19-2818; Rev 1; 8/03 Multirate Laser Driver with Extinction Ratio Control ♦ Automatic Power Control (APC) ♦ Modulation Compensation ♦ On-Chip Temperature Compensation ♦ Self-Biased Inputs for AC-Coupling ♦ Ground-Referenced Current Monitors ♦ Laser Safety, Shutdown, and Alarm Outputs Ordering Information PART TEMP RANGE PIN-PACKAGE MAX3737ETJ -40°C to +85°C 32 Thin QFN MAX3737EGJ -40°C to +85°C 32 QFN 26 APCFILT1 27 APCFILT2 28 APCSET 29 MODSET 30 MODBCOMP TOP VIEW 31 TH_TEMP 32 MODTCOMP Pin Configurations GND 1 24 MD TX_DISABLE 2 23 VCC VCC 3 22 OUT+ IN+ 4 21 OUT+ IN- 5 20 OUT- MAX3737EGJ 15 16 GND BIAS GND 17 14 8 13 BC_MON VBS VCC SHUTDOWN OUT- 18 12 19 7 TX_FAULT 6 11 VCC PC_MON 10 Functional Diagram and Typical Application Circuit appear at end of data sheet. ♦ 100mA Bias Current VCC 1Gbps/2Gbps Fibre Channel SFF/SFP and GBIC Transceivers ♦ 85mA Modulation Current GND Gigabit Ethernet SFF/SFP and GBIC Transceivers ♦ 47mA Power-Supply Current 9 Multirate OC-3 to OC-48 FEC Transceivers ♦ Single +3.3V Power Supply MC_MON Applications Features 5mm x 5mm QFN *THE EXPOSED PADDLE MUST BE SOLDERED TO SUPPLY GROUND TO ACHIEVE SPECIFIED PERFORMANCE. Pin Configurations continued at end of data sheet. ________________________________________________________________ Maxim Integrated Products 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. 1 MAX3737 General Description The MAX3737 is a +3.3V laser driver designed for multirate transceiver modules with data rates from 155Mbps to 2.7Gbps. Lasers can be DC-coupled to the MAX3737 for reduced component count and ease of multirate operation. Laser extinction ratio control (ERC) combines the features of automatic power control (APC), modulation compensation, and built-in thermal compensation. The APC loop maintains constant average optical power. Modulation compensation increases the modulation current in proportion to the bias current. These control loops combined with thermal compensation maintain a constant optical extinction ratio over temperature and lifetime. The MAX3737 accepts differential data input signals. The wide 5mA to 60mA (up to 85mA AC-coupled) modulation current range and up to 100mA bias current range makes the MAX3737 ideal for driving FP/DFB lasers in fiber-optic modules. External resistors set the required laser current levels. The MAX3737 provides transmit disable control (TX_DISABLE), single-point fault tolerance, bias-current monitoring, modulation-current monitoring, and photocurrent monitoring. The device also offers a latched failure output (TX_FAULT) to indicate faults, such as when the APC loop is no longer able to maintain the average optical power at the required level. The MAX3737 is compliant with the SFF8472 transmitter diagnostic and SFP MSA timing requirements. The MAX3737 is offered in a 5mm x 5mm 32-pin thin QFN and QFN package and operates over the -40°C to +85°C extended temperature range. 25 VMD KIT ATION EVALU E L B A AVAIL MAX3737 Multirate Laser Driver with Extinction Ratio Control ABSOLUTE MAXIMUM RATINGS Supply Voltage VCC...............................................-0.5V to +6.0V IN+, IN-, TX_DISABLE, TX_FAULT, SHUTDOWN, MC_MON, BC_MON, PC_MON, VBS, VMD, APCFILT1, APCFILT2, MD, TH_TEMP, MODTCOMP, MODBCOMP, MODSET, and APCSET Voltage .......................................-0.5V to VCC + 0.5V OUT+, OUT-, BIAS Current.............................-20mA to +150mA Continuous Power Dissipation (TA = +85°C) 32-Pin QFN (derate 21.2mW/°C above +85°C) ...............1.3W Operating Junction Temperature Range ...........-55°C to +150°C Storage Temperature Range .............................