19-3387; Rev 0; 8/04
1Gbps to 4.25Gbps Multirate VCSEL
Driver with Diagnostic Monitors
General Description
The MAX3795 is a high-speed VCSEL driver for small-
form-factor (SFF) and small-form-factor pluggable (SFP)
fiber optic transmitters. It contains a bias generator, a
laser modulator, and comprehensive safety features.
The automatic power control (APC) adjusts the laser
bias current to maintain average optical power over
changes in temperature and laser properties. The dri-
ver accommodates common-cathode and differential
configurations.
The MAX3795 operates up to 4.25Gbps. 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 MAX3795 interfaces with the Dallas
DS1856/DS1859 to meet SFF-8472 timing and diagnos-
tic requirements. The MAX3795 accommodates various
VCSEL packages, including low-cost TO-46 headers.
The MAX3795 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 (MSAs).
The MAX3795 is available in a compact 4mm
✕
4mm,
24-pin thin QFN package and operates over the -40°C
to +85°C temperature range. The MAX3795 is pin-for-
pin compatible with the MAX3740A and is available in
lead-free packages.
♦
3.3V ±10% Single Supply
♦
2mA to 15mA Modulation Current
♦
1mA to 15mA Bias Current
♦
52ps Transition Time
♦
8.4ps Deterministic Jitter
♦
Optional Peaking Current to Improve VCSEL Edge
Speed
♦
Supports Common-Cathode and Differential
Configuration
♦
Safety Circuits Compliant with SFF and SFP
MSAs
♦
Pin Compatible to MAX3740A
Features
♦
Supports All SFF-8472 Digital Diagnostics
MAX3795
Ordering Information
PART
MAX3795ETG
MAX3795ETG+
TEMP RANGE
PIN-PACKAGE
-40°C to +85°C 24 Thin QFN (4mm x 4mm)
-40°C to +85°C 24 Thin QFN (4mm x 4mm)
+Denotes
lead-free package.
Applications
PWRMON
Pin Configuration
COMP
REF
V
CC
Multirate (1Gbps to 4.25Gbps) SFP/SFF Modules
Gigabit Ethernet Optical Transmitters
Fibre-Channel Optical Transmitters
TOP VIEW
24
23
22
21
20
19
18
17
16
BIASMON
MD
GND
TX_DISABLE
IN+
IN-
FAULT
SQUELCH
1
2
3
4
5
6
10
11
12
BIAS
BIASSET
V
CC
OUT+
OUT-
GND
MAX3795
15
14
13
7
8
9
THIN QFN (4mm x 4mm)
EXPOSED PAD IS CONNECTED TO GND
________________________________________________________________
Maxim Integrated Products
PEAKSET
MODSET
V
CC
GND
TC1
TC2
1
For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.
1Gbps to 4.25Gbps Multirate VCSEL Driver
with Diagnostic Monitors
MAX3795
ABSOLUTE MAXIMUM RATINGS
Supply Voltage (V
CC
) ............................................-0.5V to +4.0V
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
+ 1V)
Current into FAULT ............................................ -1mA to +25mA
Current into OUT+, OUT- ....................................................60mA
Continuous Power Dissipation (T
A
= +85°C)
24-Pin Thin QFN
(derate 20.8mW/°C above +85°C).................................1354mW
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,
R
PEAK
= 1.18kΩ
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
Maximum Bias Pin Voltage
Bias Current
Accuracy of Programmed Bias
Current
V
BIAS-MAX
I
BIAS
∆BIAS
Referenced to V
CC
Minimum
Maximum
5mA
≤
I
BIAS
≤
15mA
1mA
≤
I
BIAS
≤
5mA
15
-8
-12
+8
+12
-0.65
1
V
mA
%
(Note 3)
(Note 3)
25
6
0.02
0.02
5.00
5.00
85
mV
P-P
mV
P-P
µs
µs
R
PULL
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
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
35
71
15
5
7
10
81
mA
MAX
UNITS
Supply Current
I
CC
2
_______________________________________________________________________________________
1Gbps to 4.25Gbps Multirate 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
Normal operation (FAULT = low)
C
COMP
= 0.047µF,
∆I
PD
/
∆I
LASER
= 0.02
V
PWRMON
/ (V
REF
- V
MD
)
Minimum
Maximum
2.4
1.75
85
f < 4GHz
f < 4GHz
Current into OUT+
R
LOAD
≤
50Ω
DC tested
TC1 is shorted to TC2
R
PEAKSET
= 10kΩ
R
PEAKSET
= 1kΩ
R
OUT
Single-ended resistance
42
-10
0.2
2
75
50
0
Temperature range 0°C to +70°C
t
R
t
F
50Ω load, no peaking,
5mA
≤
I
MOD
≤
15mA
50Ω load, no peaking,
5mA
≤
I
MOD
≤
15mA
-40°C to +85°C
+100°C
-40°C to +85°C
+100°C
+5000
49
58
56
64
79
72
ps
58
Minimum
Maximum
15
15
50
+10
100
12.7
11
2
115
1.85
-2
V
MD
V
REF
APC loop is closed
1
1.2
V
REF
-
0.2
1.8
0
0.7
90
2.15
