19-2247; Rev 1; 4/02 2.5Gbps Laser Driver with Automatic Modulation Control Features ♦ Single +3.3V or +5V Power Supply ♦ 68mA Supply Current ♦ Up to 2.5Gbps (NRZ) Operation ♦ Feedback Control for Constant Average Power ♦ Feedback Control for Constant Extinction Ratio ♦ Programmable Bias Current Up to 100mA ♦ Programmable Modulation Current Up to 60mA ♦ 84ps Rise/Fall Time ♦ Selectable Data Retiming Latch ♦ Bias and Modulation Current Monitors ♦ Failure Detector ♦ ESD Protection Ordering Information Applications PART SONET/SDH Transmission Systems Add/Drop Multiplexers TEMP. RANGE PIN-PACKAGE MAX3865EGJ -40°C to +85°C 32 QFN MAX3865E/D -40°C to +85°C Dice* *Dice are designed to operate from -40°C to +85°C , but are tested and guaranteed at TA = +25°C only. Contact factory for availability. Digital Cross-Connects Section Regenerators Pin Configuration appears at end of data sheet. 2.5Gbps Optical Transmitters Typical Applications Circuit +3.3V +3.3V LED +3.3V 200Ω 200Ω 20Ω DATA+ 50Ω DATA+ FAIL EN1 MODMON DATA- BIASMON 50Ω EN0 VCC DATA- RTEN LP LASER LP 0.056µF MODN 20Ω MODQ 20Ω 15Ω 0.056µF VDR MAX3865 BIAS BIAS_X VCR 50Ω CLK- MD MD_X RMODMAX RBIASMAX APCSET CLK- BIASMAX CLK+ MODMAX 50Ω GND 2.5Gbps SERIALIZER CLK+ AMCSET +3.3V MAX3892 RAPCSET REPRESENTS A CONTROLLED-IMPEDANCE TRANSMISSION LINE RAMCSET †Covered by U.S. Patent numbers 5,883,910, 5,850,409, and other patent pending. ________________________________________________________________ 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 MAX3865† General Description The MAX3865 is designed for direct modulation of laser diodes at data rates up to 2.5Gbps. It incorporates two feedback loops, the automatic power-control (APC) loop and the automatic modulation-control (AMC) loop, to maintain constant average optical output and extinction ratio over temperature and laser lifetime. External resistors or current output DACs may set the laser output levels. The driver can deliver up to100mA of laser bias current and up to 60mA laser modulation current with a typical (20% to 80%) edge speed of 84ps. The MAX3865 accepts differential clock and data input signals with on-chip 50Ω termination resistors. The inputs can be configured for CML or other high-speed logic. An input data-retiming latch can be enabled to reject input pattern-dependent jitter when a clock signal is available. The MAX3865 provides laser bias current and modulation current monitors, as well as a failure detector, to indicate the laser operating status. These features are all implemented on an 81mil ✕ 103mil die; the MAX3865 is also available as a 32-pin QFN package. MAX3865 2.5Gbps Laser Driver with Automatic Modulation Control ABSOLUTE MAXIMUM RATINGS Voltage at Any Pin...............................................................+7.0V Supply Voltage (VCC) ............................................-0.5V to +7.0V Voltage at VCR, VDR, DATA+, DATA-, CLOCK+, and CLOCK- Pins ..................-0.5V to (VCC + 0.5V) Voltage at DATA+ and DATA- Pins ..................................(VDR - 1.2V) to (VDR + 1.2V) Voltage at CLK+ and CLK- Pins ......(VCR - 1.2V) to (VCR + 1.2V) Voltage at MODQ and MODN Pins ................0V to (VCC + 1.5V) Voltage at Any Other Pins (RTEN, EN0, EN1, FAIL, MODMAX, BIASMAX, AMCSET, APCSET, MD_X, BIAS, BIAS_X, BIASMON, MODMON) ............-0.5V to (VCC + 0.5V) Current into BIAS Pin ......................................-20mA to +150mA Current into MODQ and MODN Pins ..............