-55°C to +150°C Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. ELECTRICAL CHARACTERISTICS (VCC = +2.97V to +3.63V, TA = -40°C to +85°C. Typical values are at VCC = +3.3V, IBIAS = 60mA, IMOD = 60mA, TA = +25°C, unless otherwise noted.) (Notes 1, 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS (Note 3) 47 60 mA f ≤ 1MHz, 100mVP-P (Notes 4, 6) 33 POWER SUPPLY Supply Current Power-Supply Noise Rejection ICC PSNR dB I/O SPECIFICATIONS Differential Input Swing VID Common-Mode Input VCM DC-coupled, Figure 1 0.2 2.4 VP-P 1.7 VCC VID/4 V 1 100 mA LASER BIAS Bias-Current Setting Range Bias Off Current TX_DISABLE = high Bias-Current Monitor Ratio IBIAS/IBC_MON 68 (Note 5) 5 82 0.1 mA 95 mA/mA 85 mA LASER MODULATION Modulation-Current Setting Range IMOD Output Edge Speed 20% to 80% (Notes 6, 7) Output Overshoot/Undershoot (Note 7) Random Jitter (Notes 6, 7) 2.7Gbps 1.25Gbps Deterministic Jitter (Notes 6, 8) 622Mbps 155Mbps Modulation-Current Temperature Stability 2 (Note 6) 5mA ≤ IMOD ≤ 10mA 71 80 10mA < IMOD ≤ 85mA 52 80 ±6 0.65 5mA ≤ IMOD ≤ 10mA % 1.3 25.6 40 10mA < IMOD ≤ 85mA 16 40 5mA ≤ IMOD ≤ 10mA 32 41 10mA < IMOD ≤ 85mA 15 41 5mA ≤ IMOD ≤ 10mA 39 46 10mA < IMOD ≤ 85mA 21 46 5mA ≤ IMOD ≤ 10mA 65 100 10mA < IMOD ≤ 85mA 46 70 ±150 ±480 _______________________________________________________________________________________ ps ps psP-P ppm/°C Multirate Laser Driver with Extinction Ratio Control (VCC = +2.97V to +3.63V, TA = -40°C to +85°C. Typical values are at VCC = +3.3V, IBIAS = 60mA, IMOD = 60mA, TA = +25°C, unless otherwise noted.) (Notes 1, 2) PARAMETER SYMBOL CONDITIONS MIN TYP MAX 5mA ≤ IMOD ≤ 10mA ±20 10mA < IMOD ≤ 85mA ±15 Modulation-Current Setting Error 15Ω load, TA = +25°C Modulation Off Current TX_DISABLE = high Modulation-Current Monitor Ratio IMOD/IMC_MON 223 Average current into the MD pin 18 262 UNITS % 0.1 mA 302 mA/mA 1500 µA 1.4 V 1.15 mA/mA ±480 ppm/°C ±15 % EXTINCTION RATIO CONTROLS Monitor-Diode Input Current Range IMD MD Pin Voltage MD-Current Monitor Ratio IMD/IPC_MON APC Loop Time Constant CAPC_FILT = 0.01µF, ∆IMD/∆IBIAS = 1/70 0.85 1.0 3.3 APC Setting Stability ±100 APC Setting Accuracy TA = +25°C IMOD Compensation Setting Range by Bias K IMOD Compensation Setting Range by Temperature Threshold Setting Range for Temperature Compensation µs K = ∆IMOD/∆IBIAS 0 1.5 mA/mA TC TC = ∆IMOD/∆Τ (Note 6) 0 1.0 mA/°C TTH (Note 6) 10 60 °C LASER SAFETY AND CONTROL Bias and Modulation Turn-Off Delay CAPC_FILT = 0.01µF, ∆IMD/∆IBIAS = 1/80 (Note 6) 5 µs Bias and Modulation Turn-On Delay CAPC_FILT = 0.01µF, ∆IMD/∆IBIAS = 1/80 (Note 6) 600 µs 1.39 V Threshold Voltage at Monitor Pins VREF Figure 5 1.14 1.3 INTERFACE SIGNALS TX_DISABLE Input High VHI TX_DISABLE Input Low VLO TX_DISABLE Input Current 2.0 0.8 VHI = VCC 15 VLO = GND TX_FAULT Output Low Sinking 1mA, open collector Shutdown Output High Sourcing 100µA Shutdown Output Low Sinking 100µA Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: Note 7: Note 8: V RPULL = 7.5kΩ -450 -800 0.4 VCC 0.4 V µA V V 0.4 V AC characterization is performed using the circuit in Figure 2 using a PRBS 223 - 1 or equivalent test pattern. Specifications at -40°C are guaranteed by design and characterization. Excluding IBIAS and IMOD. Input data is AC-coupled. TX_FAULT open, SHUTDOWN open. Power-supply noise rejection (PSNR) = 20log10(Vnoise (on VCC)/∆VOUT). VOUT is the voltage across the 15Ω load when IN+ is high. The minimum required voltage at the OUT+ and OUT- pins is +0.75V. Guaranteed by design and characterization. Tested with 00001111 pattern at 2.7Gbps. DJ includes pulse-width distortion (PWD). _______________________________________________________________________________________ 3 MAX3737 ELECTRICAL CHARACTERISTICS (continued) Typical Operating Characteristics (VCC = +3.3V, CAPC = 0.01µF, IBIAS = 20mA, IMOD = 30mA, TA = +25°C, unless otherwise noted.) 1310nm FP LASER Er = 8.2dB 54ps/div MAX3737 toc02 1310nm FP LASER Er = 8.2dB OPTICAL EYE DIAGRAM (1.25Gbps, 27 - 1PRBS, 940MHz FILTER) MAX3737 toc01 OPTICAL EYE DIAGRAM (2.7Gbps, 27 - 1PRBS, 2.3GHz FILTER) 116ps/div OPTICAL EYE DIAGRAM (155Mbps, 27 - 1PRBS, 117MHz FILTER, CAPC = 0.1µF) MAX3737 toc04 MAX3737 toc03 ELECTRICAL EYE DIAGRAM (IMOD = 30mA, 2.7Gbps, 27 - 1PRBS) 75mV/div 920ps/div 52ps/div BIAS-CURRENT MONITOR GAIN vs. TEMPERATURE VCC = 3.63V VCC = 3.3V 50 45 VCC = 2.97V 40 88 86 84 82 80 78 76 70 -20 0 20 40 TEMPERATURE (°C) 4 60 80 1.05 1.00 0.95 0.85 72 -40 1.10 0.90 74 35 1.15 IMD/IPC_MON (mA/mA) 55 1.20 MAX3737 toc06 60 90 IBIAS/IBC_MON (mA/mA) IMOD = 60mA IBIAS = 60mA