SY88982L
3.3V, 2.7Gbps High-Current, Low-Power
Laser Driver for FP/ DFB Lasers
December 2009 1 M9999-121009-
A
hbwhelp@micrel.com or (40 8) 955-1690
Gener al De s cr iption
The SY88982L is a single 3.3V supply, low power
consumption, small form factor driver for
telecom/datacom applications using FP/DFB lasers
at data rates up to 2.7Gbps. The driver can deliver
modulation current up to 90mA, and the high
compliance voltage if offers, makes the part suitable
for high-current operation (with the laser AC- or DC-
coupled to it). This device is intended to be used
with Micrel’s MIC3003 Optical Transceiver
Management IC, which allows for both modulation
and bias current control and monitoring, automatic
power control, and temperature compensation.
All support documentation can be found on Micrel’s
web site at: www.micrel.com.
Features
• 2.4V minimum laser compliance voltage for high-
current DC-coupled applications
• 48mA power supply current typical
• Operation up to 2.7Gbps
• Modulation current up to 90mA
• Designed for use with the MIC 30 03
• Laser may be DC- or AC-coupled
• Small form factor 16-pin (3mm x 3mm) QFN
package
Applications
• Multi-rate LAN, MAN applications up to 2.7Gbps:
FC, GbE, SONET OC3/12/24/48 and SDH
STM1/4/8/16
• SFF, SFP modules
Markets
• Telecom, Datacom
________________________________________________________________
Typical Application
Laser DC-Coupled to the Driver
Laser AC-Coupled to the Driver
Micrel, Inc.
SY88982L
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Functional Block Diagram
Ordering Information(1)
Part Number Package Type Operating Range Package Marking Lead Finish
SY88982LMG QFN-16 Industrial 982L with Pb-Free bar-line indi cator NiPdAu Pb-Free
SY88982LMGTR
(2)
QFN-16 Industrial 982L with Pb-Free bar-l ine ind i cator NiPdAu Pb-Free
Notes:
1. Contact factory f or die availabi lity. Dice are guarant eed at TA = +25°C, DC Electricals only.
2. Tape and Reel.
Pin Configuration
16-Pin QFN
Micrel, Inc.
SY88982L
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Pin Description
Pin Number Pin Name Pin Function
1, 4, 7, 8, 13 GND Ground. Ground and exposed pad must be connected to the plan e of the most negativ e
potential.
2 DIN+ Non-Inverting Input Data. Internally terminated with 50Ω to a referen ce vol tage.
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 curre nt setti ng and contr ol. The vol tage applied to this pin will set the modulation
current. To be connected to the MIC3003 pin 24 (VMO D +). Input impedance 25kΩ.
16 /EN A high level signal applied to this pin will disable the output stage of the driver. Internally
pulled down with 25kΩ resistor.
Truth Table
DIN+
DIN-
/EN
MOD+
(1)
MOD-
Laser Output
(2)
L H L H L L
H L L L H H
X X H H H L
Notes:
1. IMOD = 0 when MOD+ = H.
2. Assuming that the laser is tied to MOD+.
Micrel, Inc.
SY88982L
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Absolute Maximum Ratings(1)
Supply Voltage (VIN) ........................... –0.5V to +4.0V
CML Input Voltage (VIN) .......... VCC–1.2V to VCC+0.5V
TTL Control Input Voltage (VIN) ................... 0V to VCC
Lead Temperature (soldering, 20sec.) ........... +260°C
Storage Temperature (Ts) ............... –65°C to +150°C
Operating Ratings(2)
Supply Voltage (VCC)...........................+3.0V to +3.6V
Ambient Temperature (TA) ................ –40°C to +85°C
Package Thermal Resistance(3)
QFN
(θJA) Still-air ............................................. 60°C/W
(ψJB) ......................................................... 33°C/W
DC Electrical Characteristics
TA = -40°C to 85°C and VCC = +3.0V to +3.6V, un less otherwise noted. Typical val ues are VCC = +3.3V, TA = 25°C,
IMOD = 60mA.
Symbol Parameter Condition Min Typ Max Units
ICC Power Supply Current Modulation current ex clud ed 48 65
(4)
mA
VMOD_MIN Minimum Voltage Required at
the Driver Output (headroom) for
Proper Operation 0.6 V
RIN(DATA) Input Resistance (DIN+, DIN-) 45 50 55 Ω
VID Differential Input Voltage Swing 200 2400 mVPP
/EN Low 0.8 V
/EN High 2 V
RIN (IMOD_SET) IM_SET Input Resistance 25 kΩ
VIM_SET Voltage Range on IM_SET Pin IMOD range 10mA – 90mA 1.2 V
AC Electrical Characteristics
TA = -40°C to 85°C and VCC = +3.0V to +3.6V, un less otherwise noted. Typical val ues are VCC = +3.3V, TA = 25°C,
IMOD = 60mA.
Symbol Parameter Condition Min Typ Max Units
Data Rate NRZ 0.155 2.7 Gbps
IMOD Modulation Current(5) AC-coupled 10 90 mA
DC-coupled 10 70(6) mA
IMOD_OFF Modulation OFF Current Current at MOD+ when the device is
disabled. 750 µA
tr Output Current Rise Time 20% to 80%, IMOD = 60mA, 15Ω load 55 80 ps
tf Output Current Fall Time 20% to 80%, IMOD = 60mA, 15Ω load 55 80 ps
Total Jitter @2.5Gbps data rate 20 psPP
Pulse-Width Distortion IMOD range 10mA – 90mA 20 ps
Notes:
1. Permanent device dam age may occur if absolute maximum rati ngs are exceeded. This is a stress rating only and functi onal operati on is
not implied at conditions other than thos e detai l ed in the operational sections of this data sheet. Exposure to absolute maximum ra tings
conditi ons for extended periods may aff ect device rel i ability.
