19-3848; Rev 3; 5/12 KIT ATION EVALU E L B A IL AVA 155Mbps to 2.5Gbps Burst-Mode Laser Driver Features The MAX3643 burst-mode laser driver provides bias and modulation current drive for PON burst-mode ONT applications. It is specifically designed for use with a low-cost external controller for the APC (and if desired, AMC) loop. A high-speed differential burst-enable input enables the driver to switch the laser from a dark (output off) condition to full on-condition in less than 2ns. When BEN is inactive, typical modulation and bias currents are 5µA each. Laser modulation current can be set from 10mA to 85mA and bias current can be set from 1mA to 70mA using the MODSET and BIASSET inputs. A sample-andhold circuit is provided to capture the monitor diode output during short PON bursts, if needed, and the BEN high-speed signal is mirrored on an LVCMOS output to be used by the controller operating the APC/AMC loop. o 10mA to 85mA Modulation Current o 1mA to 70mA Bias Current o Monitor Diode Sample and Hold o 45ps Output Transition Time o 2ns Turn-On/-Off Time o Reference Voltage Generator o LVPECL High-Speed Inputs (Data, Burst Enable) Ordering Information PART The MAX3643 burst-mode laser driver is packaged in a 4mm x 4mm, 24-pin thin QFN package. It operates from -40°C to +85°C. TEMP RANGE PIN-PACKAGE MAX3643ETG -40°C to +85°C 24 TQFN-EP* MAX3643ETG+ -40°C to +85°C 24 TQFN-EP* +Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed paddle. Applications A/B/G/XGPON ONT Modules Up to 2.5Gbps Pin Configuration appears at end of data sheet. 1.25Gbps IEEE EPON ONT Modules Typical Application Circuit 3.3V 15Ω 3.3V +3.3V 130Ω FILTER 130Ω VCC SERIAL DATA SOURCE 10nH Z0 = 50Ω IN+ Z0 = 50Ω IN- 15Ω OUT5.6Ω OUT+ 82Ω 82Ω 10pF 5.6Ω 75Ω 1kΩ BIAS+ MAX3643 27pF 3.3V +3.3V 10Ω BIAS- 82Ω BCMON BENOUT BIASSET VBSET VREF BEN- MODSET Z0 = 50Ω VMSET BEN+ IMAX MDIN Z0 = 50Ω EN BURST CONTROL 130Ω GND 130Ω MDOUT 82Ω BMD MON1 3kΩ 1kΩ 1kΩ DS1875 BEN BIAS MOD PON TRIPLEXER AND SFP CONTROLLER ________________________________________________________________ Maxim Integrated Products For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. 1 MAX3643 General Description MAX3643 155Mbps to 2.5Gbps Burst-Mode Laser Driver ABSOLUTE MAXIMUM RATINGS Supply Voltage VCC ..............................................-0.5V to +4.0V Current into BIAS-, BIAS+, OUT-, OUT+ .......-20mA to +150mA Voltage at VMSET, VBSET, IN+, IN-, BEN+, BEN-, EN, MDIN, MDOUT, BENOUT, BCMON ...................-0.5V to (VCC + 0.5V) Voltage at MODSET, BIASSET, VREF, IMAX ........-0.5V to +3.0V Voltage at OUT-, OUT+, BIAS-, BIAS+ .....+0.3V to (VCC + 0.5V) Continuous Power Dissipation (TA = +85°C) 24-Pin TQFN, Multilayer Board (derate 27.8mW/°C above +85°C) ............................1807mW Operating Temperature Range ...........................-40°C to +85°C Storage Temperature Range ............................-55°C to +150°C Lead Temperature (soldering, 10s) .................................+300°C Soldering Temperature (reflow) Lead(Pb)-free..............................................................+260°C Containing lead(Pb) ....................................................