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MAX3667ECJ
Datasheet (Maxim)
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Datasheet MAX3667E-D, MAX3667ECJ Datasheet (Maxim)

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________________General Description
The MAX3667 is a complete, +3.3V laser driver with automatic power control (APC), designed for SDH/ SONET applications up to 622Mbps. It accepts differ­ential PECL inputs, provides single-ended bias and modulation currents, and operates over a -40°C to +85°C temperature range.
The APC function, which incorporates a monitor photo­diode, an external resistor, and two external capacitors, maintains constant laser output power. Two current monitors provide high-speed signals that are directly proportional to the bias and modulation currents. Additional features include disable/enable control and a slow-start feature with a minimum turn-on time of 50ns. The MAX3667 is available in die form and in a 32-pin TQFP package.
________________________Applications
622Mbps SDH/SONET Access Nodes Laser Driver Transmitters Section Repeaters
____________________________Features
♦ Single +3.3V or +5.0V Operation ♦ Automatic Average Power Control ♦ Bias Current and Modulation Current Monitor
Outputs
♦ TTL-Compatible Disable Input ♦ Temperature-Compensated Reference ♦ PECL-Compatible Data Inputs
MAX3667
+3.3V, 622Mbps SDH/SONET Laser Driver
with Automatic Power Control
________________________________________________________________
Maxim Integrated Products
1
MAX3667
MAX3691
130Ω 130Ω
50Ω
82Ω 82Ω
PECL
1µF
DISABLE
COMP
C
COMP
BIASMON MODMON APCSET
MD
MONITOR
DIODE
+3.3V
LASER DIODE
IMOD
R
FILT
22Ω
R
DAMP
4.7Ω
100Ω
470nH
4:1
SERIALIZER
WITH
CLOCK GEN
1µF
0.01µF
0.1µF
0.1µF
IBIAS
MODSETGND
IN+ IN-
BIASSET APC
C
APC
1nF
V
CC
+3.3V
____________________________________________________Typical Operating Circuit
19-1311; Rev 1; 3/98
PART
MAX3667ECJ MAX3667E/D -40°C to +85°C
-40°C to +85°C
TEMP. RANGE PIN-PACKAGE
32 TQFP Dice*
EVALUATION KIT
AVAILABLE
_______________Ordering Information
Pin Configuration appears at end of data sheet.
*
Dice are designed to operate from -40°C to +85°C but are
tested and guaranteed only at T
j
= +25°C.
For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 408-737-7600 ext. 3468.
MAX3667
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control
2 _______________________________________________________________________________________
ABSOLUTE MAXIMUM RATINGS
DC ELECTRICAL CHARACTERISTICS
(VCC= +3.3V ±5%, TA= -40°C to +85°C, unless otherwise noted.) (Notes 1, 2)
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 +7.0V
Current into IBIAS..............................................-50mA to 350mA
Current into IMOD .............................................-50mA to 200mA
Current into MD ..................................................................±7mA
Voltage at APC, MODMON,
BIASMON, COMP....................................-0.5V to (V
CC
+ 0.5V)
Voltage at IN+, IN-, DISABLE, MODSET,
BISASSET, APCSET, PULLUP..................-0.5V to (V
CC
+ 0.5V)
Continuous Power Dissipation (TA= +85°C)
TQFP (derate 11.1mW/°C above +85°C)......................721mW
Operating Temperature Range ...........................-40°C to +85°C
Operating Junction Temperature Range (die) ..-55°C to +175°C
Processing Temperature (die).........................................+400°C
Storage Temperature Range.............................-65°C to +160°C
Lead Temperature (soldering, 10sec).............................+300°C
VIN= 1.82V
VIN= 2.14V
Disable = high
(Note 5)
R
APCSET
= 33.2kΩ
Closed loop (Note 4)
R
APCSET
= 2kΩ
R
MODSET
= 33.2kΩ (Note 10)
R
MODSET
= 2kΩ (Note 10)
R
MODSET
= 33.2kΩ, open loop (Note 8)
R
MODSET
= 2kΩ, open loop (Note 8)
R
BIASSET
= 33.2kΩ
R
BIASSET
= 2kΩ
R
BIASSET
= 2kΩ, closed loop (Notes 4, 9)
R
