SY88422L
4.25Gbp s La ser D riv er with I nte grat ed B ias
Micrel Inc. • 2180 Fortune Drive • San Jose, CA 95131 • USA • tel +1 (408) 944-0800 • fax + 1 (408) 474-1000 • http://www.micrel.com
November 2007
M9999-112607-A
hbwhelp@micrel.com or (408) 955-1690
General Description
The SY88422L is a single 3.3V supply, small form factor
laser driver for telecom/datacom applications up to
4.25Gbps. The driver can deliver modulation current up to
90mA and a bias current up to 100mA.
Datasheets and support documentation can be found on
Micrel’s web site at: www.m ic rel.c om.
Features
• 35mA power supply current typical
• Operation up to 4.25Gbps
• Modulation current up to 90mA
• Bias current up to 100mA
• Available in 16-pin small form factor (3mm x 3mm) QFN
package
Applications
• Multi-rate LAN, MAN applications up to 4.25Gbps:
FC, GbE, SONET/SDH
• SFF, SFP, LX-4 Modules
___________________________________________________________________________________________________________
Typical Application
Micrel, Inc.
SY88422L
November 2007 2 M9999-112607-A
hbwhelp@micrel.com or (408) 955-1690
Ordering Information(1)
Part Number Package
Type Operating
Range Package Marking Lead Finish
SY88422LMG QFN-16 Industrial 422L with Pb-Fr ee bar-l ine ind i cator NiPdAu Pb-Free
SY88422LMGTR(2) QFN-16 Industrial 422L with Pb-Free bar-l ine ind icator NiPdAu Pb-Free
Notes:
1. Contact f act ory for die availabi lit y. Dice are guaranteed at TA = +25°C, DC Electricals only.
2. Tape and Reel.
Pin Configuration
16-Pin QFN
Micrel, Inc.
SY88422L
November 2007 3 M9999-112607-A
hbwhelp@micrel.com or (408) 955-1690
Pin Description
Pin Name Pin Number Pin Function
1, 4, 9, 12 VCC Supply Voltage. Bypass with a 0.1µF//0.01µF low ESR capacitor as close to VCC pin as
possible.
7, 8, 14 GND Ground. Grou nd and exposed pad must be conne cted to the plan e of the most negativ e
potential.
2 DIN+ Non-inverting input data. Internally terminated with 50Ω to a refer en ce voltage.
3 DIN– Inverting input data. Internally terminated with 50Ω to a reference voltage.
5 MODSET Modulation current setting and control. The voltage applied to this pin will set the modulation
current. Input impedance 25kΩ.
6 /EN Active Low TTL. The driver is disabled when this pin is unco nnec ted or /EN asser ted hig h. T he
driver is enabled when /EN is asserted low.
10 MOD– Inverted modulation current output. Outputs modulation current when input data is negative.
11 MOD+ Non-inverted modulation current output. Outputs modulation current when input data is posi tiv e.
13 BIAS BIAS Current Output
15 BIASMON Bias monitor. Install an external resistor from this pin to GND to convert the output current to a
voltage proportional to the bias current
16 BIASSET Bias current setting. The voltage applied to this pin will set the bias current. Input impedance
25kΩ.
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 or NC H L L
Notes:
1. IMOD = 0 when MOD+ = H.
2. Assum i ng that the laser cathode is tied to MOD+.
Micrel, Inc.
SY88422L
November 2007 4 M9999-112607-A
hbwhelp@micrel.com or (408) 955-1690
Absolute Maximum Ratings(1)
Supply Voltage (VCC) .................................... –0.5V to +4.0V
CML Input Voltage (VIN) .................... VCC–1.2V to VCC+0.5V
TTL Control Input Voltage (VI)............................... 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, unless otherwise noted. Typical values are VCC = +3.3V, TA = 25°C, IMOD =
30mA, IBIAS = 2 0mA .
Symbol Parameter Condition Min Typ Max Units
ICC Power Supply Current Modulation currents ex cluded 35 56(4) mA
VMOD_C Compliance Voltage VCC-1.5 VCC V
VBIAS_C Compliance Voltage VCC-2.3 VCC V
RIN(DATA) Input Resistance at DIN+, DIN-,
Single Ended 45 50 55 Ω
VDIFF_IN (DIN) Differential Input Voltage Swing 100 2400 mVpp
VIL (/EN) Input Low Voltag e 0.8 V
VIH (/EN) Input High Voltage 2 V
RIN (MODSET) MODSET Input Resistance 25 kΩ
VMODSET Voltage Range on MODSET Pin IMOD range 10mA to 90mA 1.2 V
RIN (BIASSET) BIASSET Input Resistance 25 kΩ
VBIASSET Voltage Range on BIASSET Pin IBIAS range 10mA to 100m A 1.2 V
Notes:
1. Permanent device dam age may occur if absolute maximum ratings are exceeded. This is a stress rating only and functi onal operati on is not impli ed
at conditions other than those detailed in the operational sections of this data sheet. Exposure to absolute maximum ratings conditi ons for extended
periods may affect device reliabil ity.