+240°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. OPERATING CONDITIONS PARAMETER SYMBOL Supply Turn-On Time CONDITIONS 10% to 90% Ambient Temperature MIN TYP MAX UNITS 0.001 1000 ms -40 +85 °C 2500 Mbps Data Rate Voltage at VMSET, VBSET 0 1.4 V Voltage at BCMON 0 1.4 V Voltage at MDIN 0 2.56 V ELECTRICAL CHARACTERISTICS (VCC = 3.0V to 3.6V, TA = -40°C to +85°C. Typical values are at VCC = 3.3V, TA = +25°C, IBIAS = 20mA, IMOD = 30mA, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS Supply Current ICC Excluding laser bias and mode currents, max at IMOD = 85mA, IBIAS = 70mA I/O SPECIFICATIONS LVPECL Differential Input VIN VIN = (VIN+) - (VIN-) LVPECL Common-Mode Input Voltage LVCMOS Output High Voltage I OH = -100µA LVCMOS Output Low Voltage I OL = 100µA Td MAX UNITS 32 51 mA 1600 mVP-P VCC 1.32 VCC VIN / 4 V VCC 0.2 V 0.2 CL = 20pF, from BEN zero crossing to 67% CMOS level LVCMOS Input Pullup TYP 200 VCC 1.49 VCM BENOUT Propagation Delay MIN 30 ns 75 LVCMOS Input Current V k VIN = 0V or VIN = VCC 50 µA LVCMOS Input High Voltage 2.0 VCC V LVCMOS Input Low Voltage 0.2 0.8 V 70 mA 50 µA mA/mA BIAS GENERATOR SPECIFICATIONS Bias Current Range Bias Current, Burst Off BIASSET Current Gain 2 IBIAS IBIAS, OFF GBIAS VBIAS+, VBIAS- 0.6V 1 BEN = low or EN = high 5 1mA IBIAS < 2mA, VBSET = VREF 88 2mA IBIAS < 10mA, VBSET = VREF 70 88 110 10mA IBIAS < 70mA, VBSET = VREF 82.5 88 94.5 _______________________________________________________________________________________ 155Mbps to 2.5Gbps Burst-Mode Laser Driver (VCC = 3.0V to 3.6V, TA = -40°C to +85°C. Typical values are at VCC = 3.3V, TA = +25°C, IBIAS = 20mA, IMOD = 30mA, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS BIASSET Current Gain Linearity 5mA IBIAS 70mA (Note 13) 5mA IBIAS 70mA (Note 14) Bias Current Overshoot VCC turn-on/-off < 1s BIASSET Current Gain Stability Bias Current Monitor Gain GBSM MAX UNITS -4.4 +4.4 % -3.75 +3.75 % 11 1mA IBIAS < 5mA Bias Current Monitor Gain Stability BIASSET Resistor 2mA IBIAS 70mA, VBSET = VREF MIN 5mA IBIAS 70mA RBIAS TYP 14 10 % 17 mA/A ±4 -5 40 % +5 50 60 85 mA 5 120 µA MODULATOR SPECIFICATIONS Modulation Current Range Modulation Current Off IMOD IMOD, OFF Instantaneous Voltage at OUT+ MODSET Current Gain GMOD MODSET Current Gain Stability MODSET Current Gain Linearity 10 BEN = low or EN = high or VIN = low 10mA IMOD < 60mA 0.6 60mA IMOD 85mA 0.75 10mA < IMOD < 85mA, VMSET = VREF 82.5 (Note 13) -4.4 (Note 14) -2.2 IBIASSET = 0.15mA, IMODSET = 0.7mA V 88 tR Modulation Current Fall Time tF Deterministic Jitter Random Jitter +2.2 % 1 % 1 20% to 80% 45 85 ps 20% to 80% 45 85 ps (Note 3) 17 45 psP-P 0.8 1.4 psRMS 50 60 1.4 V (Note 4) MODSET Resistor % 1.7 IMODSET = IBIASSET = 0.55mA Modulation Current Rise Time mA/mA 0.5 IMODSET = IBIASSET = 0.15mA IMODSET = IBIASSET = 0.4mA MODSET, BIASSET Gain Matching (Note 15) 94.5 +4.4 RMOD 40 MODSET, BIASSET OPERATIONAL AMPLIFIER SPECIFICATIONS MODSET, BIASSET Voltage Range 0.005 Voltage Error (Note 5) Input Leakage VMSET and VBSET pins 0.1 ±5 mV 1.5 µA TURN-OFF/-ON SPECIFICATIONS Burst-Enable Time (Notes 2, 6, 7) 2.3 ns Burst-Disable Time (Notes 2, 6, 8) 2.0 ns 2.56 V ±1 mV ±2.56 mV SAMPLE/HOLD SPECIFICATIONS MDIN Voltage Range 0.05 MDOUT Settling Relative to final value at 3µs, CL < 20pF Sample/Hold Droop After 100µs (Note 9) Bias Current Overshoot VCC turn-on/-off < 1s, IBIAS 20mA 10 % IBIAS < 20mA 2 mA _______________________________________________________________________________________ 3 MAX3643 ELECTRICAL CHARACTERISTICS (continued) MAX3643 155Mbps to 2.5Gbps Burst-Mode Laser Driver ELECTRICAL CHARACTERISTICS (continued) (VCC = 3.0V to 3.6V, TA = -40°C to +85°C. Typical values are at VCC = 3.3V, TA = +25°C, IBIAS = 20mA, IMOD = 30mA, unless otherwise noted.) (Note 1) PARAMETER SYMBOL CONDITIONS MIN Final value measured after 10µs (MDOUT - MDIN), burst width > 576ns Sampling Error TYP MAX UNITS 3 ±14 mV 1.235 