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.
♦
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
Features
♦
Supports all SFF-8472 Digital Diagnostics
MAX3740A
Ordering Information
PART
MAX3740AETG
MAX3740AETG+
TEMP RANGE
-40°C to +85°C
-40°C to +85°C
PIN-PACKAGE
24 Thin QFN-EP*
24 Thin QFN-EP*
+
Denotes a lead(Pb)-free/RoHS-compliant package.
*EP
= Exposed pad.
Applications
Multirate (1Gbps to 3.2Gbps) SFP/SFF Modules
Gigabit Ethernet Optical Transmitters
Fibre Channel Optical Transmitters
Infiniband Optical Transmitters
Typical Application Circuit
+3.3V
4.7kΩ
†
V
CC
FAULT
PWRMON
MODSET
TX_DISABLE
SQUELCH
R
MODSET
0.1μF
IN+
IN-
0.1μF
TC1
R
TC
†
MAX3740A
REF
COMP
0.047μF
MD
BIAS
L1*
R
PWRSET
TC2
OUT+
BIASSET
R
BIASSET
OUT-
GND PEAKSET
BIASMON
0.01μF
C
F†
0.01μF
50Ω
R
F†
R
PEAKSET
†
R
BIASMON
†
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.
3.2Gbps SFP VCSEL Driver with Diagnostic
Monitors
MAX3740A
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (V
CC
) ..............................................-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 (V
CC
+ 0.5V)
Voltage at OUT+, OUT- .........................(V
CC
- 2V) to (V
CC
+ 2V)
Current into FAULT ............................................ -1mA to +25mA
Current into OUT+, OUT- ....................................................60mA
Continuous Power Dissipation (T
A
= +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
(V
CC
= +2.97V to +3.63V, T
A
= -40°C to +85°C. Typical values are at V
CC
= +3.3V, TC1 and TC2 are shorted, PEAKSET open, T
A
=
+25°C, unless otherwise noted.)
PARAMETER
SYMBOL
CONDITIONS
SQUELCH set low,
I
MOD
= 2mA
P-P
TX_DISABLE set low,
peaking is not used
I
MOD
= 15mA
P-P
(Note 1)
Additional current when peaking is used
(Note 2)
Additional current when SQUELCH is high
I
CC-SHDN
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
I
BIAS
ΔBIAS
Minimum
Maximum
5mA
≤
I
BIAS
≤
15mA
1mA
≤
I
BIAS
≤
5mA
15
-8
-12
+8
+12
1
mA
%
(Note 3)
(Note 3)
25
10
0.02
0.02
5.00
5.00
85
mV
P-P
mV
P-P
µs
µs
V
IH
V
IL
The time for I
CC
to reach I
CC-SHDN
when
TX_DISABLE transitions high
50
4.7
2.0
0.8
10.0
kΩ
V
V
µs
V
OH
V
OL
R
LOAD
= 10kΩ to 2.97V
R
LOAD
= 4.7kΩ to 3.63V
2.4
0.4
V
V
Total current when TX_DISABLE is high
MIN
TYP
32
55
15
5
3.9
68
mA
20
10
5
MAX
UNITS
Supply Current
I
CC
2
_______________________________________________________________________________________
3.2Gbps SFP VCSEL Driver with Diagnostic
Monitors
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +2.97V to +3.63V, T
A
= -40°C to +85°C. Typical values are at V
CC
= +3.3V, TC1 and TC2 are shorted, PEAKSET open, T
A
=
+25°C, unless otherwise noted.)
PARAMETER
Bias Current During Fault
BIASMON Gain
BIASMON Stability
AUTOMATIC POWER CONTROL (APC)
MD Nominal Voltage
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
Tolerance of Programmed
Modulation Current
Minimum Programmable
Temperature Coefficient
Maximum Programmable
Temperature Coefficient
Modulation Transition Time
Deterministic Jitter
Random Jitter
Laser Modulation During Fault or
while Squelch is Active
Input Resistance
Input Bias Voltage
V
IN
t
R
, t
F
DJ
RJ
I
MOD_OFF
Differential resistance
85
Temperature range 0°C to +70°C
5mA
≤
I
MOD
≤
15mA, 20% to 80% (Note 6)
5mA
≤
I
MOD
≤
15mA, 3.2Gbps (Notes 6, 8)
(Note 6)
TC1 is shorted to TC2
-10
0
+5000
65
12
1.3
15
100
V
CC
-
0.3
95
20
4
50
115
I
MOD
V
ID
Minimum
Maximum
Single-ended resistance at OUT+
Single-ended resistance at OUT-
Minimum
Maximum
15
0.2
2
80
+10
2200
80
72
105
100
2
250
mV
P
-
P
Ω
mA
P
-
P
mA
mA
ps
%
ppm/°C
ppm/°C
ps
ps
P-P
ps
RMS
µA
P-P
Ω
V
Normal operation (FAULT = low)
C
COMP
= 0.047µF (Note 6)
V
PWRMON
/ (V
REF
- V
MD
)
-2
5
1.85
V
MD
V
REF
APC loop is closed
1
1.2
V
REF
-
0.16
1.8
0
0.7
20
2.15
2.45
+2
2
2.2
V
V
V
µA
µs
V/V
SYMBOL
I
BIAS_OFF
CONDITIONS
Current out of the BIAS pin
1mA < I
BIAS
< 3mA
3mA
≤
I
BIAS
≤
15mA
(Notes 5,6)
0.0875
0.085
-10
MIN
TYP
1.5
0.105
0.105
MAX
10
0.1375
0.125
+10
UNITS
µA
mA/mA
%
MAX3740A
_______________________________________________________________________________________
3
3.2Gbps SFP VCSEL Driver with Diagnostic
Monitors
MAX3740A
ELECTRICAL CHARACTERISTICS (continued)
(V
CC
= +2.97V to +3.63V, T
A
= -40°C to +85°C. Typical values are at V
CC
= +3.3V, TC1 and TC2 are shorted, PEAKSET open, T
A
=
+25°C, unless otherwise noted.)