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 devic es most negative pot ent i al on the PCB. ψJB uses a 4-
layer and θJA in still air unless otherwise stated.
4. ICC = 56mA for worst-case conditions with IMOD = 90mA and BIAS=100 mA, TA = +85°C, VCC = 3.6V.
Micrel, Inc.
SY88422L
November 2007 5 M9999-112607-A
hbwhelp@micrel.com or (408) 955-1690
AC Electrical Characteristics
TA = –40°C to +85°C and VCC = +3.0V to +3.6V, unless otherwise noted. Typical values are VCC = +3.3V, TA = 25°C, IMOD =
30mA, IBIAS = 2 0mA .
Symbol Parameter Condition Min Typ Max Units
Data Rate NRZ 0.1 4.25 Gbps
IMOD Modulation Current(5) Laser or equivalent load AC-coupled to
the driver 10 90 mA
IMOD_OFF Modulation OFF Current Current at MOD+ and MOD- when the
device is disabled 150 µA
tr Output Current Rise Time 20% to 80%, 15 Ω load 50 70 ps
tf Output Current Fall Time 20% to 80%, 15 Ω load 50 70 ps
Total Jitter 20 psPP
IBIAS Bias Current(5) 5 100 mA
IBias_OFF Bias OFF Current Current at BIAS when the device is
disabled 150 µA
Notes:
5. Load = 15Ω.
Test Circuit
Micrel, Inc.
SY88422L
November 2007 8 M9999-112607-A
hbwhelp@micrel.com or (408) 955-1690
Input and Output Stages
Figure 1a. Simplified Input Stage
Figure 1b. Simplified Output Stage
Interfacing the Input to Differential Logic Drivers
Figure 2a. AC-Coupling to LVPECL Driver
Figure 2b. AC-Coupling to CML Driver
Micrel, Inc.
SY88422L
November 2007 9 M9999-112607-A
hbwhelp@micrel.com or (408) 955-1690
Application Hints
The t ypical ap pl icati ons dra w ing on t h e f ront page shows
how to connect the driver to the laser differentially. To
drive the laser single ended, just disconnect MOD- from
the laser anode and pull it up to VCC with a resistor equal
to the equiva lent resistor of the load on MOD+, dam ping
resistor plus the laser equivalent resistor. Differential
drive improves transition time and laser response.
Driving the laser differentially will also minimize the cross
talk with the rest of the circuitry on the board especially
the receiver.
If we refer to Figure 3, the m odulation current out of the
driver is split between the pull-up net work and the laser.
If, for example, the total pull-up resistor is twice the sum
of the damping resistor and laser equivalent series
resistance, only two thirds (2/3) of the modulation current
will be used by the laser. To keep most of the
modulation current going through the laser, try to keep
the total pull-up resistors 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
off ering headroom for the dr iver equal to V CC and alm ost
all the modulation current goes into the laser. The
inductor alone will cause signal distortion, and, to
improve that, a combination of resistor and inductor can
be used as shown in Figure 3. In this case, the
headroom of the driver is VCC – R1 * αImod, where αImod
is the portio n of t he modulation curr en t that goes thr o u gh
the pull-up net wor k.
The coupling capacitor creates a low-frequency cutoff in
the circuit, and its value must be chosen to
accommodate the lowest and the highest data rates. If
the value of the cap is too high, it will degrade the
performance at higher data rates, and, if its value is too
small, it wo n’t be ab le to ho ld a cons ta nt c harge betwe en
the first bit and th e last bi t o f a long s tring of ident ic al bi ts
in a low da ta r at e ap pl ication. T his lea ds in bot h c ases to
higher pattern-dependant jitter in the transmitter signal.
0.01µ-to-0.1µF is found to be good range for all
applications from 155Mbps to 4.25Gbps.
Figure 3. AC-Coupling the Laser to the Driver
Micrel, Inc.
SY88422L
November 2007 10 M9999-112607-A
hbwhelp@micrel.com or (408) 955-1690
Package Information
16-Pin QFN
MICREL, INC. 2180 FORTUNE DRIVE SA N JOSE, CA 95131 USA
TEL +1 (408) 944-0800 FAX +1 (408) 474-1000 WEB http:/ /www .micrel. com
The information furnished by Micrel in this data sheet is believed to be accurate and reliable. However, no respons i bility is assumed by Micrel for its
use. Micrel reserves the right to change circuit ry and specific ations at any time without notification to the customer.
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Purchaser’s use or sale of Micrel Products for use in lif e
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indemnify Micrel f or any damages resulting from such use or sale.
© 2007 Micrel, Incorporated.