-20mA to +100mA Current into MD Pin...........................................-10mA to +10mA Operating Junction Temperature .....................-55°C to +150°C Storage Temperature Range .............................-55°C to +150°C Continuous Power Dissipation (TA = +85°C) 32-Pin QFN (derate 21.2mW/°C above +85°C) ................1.3W Lead Temperature (soldering, 10s) .................................+300°C Processing Temperature (die) .........................................+400°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 = +3.14V to +3.6V or +4.5V to +5.5V, TA = -40°C to +85°C. Typical values are at VCC = +3.3V, IBIAS = 50mA, IMOD = 30mA, TA = +25°C, unless otherwise noted.) (Notes 1, 2, 3) PARAMETER SYMBOL TYP MAX VCC = +3.14V to +3.6V (Note 4) CONDITIONS 68 85 69 90 Power-Supply Current ICC VCC = +4.5V to +5.5V, typical current at VCC = +5.0V (Note 4) Differential Input Voltage VID Data and clock inputs (Figure 2) MIN mA 0.2 1.6 Vp-p Data and clock inputs (Figure 2) (Note 5) 1.3 VCC + 0.4V V Single-Ended Input Resistance Input to VDR, VCR 40 60 Ω Input Return Loss, for Data+, Data-, Clock+, and Clock- f ≤ 2.7GHz 20 2.7GHz < f < 4GHz 17 Instantaneous Input Voltage RLIN Bias-Current Setting Range EN0, EN1 = low Bias-Current Setting Accuracy APC off IBIAS = 100mA IBIAS = 1mA (Note 5) 100 mA 0.1 mA ±15 % mA VCC + 0.4 1 48 IMOD Modulation Off Current 5 EN0, EN1 = low Modulation-Current Setting Accuracy AMC off Compliance Voltage for MODQ and MODN (Note 5) IMOD = 60mA IMOD = 5mA +3.14V ≤ VCC ≤ +3.6V 1.8 +4.5V ≤ VCC ≤ +5.5V 1.8 60 mA 0.1 mA ±15 % mA VCC + 1.2 5.5 32 Compliance Voltage for BIASMON and MODMON (Note 5) VMD 1.0 _______________________________________________________________________________________ V mA/mA VCC + 0.4 1.8 V mA/mA ±0.25 IMOD to IMODMON Ratio Voltage at MD Pin dB ±0.1 IBIAS to IBIASMON Ratio Modulation-Current Setting Range 50 1 Bias Off Current Compliance Voltage for BIAS and BIAS_X 2 UNITS V V 2.5Gbps Laser Driver with Automatic Modulation Control (VCC = +3.14V to +3.6V or +4.5V to +5.5V, TA = -40°C to +85°C. Typical values are at VCC = +3.3V, IBIAS = 50mA, IMOD = 30mA, TA = +25°C, unless otherwise noted.) (Notes 1, 2, 3) PARAMETER SYMBOL Bias-Setting Accuracy at MD Pin Modulation-Setting Accuracy at MD Pin CONDITIONS MIN TYP MAX IMD = 1mA ±15 % IMD = 36µA ±10 µA (Note 6) IMD = 1mA ±15 % IMD = 36µA ±10 µA EN0, EN1, and RTEN Input High 2.0 V EN0, EN1, and RTEN Input Low 0.8 FAIL Output High UNITS Source 50µA 2.4 V V FAIL Output Low Sink 100µA 0.4 V FAIL Current Low state, VOL forced to VCC 5.0 mA Setup/Hold Time tSU, tHD Output Edge Speed t R , tF (Figure 2) (Note 5) 100 ps Load = 20Ω, 20% to 80% (Notes 5, 7) 84 Output Overshoot (Notes 5, 7) 9 130 % Enable/Startup APC and AMC off 150 ns Maximum CID (Notes 2, 5) Deterministic Jitter (Notes 2, 5) 22 Random Jitter (Notes 5, 7) 1.6 psRMS 1 MHz AMC Pilot Tone Frequency Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: Note 7: fAMC 80 ps bit 50 psp-p AC characterization performed using the circuit in Figure 1. Measured using a 2.5Gbps 213 - 1 PRBS with 80 0’s and 80 1’s input data pattern. Specifications at -40°C are guaranteed by design and characterization. VCC current excludes the current into MODQ, MODN, BIAS, BIAS_X, MODMON, and BIASMON pins. Guaranteed by design and characterization. Measured with low-frequency data. Instantaneous current into MD pin range is 36µA to 1000µA. Measured using a 2.5Gbps repeating 