SY88992L
3.3V, 4.25Gbp s VCS EL Driver
Januar y 2006
M9999-011306-A
hbwhelp@micrel.com or (408) 955-1690
Gener al De s cr iption
The SY88992L is a single supply 3.3V, low power
consumption, small-form factor VCSEL driver ideal for
use in datacom applications; Ethernet, GbE (Gigabit
Ethernet), and FC (Fibre Channel) applications that
operate from 100Mbps up to 4.25Gbps. The
modulation current is set by applying an external
voltage at the IM_SET pin. The driver features an
adjustable peaking option with variable amplitude and
duration t o improve V CSEL edge res ponse. T he driver
can deliver modulation current up to 25mA and a
peaking current up to 35% of the modulation current.
This device is intended to be used with Micrel’s
MIC3001 Optical Transceiver Management IC, which
allows for both modulation and bias current control an d
monitoring, APC (Automatic Power Control), and
temperature compensation.
All support documentation can be found on Micrel’s
web site at: www.micrel.com.
Features
• Up to 25mA modulation current
• Operates from 100Mbps to 4.25Gbps
• Peaking with variable duration option for better
VCSEL response
• Dual peaking, on the rise and falling edges
• Peaking current proportional to modulation current
• Easy modulation current setting
• Fully controllable with Micrel MIC3001
• Small (3mm x 3mm) 16 pin QFN package
Applications
• Multirate LAN, SAN applications up to 4.25Gbps:
Ethernet, GbE, FC
• SFF, SFP Modules
Markets
• Datacom
________________________________________________________________
Typical Application
Micrel, Inc.
SY88992L
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Functional Block Diagram
Ordering Information(1)
Part Number Package
Type Operating
Range Package Marking Lead Finish
SY88992LMG QFN-16 Industrial 992L with Pb-Free bar-l ine ind icator NiPdAu Pb-Free
SY88992LMGTR
(2)
QFN-16 Industrial 992L with Pb-Free bar-l ine ind i cator NiPdAu Pb-Free
Notes:
1. Contact f act ory for die avail abi lit y. Dice are guaranteed at TA = +25°C, DC Electricals only.
2. Tape and Reel.
Pin Configuration
16-Pin QFN
Micrel, Inc.
SY88992L
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Pin Description
Pin Number Pin Name Pin Function
2 DIN+ Non-Inverting Input Data. Internally terminated with 50Ω to a referen ce voltage.
3 DIN- Inverting Input Data. Internally terminated with 50Ω to a reference voltage.
6 IP_SET1 Peaking Current Setting. Connect this pin to GND and keep pins 7 and 8 open to set
peaking-to-modulation current ratio to 5%. Combinations of the three pins, as shown
in table below, will set different ratios up to 35%.
7 IP_SET2 Peaking Current Setting. Connect this pin to GND and keep pins 6 and 8 open to set
peaking-to-modulation current ratio to 10%. Combinations of the three pins, as shown
in table below, will set different ratios up to 35%.
8 IP_SET3 Peaking Current Setting. Connect this pin to GND and keep pins 6 and 7 open to set
peaking-to-modulation current ratio to 20%. Combinations of the three pins, as shown
in table below, will set different ratios up to 35%.
10 MOD- Inverted Modulation Current Output. Provides modulation current when input data is
negative.
11 MOD+ Non-Inverted Modulation Current Output. Provides modulation current when input
data is positive.
13 IM_SET Modulation Current Setting. The modulation current is set by applying a 0V to 1.2V
voltage at this pin.
14 IPD_SET Peaking Duratio n Sett ing . T he peak ing curr ent dur at ion is set by installing a re si stor
between this pin and ground. The plot on page 6 shows peaking duration versus the
value of the resistor installed.
16 /EN A low level signal applied to this pin will enable the output stage of the driver.
Internally pulled down to ground with 75kΩ resistor.
1, 4, 9, 12 GND Ground. Grou nd and exposed pad must be connected to the plan e of the most
negative potential.
5, 15 VCC Supply Voltage. Bypass with a 0.1µF//0.01µF low ESR capacitor as close to VCC pin
as possible.
Truth Table
DIN+ DIN- /EN MOD+
(1)
MOD- VCSEL 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 a common anode VCSEL with its cathode tied to MOD+.
Peaking Current-to-Modulation Current Ratio Setting
IP/IMOD 0 % 5 % 10 % 15 % 20 % 25 % 30 % 35 %
IP_SET1 NC GND NC GND NC GND NC GND
IP_SET2 NC NC GND GND NC NC GND GND
IP_SET3 NC NC NC NC GND GND GND GND
Micrel, Inc.