2.45
0.25
+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
0.0875
0.085
-10
MIN
TYP
1.5
0.105
0.105
MAX
10
0.1375
0.125
+10
UNITS
µA
mA/mA
%
MAX3795
G
BIASMON
I
BIASMON
/ I
BIAS
(Notes 2, 4)
LASER MODULATOR (Load is 50Ω AC-Coupled to OUT+)
Differential Input Voltage
Input Common-Mode Voltage
Differential Input Resistance
Single-Ended Input Return Loss
Differential Input Return Loss
Modulation Current
Laser Modulation During Fault or
Squelch Active
Tolerance of Programmed
Modulation Current
Minimum Peaking Current
Maximum Peaking Current
Peaking Current Duration
Output Resistance
Minimum Programmable
Temperature Coefficient
Maximum Programmable
Temperature Coefficient
V
ID
V
CM
R
IN
S11
SDD11
I
MOD
I
MOD_OFF
V
P-P
V
Ω
dB
dB
mA
µA
P-P
%
mA
mA
ps
Ω
ppm/°C
ppm/°C
Modulation Transition Time
(Note 2)
_______________________________________________________________________________________
3
1Gbps to 4.25Gbps Multirate VCSEL Driver
with Diagnostic Monitors
MAX3795
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
Deterministic Jitter
Random Jitter
SYMBOL
DJ
RJ
CONDITIONS
-40°C to +85°C
5mA
≤
I
MOD
≤
15mA,
4.25Gbps, K28.5 (Notes 2, 5) +100°C
APC closed loop
APC open loop (Note 2)
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 2)
Time from rising edge of TX_DISABLE to
I
BIAS
and I
MOD
at 99% of steady state
(Note 2)
Time to set V
FAULT
= low after power-on or
after rising edge of TX_DISABLE (Note 2)
Time after power-on to transmitter-on with
TX_DISABLE low (Note 2)
Time from fault occurrence to V
FAULT
=
high; C
FAULT
< 20pF, R
FAULT
= 4.7kΩ
(Note 2)
Time from fault to I
BIAS
= I
BIAS_OFF
and
I
MOD
= I
MOD_OFF
; measured with a
continuously occurring fault (Note 2)
Time TX_DISABLE must be held high to
reset FAULT (Note 2)
0.7
-0.250
0.7
MIN
TYP
8.4
12.7
0.5
0.5
0.8
-0.2
0.8
1.8
0.9
0.9
-0.150
0.9
5
MAX
15.6
UNITS
ps
P-P
ps
RMS
SAFETY FEATURES (see the
Typical Operating Characteristics)
High-Current Fault Threshold
V
BIAS
Fault Threshold
Power-Monitor Fault Threshold
TX Disable Time
V
BMTH
V
BTH
V
PMTH
t_
OFF
V
V
V
µs
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
t_
FLTDLY
1
5
µs
TX_DISABLE Reset
t_
RESET
1
µs
Note 1:
Supply current measurements exclude I
BIAS
from the total current.
Note 2:
AC characteristics guaranteed by design and characterization.
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:
Variation of bias monitor gain for any single part over the range of V
CC
, temperature, 3mA < I
BIAS
< 15mA.
Note 5:
Deterministic jitter measured at 4.25Gbps with a K28.5 pattern (00111110101100000101).
4
_______________________________________________________________________________________
1Gbps to 4.25Gbps Multirate VCSEL Driver
with Diagnostic Monitors
MAX3795
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 DIAGRAM
MAX3795 toc01
ELECTRICAL EYE DIAGRAM
MAX3795 toc02
OPTICAL EYE DIAGRAM
MAX3795 toc03
4.25Gbps, K28.5, 10mA MODULATION,
PEAKING OFF
1Gbps, K28.5, 10mA MODULATION,
R
PEAKSET
= 1.4kΩ
1Gbps, K28.5, -3dBm, 850nm VCSEL
ADVANCED OPTICAL COMPONENTS,
1
HFE4191-541
75mV/div
75mV/div
2
3
40ps/div
152ps/div
135ps/div
OPTICAL EYE DIAGRAM
MAX3795 toc04
OPTICAL EYE DIAGRAM
MAX3795 toc05
I
BIASMON
vs. BIAS CURRENT
1.6
1.4
I
BIASMON
(mA)
1.2
1.0
0.8
0.6
0.4
0.2
0
MAX3795 toc06
4.25Gbps, K28.5, -7dBm, 850nm VCSEL,
ADVANCED OPTICAL COMPONENTS
HFE4191-541
3.125Gbps, K28.5, -7dBm, 850nm VCSEL,
ADVANCED OPTICAL COMPONENTS
HFE4191-541
1.8
34ps/div
50ps/div
0
4
8
BIAS CURRENT (mA)
12
16
DETERMINISTIC JITTER
vs. MODULATION CURRENT
MAX3795 toc07
RANDOM JITTER
vs. MODULATION CURRENT
MAX3795 toc08
TRANSITION TIME
vs. MODULATION CURRENT
MEASURED FROM 20%
FALL TIME
MAX3795 toc09
40
35
DETERMINISTIC JITTER (ps
P-P
)
30
25
20
15
10
5
0
0
2
4
6
8
3.5
3.0
RANDOM JITTER (ps
RMS
)
2.5
2.0
1.5
1.0
0.5
0
I
BIAS
= 5mA
70
60
TRANSITION TIME (ps)
50
40
30
20
10
RISE TIME
10 12 14 16 18 20
0
2
4
6
8
10 12 14 16 18 20
0
2
4
6
8
10
12
14
MODULATION CURRENT (mA
P-P
)
MODULATION CURRENT (mA
P-P
)
MODULATION CURRENT (mA)
_______________________________________________________________________________________
5
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