0000 0000 1111 1111 pattern. _______________________________________________________________________________________ 3 MAX3865 ELECTRICAL CHARACTERISTICS (continued) MAX3865 2.5Gbps Laser Driver with Automatic Modulation Control VCC RTEN DATA- 50Ω VCC VCC 33Ω DATA- OSCILLOSCOPE 0.1µF MODN DATA+ PATTERN GENERATOR 50Ω DATA+ VCC 50Ω MODQ VDR VCR CLK+- 50Ω 33Ω CLK+ MAX3865 50Ω VCC BIAS CLK- 50Ω 0.1µF CLK- BIAS_X GND EN1 EN0 VCC Figure 1. Test Circuit VCC + 0.4V CLK+ 0.1V–0.8V CLK1.3V tSU tHD VCC + 0.4V DATA+ 0.1V–0.8V DATA1.3V (DATA+) - (DATA-) IMODQ VID = 0.2Vp-p–1.6Vp-p 5mA–60mA Figure 2. Required Input Signal, Setup/Hold-Time Definition, and Output Polarity 4 _______________________________________________________________________________________ 2.5Gbps Laser Driver with Automatic Modulation Control OPTICAL EYE DIAGRAM (EXTINCTION RATIO = 8.25dB, 213-1 PRBS AT 2.5Gbps, 1.87GHz FILTER) MAX3865 toc01 PATTERN 213 - 1 PRBS DATA RATE = 2.5Gbps 58ps/div 58ps/div 58ps/div SUPPLY CURRENT (ICC) vs. TEMPERATURE (EXCLUDES BIAS AND MODULATION CURRENTS) DETERMINISTIC JITTER vs. TEMPERATURE (IMODQ = 60mA) TYPICAL DISTRIBUTION OF RISE TIME (WORST-CASE CONDITIONS) VCC = +3.3V 65 60 80 70 60 50 40 30 20 55 25 PERCENT OF UNITS (%) VCC = +5.0V 70 90 DETERMINISTIC JITTER (ps) 75 30 MAX3865 toc05 MAX3865 toc04 100 20 MAX 3865 toc06 PATTERN 213 - 1 PRBS DATA RATE = 2.5Gbps 80 ELECTRICAL MEASUREMENT IMODQ = 60mA VCC = +3.14V TA = +85°C 15 10 5 10 50 0 10 35 60 85 0 -40 -20 0 20 40 60 80 RISE TIME (ps) TYPICAL DISTRIBUTION OF FALL TIME (WORST-CASE CONDITIONS) 20 ELECTRICAL MEASUREMENT IMODQ = 60mA VCC = +3.14V TA = +85°C DIFFERENTIAL |S11| vs. FREQUENCY -15 15 10 MAX3865 toc08 30 25 100 102 104 106 108 110 112 114 116 118 120 TEMPERATURE (°C) TEMPERATURE (°C) -17 -19 -21 |S11| (dB) -15 MAX 3865 toc07 -40 PERCENT OF UNITS (%) SUPPLY CURRENT (mA) MAX3865 toc03 ELECTRICAL EYE DIAGRAM (IMODQ = 30mA) MAX3865 toc02 ELECTRICAL EYE DIAGRAM (IMODQ = 60mA) -23 -25 -27 -29 -31 5 -33 0 -35 100 102 104 106 108 110 112 114 116 118 120 FALL TIME (ps) 0 500 1000 1500 2000 2500 3000 3500 4000 FREQUENCY (MHz) _______________________________________________________________________________________ 5 MAX3865 Typical Operating Characteristics (TA = +25°C, unless otherwise noted.) 2.5Gbps Laser Driver with Automatic Modulation Control MAX3865 Pin Description 6 PIN NAME 1, 8, 19, 22, 28 VCC FUNCTION Positive Supply Voltage 2 DATA- Complementary Data Input, with On-Chip Termination 3 DATA+ Data Input, with On-Chip Termination 4 VDR Termination Reference Voltage for Data Inputs 5 VCR Termination Reference Voltage for Clock Inputs 6 CLK+ Clock Input for Data Retiming, with On-Chip Termination 7 CLK- Complementary Clock Input for Data Retiming, with On-Chip Termination 9, 16, 23, 24, 25 GND No Internal Connection. Tie to ground. 10 RTEN 11 EN0 Data Retiming Enable Input, TTL Compatible, Active-High Operating Mode Input, TTL Compatible 12 EN1 Operating Mode Input, TTL Compatible 13 FAIL Fault Warning, TTL Compatible. Low for fault condition. 14 BIASMON 15 MODMON 17 BIAS_X 18 BIAS Bias-Current Monitor. Open-collector type, tie to VCC if not used. Modulation-Current Monitor. Open-collector type, tie to VCC if not used. Bias Shunt. Always tie to the BIAS pin. Laser Bias-Current Output. Connect to the laser via an inductor. 