SY88992L
Januar y 2006 4 M9999-011306-
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hbwhelp@micrel.com or (408) 955-1690
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, unless otherwise noted. Typical values are at: VCC = 3.3V, TA = 25°C,
IMOD = 13mA(4)
Symbol Parameter Condition Min Typ Max Units
ICC Power Supply Current Peaking not used 57 95 mA
Maximum peaking used 70 110 mA
IMOD(4) Modulation Current AC-coupled 3 25 mA
IMOD_OFF Modulation OFF Current Current at MOD+ and MOD- when
the part is disabled 100 µA
VMOD_MIN Minimum Voltage required at the
driver output (headroom) for proper
operation
1.5 V
RIN Input Resistance (DIN+-to-DIN-) 90 100 110 Ω
VID Differential Input Voltage Swing 200 2400 mVPP
VIM_SET Voltage Range on IM_SET IMOD range 3mA – 25mA
(4)
1.2 V
VIL /EN Input Low 0.8 V
VIH /EN Input High 2 V
Input Impedance at /EN 75 kΩ
Notes:
1. Permanent device dam age may occur if absolute maximum ratings are exceeded. This is a stress rating only and funct i 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
conditions for extended periods may aff ect device reli abili t y.
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. θJB
uses a 4-layer and θJA in still air unless otherwise stated.
4. IMOD is defined as the current at the output of the driver. That current splits between the pull-up network at the output and the VCSEL. For a
nominal pull-up resist or of 75Ω at the output of the driver and a nominal 50Ω VCSEL equivalent resistor, 60% of that current goes to the
VCSEL.
Micrel, Inc.
SY88992L
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AC Electrical Characteristics
TA = -40°C to +80°C and VCC = 3.0 to 3.6V, unless otherwise noted. Typical values are at VCC = 3.3V, TA = 25°C,
IMOD = 13mA(5), and AC-coupled 50Ω load to ground with 75Ω pull-up (see Figure below).
Symbol Parameter Condition Min Typ Max Units
Data Rate NRZ 0.1 4.25 Gbps
tOFF(6) Turn OFF Time 50Ω load 1 1.5 ns
tON(7) Turn ON Time 50Ω load 1.8 2.5 ns
tr Output Current Rise Time
20% to 80%, IMOD = 13mA, no
peaking, 50Ω load 65 95 ps
20% to 80%, IMOD = 13mA,
IP/IMOD=20%, RIPD=1.5kΩ 60 75 ps
tf Output Current Fall Time
20% to 80%, IMOD = 13mA, no
peaking, 50Ω load 65 95 ps
20% to 80%, IMOD = 13mA,
IP/IMOD=20%, RIPD=1.5kΩ 60 75 ps
Total Jitter @ 2.5Gbps data rate, 50Ω load 30 psPP
Pulse-Width Distortion 50Ω load 20 ps
(IP / IMOD)
Max Maximum Peaking Current-to-
Modulation Current Ratio 35 %
tP Peaking Current Duration(8) IMOD = 13mA, RIPD_SET = 0Ω 150 ps
Notes:
5. IMOD is defined as the current at the output of the driver. That current splits between the pull-up network at the output and the VCSEL. For a
nominal pull-up resist or of 75Ω at the output of the driver and a nominal 50Ω VCSEL equivalent resist or, 60% of that current goes to the
VCSEL.
6. Turn-OFF tim e is defined as the delay between the tim e the signal at /EN rises to 50% of its amplitude and the time when the output of the
driver reaches 10% of its steady-state am plit ude.
7. Turn-ON time is defined as the delay between the time the signal at /EN falls to 50% of its amplitude and the time when the output of the
driver reaches 90% of its steady-state am plit ude.
8. The peaki ng current duration is the time between the start of the peaking current, which is t he same as the start of the modulation current
transition, and the time when the peaking current reaches its maximum, i.e., the top of the peak.
Test Circuit
Micrel, Inc.
SY88992L
Januar y 2006 8 M9999-011306-
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hbwhelp@micrel.com or (408) 955-1690
Peaking Variation with IP/IMOD Ratio and Peaking Duration
As it can be seen on the set of electrical waveforms below, the amplitude of the peak increases with the peaking-
to-modulation current ratio and the width of the peak increases with peaking duration.
Increasing Peaking Duration
Increasing Peaking Percentage
Micrel, Inc.
