SY84782U
Low Power 2.5V 1.25Gbps FP/DFB Laser
Diode Driver
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
August 11, 2015
Revision 2.0
hbwhelp@micrel.com or (408) 955-1690
General Description
The SY84782U is a single 2.5V supply, ultra-low power,
small form factor laser diode driver for telecom/datacom
applications. Intend ed t o driv e FP/DF B lasers at dat a r ates
up to 1.25Gbps, it is especially useful for Compact SFP,
SFP, and SFF modules where power requirements are
quite stringent. The driver can deliver modulation current
up to 90mA and offers a high compliance voltage, all of
which make the SY84782U suitable for high current
operations in both AC- and DC-c oupl ed app licat io ns.
The SY84782U is intended to be used with Micrel’s
MIC3003 Optical Transceiver Management IC, which
allows for both modulation and bias current control and
monitor ing. Fur th ermore, the MIC30 03 offers power contr ol
and temperature compensation.
This device operates across the industrial temperature
range (–40 °C to +95°C ) and is av ailable in a small 3m m ×
3mm QFN package.
All datasheets and support documentation can be found
on Micrel’s website at: www.micrel.com.
Features
• 2.5V power supply option
• Ultra low power consumption (63mW typ)
• Multirate up to 1.25Gbps
• Fast rise and fall time
• Modulation current up to 90mA
• Laser can be DC- or AC-coupled
• Small form factor 16-pin (3mm × 3mm) QFN package
• MIC3003G compatible
• Extensive temperature range (–40°C to +95°C)
Applications
• Multirate LAN, MAN applications: Fibre Cha nne l, GbE,
SONET OC3/12/24, and SDH STM1/4/8
• CSFP/SFF/SFP optical modules
___________________________________________________________________________________________________________
Typical Appli cation
DC-Coupled Laser
AC-Coupled Laser
Micrel, Inc.
SY84782U
August 11, 2015
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Ordering Information
Part Number Package Type Operating Range Package Marking Lead Finish
SY84782UMG QFN-16 Industrial 782U Pb-Free Bar-Line Indicator Pb-Free
SY84782UMG TR(1) QFN-16 Industrial 782U Pb-Free Bar-Line Indicator Pb-Free
Note:
1. Tape and Reel
Pin Configuration
16-Pin QFN
Pin Description
Pin Number Pin Name Pin Function
1, 4, 7,
8, 13 GND,
ePad Device Ground. Ground and exposed pad must be connected to the plane of the most negative
potential.
2 DIN+ Non-Inverting Input Data. Internally terminated with 50Ω to a r eferen ce vol tag e
3 DIN- Inverting Input Data. Internally terminated with 50Ω to a reference voltage
5, 6 VCC Supply Voltage. Bypass with a 0.1µF || 0.01µF low-ESR capacitor as close to VCC pin as possible.
9, 10 MOD- Inverted Modulation Current Output. Provides modulation current when input data is negative
11, 12 MOD+ Non-Inverted Modulation Current Output. Provides modulation current when input data is positive.
14 VREF Reference Voltage. Install a 0.1µF capacitor between VREF and VCC
15 IM_SET Modulation current setting and control. The voltage applied to this pin will set the modulation current.
To be connected to the MIC3003 Pin 24 (VMOD+). Input impedance 25kΩ.
16 /EN Enable Pin. A high level signal applied to this pin will pull the MOD+ output HIGH and MOD- output
LO W. Internally pulled dow n with a 75kΩ resistor.
Truth Table
DIN+
DIN-
/EN
MOD+ (2)
MOD-
Laser Output (3)
L H L H L L
H L L L H H
X X H H L L
Notes:
2. IMOD = 0 when MOD+ = H.
3. A ssumi ng that laser is tied to MOD+.
Micrel, Inc.
SY84782U
August 11, 2015
3 Revision 2.0
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Absolute Maximum Ratings(4)
Supply Voltage (VCC) .................................. –0.5V to +3.0V
Input Voltage (VIN) .......................................... –0.5V to VCC
TTL Control Input Voltage (VIN) ........................... 0V to VCC
Lead Temperature (soldering, 20s) .......................... +260°C
Storage Temperature (TS) ....................... –65°C to +150°C
Operating Ratings(5)
Suppl y Voltage (VCC) .............................. 2.375V to 2.625V
Ambient Temperature (TA) ......................... –40°C to +95°C
Package Thermal Resistance(6)
Still-Air (θJA) ....................................................... 60°C/W
Junction-to-Board (ΨJB) ..................................... 33°C/W
DC Electrical Characteristics(7)
VCC = 2.5V ±5%, TA = –40°C to +95°C. Typical values are VCC = 2.5V, TA = 25°C, IMOD = 60mA.