1.295 V 5.5 µs BANDGAP VOLTAGE REFERENCE SPECIFICATIONS VREF Output RL > 10k, CL < 50pF 1.175 MODULATION/BIAS CURRENT DISABLE Enable Time Disable Time 5mA < IBIAS, 10mA < IMOD (Note 10) (Notes 2, 11) RIMAX Range Current Limit (Tested with IBIAS = IMOD) 3 375 ns 15 k mA RIMAX = 3k 155 IBIAS+I MOD RIMAX = 5k 100 150 50 75 RIMAX = 10k OPTICAL EVALUATION Eye Margin (Note 12) 155.52Mbps 49 622.08Mbps 45 1.24416Gbps 38 2.48832Gbps 18 % Note 1: DC parameters are production tested at TA = +25°C, guaranteed by design and characterization at TA = -40°C. AC parameters are guaranteed by design and characterization. Note 2: For 10mA ≤ IMOD ≤ 85mA and 4mA ≤ IBIAS ≤ 70mA. Note 3: Deterministic jitter measured with a continuous pattern of 27-1 PRBS, 80 ones, 27-1 PRBS, 80 zeros at 1.25Gbps, and both LVPECL inputs terminated by the network shown in Figure 3. Note 4: Random jitter, rise time, fall time measured with 0000011111 pattern at 1.25Gbps. Note 5: Voltage difference between VMSET and MODSET or VBSET and BIASSET excluding IR drops. The maximum operating voltage at VMSET or VBSET must be less than 1.4V for proper operation. Note 6: Turn-on/-off time is when the BEN+/BEN- LVPECL inputs are used to control modulation and bias currents. Note 7: Burst-enable delay is measured between the time at which the rising edge of the differential burst-enable input reaches the midpoint, and the time at which the combined output currents (bias plus modulation) reach 90% of their final level. Note 8: Burst-disable delay is measured between the time at which the falling edge of the differential burst-enable input reaches the midpoint, and the time at which the combined output currents (bias plus modulation) fall below 10% of the bias-on current. Note 9: Droop measured with sample/hold output load of 10MΩ. Note 10: Enable delay is measured between the time at which the falling edge of the EN input reaches ≤ 0.8V, and the time at which the combined output currents (bias plus modulation) reach 90% of their final level. Note 11: Disable delay is measured between the time at which the rising edge of the EN input reaches ≥ 2V, and the time at which the combined output currents (bias plus modulation) fall below 10% of the bias-on current. Note 12: Excelight SLT2886-LR laser. Note 13: Current gain stability = [(Gain – nominal Gain) / nominal Gain], nominal Gain at VCC = 3.3V, TA = +25°C. Note 14: Gain linearity = (Gainmax – Gainmin), Gainavg = Gainmax + Gainmin Gainavg 2 Note 15: Gain matching = Gain mod / Gainbias − Gain mod nom / Gainbiasnom , nominal at VCC = 3.3V, TA = +25°C. Gain mod nom / Gainbiasnom 4 _______________________________________________________________________________________ 155Mbps to 2.5Gbps Burst-Mode Laser Driver MAX3643 toc01 EXCELIGHT SLT2886-LR LASER AVERAGE OPTICAL POWER = -6dBm EXTINCTION RATIO = 15dB MASK MARGIN = 49% OPTICAL EYE DIAGRAM (1.24416Gbps, 933MHz FILTER, PATTERN = 223 - 1 PRBS) OPTICAL EYE DIAGRAM (622.08Mbps, 467MHz FILTER, PATTERN = 223 - 1 PRBS) MAX3643 toc03 MAX3643 toc02 EXCELIGHT SLT2886-LR LASER AVERAGE OPTICAL POWER = -6dBm EXTINCTION RATIO = 14dB MASK MARGIN = 38% EXCELIGHT SLT2886-LR LASER AVERAGE OPTICAL POWER = -6dBm EXTINCTION RATIO = 15dB MASK MARGIN = 45% OPTICAL EYE DIAGRAM (2.48832Gbps, 2.3GHz FILTER, PATTERN = 223 - 1 PRBS) ELECTRICAL EYE DIAGRAM (2.5Gbps, IMOD = 30mA, PATTERN = PRBS 27 - 1 + 80 CID) SUPPLY CURRENT vs. TEMPERATURE (IBIAS = 20mA, IMOD = 30mA) MAX3643 toc05 MAX3643 toc04 60 MAX3643 toc06 OPTICAL EYE DIAGRAM (155.52Mbps, 117MHz FILTER, PATTERN = 223 - 1 PRBS) EXCLUDES BIAS AND MODULATION CURRENT 55 50 ICC (mA) 45 40 35 30 25 20 15 10 EXCELIGHT SLT2886-LR LASER AVERAGE OPTICAL POWER = -6dBm EXTINCTION RATIO = 10dB MASK MARGIN = 18% 100ps/div -40 -20 0 20 40 60 80 TEMPERATURE (°C) _______________________________________________________________________________________ 5 MAX3643 Typical Operating Characteristics (Typical values are at VCC = 3.3V, TA = +25°C, data pattern = 27-1 PRBS + 80 ones + 27-1 PRBS + 80 zeros, unless otherwise noted.) Typical Operating Characteristics (continued) (Typical values are at VCC = 3.3V, TA = +25°C, data pattern = 27-1 PRBS + 80 ones + 27-1 PRBS + 80 zeros, unless otherwise noted.) RANDOM JITTER vs. MODULATION AMPLITUDE DETERMINISTIC JITTER vs. MODULATION AMPLITUDE 1.1 1.0 RANDOM JITTER (psRMS) 24 21 18 15 12 9 MAX3643 toc08 27 DJ (psP-P) 1.2 MAX3643 toc07 30 0.9 0.8 0.7 0.6 0.5 0.4 6 3 0.3 0 0.2 10 20 50 60 40 IMOD (mA) 30 70 10 80 20 50 60 70 80 IBIAS vs. IBIASSET IMOD vs. IMODSET 70 MAX3643 toc10 90 MAX3643 toc09 80 80 70 60 IBIAS (mA) 60 50 40 50 40 30 30 20 20 10 10 0 0 0 200 400 600 0 1000 800 200 400 600 800 IMODSET (µA) IBIASSET (µA) BIAS CURRENT MONITOR GAIN (IBCMON/IBIAS) vs. TEMPERATURE IMOD vs. VMSET (RMODSET = 1kΩ) 90 MAX3643 toc11 17 80 70 IMOD (mAP-P) 16 15 14 1000 MAX3643 toc12 IMOD (mA) 40 30 IMOD (mA) 90 GAIN (mA/A) MAX3643 155Mbps to 2.5Gbps Burst-Mode Laser Driver 60 50 40 30 20 13 10 0 12 -40 -20 0 20 40 TEMPERATURE (°C) 6 60 80 0 0.2 0.4 0.6 0.8 1.0 1.2 VMSET (V) _______________________________________________________________________________________ 155Mbps to 2.5Gbps Burst-Mode Laser Driver IBIAS + IMOD CURRENT THRESHOLD vs. RIMAX IBIAS vs. VBSET (RBIASSET = 1kΩ) 70 IBIAS (mA) 60 50 40 30 20 MAX3643 toc14 80 MAX3643 toc15 160 140 CURRENT THRESHOLD (mA) MAX3643 toc13 90 TIMING DIAGRAM, BURST-ON (933MHz FILTER ON OUT+) VOUT+ 120 100 VBIAS+ 80 60 VBEN+ 40 20 10 0 0 0 0.2 0.4 0.6 0.8 0 1.0 5 10 15 20 25 30 500ps/div RIMAX (kΩ) VBSET (V) SAMPLE/HOLD (10MΩ LOAD, 2.8µs SAMPLE AND 100µs HOLD, MDIN = 1.56V) TIMING DIAGRAM, BURST-OFF (933MHz FILTER ON OUT+) MAX3643 toc17 MAX3643 toc16 VOUT+ 1.56V MDOUT 1.22V VBIAS+ BEN+ VBEN+ 500ps/div 20µs/div _______________________________________________________________________________________ 7 MAX3643 Typical Operating Characteristics (continued) (Typical values are at VCC = 3.3V, TA = +25°C, data pattern = 27-1 PRBS + 80 ones + 27-1 PRBS + 80 zeros, unless otherwise noted.) 155Mbps to 2.5Gbps Burst-Mode Laser Driver MAX3643 Pin Description 8 PIN NAME 1 VCCA 2 IN+ FUNCTION Analog Supply Voltage Noninverted Data Input, LVPECL Compatible 3 IN- 4 VCCS Signal Supply Voltage Inverted Data Input, LVPECL Compatible 5 BEN+ Noninverted Burst-Enable Input, LVPECL Compatible 6 BEN- Inverted Burst-Enable Input, LVPECL Compatible 7 BENOUT 8 EN 9 BCMON 10 IMAX 11 MDOUT 12 MDIN Monitor Diode In. Analog Input for sample/hold. 13 BIAS- Connect BIAS- to VCC Through a 10 Resistor and Switching Diode Burst-Enable Output, LVCMOS. Signal replicates BEN input. Enable Input LVCMOS. Active low enables BIAS± and OUT± outputs. Bias Current Monitor. Current out of this pin develops a ground-referenced voltage across an external resistor proportional to the bias current. Current-Limit Reference. Connect a resistor from IMAX to GND to set maximum IBIAS plus IMOD. Monitor Diode Out. Analog Output for sample/hold. 14 BIAS+ Laser Bias Current Output. Modulation current flows into this pin when BEN input is high. 15, 18 VCCO Output Supply Voltage 16 OUT+ Laser Modulation Current Output. Modulation current flows into this pin when both BEN and IN inputs are high. 17 OUT- Connect OUT- to Laser Diode Anode Through a 15 Resistor and Switching Diode 19 GND Supply Ground. This pin must be connected to ground. 