgement during
all byte write operations. See Figure 11 for more detail.
Acknowledge Polling: Any time EEPROM is written,
the DS3881 requires the EEPROM write time (tW) after
the stop condition to write the contents to EEPROM.
During the EEPROM write time, the DS3881 will not
acknowledge its slave address because it is busy. It is
possible to take advantage of that phenomenon by
repeatedly addressing the DS3881, which allows the
next byte of data to be written as soon as the DS3881 is
ready to receive the data. The alternative to acknowl-
edge polling is to wait for a maximum period of tWto
elapse before attempting to write again to the DS3881.
EEPROM Write Cycles: The number of times the
DS3881’s EEPROM can be written before it fails is
specified in the
Nonvolatile Memory Characteristics
table. This specification is shown at the worst-case
write temperature. The DS3881 is typically capable of
handling many additional write cycles when the writes
are performed at room temperature.
Reading a Data Byte from a Slave: To read a single
byte from the slave the master generates a start condi-
tion, writes the slave address byte with R/W= 0, writes
the memory address, generates a repeated start condi-
tion, writes the slave address with R/W= 1, reads the
data byte with a NACK to indicate the end of the trans-
fer, and generates a stop condition. See Figure 11 for
more detail.
7-BIT SLAVE ADDRESS
MOST
SIGNIFICANT BIT
A
1, A0 PIN VALUE DETERMINES
READ OR WRITE
R/W
10100A
1
A
0
Figure 10. DS3881’s Slave Address Byte
DS3881
Single-Channel Automotive CCFL Controller
26 ____________________________________________________________________
Applications Information
Addressing Multiple DS3881s
On a Common I2C Bus
Each DS3881 responds to one of four possible slave
addresses based on the state of the address input pins
(A0 and A1). For information about device addressing,
see the
I
2
C Communication
section.
Setting the RMS Lamp Current
Resistor R7 and R8 in the
Typical Operating Circuit
set
the lamp current. R7 and R8 = 140Ωcorresponds to a
5mARMS lamp current as long as the current waveform
is approximately sinusoidal. The formula to determine
the resistor value for a given sinusoidal lamp current is:
Component Selection
External component selection has a large impact on the
overall system performance and cost. The two most
important external components are the transformers
and n-channel MOSFETs.
The transformer should be able to operate in the 40kHz
to 80kHz frequency range of the DS3881, and the turns
ratio should be selected so the MOSFET drivers run at
28% to 35% duty cycle during steady state operation.
The transformer must be able to withstand the high
open-circuit voltage that is used to strike the lamp.
Additionally, its primary/secondary resistance and induc-
tance characteristics must be considered because they
contribute significantly to determining the efficiency and
transient response of the system. Table 9 shows a trans-
former specification that has been used for a 12V invert-
er supply, 438mm x 2.2mm lamp design.
The n-channel MOSFET must have a threshold voltage
that is low enough to work with logic-level signals, a low
on-resistance to maximize efficiency and limit the n-
channel MOSFET’s power dissipation, and a break-
down voltage high enough to handle the transient. The
breakdown voltage should be a minimum of 3x the
inverter voltage supply. Additionally, the total gate
charge must be less than QG, which is specified in
the
Recommended Operating Conditions
table. These
specifications are easily met by many of the dual n-
channel MOSFETs now available in 8-pin SO pack-
ages.
Table 10 lists suggested values for the external resistors
and capacitors used in the
Typical Operating Circuit
.
Power-Supply Decoupling
To achieve best results, it is highly recommended that
a decoupling capacitor is used on the IC power-supply
pin. Typical values of decoupling capacitors are 0.01µF
or 0.1µF. Use a high-quality, ceramic, surface-mount
capacitor, and mount it as close as possible to the VCC
and GND pins of the IC to minimize lead inductance.
R
Ix
LAMP RMS
71
2
()
=
XXXXXXXX
101 0 A
00A1
0
COMMUNICATIONS KEY
WRITE A SINGLE BYTE
8-BITS ADDRESS OR DATA
WHITE BOXES INDICATE THE MASTER IS
CONTROLLING SDA
NOTES
2) THE FIRST BYTE SENT AFTER A START CONDITION IS
ALWAYS THE SLAVE ADDRESS FOLLOWED BY THE
READ/WRITE BIT.
SHADED BOXES INDICATE THE SLAVE IS
CONTROLLING SDA
START ACK
NOT
ACK
S
SA
AAP
DATA
MEMORY ADDRESS
101 0 A
00A1
0101 0 A
01A1
0
READ A SINGLE BYTE
SA
ASR AN
P
DATA
MEMORY ADDRESS
A
PN
SR
STOP
REPEATED
START
1) ALL BYTES ARE SENT MOST SIGNIFICANT BIT FIRST.