BIASSET
= 33.2kΩ, open loop (Note 8)
Disable = high
Disable = high or low
R
MODSET
= 2kΩ (Note 10)
R
BIASSET
= 2kΩ, open loop (Note 8)
R
BIASSET
= 2kΩ
CONDITIONS
V2.0V
DIH
TTL Disable High Voltage
µA2 10I
IH
PECL Input Low Current
µA4.5 10I
IH
PECL Input High Current
V1.82V
IL
PECL Input Low Voltage
V2.14V
IH
PECL Input High Voltage
164 205 250
A/A
135 170 205
A
I
I
APCSET
to IBIAS Gain
152 190 230
A/A
152 190 230
A
I
I
MODSET
to I
QMOD
Gain
128 160 195
A/A
145 170 200
A
I
I
BIASSET
to IBIAS Gain
A/A26 33 40A
I
MODMON to I
QMOD
Gain
A/A30 38 46A
I
BIASMON to IBIAS Gain
µA5 250I
BIAS
Bias Off Current
mA5 90I
BIAS
mA112 133I
CC
Supply Current (Note 3) Bias Current Range
1100
ppm/°C
1100
Modulation Current Stability
480
1000
µA20 250I
BIAS
Modulation Off Current
Ω26 31 35R
PULL-UP
Internal Pull-Up Resistor (Note 6)
V0.91 1.01 1.11V
REF
Reference Voltage (Note 7)
ppm/°C
500
Bias Current Stability
UNITSMIN TYP MAXSYMBOLPARAMETER
µA4I
DIL
TTL Disable Low Current
µA1I
DIH
TTL Disable High Current
V0.8V
DIL
TTL Disable Low Voltage
MAX3667
+3.3V, 622Mbps SDH/SONET Laser Driver
with Automatic Power Control
_______________________________________________________________________________________ 3
Note 1: Dice are tested at TA= +27°C. Note 2: Minimum voltage at IBIAS = V
CC
- 1.6V.
Note 3: The sum of the currents flowing into V
CC
and PULLUP with R
BIASSET
= R
MODSET
= R
APCSET
= 2kΩ, IN+ = 1.82V,
IN- = 2.14V.
Note 4: APC is connected to BIASSET for closed-loop operation. Note 5: Bias current range is guaranteed by the I
BIASSET
to IBIAS gain test.
Note 6: R
PULL-UP
is connected between IMOD and PULLUP.
Note 7: V
REF
is the voltage on BIASSET, MODSET, or APCSET with R
BIASSET
= R
MODSET
= R
APCSET
= 2kΩ.
Note 8: APC is disconnected from BIASSET for open-loop operation. Note 9: Bias current stability is guaranteed by design and characterization. Note 10: I
QMOD
is the current flowing into the collector of Q
MOD
(Figure 1).
Note 11: AC parameters are guaranteed by design and characterization. Note 12: Modulation current range is guaranteed by the I
MODSET
to I
QMOD
gain test.
Note 13: Input signal is a 155Mbps 1-0 pattern. PWD = [(width of wider pulse) - (width of narrower pulse)] / 2.
Disable = high
Disable = high
Closed loop (Note 4)
R
APCSET
= 33.2kΩ
R
APCSET
= 2kΩ
VIN= 3.52V
VIN= 3.84V
R
MODSET
= 33.2kΩ (Note 10)
R
MODSET
= 2kΩ (Note 10)
R
BIASSET
= 2kΩ
R
MODSET
= 2kΩ (Note 10)
R
BIASSET
= 2kΩ
R
BIASSET
= 33.2kΩ
CONDITIONS
µA8I
IH
PECL Input Low Current
µA9I
IH
PECL Input High Current
V3.52V
IL
PECL Input Low Voltage
V3.84V
IH
PECL Input High Voltage
µA32 250Modulation Off Current
µA2 250
mA134 160I
CC
Supply Current (Note 3) Bias Off Current
145 182 220
A/A
132 166 200
A
I
I
APCSET
to IBIAS Gain
188 230 285
A/A
168 240 315
A
I
I
MODSET
to I
QMOD
Gain
A/A38A
I
BIASMON to IBIAS Gain
A/A26 33 40A
I
MODMON to I
QMOD
Gain
A/A
145 180 220
A
I
I
BIASSET
to IBIAS Gain
143 180 215
UNITSMIN TYP MAXSYMBOLPARAMETER
VCC= 5.0V ±5%, 20% to 80%
VCC= 3.3V ±5%, 20% to 80%
R
FILT
= 22Ω, R
DAMP
= 0Ω (Note 12)
VCC= 3.3V ±5%, 20% to 80% VCC= 5.0V ±5%, 20% to 80%
R
FILT
= 22Ω, R
DAMP
= 0Ω (Note 13)
CONDITIONS
205 400
ps
270 450
t
r
mA5 60I
MOD
Modulation Current Range Output Rise Time
ps
425 650
t
f
Output Fall Time
315 600
%±10Output Aberrations
ps70PWDPulse-Width Distortion
UNITSMIN TYP MAXSYMBOLPARAMETER
DC ELECTRICAL CHARACTERISTICS
(VCC= +5.0V ±5%, TA= -40°C to +85°C, unless otherwise noted.) (Notes 1, 2)
AC ELECTRICAL CHARACTERISTICS
(VCC= +3.3V ±5%, TA= -40°C to +85°C, R
LOAD
= 10Ω, unless otherwise noted.) (Notes 2, 11)
MAX3667
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control
4 _______________________________________________________________________________________
__________________________________________Typical Operating Characteristics
(TA = +25°C, VCC= +3.3V, unless otherwise noted.)