MAX3737 toc05 65 PHOTO-CURRENT MONITOR GAIN vs. TEMPERATURE MAX3737 toc07 SUPPLY CURRENT (ICC) vs. TEMPERATURE (EXCLUDES BIAS AND MODULATION CURRENTS) SUPPLY CURRENT (mA) MAX3737 Multirate Laser Driver with Extinction Ratio Control 0.80 -40 -15 10 35 TEMPERATURE (°C) 60 85 -40 -15 10 35 TEMPERATURE (°C) _______________________________________________________________________________________ 60 85 Multirate Laser Driver with Extinction Ratio Control MODULATION CURRENT vs. RMODSET 280 80 70 270 1.6 MAX3737 toc09 290 1.4 1.2 IMOD (mA) 260 250 240 IMD (mA) 60 50 40 220 20 210 10 1.0 0.8 0.6 30 230 0.4 0.2 0 200 10 35 60 0 1 85 10 TEMPERATURE (°C) 100 1 0.1 RMODSET (kΩ) DETERMINISTIC JITTER vs. MODULATION CURRENT 10 100 RAPCSET (kΩ) RANDOM JITTER vs. MODULATION CURRENT 45 40 MAX3737 toc12 2.0 MAX3737 toc11 50 1.5 35 RJ (psRMS) 30 25 20 1.0 15 0.5 10 5 0 0 10 20 30 40 50 60 70 80 0 90 20 40 60 80 100 IMOD (mA) IMOD (mA) TEMPERATURE COMPENSATION vs. RTH_TEMP (RMODTCOMP = 500Ω) COMPENSATION (K) vs. RMODBCOMP 10 100 MAX3737 toc14 0 MAX3737 toc13 RTH_TEMP = 12kΩ 90 80 RTH_TEMP = 7kΩ 70 RTH_TEMP = 4kΩ 1 IMOD (mA) -15 DJ (psP-P) -40 K (mA/mA) IMOD/IMC_MON (mA/mA) 90 MAX3737 toc08 300 PHOTODIODE CURRENT vs. RAPCSET MAX3737 toc10 MODULATION-CURRENT MONITOR GAIN vs. TEMPERATURE 60 RTH_TEMP = 2kΩ 0.1 50 40 30 0.01 0 0.1 1 RMODBCOMP (kΩ) 10 100 -20 0 20 40 60 80 100 TEMPERATURE (°C) _______________________________________________________________________________________ 5 MAX3737 Typical Operating Characteristics (continued) (VCC = +3.3V, CAPC = 0.01µF, IBIAS = 20mA, IMOD = 30mA, TA = +25°C, unless otherwise noted.) Typical Operating Characteristics (continued) (VCC = +3.3V, CAPC = 0.01µF, IBIAS = 20mA, IMOD = 30mA, TA = +25°C, unless otherwise noted.) TEMPERATURE COMPENSATION vs. RTH_TEMP (RMODTCOMP = 10kΩ) HOT PLUG WITH TX_DISABLE LOW MAX3737 toc15 MAX3737 toc16 44 RTH_TEMP = 12kΩ 42 3.3V VCC RTH_TEMP = 7kΩ 40 IMOD (mA) MAX3737 Multirate Laser Driver with Extinction Ratio Control RTH_TEMP = 4kΩ 0V LOW 38 FAULT RTH_TEMP = 2kΩ 36 TX_DISABLE LOW 34 t_init = 60ms 32 LASER OUTPUT 30 -20 0 20 40 60 80 100 20ms/div TEMPERATURE (°C) TRANSMITTER DISABLE TRANSMITTER ENABLE MAX3737 toc18 MAX3737 toc17 VCC 3.3V 3.3V FAULT LOW TX_DISABLE HIGH VCC FAULT t_on = 75µs LOW TX_DISABLE LOW t_off = 134ns HIGH LOW LASER OUTPUT LASER OUTPUT 40ns/div 20µs/div FAULT RECOVERY TIME RESPONSE TO FAULT MAX3737 toc20 MAX3737 toc19 VPC_MON EXTERNALLY FORCED FAULT VPC_MON EXTERNAL FAULT REMOVED t_fault = 0.9µs FAULT TX_DISABLE FAULT LOW HIGH LOW TX_DISABLE HIGH LOW LASER OUTPUT LASER OUTPUT 1µs/div 6 LOW HIGH LOW t_init = 68ms 100ms/div _______________________________________________________________________________________ Multirate Laser Driver with Extinction Ratio Control PIN NAME FUNCTION 1, 10, 15, 16 GND 2 TX_DISABLE 3, 6, 11, 18, 23 VCC 4 IN+ Noninverted Data Input 5 IN- Inverted Data Input 7 PC_MON Photodiode-Current Monitor Output. Current out of this pin develops a ground-referenced voltage across an external resistor that is proportional to the monitor-diode current. 8 BC_MON Bias-Current Monitor Output. Current out of this pin develops a ground-referenced voltage across an external resistor that is proportional to the bias current. 9 MC_MON Modulation-Current Monitor Output. Current out of this pin develops a ground-referenced voltage across an external resistor that is proportional to the modulation current amplitude. 12 TX_FAULT Open-Collector Transmit Fault Indicator (Table 1) 13 SHUTDOWN 14 VBS Bias Voltage Sense. Isolated tap (3kΩ ±15%) on the bias output reduces component count when a precision bias sense resistor is used. 17 BIAS Laser Bias-Current Output 19, 20 OUT- Inverted Modulation-Current Output (Connect Pins 19 and 20 Together). IMOD flows into this pin when input data is low. 21, 22 OUT+ Noninverted Modulation-Current Output (Connect Pins 21 and 22 Together). IMOD flows into this pin when input data is high. 24 MD 25 VMD Monitor Photodiode Voltage Sense. Isolated tap (3kΩ ±15%) on the MD input reduces component count when a precision photodiode current-sense resistor is used. 26 APCFILT1 Connect a capcitor (CAPC) between pin 26 (APCFILT1) and pin 27 (APCFILT2) to set the dominant pole of the APC feedback loop. 27 APCFILT2 (See Pin 26.) 