20 MODN 21 MODQ Modulation-Current Output to Dummy Load Modulation-Current Output to Laser 26 MD Feedback Input from Monitor Diode 27 MD_X 29 AMCSET Monitor Diode Modulation-Current (Peak-to-Peak) Set Point 30 APCSET Monitor Diode Bias-Current (Average) Set Point 31 MODMAX 32 BIASMAX EP Exposed Paddle Monitor Diode Shunt. Connect to GND when laser diode to monitor current gain ≤ 0.005. Connect to the MD pin for gain ≥ 0.02. For 0.005 < gain < 0.02 connect to either GND or the MD pin. Connect an external resistor to ground to program IMOD in the MANUAL and APC modes. The resistor sets the maximum IMOD in AMC mode. The AMC loop may reduce IMOD from its maximum but cannot add to it. Connect an external resistor to ground to program IBIAS in the MANUAL mode. The resistor sets the maximum IBIAS in the APC and AMC modes. The APC loop may reduce IBIAS from its maximum but cannot add to it. The exposed paddle and corner pins must be soldered to ground. _______________________________________________________________________________________ 2.5Gbps Laser Driver with Automatic Modulation Control EN0 EN1 OPERATING MODE 0 0 Shutdown DESCRIPTION 0 1 Manual BIASMAX programs laser bias, MODMAX programs modulation 1 0 APC APCSET programs laser bias, MODMAX programs modulation 1 1 AMC AMCSET programs modulation current and APCSET programs bias Bias and modulation currents off Detailed Description The MAX3865 laser driver consists of two main parts: a high-speed modulation driver and biasing block as shown in Figure 4. Outputs to the laser diode are a switched modulation current and a steady bias current. Two servo loops may be enabled to control bias and modulation currents for constant optical power and extinction ratio. The MAX3865 requires a laser with a built-in monitor diode to provide feedback about the optical output. The average laser power, as sensed by the monitor diode, is controlled by the APC servo loop. Peak-topeak modulation current is controlled by the AMC servo loop. The modulation output stage uses a programmable current source with a maximum current of 60mA. A high-speed differential pair switches this source to the laser diode. The clock and data inputs to the modulation driver may use CML, PECL, and other logic levels. The optional clock signal can be used to synchronize data transitions for minimum pattern-dependent jitter. Clock/Data Input Logic Levels The MAX3865 is directly compatible with VCC-referenced CML. Other logic interfaces are possible. For VCC-referenced CML or AC-coupled logic, tie VDR and VCR to VCC. For other DC-coupled differential signals, float VDR and VCR (Figure 5). To prevent excess power dissipation in the input matching resistors, keep the instantaneous input voltage within 1.2V of VDR or VCR as specified in the electrical characteristics. Optional Input Data Retiming To eliminate pattern-dependent jitter in the input data, a synchronous differential clock signal should be connected to the CLK+ and CLK- inputs, and the RTEN control input should be tied high. Input data retiming occurs on the rising edge of CLK+. If RTEN is tied low, the retiming function is disabled and the input data is directly connected to the output stage. When no clock is available, tie CLK+ to VCC, ground CLK- through a 1.5kΩ resistor, and leave VCR open. Operating Mode The MAX3865 can be set in four operating modes, depending on applications requirements. Mode selection is by two TTL-compatible inputs (see Table 1). APC Loop In APC mode, a servo loop maintains the average current from the monitor diode at a level set by the APCSET input. Laser