20 MODSET 21 VMSET 22 VREF 23 VBSET 24 BIASSET — EP Modulation Current Set. Current from this pin to ground sets the laser modulation current. MODSET Reference. A ground-referenced voltage at this point establishes the MODSET reference. Reference Voltage Output. May be used for VMSET, VBSET. BIASSET Reference. A ground-referenced voltage at this point establishes the BIASSET reference. Bias Current Set. Current from this pin to ground sets the laser bias current. Exposed Paddle (Ground). The exposed pad must be soldered to the circuit board ground for proper thermal and electrical operation. _______________________________________________________________________________________ 155Mbps to 2.5Gbps Burst-Mode Laser Driver MAX3643 VCC LP RP 15Ω OUT+ MAX3643 RD OUT- IN+ RCOMP RD BIAS+ CCOMP LVPECL IN- BIAS- 10Ω VCC BEN+ LVPECL BENCMOS BENOUT IMAX LIMIT LIMIT VCC VCC MDIN CMOS EN I1 IM = 88 x I1 IB = 88 x I2 I2 MDOUT VCC IBCMON = IB x 0.014 1.2V RMOD VREF VMSET MODSET VBSET RBIAS BIASSET BCMON Figure 1. Functional Diagram _______________________________________________________________________________________ 9 MAX3643 155Mbps to 2.5Gbps Burst-Mode Laser Driver Detailed Description The MAX3643 laser driver includes a bias current generator, bias current monitor, modulation current generator, laser drive outputs, and monitor diode sample and hold. LVPECL-compatible inputs are provided for both high-speed data and burst enable. The high-speed burst-enable input signal is replicated on an LVCMOS output for use by the controller. Laser Diode Modulation and Bias Current Generators Laser diode modulation current amplitude is controlled by the current out of the MODSET pin, and bias current by the current out of the BIASSET pin, according to: IMOD = IMODSET x 88 IBIAS = IBIASSET x 88 A voltage source and two op amps are provided to enable IMODSET and IBIASSET to be set using either a resistor to ground or a current digital-to-analog converter (DAC). The high-impedance op amp reference input can be externally controlled, so that the modulation and bias currents can also be set using voltage DACs. Laser Diode Modulation and Bias Current Limiter Typical laser diodes have an absolute maximum rating of 150mA. To reduce the possibility of laser damage, the modulation current and bias current are shut off if the sum IMOD + IBIAS attempts to exceed the limit set by RIMAX; see the Typical Operating Characteristics. Bias Current Monitor The laser diode bias current can be monitored by measuring the voltage across an external load resistor connected from BCMON to ground. For example, a 1kΩ resistor from BCMON to ground gives the following relationship: VBCMON = IBIAS × GBSM × 1kΩ The voltage at BCMON must be below 1.4V for proper operation. Output Drivers The modulation current ranges from 10mA to 85mA, as set by the current through MODSET. The laser modulation current output OUT+ is optimized to drive a 15Ω load, and must be DC-coupled. A series damping resistor, R D , provides impedance matching to the laser diode. The combined value of the series damping resistor and the laser diode equivalent series resistance 10 should be close to 15Ω. An RC shunt compensation network, RCOMP/CCOMP, connected between the laser diode cathode and ground should also be provided to reduce optical output