28 APCSET A resistor connected from this pin to ground sets the desired average optical power. 29 MODSET A resistor connected from this pin to ground sets the desired constant portion of the modulation current. 30 MODBCOMP Modulation-Current Compensation from Bias. Couples the bias current to the modulation current. Mirrors IBIAS through an external resistor. Leave open for zero coupling. 31 TH_TEMP Threshold for Temperature Compensation. A resistor at this pin programs the temperature, above which compensation is added to the modulation current. Ground Transmitter Disable, TTL. Laser output is disabled when TX_DISABLE is asserted high or left unconnected. The laser ouput is enabled when this pin is asserted low. +3.3V Supply Voltage Shutdown Driver Output. Voltage output to control an external transistor for optional shutdown circuitry. Monitor Photodiode Input. Connect this pin to the anode of a monitor photodiode. A capacitor to ground is required to filter the high-speed AC monitor photocurrent. 32 Modulation-Current Compensation from Temperature. A resistor at this pin sets the temperature MODTCOMP coefficient of the modulation current when above the threshold temperature. Leave open for zero temperature compensation. EP Exposed Pad Ground. Solder the exposed pad to the circuit board ground for specified thermal and electrical performance. _______________________________________________________________________________________ 7 MAX3737 Pin Description MAX3737 Multirate Laser Driver with Extinction Ratio Control VCC VOLTAGE SINGLE ENDED VIN+ VIN- 100mV (MIN) 1200mV (MAX) VCC 30Ω 30Ω MAX3737 OUT- DIFFERENTIAL (VIN+) - (VIN-) Z0 = 30Ω OUT- 30Ω 0.5pF 200mVP-P (MIN), 2400mV (MAX) OUT+ CURRENT IOUT+ Z0 = 30Ω OUT+ IOUT+ Z0 = 50Ω 75Ω IMOD TIME OSCILLOSCOPE Figure 1. Required Input Signal and Output Polarity SOURCE NOISE VOLTAGE SUPPLY 50Ω Figure 2. Test Circuit for Characterization HOST BOARD FILTER DEFINED BY SFP MSA L1 1µH C1 0.1µF C2 10µF MODULE TO LASER DRIVER VCC OPTIONAL C3 0.1µF OPTIONAL Figure 3. Supply Filter Detailed Description The MAX3737 laser driver consists of three main parts: a high-speed modulation driver, biasing block with ERC, and safety circuitry. The circuit design is optimized for high-speed, low-voltage (+3.3V) operation (Figure 4). High-Speed Modulation Driver The output stage is composed of a high-speed differential pair and a programmable modulation current source. The MAX3737 is optimized for driving a 15Ω load. The minimum instantaneous voltage required at OUT+ is 0.7V for modulation current up to 60mA and 0.75V for currents from 60mA to 85mA. Operation above 60mA can be accomplished by AC-coupling or with sufficient voltage at the laser to meet the driver output voltage requirement. To interface with the laser diode, a damping resistor (RD) is required. The combined resistance due to the series damping resistor and the equivalent series resistance (ESR) of the laser diode should equal 15Ω. To further damp aberrations caused by laser diode parasitic inductance, an RC shunt network may be necessary. Refer to Maxim Application Note HFAN 02.0: Interfacing Maxim’s Laser Drivers to Laser Diodes for more information. 8 At data rates of 2.7Gbps, any capacitive load at the cathode of a laser diode degrades optical output performance. Because the BIAS output is directly connected to the laser cathode, minimize the parasitic capacitance associated with the pin by using an inductor to isolate the BIAS pin parasitics from the laser cathode. Extinction Ratio Control The extinction ratio (r e ) is the laser on-state power divided by the off-state power. Extinction ratio remains constant if peak-to-peak and average power are held constant: re = (2PAVG + PP-P) / (2PAVG - PP-P) Average power is regulated using APC, which keeps constant current from a photodiode coupled to the laser. Peak-to-peak power is maintained by compensating the