Figure 11. I2C Communications Examples
DS3881
Single-Channel Automotive CCFL Controller
____________________________________________________________________ 27
Table 9. Transformer Specifications (as Used in the
Typical Operating Circuit
)
PARAMETER CONDITIONS MIN TYP MAX UNITS
Turns Ratio (Secondary/Primary) (Notes 1, 2, 3) 40
Frequency 40 80 kHz
Output Power 6W
Output Current 58mA
Primary DCR Center tap to one end 200 mΩ
Secondary DCR 500 Ω
Primary Leakage 12 µH
Secondary Leakage 185 mH
Primary Inductance 70 µH
Secondary Inductance 500 mH
100ms minimum 2000
Secondary Output Voltage Continuous 1000 VRMS
Note 1: Primary should be Bifilar wound with center tap connection.
Note 2: Turns ratio is defined as secondary winding divided by the sum of both primary windings.
Note 3: 40:1 is the nominal turns ratio for driving a 438mm x 2.2mm lamp with a 12V supply. Refer to Application Note 3375 for more
information.
Table 10. Resistor and Capacitor Selection Guide
DESIGNATOR QTY VALUE TOLERANCE
(%) AT +25°C
TEMPERATURE
COEFFICIENT NOTES
R5, R6 1 10kΩ1——
R3, R4 1 12.5kΩ to
105kΩ1 — See the Setting the SVM Threshold Voltage section.
R9 1 20kΩ to
40kΩ1≤153ppm/°C 2% or less total tolerance. See the Lamp Frequency
Configuration section to determine value.
R10 1 18kΩ to
45kΩ1≤153ppm/°C 2% or less total tolerance. See the Lamp Frequency
Configuration section to determine value.
R1 1 4.7kΩ5 Any grade —
R2 1 4.7kΩ5 Any grade —
R11 1 4.7kΩ5 Any grade —
R7 1/Chan 140Ω1 — See the Setting the RMS Lamp Current section.
C8 1/Chan 100nF 10 X7R
C ap aci tor val ue w i l l al so affect LC M b i as vol tag e d ur i ng
p ow er - up . A l ar g er cap aci tor m ay cause a l ong er ti m e
for V
D C B
to r each i ts nor m al op er ati ng l evel .
C2 1/Chan 10pF 5 ±1000ppm/°C 2kV to 4kV breakdown voltage required.
C3 1/Chan 27nF 5 X7R
C ap aci tor val ue w i l l al so affect LC M b i as vol tag e d ur i ng
p ow er - up . A l ar g er cap aci tor m ay cause a l ong er ti m e
for V
D C B
to r each i ts nor m al op er ati ng l evel .
C1 1/Chan 33µF 20 Any grade —
C7 2/DS3881 0.1µF 10 X7R Place close to VCC and GND on DS3881.
DS3881
Single-Channel Automotive CCFL Controller
Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are
implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.
28
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© 2007 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.
is a registered trademark of Dallas Semiconductor Corporation.
Heaney
INVERTER SUPPLY
VOLTAGE (VINV)
(8V TO 16V)
GA1
LAMP CURRENT MONITOR
CCFL LAMP
GB1
OVD1
VCC
VCC VCC
VCC
BRIGHT
SVMH
LAMP BRIGHTNESS
TRANSFORMER
DUAL POWER
MOSFET
DEVICE
SUPPLY VOLTAGE
(5V ±5%)
OVERVOLTAGE DETECTION
LCM1
GND
LAMP FREQUENCY
INPUT/OUTPUT LSYNC
SCL
SDA
I2C
CONFIGURATION
AND CONTROL PORT
FAULT
PSYNC
DPWM SIGNAL
INPUT/OUTPUT
LOSC
POSC
LCO
PDN
LAMP ON/OFF
LAMP CURRENT
OVERDRIVE ENABLE
SVML
A0
A1
HARDWARE
CONTROL
STEP LAMP
FREQUENCY STEP
GND_S
R1 R2
R7
R9 R10
C2
C3
C7
R11
C8
R3 R4
R5 R6
C1
DS3881
Typical Operating Circuit
Chip Information
TRANSISTOR COUNT: 38,000
SUBSTRATE CONNECTED TO GROUND
Package Information
For the latest package outline information, go to
www.maxim-ic.com/DallasPackInfo.
Revision History
Pages changed at Rev 1: 1, 19
