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19-3118; Rev 3; 1/10
3.2Gbps SFP VCSEL Driver with Diagnostic
Monitors
General Description
The MAX3740A is a high-speed VCSEL driver for small-
form-factor (SFF) and small-form-factor pluggable (SFP)
fiber optic LAN transmitters. It contains a bias genera-
tor, a laser modulator, and comprehensive safety fea-
tures. The automatic power control (APC) adjusts the
laser bias current to maintain average optical power
over changes in temperature and laser properties. The
driver accommodates common cathode and differential
configurations.
The MAX3740A operates up to 3.2Gbps. It can switch
up to 15mA of laser modulation current and source up
to 15mA of bias current. Adjustable temperature com-
pensation is provided to keep the optical extinction
ratio within specifications over the operating tempera-
ture range. The MAX3740A interfaces with the Dallas
DS1858 to meet SFF-8472 timing and diagnostic
requirements. The MAX3740A accommodates various
VCSEL packages, including low-cost TO-46 headers.
The MAX3740A safety circuit detects faults that could
cause hazardous light levels and disables the VCSEL
output. The safety circuits are compliant with SFF and
SFP multisource agreements (MSA).
The MAX3740A is available in a compact 4mm 4mm,
24-pin thin QFN package and operates over the -40°C
to +85°C temperature range.
Applications
Multirate (1Gbps to 3.2Gbps) SFP/SFF Modules
Gigabit Ethernet Optical Transmitters
Fibre Channel Optical Transmitters
Infiniband Optical Transmitters
Features
Supports all SFF-8472 Digital Diagnostics
2mA to 15mA Modulation Current
1mA to 15mA Bias Current
Optional Peaking Current to Improve VCSEL Edge
Speed
Supports Common Cathode and Differential
Configuration
Automatic Power Control
Safety Circuits Compliant with SFF and SFP
MSAs
4mm 4mm, 24-Pin Thin QFN Package
Ordering Information
PART
TEMP RANGE PIN-PACKAGE
MAX3740AETG
-40°C to +85°C 24 Thin QFN-EP*
MAX3740AETG+ -40°C to +85°C 24 Thin QFN-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
Typical Application Circuit
+3.3V
TX_DISABLE
SQUELCH
VCC
FAULT
PWRMON
MODSET
4.7kΩ
RMODSET
0.1μF
IN+
MAX3740A
REF
COMP
0.1μF
RTC†
IN-
TC1
MD
BIAS
0.047μF
RBIASSET
TC2
BIASSET
GND PEAKSET
0.01μF
OUT+
OUT-
BIASMON 0.01μF
50Ω
RPEAKSET
RBIASMON
RPWRSET
L1*
CF†
RF†
OPTIONAL COMPONENT
*FERRITE BEAD
________________________________________________________________ Maxim Integrated Products 1
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.

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3.2Gbps SFP VCSEL Driver with Diagnostic
Monitors
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (VCC) ..............................................-0.5V to 6.0V
Voltage at TX_DISABLE, IN+, IN-, FAULT,
SQUELCH, TC1, TC2, MODSET, PEAKSET, BIASSET,
BIAS, BIASMON, COMP, MD, REF,
PWRMON ...............................................-0.5V to (VCC + 0.5V)
Voltage at OUT+, OUT- .........................(VCC - 2V) to (VCC + 2V)
Current into FAULT ............................................ -1mA to +25mA
Current into OUT+, OUT- ....................................................60mA
Continuous Power Dissipation (TA = +85°C)
24-Lead Thin QFN
(derate 20.8mW/°C above +85°C).................................1354mW
Operating Temperature Range ...........................-40°C to +85°C
Storage Temperature Range .............................-55°C to +150°C
Lead Temperature (soldering, 10s) .................................+300°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.
