Rainbow Electronics MAX3795 User Manual
General Description
The MAX3795 is a high-speed VCSEL driver for smallform-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 driver 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 compensation is provided to keep the optical extinction
ratio within specifications over the operating temperature range. The MAX3795 interfaces with the Dallas
DS1856/DS1859 to meet SFF-8472 timing and diagnostic 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-forpin compatible with the MAX3740A and is available in
lead-free packages.
Applications
Multirate (1Gbps to 4.25Gbps) SFP/SFF Modules
Gigabit Ethernet Optical Transmitters
Fibre-Channel Optical Transmitters
Features
♦ Supports All SFF-8472 Digital Diagnostics
♦ 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
MAX3795
1Gbps to 4.25Gbps Multirate VCSEL
Driver with Diagnostic Monitors
________________________________________________________________ Maxim Integrated Products 1
Ordering Information
19-3387; Rev 0; 8/04
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.
PART
TEMP RANGE
PIN-PACKAGE
MAX3795ETG
24 Thi n QFN ( 4m m x 4m m )
MAX3795ETG+
24 Thi n QFN ( 4m m x 4m m )
24
23
22
21
20
19
PWRMON
REF
MD
COMP
VCCBIASMON
7
8
9
10
11
12
V
CC
TC1
TC2
GND
MODSET
PEAKSET
13
14
15
16
17
18
EXPOSED PAD IS CONNECTED TO GND
GND
OUT-
OUT+
V
CC
BIASSET
BIAS
6
5
4
3
2
1
SQUELCH
FAULT
IN-
IN+
TX_DISABLE
GND
MAX3795
THIN QFN (4mm x 4mm)
TOP VIEW
Pin Configuration
+Denotes lead-free package.
-40°C to +85°C
-40°C to +85°C
MAX3795
1Gbps to 4.25Gbps Multirate VCSEL Driver
with Diagnostic Monitors
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
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.
Supply Voltage (VCC) ............................................-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 (VCC+ 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
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
CONDITIONS
UNITS
I
MOD
= 2mA
P-P
35
SQUELCH set low,
TX_DISABLE set low,
peaking is not used
(Note 1)
I
MOD
= 15mA
P-P
71 81
Additional current when peaking is used,
R
PEAK
= 1.18kΩ
15
I
CC
Additional current when SQUELCH is high 5 10
Supply Current
Total current when TX_DISABLE is high 7
mA
FAULT OUTPUT
Output High Voltage V
OH
R
LOAD
= 10kΩ to 2.97V 2.4 V
Output Low Voltage V
OL
R
LOAD
= 4.7kΩ to 3.63V 0.4 V
TX_DISABLE INPUT
Input Impedance R
PULL
4.7 8
kΩ
Input High Voltage V
IH
2.0 V
Input Low Voltage V
IL
0.8 V
Power-Down Time
The time for I
CC
to reach I
CC-SHDN
when
TX_DISABLE transitions high
50 µs
SQUELCH
Squelch Threshold 25 85
mV
P-P
Squelch Hysteresis 6
mV
P-P
Time to Squelch Data (Note 3)
µs
Time to Resume from Squelch (Note 3)
µs
BIAS GENERATOR
Maximum Bias Pin Voltage
Referenced to V
CC
V
Minimum 1
Bias Current I
BIAS
Maximum 15
mA
5mA ≤ I
BIAS
≤ 15mA -8 +8
Accuracy of Programmed Bias
Current
∆BIAS
1mA ≤ I
BIAS
≤ 5mA -12
%
SYMBOL
MIN TYP MAX
I
CC-SHDN
V
BIAS-MAX
0.02 5.00
0.02 5.00
-0.65
10.0
+12
MAX3795
1Gbps to 4.25Gbps Multirate VCSEL Driver
with Diagnostic Monitors
_______________________________________________________________________________________ 3
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
MIN
TYP
MAX
UNITS
Bias Current During Fault
Current out of the BIAS pin 1.5 10 µA
BIASMON Gain
I
BIASMON
/ I
BIAS
mA/mA
BIASMON Stability (Notes 2, 4) -10
%
AUTOMATIC POWER CONTROL (APC)
MD Nominal Voltage V
MD
APC loop is closed 1
0.2
2V
Voltage at REF V
REF
1.2 1.8 2.2 V
MD Voltage During Fault 0V
MD Input Current Normal operation (FAULT = low) -2 0.7 +2 µA
APC Time Constant C
COMP
= 0.047µF, ∆IPD / ∆I
LASER
= 0.02 90 µs
PWRMON Nominal Gain V
PWRMON
/ (V
REF
- VMD)
V/V
LASER MODULATOR (Load is 50Ω AC-Coupled to OUT+)
Minimum
Differential Input Voltage V
ID
Maximum 2.4
V
P-P
Input Common-Mode Voltage V
CM
V
Differential Input Resistance R
IN
85 100
Ω
Single-Ended Input Return Loss S11 f < 4GHz
dB
Differential Input Return Loss
f < 4GHz 11 dB
Minimum 2
Modulation Current I