161ps/div
52mV/
div
EYE DIAGRAM
(622Mbps, 1300nm LASER,
470MHz FILTER)
MAX3667-01
2
23
- 1PRBS
I
MOD
= 15mA
DIFF. INPUT = 640mVp-p
161ps/div
20mV/
div
EYE DIAGRAM
(622Mbps, 10Ω LOAD)
MAX3667-02
2
23
- 1PRBS
I
MOD
= 15mA
DIFF. INPUT = 1.7Vp-p
10ps/div
5mV/
div
OUTPUT JITTER
(622Mbps, 10Ω LOAD)
MAX3667-03
I
MOD
= 20mA DIFF. INPUT = 1.7Vp-p ∆RMS = 3.2ps
180 160 140
0
200
1k
40k
I
BIAS
vs. R
BIASSET
60 40 20
120 100
80
MAX3667-04
R
BIASSET
(Ω)
I
BIAS
(mA)
10k
V
IBIAS
= 1.7V
10Ω LOAD
0
30 20 10
60 50 40
70
80
1k 10k 40k
I
BIAS
vs. R
APCSET
(VARYING MONITOR-TO-LASER
CURRENT GAIN)
MAX3667-07
R
APCSET
(Ω)
I
BIAS
(mA)
GAIN = 90
GAIN = 60
GAIN = 30
GAIN = 15
160 140 120
0
I
QMOD
vs. R
MODSET
60 40 20
100
80
MAX3667-05
R
MODSET
(Ω)
I
QMOD
(mA)
200
1k
40k10k
10Ω LOAD
0
0.4
0.3
0.2
0.1
0.7
0.6
0.5
0.8
0.9
1k 10k 40k
IMD vs. R
APCSET
R
APCSET
(Ω)
I
MD
(mA)
APC LOOP CLOSED R
BIASSET
= 2kΩ
R
MODSET
= 2kΩ MONITOR-TO-LASER CURRENT GAIN = 82
MAX3667-06
0
20
60
40
100
80
120
-40 -15 10 35 60 85
PULSE-WIDTH DISTORTION
vs. TEMPERATURE
MAX3667toc08
PULSE-WIDTH DISTORTION (ps)
TEMPERATURE (°C)
VCC = +3.3V
VCC = +5.0V
I
MOD
= 30mA
0
20
60
40
100
80
120
10 20 30 40 50 5545352515 60
PULSE-WIDTH DISTORTION
vs. I
MOD
MAX3667toc09
PULSE-WIDTH DISTORTION (ps)
I
MOD
(mA)
VCC = +3.3V
VCC = +5.0V
MAX3667
+3.3V, 622Mbps SDH/SONET Laser Driver
with Automatic Power Control
_______________________________________________________________________________________ 5
10
1k
100
100k
10k
100G
10G
1G
1pF 100pF 10nF 1µF 100µF
APC BANDWIDTH vs. C
COMP
(VARYING MONITOR-TO-LASER
CURRENT GAIN)
MAX3667-10
C
COMP
APC BANDWIDTH (Hz)
MEASURED RESULTS
GAIN = 90
GAIN = 30
GAIN = 60
SIMULATED RESULTS
____________________________Typical Operating Characteristics (continued)
(TA = +25°C, VCC= +3.3V, unless otherwise noted.)