aberrations and duty-cycle distortion caused by laser diode parasitic inductance. The values of RCOMP and CCOMP can be adjusted to match the laser diode and PCB layout characteristics for optimal optical eye performance (refer to Application Note 274: HFAN-02.0: Interfacing Maxim Laser Drivers with Laser Diodes). The OUT- pin is connected through a 15Ω resistor and switching diode to the laser diode anode. The switching diode at OUT- improves the optical output eye and burst-enable delay by better matching the laser diode characteristics. For data rates greater than 1Gbps, a parallel RL peaking network, RP/LP, connected between the laser diode anode and VCC is recommended. This network creates a differential drive for the laser diode to improve rise/fall times and reduce jitter. The values of RP and LP are also adjusted to match the laser diode and PCB layout characteristics for optimal optical eye performance. The bias current ranges from 1mA to 70mA, as set by the current through BIASSET. Current in the BIAS output switches at high speed when bursting; therefore, the BIAS+ pin should be connected directly through a resistor, equal to RD as determined above, to the laser cathode. The BIAS- pin is connected through a 10Ω resistor and switching diode to VCC. When the BEN input is high, the laser driver sinks bias and modulation current according to the settings at MODSET and BIASSET. When the BEN input is low, the BIAS+ and OUT+ currents both shut off within 2ns. Note that when BEN is low, the bias current is shunted through the BIAS- output and the modulation current through the OUT- output. Monitor Diode Sample and Hold Laser monitor diode current is only generated when there is an optical output (BEN is active). When BEN is inactive, the monitor current is zero, reflecting the fact that the laser is off. A sample-and-hold circuit, triggered by the state of the BEN input, is provided in the MAX3643. During the burst-enable active period, the voltage present at MDIN is stored on an internal sample-and-hold capacitor; and during the burst-enable inactive period, that voltage is output on MDOUT; see the timing diagram in Figure 2. While the internal sample-and-hold is sampling (BEN active), MDOUT voltage takes a 1.2V reference level. ______________________________________________________________________________________ 155Mbps to 2.5Gbps Burst-Mode Laser Driver MAX3643 BURST-ENABLE (BEN±) IN ≤ 125µs FOR BPON/GPON INTERNAL MDIN VOLTAGE SAMPLER BENOUT OUTPUT 3µs MDOUT < 2.56mV 1.2V 100µs Figure 2. Sample-and-Hold Timing Diagram Enable Input An LVCMOS input, EN, is provided to disable both bias and modulation currents under external control. The maximum time to disable laser current with the EN control is 375ns. IMOD = IMODSET x 88 To program the laser modulation current using a resistor or digital potentiometer, connect VMSET to VREF, attach a resistor from the MODSET pin to ground, and set the current according to: Setting the Current Limit A current limiter is provided to protect the laser diode by shutting down both bias and modulation currents when total current exceeds a value set by the resistor connected from IMAX to ground. Do not use less than 3kΩ RIMAX. See the IBIAS + IMOD Current Threshold vs. RIMAX graph in the Typical Operating Characteristics. Programming the MODSET and BIASSET Inputs To program the laser modulation current using a current DAC, connect VMSET to VREF, attach the DAC to the MODSET pin and set the current according to: IMOD = 1.2V × 88 RMODSET + RMOD To program the