19-1311; Rev 1; 3/98 KIT ATION EVALU LE B A IL A AV +3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control ____________________________Features 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. ♦ Single +3.3V or +5.0V Operation 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. ♦ Automatic Average Power Control ♦ Bias Current and Modulation Current Monitor Outputs ♦ TTL-Compatible Disable Input ♦ Temperature-Compensated Reference ♦ PECL-Compatible Data Inputs _______________Ordering Information TEMP. RANGE PIN-PACKAGE MAX3667ECJ PART -40°C to +85°C 32 TQFP MAX3667E/D -40°C to +85°C Dice* *Dice are designed to operate from -40°C to +85°C but are tested and guaranteed only at Tj = +25°C. ________________________Applications 622Mbps SDH/SONET Access Nodes Pin Configuration appears at end of data sheet. Laser Driver Transmitters Section Repeaters ____________________________________________________Typical Operating Circuit +3.3V 0.1µF +3.3V CCOMP 50Ω 1µF COMP BIASMON MODMON APCSET VCC MD MONITOR DIODE 1µF LASER DIODE 0.1µF RDAMP 4.7Ω IMOD MAX3691 4:1 SERIALIZER WITH CLOCK GEN 130Ω 130Ω RFILT 22Ω MAX3667 IN+ PECL 82Ω 0.01µF IN- 470nH 82Ω IBIAS GND DISABLE MODSET BIASSET APC 100Ω CAPC 1nF ________________________________________________________________ Maxim Integrated Products 1 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 ________________General Description MAX3667 +3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control 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 = +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 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 = -40°C to +85°C, unless otherwise noted.) (Notes 1, 2) PARAMETER Supply Current (Note 3) SYMBOL ICC CONDITIONS MIN Closed loop (Note 4) TYP MAX UNITS 112 133 mA 90 mA Bias Current Range IBIAS (Note 5) Bias Off Current IBIAS Disable = high 5 250 µA Modulation Off Current IBIAS Disable = high 20 250 µA 26 31 35 Ω 0.91 1.01 1.11 V Internal Pull-Up Resistor (Note 6) Reference Voltage (Note 7) RPULL-UP VREF Bias Current Stability Disable = high or low 5 RBIASSET = 2kΩ, open loop (Note 8) 500 RBIASSET = 33.2kΩ, open loop (Note 8) 1000 RBIASSET = 2kΩ, closed loop (Notes 4, 9) Modulation Current Stability ppm/°C 480 RMODSET = 2kΩ, open loop (Note 8) 1100 RMODSET = 33.2kΩ, open loop (Note 8) 1100 ppm/°C BIASMON to IBIAS Gain AI RBIASSET = 2kΩ 30 38 46 A/A MODMON to IQMOD Gain AI RMODSET = 2kΩ (Note 10) 26 33 40 A/A IBIASSET to IBIAS Gain AI RBIASSET = 2kΩ 145 170 200 RBIASSET = 33.2kΩ 128 160 195 IMODSET to IQMOD Gain AI RMODSET = 2kΩ (Note 10) 152 190 230 RMODSET = 33.2kΩ (Note 10) 152 190 230 IAPCSET to IBIAS Gain AI RAPCSET = 2kΩ 135 170 205 RAPCSET = 33.2kΩ 164 205 250 PECL Input High Voltage VIH PECL Input Low Voltage VIL 1.82 V PECL Input High Current IIH VIN = 2.14V 4.5 10 µA PECL Input Low Current IIH VIN = 1.82V 2 10 µA 2.14 A/A A/A A/A V TTL Disable High Voltage VDIH TTL Disable Low Voltage VDIL TTL Disable High Current IDIH 1 µA TTL Disable Low Current IDIL 4 µA 2 2.0 V 0.8 _______________________________________________________________________________________ V +3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control MAX3667 DC ELECTRICAL CHARACTERISTICS (VCC = +5.0V ±5%, TA = -40°C to +85°C, unless otherwise noted.) (Notes 1, 2) PARAMETER Supply Current (Note 3) SYMBOL ICC CONDITIONS MIN Closed loop (Note 4) TYP MAX UNITS 134 160 mA Bias Off Current Disable = high 2 250 µA Modulation Off Current Disable = high 32 250 µA BIASMON to IBIAS Gain AI RBIASSET = 2kΩ MODMON to IQMOD Gain AI RMODSET = 2kΩ (Note 10) 26 33 38 40 A/A RBIASSET = 2kΩ 145 180 220 RBIASSET = 33.2kΩ 143 180 215 RMODSET = 2kΩ (Note 10) 168 240 315 RMODSET = 33.2kΩ (Note 10) 188 230 285 RAPCSET = 2kΩ 132 166 200 RAPCSET = 33.2kΩ 145 182 220 A/A IBIASSET to IBIAS Gain AI IMODSET to IQMOD Gain AI IAPCSET to IBIAS Gain AI PECL Input High Voltage VIH PECL Input Low Voltage VIL PECL Input High Current