MOD
Current into OUT+
R
LOAD
≤ 50Ω
Maximum 15
mA
Laser Modulation During Fault or
Squelch Active
DC tested 15 50
µA
P-P
Tolerance of Programmed
Modulation Current
TC1 is shorted to TC2 -10
%
Minimum Peaking Current R
PEAKSET
= 10kΩ 0.2 mA
Maximum Peaking Current R
PEAKSET
= 1kΩ 2mA
Peaking Current Duration 75 ps
Output Resistance
R
OUT
Single-ended resistance 42 50 58 Ω
Minimum Programmable
Temperature Coefficient
0
ppm/°C
Maximum Programmable
Temperature Coefficient
Temperature range 0°C to +70°C
ppm/°C
49 72
t
R
50Ω load, no peaking,
5mA ≤ I
MOD
≤ 15mA
+100°C 58
56 79
Modulation Transition Time
(Note 2)
t
F
50Ω load, no peaking,
5mA ≤ I
MOD
≤ 15mA
+100°C 64
ps
I
BIAS_OFF
G
BIASMON
SDD11
I
MOD_OFF
1mA < I
3mA ≤ I
< 3mA 0.0875 0.105 0.1375
BIAS
< 15mA 0.085 0.105 0.125
BIAS
V
REF
1.85 2.15 2.45
- 40°C to + 85° C
- 40°C to + 85° C
1.75
12.7
+5000
+10
-
0.25
115
+10
MAX3795
1Gbps to 4.25Gbps Multirate VCSEL Driver
with Diagnostic Monitors
4 _______________________________________________________________________________________
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
CONDITIONS
UNITS
8.4
Deterministic Jitter DJ
5m A ≤ I
M OD
≤ 15m A,
+100°C
ps
P-P
APC closed loop 0.5
Random Jitter RJ
APC open loop (Note 2) 0.5 0.9
ps
RMS
SAFETY FEATURES (see the Typical Operating Characteristics)
High-Current Fault Threshold V
BMTH
V
BIASMON
> V
BMTH
causes a fault 0.7 0.8 0.9 V
V
BIAS
Fault Threshold V
BTH
V
BIAS
referenced to V
CC
V
Power-Monitor Fault Threshold V
PMTH
V
PWRMON
> V
PMTH
causes a fault 0.7 0.8 0.9 V
TX Disable Time t_
OFF
Time from rising edge of TX_DISABLE to
I
BIAS
= I
BIAS_OFF
and I
MOD
= I
MOD_OFF
(Note 2)
1.8 5 µs
TX Disable Negate Time t_
ON
Time from rising edge of TX_DISABLE to
I
BIAS
and I
MOD
at 99% of steady state
(Note 2)
55 500 µs
Fault Reset Time t_
INIT
1
Time to set V
FAULT
= low after power-on or
after rising edge of TX_DISABLE (Note 2)
60 200 ms
Power-On Time t_
INIT
2
Time after power-on to transmitter-on with
TX_DISABLE low (Note 2)
60 200 ms
Fault Assert Time
Time from fault occurrence to V
FAULT
=
high; C
FAULT
< 20pF, R
FAULT
= 4.7kΩ
(Note 2)
1.4 50 µs
Fault Delay Time
Time from fault to I
BIAS
= I
BIAS_OFF
and
I
MOD
= I
MOD_OFF
; measured with a
continuously occurring fault (Note 2)
15µs
TX_DISABLE Reset
Time TX_DISABLE must be held high to
reset FAULT (Note 2)
1µs
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).
SYMBOL
4.25G b p s, K28.5 ( N otes 2, 5)
- 40°C to + 85° C
MIN TYP MAX
15.6
12.7
-0.250 -0.2 -0.150
t_
FAULT
t_
FLTDLY
t_
RESET
MAX3795
1Gbps to 4.25Gbps Multirate VCSEL Driver
with Diagnostic Monitors
_______________________________________________________________________________________ 5
ELECTRICAL EYE DIAGRAM
MAX3795 toc01
40ps/div
75mV/div
4.25Gbps, K28.5, 10mA MODULATION,
PEAKING OFF
ELECTRICAL EYE DIAGRAM
MAX3795 toc02
152ps/div
75mV/div
1Gbps, K28.5, 10mA MODULATION,
R
PEAKSET
= 1.4kΩ
OPTICAL EYE DIAGRAM
MAX3795 toc03
135ps/div
1
2
3
1Gbps, K28.5, -3dBm, 850nm VCSEL
ADVANCED OPTICAL COMPONENTS,
HFE4191-541
OPTICAL EYE DIAGRAM
MAX3795 toc04
34ps/div
4.25Gbps, K28.5, -7dBm, 850nm VCSEL,
ADVANCED OPTICAL COMPONENTS
HFE4191-541
OPTICAL EYE DIAGRAM
MAX3795 toc05
50ps/div
3.125Gbps, K28.5, -7dBm, 850nm VCSEL,
ADVANCED OPTICAL COMPONENTS
HFE4191-541
I
BIASMON
vs. BIAS CURRENT
MAX3795 toc06
BIAS CURRENT (mA)
I
BIASMON
(mA)
1284
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
0
016
DETERMINISTIC JITTER
vs. MODULATION CURRENT
MAX3795 toc07
MODULATION CURRENT (mA
P-P
)
DETERMINISTIC JITTER (ps
P-P
)
5
10
15
20
25
30
35
40
0
024681012 14 16 18 20
RANDOM JITTER
vs. MODULATION CURRENT
MAX3795 toc08
MODULATION CURRENT (mA
P-P
)
RANDOM JITTER (ps
RMS
)
0.5
1.0
1.5
2.0
2.5
3.0
3.5
0
02468101214 16 18 20
I
BIAS
= 5mA
TRANSITION TIME
vs. MODULATION CURRENT
MAX3795 toc09
MODULATION CURRENT (mA)
TRANSITION TIME (ps)
10
20
30
40
50
60
70
024681012 14
MEASURED FROM 20%
FALL TIME
RISE TIME
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.)
Loading...