80
100
90
120 110
130
160
140
150
-40 -15 10 35 60 85
SUPPLY CURRENT vs. TEMPERATURE
MAX3667-11
TEMPERATURE (°C)
I
SUPPLY
(mA)
EXCLUDING I
BIAS
R
MODSET
= R
BIASSET
= 2kΩ
10Ω LOAD
VCC = +5.0V
VCC = +3.3V
______________________________________________________________Pin Description
NAME FUNCTION
1, 2, 23, 24 V
CC
Supply Voltage Input
3, 6, 8, 13, 14,
15, 18, 20, 22
GND Ground
PIN
4 IN+ Positive PECL-Compatible Input 5 IN- Negative PECL-Compatible Input
11 APC Feedback Current for Closed-Loop Laser-Diode Bias Control
10 MODSET Adjustment for Laser-Diode Modulation Current
9, 26, 28, 31 N.C. No Connection
7 DISABLE Disable Input. High = disable, TTL-compatible input.
25 MD Input for PIN Monitor Diode Current
19, 21 IMOD Laser-Diode Modulation Current
17 PULLUP VCCSupply for Internal 31Ω Pull-Up Resistor
16 IBIAS Laser-Diode DC Bias Current
12 BIASSET Open-Loop Adjustment for Laser-Diode Bias Current
32 COMP External Compensation Capacitor for Closed-Loop Laser-Diode Bias Current Control Stability
30 MODMON IMOD Current Monitor (gain = 1/33 I
QMOD
). Open PNP collector, connect to ground if not used.
29 BIASMON IBIAS Current Monitor (gain = 1/38 IBIAS). Open PNP collector, connect to ground if not used.
27 APCSET Closed-Loop Adjustment for Laser-Diode Bias Current
MAX3667
_______________Detailed Description
Low-voltage operation of laser diodes and optical transmitters produces stringent headroom conditions for laser drivers. Fast changes in modulation current produce large inductive voltage spikes, creating device saturation problems. Therefore, for +3.3V operation, the MAX3667’s modulation current should be AC coupled to the cathode of a laser diode. The recommended DC blocking capacitor value is 1µF. A simplified block dia­gram of the modulation driver is shown in Figure 1.
The IMOD pin is internally biased through a 31Ω pull-up resistor. This design decouples the headroom associat­ed with the modulation driver from the forward voltage drop of the laser diode, allowing the circuit to tolerate greater di/dt voltage transients. The design of the MAX3667 assumes a maximum DC forward-voltage drop of 1.6V across the laser diode. Bias current is DC coupled to the laser diode separately at the IBIAS out­put. In most applications, some small amount of resis­tance should be added in series with the DC blocking capacitor to help damp out the aberrations created by parasitic elements.
Automatic Power Control
The automatic power control (APC) feature allows an optical transmitter to maintain constant power, despite changes in laser efficiency due to temperature and aging. The APC loop requires the use of a PIN monitor photodiode, which generates a current proportional to the laser diode output power. A scaled version of the current flowing into the MD pin is compared to a scaled version of the current flowing out of the APCSET pin. When these currents are of equal value, the inputs of the operational transconductance amplifier (OTA) are balanced, and COMP is forced to approximately 1V.
When the average value of the monitor diode current exceeds the value established by the APCSET current, the COMP voltage is forced lower. If the average value of the monitor diode current is less than the value established by the APCSET current, the COMP node voltage is forced higher. The output of the OTA (the APC pin), when connected directly to BIASSET (closed­loop condition), is used as an error signal to adjust the bias current flowing into BIASSET. The maximum OTA output current is approximately ±250µA.
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control
6 _______________________________________________________________________________________
MAX3667
INPUT
(MODULATION)
31Ω
V
CC
V
CC
V
CC
INPUT (BIAS)
LASER DIODE
R
FILT
22Ω
R
DAMP
4.7Ω
0.01µF
1µF
MODMON
IBIASIMOD
Q
MOD
I
QMOD
BIASMON
Figure 1. Simplified Modulation Driver Block Diagram
Closed-loop operation requires the user to establish three internal currents with external resistors placed between ground and the BIASSET, MODSET, and APC­SET pins. See the
Design Procedures
section for guide-
lines on selecting these resistor values.
Open-Loop Operation
If desired, the MAX3667 is fully operational without the use of the APC loop. In these types of applications, the laser diode current is set solely by the external resistors connected to the BIASSET and MODSET pins. See the
Design Procedures
section for instructions on setting
up the MAX3667 for open-loop operation.