Symbol
Parameter
Condition
Min.
Typ.
Max.
Units
ICC Power Supply Current Modulation current ex clud ed 24 30
(8)
mA
VMOD_MIN Minimum voltage required
at driver output for prop er
operation 0.6 V
RiIN(DATA) Input Resistance (DIN+, DIN-) 45 50 55 Ω
RiIN(IMOD_SET) Input Resistance (IM_SET) 25 kΩ
VID Differential Input Voltage Swing 200 2400 mVpp
VIH_EN /EN Input High 2 V
VIL_EN /EN Input Low 0.8 V
VIM_SET Voltage Range on IM_SET Pin IMOD range 10mA – 90mA 1.2 V
AC Electrical Characteristics(7)
VCC = 2.5V ±5%, TA = –40°C to +95°C. Typical values are VCC = 2.5V, TA = 25°C, IMOD = 60mA.
Symbol Parameter Condition Min. Typ. Max. Units
Data Rate NRZ Data 0.155 1.25 Gbps
IMOD Modulation Current
(15Ω Load) AC-Coupled 10 90 mA
DC-Coupled 10 70
(9)
IMOD_OFF Modulation OFF curr ent Current at MOD+ when the
device is disabled 750 µA
Total Jitter @ 1.25Gbps data rate 20 pspp
Pulse-Width Distortion IMOD range 10mA – 90mA 20 ps
tr, tf Output Rise/Fall Times
(20% to 80%) 15Ω Load 100 140 ps
Notes:
4. Exceeding the absolute maxim um rating may damage the device.
5. The device is not guaranteed to functi on outside its operati ng rating.
6. Package therm al resistance assumes exposed pad is soldered (or equivalent) to the devices most negative potential on the PCB.
7. Specific at i on for packaged product only.
8. Icc = 30mA (excluding IMOD) for worst case conditions with VCC = 2.625V, TA = 85°C, IMOD = 60mA.
9. A ssumi ng VCC = 2.375V, laser band gap voltage = 1V, laser package inductance = 1nH, laser equivalent series resist or = 5Ω, and damping resistor =
10Ω.
Micrel, Inc.
SY84782U
August 11, 2015
4 Revision 2.0
hbwhelp@micrel.com or (408) 955-1690
Typical Operating Characteristics
VCC = 2.5V ±5%, TA = –40°C to +95°C. Typical val ues are VCC = 2.5V, TA = 25°C, IMOD = 60mA.
I M_SET vs Modulation Current
0
10
20
30
40
50
60
70
80
90
100
0200 400 600 800 1000
I M _ SET Volt age ( mV)
IMOD (mA)
Suppl y Current vs IMOD
(IMOD Excluded)
10
15
20
25
30
010 20 30 40 50 60 70 80 90 100
Modulation Current (m A )
Supply Curr ent (m A)
I
MOD
vs V
MOD
( Com pliance Voltage)
0
10
20
30
40
50
60
70
80
90
100
00.2 0.4 0.6 0.8 11.2
VMOD (V)
IMOD (mA)
Functional Block Diagram
Micrel, Inc.
SY84782U
August 11, 2015
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Application Information
The t ypic al applications diagram on the first page shows
how to connect the driver to the laser single-ended. To
impr ove trans it ion time and las er response, the laser c an
be driven differentially, as shown in Figures 3 and 4.
Driving the l aser dif fer ential ly will also m inim ize cros stalk
with the res t of the c ircuitr y on the board, particu larly the
receiver.
Figure 3. Laser DC-Coupled
Figure 4. Laser AC-Coupled
DC-Coupling
In addition to the low power consumption and high
modulation current, the SY84782U offers a high
complia nce volta ge. The m inimum voltage needed a t the
output of the driver for proper operation is less than
600mV, leaving a large headroom, VCC – 600mV, to the
laser with the dam ping resistor. T o show the im portance
of this high compliance voltage, consider the voltage
drops along the path from VCC to ground through the
laser, damping resistor, and driver:
VCC = Driver Headroom + VRd + Vlaser
VRd = Rd x IMOD
Vlaser = Vband-gap + Rlaser x IMOD + Ldi/dt
Vband-gap + Rlaser x IMOD = 1.6V at maximum for a
Fabry Perrot or a DFB laser.
