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19-1311; Rev 1; 3/98
KIT ATION EVALU E AILABL AV
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control
____________________________Features
o Single +3.3V or +5.0V Operation o Automatic Average Power Control o Bias Current and Modulation Current Monitor Outputs o TTL-Compatible Disable Input o Temperature-Compensated Reference o PECL-Compatible Data Inputs
________________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 -40C to +85C temperature range. A temperature-stabilized reference voltage simplifies laser current programming. It allows external programming of the modulation current between 5mAp-p and 60mAp-p, and of the bias current between 5mA and 90mA. 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.
MAX3667
_______________Ordering Information
PART MAX3667ECJ MAX3667E/D TEMP. RANGE -40C to +85C -40C to +85C PIN-PACKAGE 32 TQFP Dice*
*Dice are designed to operate from -40C to +85C but are tested and guaranteed only at Tj = +25C.
________________________Applications
622Mbps SDH/SONET Access Nodes Laser Driver Transmitters Section Repeaters
Pin Configuration appears at end of data sheet.
____________________________________________________Typical Operating Circuit
+3.3V
0.1F +3.3V CCOMP 1F 50
MONITOR DIODE
LASER DIODE
0.1F
COMP
BIASMON
MODMON
APCSET
VCC
MD IMOD
1F
RDAMP 4.7
MAX3691
4:1 SERIALIZER WITH CLOCK GEN
130
130 IN+ PECL INIBIAS GND DISABLE MODSET BIASSET APC
RFILT 22
MAX3667
0.01F 470nH 100
82
82
CAPC 1nF
________________________________________________________________ Maxim Integrated Products
1
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+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control MAX3667
ABSOLUTE MAXIMUM RATINGS
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 (VCC + 0.5V) Voltage at IN+, IN-, DISABLE, MODSET, BISASSET, APCSET, PULLUP..................-0.5V to (VCC + 0.5V) Continuous Power Dissipation (TA = +85C) TQFP (derate 11.1mW/C above +85C) ......................721mW Operating Temperature Range ...........................-40C to +85C Operating Junction Temperature Range (die) ..-55C to +175C Processing Temperature (die) .........................................+400C Storage Temperature Range .............................-65C to +160C Lead Temperature (soldering, 10sec) .............................+300C
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.
DC ELECTRICAL CHARACTERISTICS
(VCC = +3.3V 5%, TA = -40C to +85C, unless otherwise noted.) (Notes 1, 2) PARAMETER Supply Current (Note 3) Bias Current Range Bias Off Current Modulation Off Current Internal Pull-Up Resistor (Note 6) Reference Voltage (Note 7) Bias Current Stability SYMBOL ICC IBIAS IBIAS IBIAS RPULL-UP VREF Disable = high or low RBIASSET = 2k, open loop (Note 8) RBIASSET = 33.2k, open loop (Note 8) RBIASSET = 2k, closed loop (Notes 4, 9) Modulation Current Stability BIASMON to IBIAS Gain MODMON to IQMOD Gain IBIASSET to IBIAS Gain IMODSET to IQMOD Gain IAPCSET to IBIAS Gain PECL Input High Voltage PECL Input Low Voltage PECL Input High Current PECL Input Low Current TTL Disable High Voltage TTL Disable Low Voltage TTL Disable High Current TTL Disable Low Current 2 AI AI AI AI AI VIH VIL IIH IIH VDIH VDIL IDIH IDIL 1 4 VIN = 2.14V VIN = 1.82V 2.0 0.8 4.5 2 RMODSET = 2k, open loop (Note 8) RMODSET = 33.2k, open loop (Note 8) RBIASSET = 2k RMODSET = 2k (Note 10) RBIASSET = 2k RBIASSET = 33.2k RMODSET = 2k (Note 10) RMODSET = 33.2k (Note 10) RAPCSET = 2k RAPCSET = 33.2k 30 26 145 128 152 152 135 164 2.14 1.82 10 10 1100 1100 38 33 170 160 190 190 170 205 46 40 200 195 230 230 205 250 (Note 5) Disable = high Disable = high 26 0.91 CONDITIONS Closed loop (Note 4) 5 5 20 31 1.01 500 1000 480 ppm/C A/A A/A A/A A/A A/A V V A A V V A A ppm/C MIN TYP 112 MAX 133 90 250 250 35 1.11 UNITS mA mA A A V
_______________________________________________________________________________________
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control
DC ELECTRICAL CHARACTERISTICS