modulation current for reduced slope efficiency (η) of the laser over time and temperature: PAVG = IMD ρMON PP-P = η x IMOD _______________________________________________________________________________________ Multirate Laser Driver with Extinction Ratio Control MAX3737 VCC SHUTDOWN MAX3737 IN+ INPUT BUFFER OUTDATA PATH IN- RD OUT+ IMOD IMOD ENABLE SAFETY LOGIC AND POWER IBIAS ENABLE DETECTOR SHUTDOWN TX_FAULT TX_DISABLE RPULL = 7.5kΩ IMD 1 BIAS VCC IBIAS VBG PC_MON xTC RMDMON IBIAS VCC x268 xK RAPCSET X1/2 IBIAS 82 IAPCSET T > TH BC_MON APCSET MD IMD RBC_MON X1 T IMOD 268 CMD MC_MON VBG RMC_MON TH_TEMP RTH_TEMP MODTCOMP RMODTCOMP MODSET RMODSET MODBCOMP RMODBCOMP APCFILT1 APCFILT2 CAPC Figure 4. Functional Diagram Modulation compensation from bias increases the modulation current by a user-selected proportion (K) needed to maintain peak-to-peak laser power as bias current increases with temperature. Refer to Maxim Application Note HFAN-02.2.1 for details: K= ∆IMOD ∆IBIAS This provides a first-order approximation of the current increase needed to maintain peak-to-peak power. Slope efficiency decreases more rapidly as temperature increases. The MAX3737 provides additional temperature compensation as temperature increases past a user-defined threshold (TTH). Safety Circuitry The safety circuitry contains a disable, input (TX_DISABLE), a latched fault output (TX_FAULT), and fault detectors (Figure 5). This circuitry monitors the operation of the laser driver and forces a shutdown if a fault is detected (Table 1). The TX_FAULT pin should be pulled high with a 4.7kΩ to 10kΩ resistor to VCC as required by the SFP MSA. A single-point fault can be a short to VCC or GND. See Table 2 to view the circuit response to various single-point failures. The transmit fault condition is latched until reset by a toggle of TX_DISABLE or VCC. The laser driver offers redundant laser diode shutdown through the optional shutdown circuitry as shown in the Typical Operating Circuit. This shutdown transistor prevents a single-point fault at the laser from creating an unsafe condition. _______________________________________________________________________________________ 9 MAX3737 Multirate Laser Driver with Extinction Ratio Control Table 1. Typical Fault Conditions 1 If any of the I/O pins is shorted to GND or VCC (single-point failure; see Table 2), and the bias current or the photocurrent exceed the programmed threshold. 2 End-of-life (EOL) condition of the laser diode. The bias current and/or the photocurrent exceed the programmed threshold. 3 Laser cathode is grounded and photocurrent exceeds the programming threshold. 4 No feedback for the APC loop (broken interconnection, defective monitor photodiode), and the bias current exceeds the programmed threshold. Table 2. Circuit Responses to Various Single-Point Faults PIN TX_FAULT CIRCUIT RESPONSE TO OVERVOLTAGE OR SHORT TO VCC CIRCUIT RESPONSE TO UNDERVOLTAGE OR SHORT TO GROUND Does not affect laser power. Does not effect laser power. Modulation and bias currents are disabled. Normal condition for circuit operation. IN+ The optical average power increases and a fault occurs if VPC_MON exceeds the threshold. The APC loop responds by decreasing the bias current. The optical average power decreases and the APC loop responds by increasing the bias current. A fault state occurs if VBC_MON exceeds the threshold voltage. IN- The optical average power decreases and the APC loop responds by increasing the bias current. A fault state occurs if VBC_MON exceeds the threshold voltage. The optical average power increases and a fault occurs if VPC_MON exceeds the threshold. The APC loop responds by decreasing the bias current. MD This disables bias current. A fault state occurs. The APC circuit responds by increasing bias current until a fault is detected, then a fault* state occurs. SHUTDOWN Does not affect laser power. If the shutdown circuitry is used, laser current is disabled. Does not affect laser power. BIAS In this condition, laser forward voltage is 0V and no light is emitted. Fault state* occurs. If the