Disable Control
The MAX3667 provides a single-ended TTL-compatible disable control pin. The IBIAS, IMOD, and APCSET cur­rents are disabled when the voltage on this pin is set high. However, the internal voltage reference and other sections of the MAX3667 remain active to ensure pre­dictable operation and faster enable response times. The disable response time is approximately 25ns.
Temperature Considerations
The MAX3667 contains a voltage reference that is fully temperature compensated. This reference is used throughout the circuit, as well as for programming the
MAX3667
+3.3V, 622Mbps SDH/SONET Laser Driver
with Automatic Power Control
_______________________________________________________________________________________ 7
MAX3667
MODSET
1.0V 1.0V 1.0V
IN+
DISABLE
IBIAS
MD
PULLUP
IMOD
COMP
APC
31Ω
IN-
MODMON BIASSET BIASMON APCSET
1.0V
OTA
REFERENCE
Figure 2. Block Diagram
MAX3667
bias, modulation, and monitor diode current levels. Where necessary, the reference is adjusted by a VBEvoltage to cancel thermal errors created by the BIASSET, MODSET, and APCSET current mirrors. This ensures that the IBIAS and IMOD currents are nearly constant over temperature with open-loop operation. With the APC loop closed, this reference helps maintain a constant average MD current (and thus a constant average laser output power) over temperature.
Bias and Modulation Current Monitors
The BIASMON and MODMON analog output monitors provide current levels that are directly proportional to the IBIAS and IMOD currents levels. These currents can be used in conjunction with other external circuitry to supervise the performance of the laser driver system without adding parasitics or reducing system perfor­mance. The gains associated with these pins, relative to IBIAS and I
QMOD
, are approximately 1/38 (for
BIASMON) and approximately 1/33 (for MODMON). In addition to a scaled copy of the modulation current,
the MODMON current contains a DC offset current used internally to keep the driver transistors functioning at high speed, even with low modulation levels. This current is not precisely controlled and should be ignored when using the MODMON feature.
__________________Design Procedure
Programming the Modulation Current
In addition to being a function of RMODSET, IMOD is also dependent on the values of the series damp­ing resistor (R
DAMP
), the shunt compensation resis-
tance (R
FILT
), and the resistance of the laser diode
(Figure 1). If I
QMOD
represents the total current flowing into the
collector of Q
MOD
, then the modulation current into the
laser diode can be represented by the following:
I
QMOD
= (AI)(I
MODSET
)
AI= I
MODSET
to I
MOD
Gain
Assuming R
FILT
= 22Ω, R
DAMP
= 4.7Ω, and r
LASER
=
4Ω, then this equation is simplified to:
I
MOD
= I
QMOD
(0.6)
For R
DAMP
= 4.7Ω, R
FILT
= 22Ω, and a laser resistance
of approximately 4Ω, refer to the I
QMOD
Current vs.
R
MODSET
graph in the
Typical Operating Characteristics
and select the value of R
MODSET
that corresponds to
the required current at +25°C.
Programming the Bias Current
(open loop)
When operating the MAX3667 without APC, program the bias-current output by adjusting the BIASSET resistor. To select this resistor, determine the desired bias cur­rent required at +25°C. Refer to the IBIAS Current vs. R
BIASSET
graph in the
Typical Operating Characteristics,
and select the value of R
BIASSET
that corresponds to the
required current.
Programming the
Automatic Power Control (APC)
When using the MAX3667’s APC feature, program the bias-current output by adjusting the APCSET resistor. To select this resistor, determine the desired monitor current to be maintained over temperature. Refer to the MD Current vs. R
APCSET
graph in the
Typical Operating
Characteristics
, and select the value of R
APCSET
that
corresponds to the required current. When using the APC feature, be sure to connect the
APC pin directly to BIASSET (see the
Typical Operating
Circuit
). In this mode, the bias-current output level is no longer controlled by the BIASSET resistor. The APCSET resistor is now controlling the output bias level. Under closed-loop conditions, R
BIASSET
assures that the feed­back current range is properly centered. It is recom­mended that R
BIASSET
be chosen to equal R
APCSET
during closed-loop operation.