(VCC = +5.0V 5%, TA = -40C to +85C, unless otherwise noted.) (Notes 1, 2) PARAMETER Supply Current (Note 3) Bias Off Current Modulation Off Current BIASMON to IBIAS Gain MODMON to IQMOD Gain IBIASSET to IBIAS Gain IMODSET to IQMOD Gain IAPCSET to IBIAS Gain PECL Input High Voltage PECL Input Low Voltage PECL Input High Current PECL Input Low Current AI AI AI AI AI VIH VIL IIH IIH VIN = 3.84V VIN = 3.52V 9 8 SYMBOL ICC Disable = high Disable = high RBIASSET = 2k RMODSET = 2k (Note 10) RBIASSET = 2k RBIASSET = 33.2k RMODSET = 2k (Note 10) RMODSET = 33.2k (Note 10) RAPCSET = 2k RAPCSET = 33.2k 26 145 143 168 188 132 145 3.84 3.52 CONDITIONS Closed loop (Note 4) MIN TYP 134 2 32 38 33 180 180 240 230 166 182 40 220 215 315 285 200 220 MAX 160 250 250 UNITS mA A A A/A A/A A/A A/A A/A V V A A
MAX3667
AC ELECTRICAL CHARACTERISTICS
(VCC = +3.3V 5%, TA = -40C to +85C, RLOAD = 10, unless otherwise noted.) (Notes 2, 11) PARAMETER Modulation Current Range Output Rise Time Output Fall Time Output Aberrations Pulse-Width Distortion Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: Note 7: Note 8: Note 9: Note 10: Note 11: Note 12: Note 13: PWD RFILT = 22, RDAMP = 0 (Note 13) SYMBOL IMOD tr tf CONDITIONS RFILT = 22, RDAMP = 0 (Note 12) VCC = 3.3V 5%, 20% to 80% VCC = 5.0V 5%, 20% to 80% VCC = 3.3V 5%, 20% to 80% VCC = 5.0V 5%, 20% to 80% MIN 5 270 205 425 315 10 70 TYP MAX 60 450 400 650 600 UNITS mA ps ps % ps
Dice are tested at TA = +27C. Minimum voltage at IBIAS = VCC - 1.6V. The sum of the currents flowing into VCC and PULLUP with RBIASSET = RMODSET = RAPCSET = 2k, IN+ = 1.82V, IN- = 2.14V. APC is connected to BIASSET for closed-loop operation. Bias current range is guaranteed by the IBIASSET to IBIAS gain test. RPULL-UP is connected between IMOD and PULLUP. VREF is the voltage on BIASSET, MODSET, or APCSET with RBIASSET = RMODSET = RAPCSET = 2k. APC is disconnected from BIASSET for open-loop operation. Bias current stability is guaranteed by design and characterization. IQMOD is the current flowing into the collector of QMOD (Figure 1). AC parameters are guaranteed by design and characterization. Modulation current range is guaranteed by the IMODSET to IQMOD gain test. Input signal is a 155Mbps 1-0 pattern. PWD = [(width of wider pulse) - (width of narrower pulse)] / 2.
_______________________________________________________________________________________
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+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control MAX3667
__________________________________________Typical Operating Characteristics
(TA = +25C, VCC = +3.3V, unless otherwise noted.)
EYE DIAGRAM (622Mbps, 1300nm LASER, 470MHz FILTER)
MAX3667-01
EYE DIAGRAM (622Mbps, 10 LOAD)
MAX3667-02
OUTPUT JITTER (622Mbps, 10 LOAD)
IMOD = 20mA DIFF. INPUT = 1.7Vp-p RMS = 3.2ps
MAX3667-03
223 - 1PRBS IMOD = 15mA
DIFF. INPUT = 640mVp-p
223 - 1PRBS IMOD = 15mA
DIFF. INPUT = 1.7Vp-p
52mV/ div
20mV/ div
5mV/ div
161ps/div
161ps/div
10ps/div
IBIAS vs. RBIASSET
MAX3667-04
IQMOD vs. RMODSET
MAX3667-05
IMD vs. RAPCSET
10 LOAD 0.8 0.7 0.6 IMD (mA) 0.5 0.4 0.3 0.2 0.1 0 APC LOOP CLOSED RBIASSET = 2k RMODSET = 2k MONITOR-TO-LASER CURRENT GAIN = 82
MAX3667-06 MAX3667toc09
180 160 140 VIBIAS = 1.7V 10 LOAD
160 140 120 IQMOD (mA) 100 80 60 40 20 0
0.9
120 IBIAS (mA) 100 80 60 40 20 0 200 1k RBIASSET () 10k 40k
200
1k RMODSET ()
10k
40k
1k RAPCSET ()
10k
40k
IBIAS vs. RAPCSET (VARYING MONITOR-TO-LASER CURRENT GAIN)
MAX3667-07
PULSE-WIDTH DISTORTION vs. TEMPERATURE
IMOD = 30mA PULSE-WIDTH DISTORTION (ps) 100 80 VCC = +3.3V 60 40 20 0 VCC = +5.0V
MAX3667toc08
PULSE-WIDTH DISTORTION vs. IMOD
120 100 80 VCC = +3.3V 60 40 20 0 VCC = +5.0V
80 70 60 50 IBIAS (mA) 40 30 20 10 0 1k RAPCSET () 10k GAIN = 30 GAIN = 60 GAIN = 90
120
GAIN = 15
PULSE-WIDTH DISTORTION (ps)
40k
-40
-15
10
35
60
85
10 15 20 25 30 35 40 45 50 55 60 IMOD (mA)
TEMPERATURE (C)
4
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+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control
____________________________Typical Operating Characteristics (continued)
(TA = +25C, VCC = +3.3V, unless otherwise noted.)