shutdown circuitry is used, laser current is disabled. OUT+ The APC circuit responds by increasing the bias current until a fault is detected, then a fault state* occurs. Fault state* occurs. If the shutdown circuitry is used, laser current is disabled. OUT- TX_DISABLE Does not affect laser power. Does not affect laser power. PC_MON Fault state* occurs. Does not affect laser power. BC_MON Fault state* occurs. Does not affect laser power. MC_MON Fault state* occurs. Does not affect laser power. APCFILT1 IBIAS increases until VBC_MON exceeds the threshold voltage. IBIAS increases until VBC_MON exceeds the threshold voltage. APCFILT2 IBIAS increases until VBC_MON exceeds the threshold voltage. IBIAS increases until VBC_MON exceeds the threshold voltage. MODSET Does not affect laser power. Fault state* occurs. APCSET Does not affect laser power. Fault state* occurs. *A fault state asserts the TX_FAULT pin, disables the modulation and bias currents, and asserts the SHUTDOWN pin. Safety Circuitry Current Monitors The MAX3737 features monitors (MC_MON, BC_MON, PC_MON) for modulation current (IMOD), bias current (IBIAS), and photocurrent (IMD). The monitors are realized 10 by mirroring a fraction of the currents and developing voltages across external resistors connected to ground. Voltages greater than VREF at MC_MON, PC_MON, or BC_MON result in a fault state. For example, connecting a ______________________________________________________________________________________ Multirate Laser Driver with Extinction Ratio Control Design Procedure When designing a laser transmitter, the optical output is usually expressed in terms of average power and extinction ratio. Table 3 gives relationships that are helpful in converting between the optical average power and the modulation current. These relationships are valid if the mark density and duty cycle of the optical waveform are 50%. For a desired laser average optical power (PAVG) and optical extinction ratio (re), the required bias and modulation currents can be calculated using the equations in Table 3. Proper setting of these currents requires knowledge of the laser to monitor transfer (ρMON) and slope efficiency (η). Programming the Monitor Diode Current Set Point The MAX3737 operates in APC mode at all times. The bias current is automatically set so average laser power is determined by the APCSET resistor: PAVG = IMD ρMON The APCSET pin controls the set point for the monitordiode current. An internal current regulator establishes the APCSET current in the same manner as the MODSET pin. See the I MD vs. R APCSET graph in the Typical Operating Characteristics and select the value of RAPCSET that corresponds to the required current at +25°C: IMD = 1 VREF × 2 RAPCSET The laser driver automatically adjusts the bias to maintain the constant average power. For DC-coupled laser diodes: I IAVG = IBIAS + MOD 2 Programming the Modulation Current with Compensation Determine the modulation current from the laser slope efficiency: IMOD = 2 × PAVG r -1 × e η re + 1 The modulation current of the MAX3737 consists of a static modulation current (IMODS), a current proportional to IBIAS, and a current proportional to temperature. The portion of IMOD set by MODSET is established by an internal current regulator, which maintains the reference voltage of VREF across the external programming resistor. See to the IMOD vs. RMODSET graph in the Typical Operating Characteristics and select the value of RMODSET that corresponds to the required current at +25°C: Table 3. Optical Power Relations SYMBOL RELATION Average power PARAMETER PAVG PAVG = (P0 + P1) / 2 Extinction ratio re r e = P1 / P 0 Optical power of a 1 P1 P1 = 2PAVG re / (re + 1) Optical power of a zero P0 P0 = 2PAVG / (re + 1) PP-P PP-P = P1 - P0 Optical amplitude η η = PP-P / IMOD Modulation current IMOD IMOD = PP-P / η Threshold current ITH P0 at I ≥ ITH Bias current (AC-coupled) IBIAS IBIAS ≥ ITH + IMOD / 2 Laser to monitor transfer ρMON IMD / PAVG Laser slope efficiency Note: Assuming a 50% average input duty cycle and mark