laser modulation current using a PWM voltage DAC (requiring a high-impedance load), attach a DAC output to the VMSET pin, connect a resistor from the MODSET pin to ground as shown in the Typical Applications Circuit, and set the current according to: IMOD = VDAC × 88 RMODSET + RMOD ______________________________________________________________________________________ 11 MAX3643 155Mbps to 2.5Gbps Burst-Mode Laser Driver This approach can also be used for a conventional voltage DAC output, if desired. In all cases, the voltage at MODSET must be kept ≤ 1.4V, which limits the range of acceptable values for RMODSET depending on the maximum modulation current. VCC 130Ω Laser diode bias current is set in the same manner as modulation current. LVPECL Data/Burst-Enable Inputs ZO = 50Ω IN+/BEN+ ZO = 50Ω IN-/BEN- LVPECL The MAX3643 data and BEN inputs are biased with an on-chip, high-impedance network. When DC-coupled, the MAX3643 operates properly with signals that meet the EC table input-swing and common-mode requirements, including LVPECL and most CML. See Figure 3 for a termination network that can be used to connect the data and BEN inputs to LVPECL data outputs. Other termination networks may also be used, as long as both the input swing and common limits are met. MAX3643 130Ω 82Ω 82Ω Figure 3. LVPECL High-Speed Inputs Sample-and-Hold Operation When the MAX3643 internal sample-and-hold is not required, the MDIN pin should be connected to ground and the MDOUT pin unconnected. If the internal sampleand-hold is required, then it is necessary to ensure that the time constant resulting from the monitor diode load resistance and the total load capacitance is compatible with the desired minimum burst interval. It is also necessary to make certain that the load at MDOUT does not exceed the capability of the MDOUT pin. Because the voltage at MDIN is not reflected to MDOUT until after the end of the laser burst, systems using the internal sample-and-hold alone cannot support continuous mode operation, often a required feature for module calibration. In this case, the voltage at MDIN can also be connected directly to a controller mux input. As long as the total capacitance (including monitor diode intrinsic capacitance, MDIN capacitance, mux off-capacitance, and wiring parasitics) is less than 50pF, and the monitor diode load resistor is less than 2kΩ, then the sample-and-hold captures a 576ns minimum burst. The MAX3643 typical MDIN capacitance is 5pF, typical monitor diode maximum capacitance is 25pF, and the typical capacitance of a mux input in the off-state is 3pF to 5pF. When the mux is in the on-state, the capacitance at the input is typically 10pF to 20pF. 12 IN+ INVCMBEN + (100mV to 800mV) VCMBEN BEN+ VCMBEN - (100mV to 800mV) 3.3V BENR1 = 1.65kΩ MAX3643 VCMBEN = +2.0V R2 = 2.54kΩ Figure 4. Single-Ended Biasing for Burst Enable If the minimum burst duration is longer than 576ns, it may be useful to connect an external capacitor in parallel with the monitor diode load to limit the effects of the data pattern on the monitor diode output. ______________________________________________________________________________________ 155Mbps to 2.5Gbps Burst-Mode Laser Driver Running Burst-Enable Single-Ended VCC See Figure 5 for setting up the single-ended LVTTL or LVCMOS biasing for burst enable. Layout Considerations To minimize inductance, keep the connections between the MAX3643 output pins and laser diode as close as possible. Place a bypass capacitor as close as possible to each VCC connection. Take