PARAMETER
High-Current Fault Threshold
V
BIAS
Fault Threshold
Power-Monitor Fault Threshold
TX Disable Time
SYMBOL
V
BMTH
V
BTH
V
PMTH
t_
OFF
CONDITIONS
V
BIASMON
> V
BMTH
causes a fault
V
BIAS
referenced to V
CC
V
PWRMON
> V
PMTH
causes a fault
Time from rising edge of TX_DISABLE to
I
BIAS
= I
BIAS_OFF
and I
MOD
= I
MOD_OFF
(Note 6)
Time from rising edge of TX_DISABLE to
I
BIAS
and I
MOD
at 99% of steady state
(Note 6)
Time to set V
FAULT
= 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 V
FAULT
=
high; C
FAULT
< 20pF, R
FAULT
= 4.7kΩ
(Note 6)
Time from fault to I
BIAS
= I
BIAS_OFF
and
I
MOD
= I
MOD_OFF
(Note 6)
Time TX_DISABLE must be held high to
reset FAULT (Note 6)
MIN
0.7
-0.250
0.7
TYP
0.8
-0.2
0.8
1.8
MAX
0.9
-0.150
0.9
5
UNITS
V
V
V
µs
SAFETY FEATURES (see the
Typical Operating Characteristics
section)
TX Disable Negate Time
t_
ON
55
500
µs
Fault Reset Time
Power-On Time
t_
INIT
1
t_
INIT
2
60
60
200
200
ms
ms
Fault Assert Time
t_
FAULT
1.4
50
µs
Fault Delay Time
TX_DISABLE Reset
t_
FLTDLY
t_
RESET
1
5
1
µs
µs
Note 1:
Supply current measurements exclude I
BIAS
from the total current.
Note 2:
Tested with R
PEAK
= 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:
V
BIAS
< V
CC
- 0.7V.
Note 5:
Variation of bias monitor gain for any single part over the range of V
CC
, temperature, 3mA < I
BIAS
< 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
_______________________________________________________________________________________
3.2Gbps SFP VCSEL Driver with Diagnostic
Monitors
Typical Operating Characteristics
(V
CC
= +3.3V, R
TC
= 0Ω, PEAKSET open, measured electrically with a 50Ω load AC-coupled to OUT+, T
A
= +25°C, unless otherwise
noted.)
ELECTRICAL EYE
MAX3740A toc01
MAX3740A
ELECTRICAL EYE WITH PEAKING
MAX3740A toc02
ELECTRICAL EYE WITH MAX PEAKING
MAX3740A toc03
3.2Gbps, K28.5, 10mA MODULATION,
PEAKING OFF
3.2Gbps, K28.5, 10mA MODULATION,
R
PEAKSET
= 2.4kΩ
3.2Gbps, K28.5, 10mA MODULATION,
R
PEAKSET
= 500Ω
73mV/div
73mV/div
73mV/div
50ps/div
50ps/div
50ps/div
OPTICAL EYE
MAX3740A toc04
OPTICAL EYE
MAX3740A toc05
I
BIASMON
vs. BIAS CURRENT
1.6
1.4
I
BIASMON
(mA)
1.2
1.0
0.8
0.6
0.4
MAX3740A toc06
E
R
= 8.2dB, 2.125Gbps, K28.5,
850nm VCSEL, WITH 2.3GHz
O-TO-E CONVERTER
E
R
= 8.2dB, 2.5Gbps, K28.5,
850nm VCSEL SONET MASK
WITH +20% MARGIN
1.8
EMCORE SC-TOSA-8585-3420 VCSEL
68ps/div
EMCORE SC-TOSA-8585-3420 VCSEL
58ps/div
0.2
0
0
4
8
BIAS CURRENT (mA)
12
16
DETERMINISTIC JITTER
vs. MODULATION CURRENT
35
DETERMINISTIC JITTER (ps
P-P
)
30
25
20
15
10
5
0
0
5
I
MOD
(mA
P-P
)
10
15
MAX3740A toc07
RANDOM JITTER
vs. MODULATION CURRENT
MAX3740A toc08
TRANSITION TIME
vs. MODULATION CURRENT
MAX3740A toc09
40
7
6
RANDOM JITTER (ps
RMS
)
5
4
3
2
1
0
0
5
I
MOD
(mA
P-P
)
10
100
90
TRANSITION TIME (ps)
80
70
60
50
40
FALL
RISE
15
2
4
6
8
10
12
14
16
I
MOD
(mA
P-P
)
_______________________________________________________________________________________
5
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