density. ______________________________________________________________________________________ 11 MAX3737 100Ω resistor to ground at each monitor output gives the following relationships: VMC_MON = (IMOD / 268) ✕ 100Ω VBC_MON = (IBIAS / 82) ✕ 100Ω VPC_MON = IMD ✕ 100Ω External sense resistors can be used for high-accuracy measurement of bias and photodiode currents. On-chip isolation resistors are included to reduce the number of components needed to implement this function. MAX3737 Multirate Laser Driver with Extinction Ratio Control IMOD = IMODS + K × IBIAS + IMODT VREF IMODS = 268 × RMODSET IMODT = TC × (T - TTH ) | T > TTH IMODT = 0 | T ≤ TTH An external resistor at the MODBCOMP pin sets current proportional to IBIAS. Open circuiting the MODBCOMP pin can turn off the interaction between IBIAS and IMOD: K= 1700 ± 10% 1000 + RMODBCOMP If I MOD must be increased from I MOD1 to I MOD2 to maintain the extinction ratio at elevated temperature, the required compensation factor is: - I I K = MOD2 MOD1 IBIAS2 - IBIAS1 A threshold for additional temperature compensation can be set with a programming resistor at the TH_TEMP pin: TTH = - 70°C + 1.45MΩ °C ± 10% 9.2kΩ + RTH _ TEMP The temperature coefficient of thermal compensation above TTH is set by RMODTCOMP. Leaving the MODTCOMP pin open disables additional thermal compensation: TC = mA ± 10% 0.5 + RMODTCOMP (kΩ) °C 1 Current Compliance (IMOD ≤ 60mA), DC-Coupled The minimum voltage at the OUT+ and OUT- pins is 0.7V. For: VDIODE—Diode bias point voltage (1.2V typ) RL—Diode bias point resistance (5Ω typ) RD—Series matching resistor (20Ω typ) For compliance: ( Current Compliance (IMOD > 60mA), AC-Coupled For applications requiring modulation current greater than 60mA, headroom is insufficient for proper operation of the laser driver if the laser is DC-coupled. To avoid this problem, the MAX3737’s modulation output can be AC-coupled to the cathode of a laser diode. An external pullup inductor is necessary to DC-bias the modulation output at VCC. Such a configuration isolates laser forward voltage from the output circuitry and allows the output at OUT+ to swing above and below the supply voltage (V CC ). When AC-coupled, the MAX3737 modulation current can be programmed up to 85mA. Refer to Maxim Application Note HFAN 02.0: Interfacing Maxim’s Laser Drivers to Laser Diodes for more information on AC-coupling laser drivers to laser diodes. For compliance: VOUT+ = VCC - IMOD 2 ( × RD + RL ≥ 0.75V Determine CAPC The APC loop filter capacitor CAPC must be selected to balance the requirements for fast turn-on and minimal interaction with low frequencies in the data pattern. The low-frequency cutoff is: C APC (µF) ≈ 68 × (η × ρMON )1.1 f3DB (kHz) High-frequency noise can be filtered with an additional cap CMD from the MD pin to ground: CMD ≈ CAPC 4 The MAX3737 is designed so that turn-on time is faster than 1ms for most laser gain values (η ✕ ρ MON ). Choosing a smaller value of C APC reduces turn-on time. Careful balance between turn-on time and low-frequency cutoff may be needed at low data rates for some values of laser gain. Interface Models Figures 6 and 7 show simplified input and output circuits for the MAX3737 laser driver. If dice are used, replace package parasitic elements with bondwire parasitic elements. ) VOUT+ = VCC - VDIODE - IMOD × RD + RL - IBIAS × RL ≥ 0.7V 12 ) ______________________________________________________________________________________ Multirate Laser Driver with Extinction Ratio Control MAX3737 POR AND COUNTER 60ms DELAY VCC MAX3737 IMOD ENABLE TX_DISABLE 100ns DELAY COUNTER 60ms DELAY IBIAS ENABLE VCC PC_MON R IMD 1 Q VREF SHUTDOWN COMP VCC RPC_MON RS LATCH CMOS BC_MON IBIAS 82 TX_FAULT S COMP VCC RBC_MON MC_MON VREF IMOD 268 TTL OPEN COLLECTOR VREF COMP RMC_MON EXCESSIVE MODULATION CURRENT Figure 5. Simplified Safety Circuit Layout Considerations VCC MAX3737 16kΩ VCC PACKAGE 0.83nH 0.11pF 5kΩ VCC 5kΩ 0.83nH 0.11pF 24kΩ Figure 6. Simplified Input Structure To minimize loss and crosstalk, keep the connections between the MAX3737 output and the laser diode as short as possible. Use good high-frequency layout techniques and multilayer boards with uninterrupted ground plane to minimize EMI and crosstalk. Circuit boards should be made using low-loss dielectrics. Use controlled-impedance lines for data inputs, as well as the module output. Laser Safety and IEC 825 Using the MAX3737 laser driver alone does not ensure that a transmitter design is IEC 825 compliant. 