extra care to minimize stray parasitic capacitance on the BIAS and MDIN pins. Use good high-frequency layout techniques and multilayer boards with uninterrupted ground planes to minimize EMI and crosstalk. IN+ IN- R3 = 5kΩ LVTTL OR LVCMOS HIGH MAX3643 Applications Information BEN+ R4 = 3kΩ LVTTL OR LVCMOS LOW VCC BENR5 = 5kΩ MAX3643 R6 = 9kΩ Laser Safety and IEC 825 Using the MAX3643 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 user must determine the level of fault tolerance required by the application, recognizing that Maxim products are neither designed nor 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 in which the failure of a Maxim product could create a situation where personal injury or death can occur. Figure 5. Single-Ended LVCMOS or LVTTL Biasing for Burst Enable Interface Model VCC VCC VCC Exposed-Paddle Package The exposed paddle on the 24-pin TQFN provides a very low thermal resistance path for heat removal from the IC. The pad is also electrical ground on the MAX3643 and must be soldered to the circuit board ground for proper thermal and electrical performance. Refer to Maxim Application Note 862: HFAN-08.1: Thermal Considerations of QFN and Other ExposedPaddle Packages for additional information. 16kΩ 5kΩ IN+/BEN+ VCC 5kΩ IN-/BEN- 24kΩ MAX3643 Figure 6. Simplified Input Circuit Schematic ______________________________________________________________________________________ 13 155Mbps to 2.5Gbps Burst-Mode Laser Driver MAX3643 Pin Configuration VCCO OUT- OUT+ VCCO BIAS+ BIAS- TOP VIEW 18 17 16 15 14 13 11 MDOUT MODSET 20 10 IMAX VMSET 21 MAX3643 VREF 22 VBSET 23 *EP 1 2 3 4 5 6 IN+ IN- VCCS BEN+ BEN- + VCCA BIASSET 24 Package Information 12 MDIN GND 19 Chip Information TRANSISTOR COUNT: 2771 PROCESS: SiGe BiPOLAR 9 BCMON 8 EN 7 BENOUT For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 24 TQFN-EP T2444-3 21-0139 90-0021 THIN QFN (4mm x 4mm) *THE EXPOSED PAD MUST BE CONNECTED TO GROUND FOR PROPER THERMAL AND ELECTRICAL PERFORMANCE. 14 ______________________________________________________________________________________ 155Mbps to 2.5Gbps Burst-Mode Laser Driver REVISION NUMBER REVISION DATE 0 11/05 1 10/08 DESCRIPTION PAGES CHANGED Initial release. — Added “155Mbps to 2.5Gbps” to the data sheet/part title. All Updated the Applications section. 1 In the Operating Conditions table, changed the data rate from 1250Mbps to 2500Mbps. 2 In the Typical Operating Characteristics, added the Electrical Eye Diagram graph. 6 2 7/10 Replaced the Typical Application Circuit; added the soldering temperature to the Absolute Maximum Ratings section; updated the optical eye mask margins in the Electrical Characteristics table; corrected equation in Note 14; added the optical eye diagrams to the Typical Operating Characteristics section; updated the pin descriptions for the pins with diodes (13, 17) in the Pin Description table; updated Figure 1; updated the Output Drivers section; updated the Layout Considerations section; added the land pattern number to the Package Information table. 3 5/12 Updated Typical Application Circuit, Electrical Characteristics table, and Typical Operating Characteristics global conditions, and added bias current overshoot parameter 1, 2, 4–10, 12, 13, 14 1–7 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. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. 15 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 2012 Maxim Integrated Products Maxim is a registered trademark of Maxim Integrated Products, Inc. MAX3643 Revision History