ELECTRICAL CHARACTERISTICS
(VCC = +2.97V to +3.63V, TA = -40°C to +85°C. Typical values are at VCC = +3.3V, TC1 and TC2 are shorted, PEAKSET open, TA =
+25°C, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
MIN TYP MAX UNITS
Supply Current
FAULT OUTPUT
Output High Voltage
Output Low Voltage
TX_DISABLE INPUT
Input Impedance
Input High Voltage
Input Low Voltage
Power-Down Time
SQUELCH
Squelch Threshold
Squelch Hysteresis
Time to Squelch Data
Time to Resume from Squelch
BIAS GENERATOR (Note 4)
Bias Current
Accuracy of Programmed Bias
Current
ICC
ICC-SHDN
SQUELCH set low,
TX_DISABLE set low,
peaking is not used
(Note 1)
IMOD = 2mAP-P
IMOD = 15mAP-P
Additional current when peaking is used
(Note 2)
Additional current when SQUELCH is high
Total current when TX_DISABLE is high
VOH
VOL
RLOAD = 10kΩ to 2.97V
RLOAD = 4.7kΩ to 3.63V
VIH
VIL
The time for ICC to reach ICC-SHDN when
TX_DISABLE transitions high
(Note 3)
(Note 3)
IBIAS
ΔBIAS
Minimum
Maximum
5mA IBIAS 15mA
1mA IBIAS 5mA
32
55 68
mA
15 20
5 10
3.9 5
2.4 V
0.4 V
4.7 10.0 kΩ
2.0 V
0.8 V
50 µs
25
10
0.02
0.02
15
-8
-12
85
5.00
5.00
mVP-P
mVP-P
µs
µs
1
mA
+8
%
+12
2 _______________________________________________________________________________________

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3.2Gbps SFP VCSEL Driver with Diagnostic
Monitors
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +2.97V to +3.63V, TA = -40°C to +85°C. Typical values are at VCC = +3.3V, TC1 and TC2 are shorted, PEAKSET open, TA =
+25°C, unless otherwise noted.)
PARAMETER
Bias Current During Fault
SYMBOL
IBIAS_OFF
BIASMON Gain
BIASMON Stability
AUTOMATIC POWER CONTROL (APC)
CONDITIONS
Current out of the BIAS pin
1mA < IBIAS < 3mA
3mA IBIAS 15mA
(Notes 5,6)
MD Nominal Voltage
VMD APC loop is closed
Voltage at REF
MD Voltage During Fault
MD Input Current
APC Time Constant
PWRMON Nominal Gain
LASER MODULATOR (Note 7)
Data Input Voltage Swing
Output Resistance
Modulation Current
Minimum Peaking Current Range
Maximum Peaking Current Range
Peaking Current Duration
VREF
Normal operation (FAULT = low)
CCOMP = 0.047µF (Note 6)
VPWRMON / (VREF - VMD)
VID
IMOD
Minimum
Maximum
Single-ended resistance at OUT+
Single-ended resistance at OUT-
Minimum
Maximum
MIN
0.0875
0.085
-10
TYP
1.5
0.105
0.105
MAX
10
0.1375
0.125
+10
UNITS
µA
mA/mA
%
1
1.2
-2
5
1.85
VREF -
0.16
1.8
0
0.7
20
2.15
2
2.2
+2
2.45
V
V
V
µA
µs
V/V
2200
80
72
15
0.2
2
80
250
mVP-P
105
Ω
100
2
mAP-P
mA
mA
ps
Tolerance of Programmed
Modulation Current
TC1 is shorted to TC2
-10 +10 %
Minimum Programmable
Temperature Coefficient
0 ppm/°C
Maximum Programmable
Temperature Coefficient
Modulation Transition Time
Deterministic Jitter
Random Jitter
Laser Modulation During Fault or
while Squelch is Active
Input Resistance
Temperature range 0°C to +70°C
tR, tF
DJ
RJ
5mA IMOD 15mA, 20% to 80% (Note 6)
5mA IMOD 15mA, 3.2Gbps (Notes 6, 8)
(Note 6)
IMOD_OFF
Differential resistance
+5000
ppm/°C
65 95
ps
12 20 psP-P
1.3 4 psRMS
15 50 µAP-P
85 100 115
Ω
Input Bias Voltage
VIN
VCC -
0.3
V
_______________________________________________________________________________________ 3

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3.2Gbps SFP VCSEL Driver with Diagnostic
Monitors
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +2.97V to +3.63V, TA = -40°C to +85°C. Typical values are at VCC = +3.3V, TC1 and TC2 are shorted, PEAKSET open, TA =