2. The data sheet limits are not guaranteed if the device is operated beyond the operating ratings.
3. Package Therm al Resistance assumes exposed pad is soldered (or equivalent) to the devices most negative potential on the PCB. ψJB
uses a 4-layer and θJA in still air unless ot herwise stated.
4. ICC = 48mA for worst-case conditions with IMOD = 90mA, TA = +85°C, VCC = 3.6 .
5. Load = 15Ω.
6. Assum i ng VCC = 3.0V, Laser bandgap voltage = 1V, laser package inductance = 1nH, laser equivalent series resistor = 5Ω, and damping
resistor = 10Ω.
Micrel, Inc.
SY88982L
December 2009 7 M9999-121009-
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hbwhelp@micrel.com or (40 8) 955-1690
Input and Output Stages
Figure 1a. Simplified Input Stage
Figure 1b. Simplified Output Stage
Interfacing the Input to Different Logic Drivers
Figure 2a. DC-Coupling to LVPECL Driver
Figure 2b. AC-Coupling to LVPECL Driver
Figure 2c. AC-Coupling to CML Driver
Figure 2d. AC-Coupling to LVDS Driver
Micrel, Inc.
SY88982AL
December 2009 8 M9999-121009-
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Application Information
The typical applications diagram on the first page
shows how to connect the driver to the laser, single
ended. To improve transition time and laser
response, the laser can be driven differentially as
shown in Figures 3 and 4. Driving the laser
differentiall y will als o minimize the crosstalk with t he
rest of the circuitry on the board, especially the
receiver.
DC-Coupling
In addition to the low power consumption and high
modulation current, the SY88982L offers a high
compliance voltage. As can be seen in the “Typical
Operating Characteristics” section (IMOD vs. VMOD
curves), the minimum voltage needed at the output
of the driver f or proper oper atio n is less than 6 00mV,
leaving a large headroom, VCC-600mV, to the laser
with the damping resistor. To show the importance
of this high com plianc e voltage, cons ider the vo ltage
drops along th e path f rom VCC to ground t hrough 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 = 70m A (42m A from 20% to 80%),
then Ldi/dt will be equal to 525m V. This number c an
be minimized by making the laser leads as short as
possible and using and RC compensation network
between the cathode of the laser and ground or
across the laser driver outputs as shown in Figure 3.
To be ab le to dri ve the l aser DC-coup led with a high
current, it is necessary to keep the damping resistor
as sm all as p ossibl e. F or ex ample, if the drop d ue 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
On the other hand, the small is the value of Rd, the
higher is the overshoot/undershoot on the optical
signal from the laser. In the circuit shown in Figure 3,
the RC compensation network across the driver
outputs (MOD+ and MOD-) allows the user Rd =
10Ω. The optical eye diagrams at data rates of
155Mbps/622Mbps/1.25Gbps/2.5Gbps, shown in
“Functional Characteristics” section, are all obtained
with the sam e circuit using Rd = 1 0Ω, 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 com pensation
network (RC) can be added at the laser cathode for
further compensation and eye smoothing.
Figure 3. Laser DC-Coupled
AC-Coupling
W hen tr ying to AC c ouple the laser t o the driver, the
headroom of the driver is no longer a problem since
it is DC isolated from the laser with the coupling
capacitor. At the output, the headroom of the driver
is determ ined b y the pu ll-u p net work. In Figure 4, th e
modulation current out of the driver is split between
the pull-up net wor k and the laser. If, for ex am ple, the
total pull-up res istor is twic e the sum of the dam ping
resistor and laser equivalent series resistance, only
two thirds (2/3) of the modulation current will be
used by the laser. So, 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 consists in 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 a 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 that, a combination of
resistors and inductors can be used (as shown on
Figure 4). In this case, the headr oom of the dri ver is
VCC-R1 x αIMOD, where αIMOD is the portion of the
modulation current that goes through the pull-up
network.
When the laser is AC-coupled to the driver, the
coupling capacitor creates a low-frequency cutoff in
the circuit, and its value mus t be chosen as large as
Micrel, Inc.
SY88982L
December 2009 9 M9999-121009-
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possible. If the value of the cap is too high, it will
slow down the fast signals edges, and, if its value is
too sm all, it won’t be able to hol d a constant chan ge
between the first bit and the last bit of a long string
of identical bits in a low data rate application. This
leads to higher pattern-dependent jitter in the
transmitter signal. 0.1µF is found to be good for all
applications from 155Mbps to 2.7Gbps.
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 pul l-up net work, and additional
power consumption.
Figure 4. Laser AC-Coupled
Micrel, Inc.
SY88982L
December 2009 10 M9999-121009-
A
hbwhelp@micrel.com or (40 8) 955-1690
Package Information
16-Pin (3mm x 3mm) QFN
MICREL, INC. 2180 FORTUNE DRIVE SAN JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WE B http:/ /www .micrel. com
The information f urnished by Micrel in this data sheet is believed to be accurate and reli able. However, no responsibility is ass umed by Mic
rel
for its use. Micrel reserves the right t o change circuitry and specifications at any time without notification to the customer.
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