bias current is varied in this mode to maintain the monitor diode current. The BIASMAX input must be set to a value larger than the maximum expected bias current. In this mode, BIASMAX limits the maximum bias current to the laser if the control loop fails. The FAIL pin will go low if average IMD ≠ IAPCSET. Mark-Density Compensation Average power control assumes 50% mark density for times greater than about 100ns. For long patterns or situations where 50% mark density does not apply, the MAX3865 provides mark-density compensation. The APCSET reference is increased by an amount proportional to the mark density multiplied by the modulation amplitude. The AMCSET input is used as an estimate of the peak-to-peak modulation current when the mark density is not 50%. Mark-density compensation is active in both APC and AMC control modes. AMC Loop In AMC mode, a servo loop maintains the peak-to-peak current from the monitor diode at a level set by the AMCSET input. Laser modulation current is varied in this mode to maintain the monitor diode current. The MODMAX input must be set to a value larger than the maximum expected modulation current. In this mode, MODMAX limits the maximum modulation current to the laser if the control loop fails. The FAIL pin will go low if peak-to-peak IMD ≠ IAMCSET. The APC loop is active when in the AMC mode. In AMC mode, mark-density compensation is automatic. _______________________________________________________________________________________ 7 MAX3865 Table 1. Mode Selection Warning Outputs A TTL-compatible, active-low warning flag, FAIL, is set when: • One or more of the programmable currents is set at greater than 150% of the rated maximum for the chip. A shorted programming resistor would cause this warning. In this case, the bias and modulation outputs are shut down to protect the laser. Table 2. Optical Power Relations • Average IMD ≠ IAPCSET in the APC or AMC mode. This could be caused by too low a setting for maximum IBIAS or by a laser that has exceeded its useful life. The FAIL flag also is set for a few microseconds following power-up, until the servo loops settle. The BIASMON and MODMON pins can be used to monitor the laser current and predict the end of the useful laser life before a failure occurs. Design Procedure When designing a laser transmitter, the optical output is usually expressed in terms of average power and extinction ratio. Table 2 gives relationships that are helpful in converting between the optical power and the PARAMETER SYMBOL Average Power PAVG Extinction Ratio re r e = P1 / P 0 Optical Power of a “1” P1 P1 = 2PAVG ✕ re/( re + 1) Optical Power of a “0” P0 P0 = 2PAVG/( re + 1) Optical Amplitude Pp-p Pp-p = P1 - P0 η η = Pp-p/IMOD Laser Slope Efficiency • Peak-to-peak IMD ≠ IAMCSET in the AMC mode. This could be caused by too low a setting for IMODMAX or by a laser which has exceeded its useful life. Laser to Monitor Diode Transfer ρMON EN0 ρMON = IMD / PAVG 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 modulation current can be calculated based on the laser slope efficiency, η, using the equations in Table 2. +5V VCC EN1 RTEN RELATION PAVG = (P0 + P1)/2 Note: Assuming a 50% average input duty cycle and mark density. +5V 20Ω MODN DATA- 20Ω IMODQ 15Ω 20Ω MODQ DATA+ IBIAS MAX3865 BIAS BIAS_X CLK+ IMD MD RMODMAX APCSET BIASMAX RBIASMAX AMCSET CLKMODMAX MAX3865 2.5Gbps Laser Driver with Automatic Modulation Control RAPCSET RAMCSET Figure 3. DC-Coupled