Pattern-Dependent Jitter
To reduce pattern-dependent-jitter (PDJ) effects, two external compensation capacitors are required to ensure that the control loop responds slowly to changes in laser efficiency. The overall time constant of the APC loop is set by the value of these capacitors, by the transfer ratio between the laser diode current and the monitor diode current, and by the MAX3667’s open­loop gain.
C
COMP
must be placed between the COMP pin and
ground; C
APC
must be placed between the APC pin
and ground (see the
Typical Operating Circuit
). For 622Mbps SDH/SONET applications, the recom­mended values of C
COMP
and C
APC
are 1µF and 1nF,
respectively.
I = I
31 R
31 R + R + r
MOD QMOD
FILT
FILT DAMP LASER
Ω
Ω
( )
 
 
 
 
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control
8 _______________________________________________________________________________________
Since the PDJ will change with changes in loop gain, it is important to choose capacitor values that are as large as is physically possible. Since each capacitor represents a different pole, for stability reasons, C
APC
should be kept substantially smaller than C
COMP
. It is
recommended that the value of C
APC
be set 1000 times
smaller than C
COMP
.
The time constant associated with the DC blocking capacitor on IMOD can also have an effect on PDJ. It is important that this time constant produce minimum droop for long consecutive bit streams.
Referring to Figure 3, the droop resulting from long time periods without transitions can be represented by the following equation:
APC operation assures that the discharge level for τ is P
AVG
. An overall droop of 6% relative to P
p-p
equates
to a 12% droop relative to P
AVG
. To ensure a droop of
less than 12% (6% relative to P
p-p
), this equation can
be solved for τ as follows:
If t1equals 100 consecutive unit intervals without a transition, then the time constant associated with the DC blocking capacitor needs to be longer than:
τAC≥ RACCAC= 7.8 (100 bits) (1.6ns/bit) = 1.25µs
The estimated value of RACis:
RAC= 31Ω  R
FILT
 (R
DAMP
+ r
LASER
)
Assuming R
FILT
= 22Ω, R
DAMP
= 4.7Ω, and r
LASER
= 4Ω:
RAC= 5.2Ω
with CAC= 1µF, τAC= 5.2µs.
Operation without APC (open loop)
When operating without APC, be sure to configure the MAX3667 as follows:
1) Disconnect APC from BIASSET.
2) Force a voltage of 1V to 2V at APC to prevent the OTA from saturating.
3) Disconnect the monitor diode.
4) Pull up the MD pin to V
CC
through a 5kΩ resistor.
5) Pull down the COMP pin to ground through a 30kΩ resistor.
Remember that the bias-current output is programmed by adjusting the BIASSET resistor when the APC loop is disconnected.
Output Current Limits
The MAX3667 is equipped with output current limiting and short-circuit protection. In +3.3V operation, I
BIAS
is
limited to approximately 170mA open loop, and I
QMOD
is limited to approximately 140mA (see
Typical
Operating Characteristics
). In +5.0V operation, I
BIAS
is
limited to approximately 300mA, and I
QMOD
is limited
to approximately 140mA. If BIASSET is shorted to ground, I
BIAS
becomes current limited. If either APCSET or MODSET is shorted to ground, the MAX3667 output is turned off. Note that in 5V operation, the I
BIAS
current limit is approximately 300mA. Care should be taken if the MAX3667 is being used with a laser diode that is sensitive to this current level.
Interface Suggestions
and Laser Compensation
Adding damping resistance in series with the laser diode (typically 3Ω to 5Ω) raises the load resistance, reduces the load frequency dependence and improves output aberrations. A series damping resistor of 4.7Ω is suggested for the MAX3667.
Series inductance at the cathode of the laser results in high-frequency loading (VL= Ldi/dt) and increased out­put aberrations. Because of reduced headroom, the output performance of the transmitted eye diagram can be significantly impacted during 3.3V operation. Assuming that laser package series inductance can not be completely eliminated, a compensation network is required. With a laser diode load of approximately 4Ω and 4nH, a series damping resistor of 4.7Ω, and a cou­pling capacitor of 0.1µF, a shunt R-C compensation network of 22Ω and 0.01µF is recommended (see
Typical Operating Circuit
). These values may need to be adjusted depending on the style of laser used. Note that it is important to place the compensation network as close to the load as possible.