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. ______________________________________________________________________________________ 13 25 VMD 26 APCFILT1 27 APCFILT2 28 APCSET 29 MODSET 30 MODBCOMP 31 TH_TEMP 32 MODTCOMP VCC VCC 3 22 OUT+ IN+ 4 21 OUT+ MAX3737ETJ VCC 17 BIAS 16 18 8 15 7 BC_MON GND PC_MON GND OUT- 14 OUT- 19 13 20 6 VBS 5 SHUTDOWN INVCC 12 OUT+ 0.11pF MD 23 11 0.82nH 24 2 VCC OUT0.11pF 1 TX_FAULT 0.82nH GND TX_DISABLE 9 PACKAGE TOP VIEW 10 VCC Pin Configurations (continued) GND Exposed-Pad (EP) Package The exposed-pad on the 32-pin QFN provides a very low thermal resistance path for heat removal from the IC. The pad is also electrical ground on the MAX3737 and should be soldered to the circuit board ground for proper thermal and electrical performance. Refer to Maxim Application Note HFAN-08.1: Thermal Considerations for QFN and Other Exposed Pad Packages at www.maximic.com for additional information. MC_MON MAX3737 Multirate Laser Driver with Extinction Ratio Control 5mm x 5mm THIN QFN *THE EXPOSED PADDLE MUST BE SOLDERED TO SUPPLY GROUND TO ACHIEVE SPECIFIED PERFORMANCE. MAX3737 Chip Information TRANSISTOR COUNT: 2727 PROCESS: SiGe/Bipolar Figure 7. Simplified Output Structure 14 ______________________________________________________________________________________ Multirate Laser Driver with Extinction Ratio Control +3.3V OPTIONAL SHUTDOWN CIRCUITRY IN+ SHUTDOWN TX_FAULT TX_DISABLE 0.1µF VCC +3.3V 0.01µF +3.3V 15Ω OUT10Ω 0.1µF OUT+ INBIAS RMODBCOMP MODBCOMP FERRITE BEAD MAX3737 MD RMODTCOMP CMD MODTCOMP RTH_TEMP RMODSET RAPCSET CAPC RMC_MON RBC_MON PC_MON BC_MON MC_MON APCFILT2 APCFILT1 APCSET MODSET TH_TEMP GND CDR RPC_MON REPRESENTS A CONTROLLED-IMPEDANCE TRANSMISSION LINE ______________________________________________________________________________________ 15 MAX3737 Typical Operating Circuit Package Information (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) 32L QFN.EPS MAX3737 Multirate Laser Driver with Extinction Ratio Control 16 ______________________________________________________________________________________ Multirate Laser Driver with Extinction Ratio Control b CL 0.10 M C A B D2/2 D/2 PIN # 1 I.D. QFN THIN.EPS D2 0.15 C A D k 0.15 C B PIN # 1 I.D. 0.35x45 E/2 E2/2 CL (NE-1) X e E E2 k L DETAIL A e (ND-1) X e CL CL L L e e 0.10 C A C 0.08 C A1 A3 PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE 16, 20, 28, 32L, QFN THIN, 5x5x0.8 mm APPROVAL COMMON DIMENSIONS DOCUMENT CONTROL NO. REV. 21-0140 C 1 2 EXPOSED PAD VARIATIONS NOTES: 1. DIMENSIONING & TOLERANCING CONFORM TO ASME Y14.5M-1994. 2. ALL DIMENSIONS ARE IN MILLIMETERS. ANGLES ARE IN DEGREES. 3. N IS THE TOTAL NUMBER OF TERMINALS. 4. THE TERMINAL #1 IDENTIFIER AND TERMINAL NUMBERING CONVENTION SHALL CONFORM TO JESD 95-1 SPP-012. DETAILS OF TERMINAL #1 IDENTIFIER ARE OPTIONAL, BUT MUST BE LOCATED WITHIN THE ZONE INDICATED. THE TERMINAL #1 IDENTIFIER MAY BE EITHER A MOLD OR MARKED FEATURE. 5. DIMENSION b APPLIES TO METALLIZED TERMINAL AND IS MEASURED BETWEEN 0.25 mm AND 0.30 mm FROM TERMINAL TIP. 6. ND AND NE REFER TO THE NUMBER OF TERMINALS ON EACH D AND E SIDE RESPECTIVELY. 7. DEPOPULATION IS POSSIBLE IN A SYMMETRICAL FASHION. 8. COPLANARITY APPLIES TO THE EXPOSED HEAT SINK SLUG AS WELL AS THE TERMINALS. 9. DRAWING CONFORMS TO JEDEC MO220. 10. WARPAGE SHALL NOT EXCEED 0.10 mm. PROPRIETARY INFORMATION TITLE: PACKAGE OUTLINE 16, 20, 28, 32L, QFN THIN, 5x5x0.8 mm APPROVAL DOCUMENT CONTROL NO. REV. 21-0140 C 2 2 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 ____________________ 17 © 2003 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products. MAX3737 Package Information (continued) (The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)