Laser Circuit 8 _______________________________________________________________________________________ 2.5Gbps Laser Driver with Automatic Modulation Control P r −1 IMOD = 2 × AVG × e re + 1 η • For DC-coupled laser diodes: IBIAS > ITH Droop = Number _ CID Data _ Rate × LP × C If droop = 6.7%, number_CID = 100 and data_rate = 2.5Gbps, then possible values for LP and C may be LP = 6µH and C = 0.056µF. Both L and C must be increased in value to reduce droop without ringing. Programming the Maximum Bias Current where ITH is the laser threshold current. • For AC-coupled laser diodes: I IBIAS > ITH + MOD 2 Given the desired parameters for operation of the laser diode, the programming of the MAX3865 is explained in the following text. Current Limits To keep the modulation current in compliance with the programmed value, the following constraint on the total modulation current must be made: DC-Coupled Laser Diodes: VCC - VDIODE - IMOD ✕ (RD + RL) - IBIAS ✕ RL ≥ 1.8V • For VDIODE—Laser diode bias point voltage (1.2V typ) RL—Laser diode bias-point resistance (5Ω typ) RD—Series matching resistor (15Ω typ) AC-Coupled Laser Diodes: To allow larger modulation current, the laser can be AC-coupled to the MAX3865 as shown in the Typical Application Circuit. In this configuration, a constant current is supplied from the inductor LP. The requirement for compliance in the AC-coupled circuit is as follows: I VCC − MOD × (RD + RL ) ≥ 1.8V 2 The AC-coupling capacitor and bias inductor form a second-order high-pass circuit. Pattern-dependent jitter results from the low-frequency cutoff of this high-pass circuit. To prevent ringing: (RD + RL ) ≥ 2 × formed by the LC circuit must be low enough to limit the droop. LP C For deviation from 50% duty cycle or for runs of consecutive identical digits (CID), the low-frequency corner In AMC (or APC) mode, the bias current needs a limit if the loop becomes open. RBIASMAX sets the maximum allowed bias current. The bias current is proportional to the current through RBIASMAX. An internal current regulator maintains the band-gap voltage of 1.2V across the programming resistors. Select the maximum IBIAS programming resistor as follows: IBIASMAX = 480 × 1.2V RBIASMAX + 2kΩ Alternatively, a current DAC forcing I DAC from the BIASMAX pin may set the current maximum: IBIASMAX = 480 ✕ IDAC When the AMC or APC loop is enabled, the actual bias current is reduced below the maximum value to maintain a constant average current from the monitor diode. With closed-loop control, the bias current will be determined by the transfer function of the monitor diode to laser-diode current. For example, if the transfer function to the monitor diode is 10.0µA/mA, then setting IMD for 500µA will result in IBIAS equal to 50mA. In manual mode, the bias current IBIAS is IBIASMAX as set by RBIASMAX. Programming the Average Monitor Diode-Current Set Point The APCSET pin controls the set point for the average monitor diode current when in AMC or APC mode. The APCSET current is externally established in the same manner as the BIASMAX pin. The average monitor diode current IMD can be programmed with a resistor as follows: average _ IMD = 5 × 1.2V RAPCSET + 2kΩ Alternatively, a current DAC at the APCSET pin can set the monitor diode current by: average IMD = 5 ✕ IDAC _______________________________________________________________________________________ 9 MAX3865 Laser Current Requirements Bias and modulation current requirements