+25°C, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
SAFETY FEATURES (see the Typical Operating Characteristics section)
High-Current Fault Threshold
VBIAS Fault Threshold
Power-Monitor Fault Threshold
VBMTH
VBTH
VPMTH
VBIASMON > VBMTH causes a fault
VBIAS referenced to VCC
VPWRMON > VPMTH causes a fault
TX Disable Time
t_OFF
Time from rising edge of TX_DISABLE to
IBIAS = IBIAS_OFF and IMOD = IMOD_OFF
(Note 6)
MIN TYP MAX UNITS
0.7 0.8 0.9
-0.250 -0.2 -0.150
0.7 0.8 0.9
V
V
V
1.8 5
µs
TX Disable Negate Time
t_ON
Time from rising edge of TX_DISABLE to
IBIAS and IMOD at 99% of steady state
(Note 6)
55 500
µs
Fault Reset Time
Power-On Time
Fault Assert Time
t_INIT1
t_INIT2
t_FAULT
Time to set VFAULT = low after power-on or
after rising edge of TX_DISABLE (Note 6)
Time after power-on to transmitter-on with
TX_DISABLE low (Note 6)
Time from fault occurrence to VFAULT =
high; CFAULT < 20pF, RFAULT = 4.7kΩ
(Note 6)
60 200 ms
60 200 ms
1.4 50
µs
Fault Delay Time
t_FLTDLY
Time from fault to IBIAS = IBIAS_OFF and
IMOD = IMOD_OFF (Note 6)
1 5 µs
TX_DISABLE Reset
t_RESET
Time TX_DISABLE must be held high to
reset FAULT (Note 6)
1 µs
Note 1: Supply current measurements exclude IBIAS from the total current.
Note 2: Tested with RPEAK = 1.18kΩ.
Note 3: Measured by applying a pattern that contains 20µs of K28.5, followed by 5µs of zeros, then 20µs of K28.5, followed by 5µs
of ones. Data rate is equal to 2.5Gbps, with inputs filtered using 1.8GHz Bessel filters.
Note 4: VBIAS < VCC - 0.7V.
Note 5: Variation of bias monitor gain for any single part over the range of VCC, temperature, 3mA < IBIAS < 15mA.
Note 6: Guaranteed by design and characterization.
Note 7: Measured electrically with a 50Ω load AC-coupled to OUT+.
Note 8: Deterministic jitter is the peak-to-peak deviation from the ideal time crossings measured with a K28.5 bit pattern at 3.2Gbps
(00111110101100000101).
4 _______________________________________________________________________________________

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3.2Gbps SFP VCSEL Driver with Diagnostic
Monitors
Typical Operating Characteristics
(VCC = +3.3V, RTC = 0Ω, PEAKSET open, measured electrically with a 50Ω load AC-coupled to OUT+, TA = +25°C, unless otherwise
noted.)
ELECTRICAL EYE
MAX3740A toc01
3.2Gbps, K28.5, 10mA MODULATION,
PEAKING OFF
ELECTRICAL EYE WITH PEAKING
MAX3740A toc02
3.2Gbps, K28.5, 10mA MODULATION,
RPEAKSET = 2.4kΩ
ELECTRICAL EYE WITH MAX PEAKING
MAX3740A toc03
3.2Gbps, K28.5, 10mA MODULATION,
RPEAKSET = 500Ω
73mV/div
73mV/div
73mV/div
50ps/div
50ps/div
50ps/div
OPTICAL EYE
MAX3740A toc04
ER = 8.2dB, 2.125Gbps, K28.5,
850nm VCSEL, WITH 2.3GHz
O-TO-E CONVERTER
EMCORE SC-TOSA-8585-3420 VCSEL
68ps/div
OPTICAL EYE
MAX3740A toc05
ER = 8.2dB, 2.5Gbps, K28.5,
850nm VCSEL SONET MASK
WITH +20% MARGIN
EMCORE SC-TOSA-8585-3420 VCSEL
58ps/div
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
IBIASMON vs. BIAS CURRENT
4 8 12
BIAS CURRENT (mA)
16
DETERMINISTIC JITTER
vs. MODULATION CURRENT
40
35
30
25
20
15
10
5
0
0 5 10 15
IMOD (mAP-P)
RANDOM JITTER
vs. MODULATION CURRENT
7
6
5
4
3
2
1
0
0 5 10 15
IMOD (mAP-P)
TRANSITION TIME
vs. MODULATION CURRENT
100
90
80 RISE
70
60 FALL
50
40
2 4 6 8 10 12 14 16
IMOD (mAP-P)
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