IIH VIN = 3.84V 9 µA PECL Input Low Current IIH VIN = 3.52V 8 µA 3.84 A/A A/A A/A V 3.52 V AC ELECTRICAL CHARACTERISTICS (VCC = +3.3V ±5%, TA = -40°C to +85°C, RLOAD = 10Ω, unless otherwise noted.) (Notes 2, 11) PARAMETER Modulation Current Range SYMBOL IMOD Output Rise Time tr Output Fall Time tf CONDITIONS RFILT = 22Ω, RDAMP = 0Ω (Note 12) 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 TYP 5 MAX UNITS 60 mA VCC = 3.3V ±5%, 20% to 80% 270 450 VCC = 5.0V ±5%, 20% to 80% 205 400 VCC = 3.3V ±5%, 20% to 80% 425 650 VCC = 5.0V ±5%, 20% to 80% 315 600 Output Aberrations Pulse-Width Distortion MIN RFILT = 22Ω, RDAMP = 0Ω (Note 13) ps ps ±10 % 70 ps Dice are tested at TA = +27°C. Minimum voltage at IBIAS = VCC - 1.6V. The sum of the currents flowing into VCC and PULLUP with RBIASSET = RMODSET = RAPCSET = 2kΩ, 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 = 2kΩ. 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. _______________________________________________________________________________________ 3 __________________________________________Typical Operating Characteristics (TA = +25°C, VCC = +3.3V, unless otherwise noted.) 223 - 1PRBS IMOD = 15mA DIFF. INPUT = 1.7Vp-p 20mV/ div 5mV/ div 161ps/div 161ps/div 0.9 MAX3667-05 10Ω LOAD 140 0.7 120 100 80 0.6 100 IMD (mA) IQMOD (mA) 120 80 60 60 40 20 0.2 20 0.1 RMODSET (Ω) IBIAS vs. RAPCSET (VARYING MONITOR-TO-LASER CURRENT GAIN) PULSE-WIDTH DISTORTION vs. TEMPERATURE GAIN = 90 60 50 GAIN = 60 40 GAIN = 30 GAIN = 15 10 40k IMOD = 30mA 100 VCC = +3.3V 60 VCC = +5.0V 20 1k 10k RAPCSET (Ω) 40k 40k 120 100 80 VCC = +3.3V 60 40 VCC = +5.0V 20 0 0 0 10k PULSE-WIDTH DISTORTION vs. IMOD 80 40 1k RAPCSET (Ω) 120 MAX3667-07 70 20 10k RBIASSET (Ω) 80 30 0 1k 200 40k MAX3667toc08 10k 0.4 0.3 PULSE-WIDTH DISTORTION (ps) 1k PULSE-WIDTH DISTORTION (ps) 200 0.5 40 0 0 APC LOOP CLOSED RBIASSET = 2kΩ RMODSET = 2kΩ MONITOR-TO-LASER CURRENT GAIN = 82 0.8 MAX3667toc09 140 IBIAS (mA) IMD vs. RAPCSET 160 MAX3667-04 VIBIAS = 1.7V 10Ω LOAD 160 10ps/div IQMOD vs. RMODSET IBIAS vs. RBIASSET 180 4 IMOD = 20mA DIFF. INPUT = 1.7Vp-p ∆RMS = 3.2ps MAX3667-06 52mV/ div OUTPUT JITTER (622Mbps, 10Ω LOAD) MAX3667-02 DIFF. INPUT = 640mVp-p MAX3667-01 223 - 1PRBS IMOD = 15mA EYE DIAGRAM (622Mbps, 10Ω LOAD) MAX3667-03 EYE DIAGRAM (622Mbps, 1300nm LASER, 470MHz FILTER) IBIAS (mA) MAX3667 +3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control -40 -15 10 35 TEMPERATURE (°C) 60 85 10 15 20 25 30 35 40 45 50 55 60 IMOD (mA) _______________________________________________________________________________________ +3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control APC BANDWIDTH vs. CCOMP (VARYING MONITOR-TO-LASER CURRENT GAIN) SUPPLY CURRENT vs. TEMPERATURE MEASURED RESULTS MAX3667-11 EXCLUDING IBIAS RMODSET = RBIASSET = 2kΩ 10Ω LOAD 150 140 1G ISUPPLY (mA) APC BANDWIDTH (Hz) 10G 160 MAX3667-10 100G GAIN = 30 100k GAIN = 90 GAIN = 60 10k 1k VCC = +5.0V 130 120 110 VCC = +3.3V 100 SIMULATED RESULTS 100 90 80 10 1pF 100pF 10nF 1µF -40 100µF -15 10 35 60 85 TEMPERATURE (°C) CCOMP ______________________________________________________________Pin Description PIN NAME FUNCTION 1, 2, 23, 24 VCC Supply Voltage Input 3, 6, 8, 13, 14, 15, 18, 20, 22 GND Ground 4 IN+ Positive PECL-Compatible Input 5 IN- Negative PECL-Compatible Input 7 DISABLE 9, 26, 28, 31 N.C. 10 MODSET 11 APC 12 BIASSET 16 IBIAS 17 PULLUP 19, 21 IMOD 25 MD 27 APCSET 29 BIASMON IBIAS Current Monitor (gain = 1/38 IBIAS). Open PNP collector, connect to ground if not used. 30 MODMON IMOD Current Monitor (gain = 1/33 IQMOD). Open PNP collector, connect to ground if not used. 32 COMP 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 31Ω Pull-Up Resistor Laser-Diode Modulation Current Input for PIN Monitor Diode Current Closed-Loop Adjustment for Laser-Diode Bias Current External Compensation Capacitor for Closed-Loop Laser-Diode Bias Current Control Stability _______________________________________________________________________________________ 5 MAX3667 ____________________________Typical Operating Characteristics (continued) (TA = +25°C, VCC = +3.3V, unless otherwise noted.) MAX3667 +3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control _______________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. VCC RFILT 1µF RDAMP 4.7Ω 22Ω LASER DIODE 0.01µF VCC INPUT (MODULATION) IMOD VCC IBIAS INPUT (BIAS) 31Ω 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 31Ω PULLUP IMOD IN+ COMP IN- OTA APC 1.0V REFERENCE 1.0V MODSET 1.0V MODMON BIASSET 1.0V BIASMON 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. 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 _______________________________________________________________________________________ 7 MAX3667 +3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control 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. 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 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 31Ω RFILT + RDAMP + r LASER 31Ω ( RFILT ) IQMOD = (AI)(IMODSET) AI = IMODSET to IMOD Gain Assuming RFILT = 22Ω, RDAMP = 4.7Ω, and rLASER = 4Ω, then this equation is simplified to: IMOD = IQMOD(0.6) 8 For RDAMP = 4.7Ω, RFILT = 22Ω, and a laser resistance of approximately 4Ω, 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 +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. RBIASSET graph in the Typical Operating Characteristics, and select the value of RBIASSET 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. 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. 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 1µF and 1nF, respectively. _______________________________________________________________________________________ +3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control -t [100% - DROOP] = e τ APC operation assures that the discharge level for τ 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 τ as follows: τ= -t = 7.8t ln[1 - 0.12] 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: τAC ≥ RACCAC = 7.8 (100 bits) (1.6ns/bit) = 1.25µs The estimated value of RAC is: RAC = 31Ω RFILT (RDAMP + rLASER) Assuming RFILT = 22Ω, RDAMP = 4.7Ω, and rLASER = 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 VCC 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. MAX3667 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: τ=∞ τAC DROOP τ << τAC Pp-p PAVG 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. 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. _______________________________________________________________________________________ 9 MAX3667 +3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control 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. 10 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 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. ______________________________________________________________________________________ +3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control ___________________Chip Topography VCC TOP VIEW 32 31 30 29 28 27 26 IMOD GND IMOD PULLUP GND GND IBIAS MD N.C. APCSET N.C. BIASMON MODMON N.C. COMP VCC 0.113" (2.870mm) GND MD 25 N.C. VCC 1 24 VCC VCC 2 23 VCC GND 3 22 GND IN+ 4 21 IMOD IN- 5 GND 6 19 IMOD DISABLE 7 18 GND GND 8 17 PULLUP MAX3667 20 GND APCSET GND N.C. GND BIASMON BIASSET APC MODMON MODSET N.C. N.C. COMP 9 10 11 12 13 14 15 16 N.C. MODSET APC BIASSET GND GND GND IBIAS VCC VCC IN+ GND IN- GND GND DISABLE 0.106" (2.692mm) TQFP ______________________________________________________________________________________ 11 MAX3667 ___________________Pin Configuration ________________________________________________________Package Information TQFPPO.EPS MAX3667 +3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control 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. 12 ______________________________________________________________________________________