can be determined from the laser threshold current and slope efficiency. The modulation and bias currents under a single operating condition are: MAX3865 2.5Gbps Laser Driver with Automatic Modulation Control Mark-Density Compensation in APC Mode When mark density is expected to deviate from 50% for periods exceeding 5% of the APC time constant, the AMCSET pin should be programmed to compensate the APC set point. The time constant is determined by the laser to monitor diode gain. τ APC = GMD = 1.5ns GMD Set the estimated peak-to-peak monitor diode current by the following equation: 1.2V RAMCSET + 2kΩ Alternatively, a current DAC at the AMCSET pin can set the monitor diode current by: Estimated IMD(p-p) = 5 ✕ IDAC Programming the Maximum Modulation Current In AMC mode, the modulation current needs a limit if the loop becomes open. RMODMAX sets the maximum allowed modulation current. The modulation current is proportional to the current through RMODMAX. Select the maximum IMOD programming resistor as follows: 1.2V <0.005 GND or Open 0.005 to 0.02 (Open or GND) or MD >0.02 MD IMD(p−p) = 5 × 1.2V RAMCSET + 2kΩ Alternatively a current DAC at the AMCSET pin can set the monitor diode current by: IMD(p-p) = 5 ✕ IDAC Laser Gain Compensation The MAX3865 may be used in closed-loop operation with a wide variety of laser-to-monitor diode gains. Table 3 shows the connection of the MD_X pin for different current-gain ranges. Current Monitor Outputs The MAX3865 provides bias and modulation current monitors. The BIASMON output sinks a current proportional to the bias current: I IBIASMON = BIAS 48 RMODMAX + 2kΩ Alternatively, a current DAC forcing I DAC from the MODMAX pin may set the current maximum IMODMAX = 320 ✕ IDAC When the AMC loop is enabled, the actual modulation current is reduced from the maximum value to maintain constant peak-to-peak current from the monitor diode. With closed-loop control, the modulation current will be determined by the transfer function of the monitor diode to laser diode current. For example, if the transfer function to the monitor diode is 10.0µA/mA, then setting IMD for 500µA will result in IMOD equal to 50mA. In manual mode, the modulation current IMOD is set by RMODMAX. 10 MD_X SHUNT CONNECTION The AMCSET pin controls the set point for the peak-topeak monitor diode current in AMC mode. The peak-topeak value of the monitor diode current can be programmed with a resistor as follows: (For example, τAPC = 150ns for GMD = 0.01mA/mA.) IMODMAX = 320 × LASER-TO-MONITOR DIODE-CURRENT GAIN Programming the Peak-to-Peak Monitor Diode-Current Set Point ∆IMONITOR ∆ILASER Estimated IMD(p−p) = 5 × Table 3. Connection of the MD_X Pin The MODMON pin sinks a current proportional to the laser modulation current: I IMODMON = MOD 32 The BIASMON and MODMON pins should not be allowed to drop below 1.8V. They should be tied to VCC when not in use. ______________________________________________________________________________________ 2.5Gbps Laser Driver with Automatic Modulation Control MAX3865 VCC RTEN 20Ω MODN o DATA MUX D MODQ 1 Q IMODO CD CLK BIAS MONITOR DIODE FEEDBACK CONTROL LOGIC EN1 LOOP MONITOR FAIL OVERCURRENT + ∑ - BIAS CONTROL x5 VBG RAMCSET + x5 VBG RAPCSET x320 MAX3865 IMD ∑ - MODULATION CONTROL SHUTDOWN EN0 MD RD IBIAS x480 VBG VBG RMODMAX RBIASMAX Figure 4. Functional Diagram VCC VCC MODQ MODN GND VDR 50Ω 50Ω DATA+ DATA- IMOD DATA AND CLOCK INPUT CIRCUITS ARE EQUIVALENT GND GND Figure 5. Equivalent Input Circuit Figure 6. Equivalent Modulation Output Circuit ______________________________________________________________________________________ 11 Applications Information Layout Considerations To minimize loss and crosstalk, keep the connections between the MAX3865 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 the clock and data inputs as well as the modulation output. References For further information, refer to the application notes for fiber optic circuits, HFAN-02, on the Maxim web page. 