Ldi/dt is the voltage drop due to the laser parasitic
inductance during IMOD transitions. Assuming L = 1nH, tf
= tf = 80ps (measured between 20% and 80% of IMOD),
and IMOD = 70mA (42mA from 20% to 80%), then Ldi/dt
will be equal to 525mV. This number can be minimized
by making the laser leads as short as possible and by
using the RC compensation network between the
cathode of the laser and ground or across the laser
driver outputs, as sho wn in Figure 3.
To be able to drive the laser DC-coupled with a high
current, it is necessary to keep the damping resistor as
small as possible. For example, if the drop due to
parasitic inductance of the laser is neglected
(compensated for) and the maximum drop across the
laser (1.6V) considered while keeping a minimum of
600mV headroom for the driver, then the maximum
damping resistor that allows a 70mA modulation current
into the laser is:
Rdmax = (VCC-0.6V-1.6V)/0.07A
The worst case will be with VCC = 3.0V, leading
to Rdmax = 11.4Ω
Micrel, Inc.
SY84782U
August 11, 2015
7 Revision 2.0
hbwhelp@micrel.com or (408) 955-1690
On the other hand, the smaller the value of Rd, the
higher is the overshoot/undershoot on the optical signal
from the laser. In the circuit shown in Figure 4, the RC
compensation network across the driver outputs (MOD+
and MOD-) allows the user Rd = 10Ω. The optical eye
diagrams at data rates of 1.25Gbps, shown in
“Function al Charac ter istics” section, are a ll obtaine d w ith
the same circuit using Rd = 10Ω, RComp = 100Ω, and
CComp = 3pF. The compensation network may change
from one board to another and from one type of laser to
another. An additional compensation network (RC) can
be added at the laser cathode for further compensation
and eye smoothing.
AC-Coupling
When trying to AC-couple the laser to the driver, the
headroom of the driver is no longer a problem since it is
DC isolated f r om the laser with t he c ou pl ing capacitor. At
the output, the headroom of the driver is determined by
the pull-up network. In Figure 4, the modulation current
out of the dr iver is split bet ween the pull -up network and
the laser. If, for example, the total pull-up resistor is
twice the sum of the damping resistor and laser
equivale nt series resis tance, then o nly two thirds (2/3) of
the modulation current will be used by the laser.
Therefore, to keep most of the modulation current going
through the laser, the total pull-up resistor must be kept
as high as possible. One solution involves using an
inductor alone as pull-up, presenting a high impedance
path for the modulation current and zero ohm (0Ω) path
for the DC current offering headroom of the driver equal
to VCC and almost all the modulation current goes into
the laser. The inductor alone will cause signal distortion,
and, to improve this phenomenon, a combination of
resistors and inductors c an be us ed (as s ho wn on Fi gu r e
4). In this case, the headroom of the driver is VCC-R1 x
αIMOD, where αIMOD is the portion of the modulation
current that goes through the pull-up net wor k .
W hen the laser is AC-coup led to the dr iver, the co upling
capacitor creates a low-frequency cutoff in the circuit,
and its va lue must be c hosen to be as lar ge as poss ible.
If the value of the cap is too high, it will slow down the
fast signals edges, and conversely, if its value is too
small, it won’t be able to hold a constant change
between the first bit and the last bit of a long string of
identica l bits in a lo w data r ate applicatio n. This leads to
higher pattern-dependent jitter in the transmitter signal.
0.1µF is found to be good for all applications from
155Mbps to 1.25Gbps.
AC-coupling the laser to the driver brings a solution to
the driver headroom problem at the expense of extra
components, loss of part of the modulation current
wasted in the pull-up network, and additional power
consumption.
Micrel, Inc.
SY84782U
August 11, 2015
8 Revision 2.0
hbwhelp@micrel.com or (408) 955-1690
Package Information and Recommended Land Pattern(10)
16-Pin (3mm × 3mm) QFN (QFN-16)
Note:
10. Package information is correct as of the publication date. For updates and most current information, go to www.micrel.com.
Micrel, Inc.
SY84782U
August 11, 2015
10 Revision 2.0
hbwhelp@micrel.com or (408) 955-1690
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-10 00 WEB http://www.micrel.com
Micrel, Inc. is a leading global manufacturer of IC solutions for t he world wide high pe rformance linear and power, LAN, and timing & communications
markets. The Company’s products include advanced mixed
-signal, analog & power semiconductors; high-
performance communication, clock
management,
MEMs-based clock oscillators & crystal-less clock generators, Ethernet switches, and physical layer transceiver ICs.
Company
customers include leading manufacturers of enterprise, consumer, industrial, mobile, telecommunications, automotive, and comp
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of distribut ors and reps worldwide.
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ormation furnished in this data
sheet. This
information is not intended as a warranty and Micrel doe
s not assume responsibility for its use.
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