APC BANDWIDTH vs. CCOMP (VARYING MONITOR-TO-LASER CURRENT GAIN)
MAX3667-10
MAX3667
SUPPLY CURRENT vs. TEMPERATURE
150 140 EXCLUDING IBIAS RMODSET = RBIASSET = 2k 10 LOAD VCC = +5.0V
MAX3667-11
100G 10G APC BANDWIDTH (Hz) 1G MEASURED RESULTS
160
ISUPPLY (mA)
100k 10k 1k 100 10 1pF
GAIN = 30 GAIN = 90 GAIN = 60
130 120 110 100
VCC = +3.3V
SIMULATED RESULTS 100pF 10nF CCOMP 1F 100F
90 80 -40 -15 10 35 60 85 TEMPERATURE (C)
______________________________________________________________Pin Description
PIN 1, 2, 23, 24 3, 6, 8, 13, 14, 15, 18, 20, 22 4 5 7 9, 26, 28, 31 10 11 12 16 17 19, 21 25 27 29 30 32 NAME VCC GND IN+ INDISABLE N.C. MODSET APC BIASSET IBIAS PULLUP IMOD MD APCSET BIASMON MODMON COMP Supply Voltage Input Ground Positive PECL-Compatible Input Negative PECL-Compatible Input Disable Input. High = disable, TTL-compatible input. No Connection Adjustment for Laser-Diode Modulation Current Feedback Current for Closed-Loop Laser-Diode Bias Control Open-Loop Adjustment for Laser-Diode Bias Current Laser-Diode DC Bias Current VCC Supply for Internal 31 Pull-Up Resistor Laser-Diode Modulation Current Input for PIN Monitor Diode Current Closed-Loop Adjustment for Laser-Diode Bias Current IBIAS Current Monitor (gain = 1/38 IBIAS). Open PNP collector, connect to ground if not used. IMOD Current Monitor (gain = 1/33 IQMOD). Open PNP collector, connect to ground if not used. External Compensation Capacitor for Closed-Loop Laser-Diode Bias Current Control Stability 5 FUNCTION
_______________________________________________________________________________________
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control 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 1F. A simplified block diagram of the modulation driver is shown in Figure 1. The IMOD pin is internally biased through a 31 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 250A.
VCC RFILT 1F RDAMP 4.7 22 0.01F LASER DIODE
VCC
IMOD
IBIAS
VCC
INPUT (MODULATION)
31
INPUT (BIAS)
MAX3667
IQMOD QMOD
MODMON
BIASMON
Figure 1. Simplified Modulation Driver Block Diagram
6 _______________________________________________________________________________________
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control MAX3667
IBIAS
DISABLE
MAX3667
MD
31
PULLUP IMOD
IN+ COMP IN-
OTA
APC
1.0V
REFERENCE
1.0V MODSET MODMON
1.0V BIASSET BIASMON
1.0V APCSET
Figure 2. 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 guidelines on selecting these resistor values.
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.
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.
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
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_______________________________________________________________________________________
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control MAX3667
bias, modulation, and monitor diode current levels. Where necessary, the reference is adjusted by a VBE voltage 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. For RDAMP = 4.7, RFILT = 22, and a laser resistance of approximately 4, refer to the IQMOD Current vs. RMODSET graph in the Typical Operating Characteristics and select the value of RMODSET that corresponds to the required current at +25C.
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 +25C. Refer to the IBIAS Current vs. RBIASSET graph in the Typical Operating Characteristics, and select the value of RBIASSET that corresponds to the required current.
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.
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. RAPCSET graph in the Typical Operating Characteristics, and select the value of RAPCSET 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, RBIASSET assures that the feedback current range is properly centered. It is recommended that RBIASSET be chosen to equal RAPCSET during closed-loop operation.