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. Chip Information TRANSISTOR COUNT: 1690 Substrate Connected To GND PROCESS: Bipolar DIE SIZE: 81mil ✕ 103mil Laser Safety and IEC 825 Using the MAX3865 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, BIASMAX MODMAX APCSET AMCSET VCC MD_X MD GND 31 30 29 28 27 26 25 TOP VIEW 32 Pin Configuration VCC 1 24 GND DATA- 2 23 GND DATA+ 3 22 VCC VDR 4 21 MODQ VCR 5 20 MODN CLK+ 6 19 VCC CLK- 7 18 BIAS VCC 8 17 BIAS_X 12 13 14 15 16 EN1 BIASMON MODMON GND 11 EN0 FAIL 9 10 GND MAX3865 RTEN MAX3865 2.5Gbps Laser Driver with Automatic Modulation Control THE EXPOSED PADDLE MUST BE SOLDERED TO SUPPLY GROUND ON THE CIRCUIT BOARD 12 ______________________________________________________________________________________ 2.5Gbps Laser Driver with Automatic Modulation Control N.C. GND BIASMAX MODMAX APCSET AMCSET VCC MD_X MD GND N.C. N.C. BP9 BP10 BP11 BP12 BP13 BP14 BP15 BP16 BP17 BP18 BP19 BP20 VCC BP8 BP21 N.C. DATA- BP7 BP22 N.C. DATA+ BP6 BP23 VCC VDR BP5 BP24 MODQ 81mil 2.06mm BP34 BP33 BP32 BP31 BP30 BP29 GND FAIL BIASMON MODMON GND GND BIAS_X BP35 BP28 GND BP1 BP36 VCC EN1 BIAS BP37 BP27 EN0 BP2 BP38 CLK- RTEN VCC BP39 BP26 GND BP3 CLK+ BP40 MODN BP4 GND BP25 VCR 103mil 2.62mm Note: N.C. means no external connection permitted. Leave these pads unconnected. ______________________________________________________________________________________ 13 MAX3865 Chip Topography MAX3865 2.5Gbps Laser Driver with Automatic Modulation Control Pad Coordinates NAME PAD VCC BP1 COORDINATES (µm) 46, 46 NAME N.C. PAD BP21 COORDINATES (µm) 2382, 1423 CLK- BP2 46, 241 N.C. BP22 2382, 1229 CLK+ BP3 46, 435 VCC BP23 2382, 1034 VCR BP4 46, 629 MODQ BP24 2382, 840 VDR BP5 46, 824 MODN BP25 2382, 646 DATA+ BP6 46, 1018 VCC BP26 2382, 451 DATA- BP7 46, 1213 BIAS BP27 2382, 257 2382, 62 VCC BP8 46, 1407 BIAS_X BP28 N.C. BP9 151, 1607 GND BP29 2287, -153 GND BP10 346, 1607 GND BP30 2093, -153 1898, -153 BIASMAX BP11 540, 1607 MODMON BP31 MODMAX BP12 735, 1607 BIASMON BP32 1704, -153 APCSET BP13 929, 1607 FAIL BP33 1510, -153 AMCSET BP14 1123, 1607 GND BP34 1315, -153 VCC BP15 1318, 1609 GND BP35 1121, -153 MD_X BP16 1512, 1609 EN1 BP36 926, -153 732, -153 MD BP17 1707, 1607 EN0 BP37 GND BP18 1901, 1607 RTEN BP38 538, -153 N.C. BP19 2095, 1607 GND BP39 343, -153 N.C. BP20 2290, 1607 GND BP40 149, -153 Coordinates are for the center of the pad. Coordinate 0, 0 is the lower left corner of the passivation opening for pad 1. 14 ______________________________________________________________________________________ 2.5Gbps Laser Driver with Automatic Modulation Control ______________________________________________________________________________________ 15 MAX3865 Package Information 2.5Gbps Laser Driver with Automatic Modulation Control MAX3865 Package Information (continued) 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. 16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.