SY88992L
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Input and Output Stages
Figure 1a. Simplified Input Stage
Figure 1b. Simplified Output Stage
Interfacing the Input to Different Logic Drivers
Figure 2a. AC-Coupling to LVPECL Driver
Figure 2b. AC-Coupling to CML Driver
Micrel, Inc.
SY88992L
Januar y 2006 10 M9999-011306-
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hbwhelp@micrel.com or (408) 955-1690
Driver’s Special Features
The SY88992L features a peaking current of
programmable amplitude and duration on both the
rising and the falling edges. The amplitude of the
peaking current is adjustable in steps of 5% of the
modulation current from 0% to 35%. As shown in the
table on p age 3, the ratio b etween the peaking c urrent
and the modulation current (IP/IMOD) can be
programmed b y connect ing pin 6 (I P_ SET1) and /or pi n
7 (IP_SET2) and/or pin 8 (IP_SET3) to ground. When
all these three pins are left open, there is no peaking
(ratio 0%). When they’re all connected to ground the
ratio is maximum (35%).
For each family of VCSELs used with the driver, the
user must try many combinations in order to get the
best response for the VCSEL. The peaking current
duration can be tuned by installing a resistor between
pin 14 and ground; 0Ω provides maximum duration
and 3kΩ or higher pr o vides the minim um duration. The
combined features will improve the VCSEL response
for a better optical signal quality. The electrical eye
diagrams on page 8 show how the signal changes as
the peaking-to-modulation current varies.
Application Hints
The typical application section on the front page shows
how to connect the driver to the VCSEL single-ended.
To improve transition time and VCSEL response, the
VCSEL ca n be dri ven dif ferenti all y, as sho wn in Figur e
3. Driving the VCSEL differentially will also minimize
the cross talk with the rest of the c irc uitr y on the boar d ,
especially with the receiver.
The driver is always AC-coupled to the VCSEL and the
headroom of the driver is determined by the pull-up
network at the output. In Figure 3, the modulation
current out of the driver is split between the pull-up
network and the VCS EL. If, for ex ample, the tot al pull-
up resistor is twice the sum of the damping resistor
and VCSEL equivalent series resistance, only two
thirds (2/3) of the modulation current will be used by
the VCSEL. Therefore, to maximize the modulation
current going through the VCSEL, the total pull-up
resistors should be kept as high as possible. One
solution cons ists of using an ind uctor alone as pull -up,
creating a high impedance path for the modulation
current and zero ohm (0Ω) path for the DC current.
This offers a headroom equal to VCC for the driver
and almost all the modulation current goes into the
VCSEL. However, using the inductor alone will cause
signal distortion. To avoid this, a combination of
resistors and inductors can be used, as shown on
figure 3. 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
network. For instance, if a modulation current out of
the driver of 25mA is considered, with a pull-up
resistor of 75Ω, and the VCSEL with the damping
resistor total resistance is 50Ω, then the modulation
current will split; 10mA to the pull-up resistor and
15mA to the l aser. The headr oom for the dr iver w ill be
VCC–75 x 10 = VCC–750mV which is way higher than
the minimum voltage required for the output stage of
the driver to operate properly.
The coupling capacitor creates a low-frequency cutoff
in the circuit. Therefore, a proper coupling capacitor
value must be chosen to accommodate different data
rates in the application. If the value of the capacitor is
too high, it may cause problems in high data rate
applicat ions. If its va lue is too sm all, it won’t be abl e to
hold a constant charge between the first bit and the
last bit in a long string of identica l bits in low data rate
application. Both cases lead to higher pattern-
dependent jitter in the transmitter signal. 0.1µF is
found to be good for applications from 155Mbps to
4.25Gbps.
Figure 3. Driving a Common Anode VCSEL Differentially
Micrel, Inc.
SY88992L
Januar y 2006
M9999-011306-A
hbwhelp@micrel.com or (408) 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) 474-10 00 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 ume d by Mi cre l
for its use. Micrel reserves the right t o change circuitry and specifi cations at any time without notification to the customer.
Micrel Products are not designed or authorized for use as components in life support appliances, devices or systems where malfunction
of a
product can reasonably be expected to result in personal i njury. Life support devices or systems are devices or systems that
(a) are intended
for surgic al im pl ant into the body or (b) support or sustai n l ife, and whose failure to perform can be reaso
nably expected to result in a significant
injury to the user. A Purchaser’s use or sale of Mic rel Products for use in life support appliances, devices or systems is a
Purchaser’s own risk
and Purchaser agrees to fully indem nify Micrel f or any damages resulting from such use or sale.
© 2006 Micrel, Incorporated.