__________________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 resistance (R FILT), and the resistance of the laser diode (Figure 1). If IQMOD represents the total current flowing into the collector of QMOD, then the modulation current into the laser diode can be represented by the following:
IMOD = IQMOD 31 RFILT + RDAMP + r LASER 31
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. CCOMP must be placed between the COMP pin and ground; CAPC must be placed between the APC pin and ground (see the Typical Operating Circuit). For 622Mbps SDH/SONET applications, the recommended values of CCOMP and CAPC are 1F and 1nF, respectively.
(
RFILT
)
IQMOD = (AI)(IMODSET) AI = IMODSET to IMOD Gain Assuming RFILT = 22, RDAMP = 4.7, and rLASER = 4, then this equation is simplified to: IMOD = IQMOD(0.6)
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+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control
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, CAPC should be kept substantially smaller than CCOMP. It is recommended that the value of CAPC be set 1000 times smaller than CCOMP. 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: [100% - DROOP] = e APC operation assures that the discharge level for is PAVG. An overall droop of 6% relative to Pp-p equates to a 12% droop relative to PAVG. To ensure a droop of less than 12% (6% relative to Pp-p), this equation can be solved for as follows: = -t = 7.8t ln[1 - 0.12]
-t
MAX3667
= AC << AC Pp-p PAVG DROOP
t1
t
Figure 3. Droop
Output Current Limits
The MAX3667 is equipped with output current limiting and short-circuit protection. In +3.3V operation, IBIAS is limited to approximately 170mA open loop, and IQMOD is limited to approximately 140mA (see Typical Operating Characteristics). In +5.0V operation, IBIAS is limited to approximately 300mA, and IQMOD is limited to approximately 140mA. If BIASSET is shorted to ground, IBIAS becomes current limited. If either APCSET or MODSET is shorted to ground, the MAX3667 output is turned off. Note that in 5V operation, the IBIAS 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.
If t1 equals 100 consecutive unit intervals without a transition, then the time constant associated with the DC blocking capacitor needs to be longer than: AC RACCAC = 7.8 (100 bits) (1.6ns/bit) = 1.25s The estimated value of RAC is: RAC = 31 RFILT (RDAMP + rLASER) Assuming RFILT = 22, RDAMP = 4.7, and rLASER = 4: RAC = 5.2 with CAC = 1F, AC = 5.2s.
Interface Suggestions and Laser Compensation
Adding damping resistance in series with the laser diode (typically 3 to 5) raises the load resistance, reduces the load frequency dependence and improves output aberrations. A series damping resistor of 4.7 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 4 and 4nH, a series damping resistor of 4.7, and a coupling capacitor of 0.1F, a shunt R-C compensation network of 22 and 0.01F 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.
9
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 VCC through a 5k resistor. 5) Pull down the COMP pin to ground through a 30k resistor. Remember that the bias-current output is programmed by adjusting the BIASSET resistor when the APC loop is disconnected.
_______________________________________________________________________________________
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control 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 100 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. 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 100.
Input Termination Requirements
The MAX3667 data inputs are PECL compatible. Standard PECL levels require 50 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. 50 input termination is also not required, but is recommended for good highfrequency termination.
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).
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 (300m).
Laser Safety and IEC 825
Using the MAX3667 laser driver alone does not ensure that a transmitter design is compliant with IEC 825. The entire transmitter circuit and component selections must be considered. Each customer must determine the level of fault tolerance required by their application, recognizing that Maxim products are not designed or authorized for use as components in systems intended for surgical implant into the body, for applications intended to support or sustain life, or for any other application where the failure of a Maxim product could create a situation where personal injury or death may occur.
__________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.
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+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control
___________________Pin Configuration
TOP VIEW
MODMON BIASMON APCSET COMP N.C. N.C. N.C.
___________________Chip Topography
VCC VCC IMOD GND IMOD PULLUP GND GND
MAX3667
MD
IBIAS MD N.C.
24 VCC 23 VCC 22 GND 21 IMOD
32 VCC VCC GND IN+ INGND DISABLE GND 1 2 3 4 5 6 7 8 9 N.C.
31
30
29
28
27
26
25
0.113" (2.870mm) GND GND GND BIASSET APC MODSET N.C.
APCSET N.C. BIASMON MODMON N.C. COMP
MAX3667
20 GND 19 IMOD 18 GND 17 PULLUP
VCC
10 MODSET 11 APC 12 BIASSET 13 GND 14 GND 15 GND 16 IBIAS
IN+ GND IN-
VCC
GND GND DISABLE
0.106" (2.692mm)
TQFP
______________________________________________________________________________________
11
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control MAX3667
________________________________________________________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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