[1 - 0.12]
-t
τ = = 7.8t
ln
[100% - DROOP] = e
-t
τ
MAX3667
+3.3V, 622Mbps SDH/SONET Laser Driver
with Automatic Power Control
_______________________________________________________________________________________ 9
DROOP
t
P
AVG
P
p-p
τ = ∞
τ << τ
AC
τ
AC
t
1
Figure 3. Droop
MAX3667
Since the IBIAS output is also connected directly to the laser cathode, any parasitic capacitance associated with this output must not be allowed to significantly load the response. To resolve this problem, place an R-L compensation network in series with the IBIAS output. The additional high-frequency impedance of this net­work will help maintain a high impedance at this node. The recommended values for this resistance and inductance are 100Ω and 470nH, respectively.
Optimize the laser diode performance by placing a bypass capacitor as close to the anode pin as possi­ble. Use good high-frequency layout techniques and multilayer boards with uninterrupted ground planes.
Input Termination Requirements
The MAX3667 data inputs are PECL compatible. Standard PECL levels require 50Ω terminations to VCC- 2V. The MAX3667’s common-mode input range is
1.5V to (VCC- 0.75V) with a minimum differential input swing of 620mVp-p. The MAX3667’s inputs need not be driven with standard PECL signals; as long as the com­mon-mode voltage and differential swing is met, the device will operate properly. 50Ω input termination is also not required, but is recommended for good high­frequency termination.
Wire Bonding
For high current density and reliable operation, the MAX3667 uses gold metalization. Make connections to the die with gold wire only, using ball-bonding tech­niques. Wedge bonding is not recommended. Die-pad size is 4 mils (100mm) square, and die thickness is 12 mils (300µm).
__________Applications Information
DC-Coupled Operation
and Output Current Limits
To improve headroom conditions for the MAX3667, AC coupling of the modulation current is required at +3.3V operation. At +5.0V operation, AC coupling is suggest­ed but not required.
For AC-coupled operation, the total output current is equal to IBIAS + IMOD / 2. For DC-coupled mod­ulation currents, the total output current is equal to IBIAS + IMOD.
Optimizing Performance
for Low Modulation Currents
The MAX3667’s dynamic range and headroom require­ments are such that, in order to meet these spec­ifications, low-current performance is compromised. If continual operation at low modulation currents (≤ 20mA) is the intended application, the MAX3667’s high-frequency performance can be improved with an external pull-up resistor. By shunting the AC current away form the laser diode, this technique reduces the output swing without reducing the operating current of the output transistor. Maintaining a higher modulation operating current level preserves the high-frequency performance of the output device. A suggested starting point for the external pull-up resistor value is 100Ω.
Modulation Currents Greater than 60mA
At +5.0V operation, the headroom conditions for the MAX3667 are improved significantly. In this mode, it is possible to achieve modulation currents greater than 60mA by floating PULLUP and driving the laser diode directly (DC-coupled IMOD).
Laser Safety and IEC 825
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control
10 ______________________________________________________________________________________
MAX3667
+3.3V, 622Mbps SDH/SONET Laser Driver
with Automatic Power Control
______________________________________________________________________________________ 11
APCSET
N.C.
BIASMON
MODMON
N.C.
COMP
V
CC
DISABLEIN-GNDV
CC
0.113"
(2.870mm)
0.106"
(2.692mm)
V
CC
IN+ GND GND
GND
IBIAS
GND GND BIASSET
APC MODSET N.C.
V
CC
IMOD IMOD PULLUP
GND GND GND
N.C.
MD
___________________Chip Topography
MAX3667
TQFP
TOP VIEW
32 28
293031
25
26
27
N.C.
MODMON
BIASMON
N.C.
COMP
APCSET
N.C.
MD
10
13
15
14
1611 12
9
N.C.
APC
MODSET
GND
BIASSET
GND
GND
IBIAS
17
18
19
20
21
22
23
V
CC
24
V
CC
GND IMOD GND IMOD GND PULLUP
2 3 4 5 6 7 8GND
DISABLE
GND
IN-
IN+
GND
V
CC
1V
CC
___________________Pin Configuration
MAX3667
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control
12 ______________________________________________________________________________________
________________________________________________________Package Information
TQFPPO.EPS
Maxim makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does Maxim assume any lia­bility arising out of the application or use of any product or circuit and specifically disclaims any and all liability, including without limitation consequential or incidental damages. “Typical” parameters can and do vary in different applications. All operating parameters, including “typicals” must be validated for each customer application by customer’s technical experts. Maxim products are not designed, intended or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the Maxim product could create a situation where personal injury or death may occur.
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