2.7Gbps, Low-Power Laser Drivers Reference Design Available Fully

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2.7Gbps, Low-Power Laser Drivers Reference Design Available Fully

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19-2529; 7/04
2.7Gbps, Low-Power Laser Drivers
Reference Design Available Fully Compliant with SFF-8472 MSAs Programmable Modulation Current from 10mA 60mA (DC-Coupled) Programmable Modulation Current from 10mA 85mA (AC-Coupled) Programmable Bias Current from 100mA Edge Transition Times <51ps 27mA (typ) Power-Supply Current Multirate 155Mbps 2.7Gbps Operation Automatic Average Power Control On-Chip Pullup Resistor TX_DISABLE 24-Pin package
MAX3735/MAX3735A
MAX3735/MAX3735A +3.3V laser drivers SFP/SFF applications from 155Mbps 2.7Gbps. devices accept differential input data provide bias modulation currents driving laser. DCcoupling laser allows multirate applications reduces number external components. MAX3735/MAX3735A fully compliant with timing SFF-8472 transmit diagnostic requirements. automatic power-control (APC) feedback loop incorporated maintain constant average optical power over temperature lifetime. wide modulation current range 10mA 60mA 85mA AC-coupled) bias current 100mA make this product ideal driving FP/DFB laser diodes fiber-optic modules. resistor range laser current settings optimized interface with DS1858 controller MAX3735/MAX3735A provide transmit-disable control, single-point latched transmit-failure monitor output, photocurrent monitoring, bias-current monitoring indicate when loop unable maintain average optical power. MAX3735A also features improved multirate operation. MAX3735/MAX3735A come package form, operate over extended temperature range -40°C +85°C.
Ordering Information
PART MAX3735E/D MAX3735ETG MAX3735EGG MAX3735AETG MAX3735AETG+ TEMP RANGE -40°C +85°C -40°C +85°C -40°C +85°C -40°C +85°C -40°C +85°C PIN-PACKAGE Dice* Thin QFN-EP** QFN-EP** Thin QFN-EP** Thin QFN-EP**
Applications
Gigabit Ethernet SFP/SFF Transceiver Modules 1G/2G Fibre Channel SFP/SFF Transceiver Modules Multirate OC48-FEC SFP/SFF Transceiver Modules
*Dice designed operate from -40°C +85°C, tested guaranteed only +25°C. **EP Exposed pad. +Denotes lead-free package. Configuration appears data sheet.
Typical Application Circuit
+3.3V OPTIONAL SHUTDOWN CIRCUITRY
+3.3V
TX_DISABLE
TX_FAULT
SHUTDOWN
OUT-
+3.3V
0.01µF
0.1µF SERDES 0.1µF
OUT+ OUT+ BIAS FERRITE BEAD
MAX3735 MAX3735A
APCFILT1 APCFILT2 BC_MON PC_MON MODSET APCSET
DS1858/DS1859 CONTROLLER MON1 M0N2 M0N3 +3.3V
CAPC
RBC_MON
RPC_MON REPRESENTS CONTROLLED-IMPEDANCE TRANSMISSION LINE
Maxim Integrated Products
pricing, delivery, ordering information, please contact Maxim/Dallas Direct! 1-888-629-4642, visit Maxim's website www.maxim-ic.com.
2.7Gbps, Low-Power Laser Drivers MAX3735/MAX3735A
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, VCC.-0.5V +6.0V Current into BIAS, OUT+, OUT- .-20mA +150mA Current into MD.-5mA +5mA Voltage IN+, IN-, TX_DISABLE, TX_FAULT, SHUTDOWN .-0.5V (VCC 0.5V) Voltage BIAS, PC_MON, BC_MON, MODSET, APCSET .-0.5V (VCC 0.5V) Voltage OUT+, OUT-.+0.5V (VCC 1.5V) Voltage APCFILT1, APCFILT2 .-0.5V Continuous Power Dissipation +85°C 24-Lead Thin (derate 20.8mW/°C above +85°C).1354mW 24-Lead (derate 20.8mW/°C above +85°C).1354mW Operating Ambient Temperature Range (TA).-40°C +85°C Storage Ambient Temperature Range.-55°C +150°C Attach Temperature.+400°C Lead Temperature (soldering, 10s) .+300°C
Stresses beyond those listed under "Absolute Maximum Ratings" cause permanent damage device. These stress ratings only, functional operation device these other conditions beyond those indicated operational sections specifications implied. Exposure absolute maximum rating conditions extended periods affect device reliability.
ELECTRICAL CHARACTERISTICS
(VCC +2.97V +3.63V, -40°C +85°C. Typical values +3.3V, IBIAS 20mA, IMOD 30mA, +25°C, unless otherwise noted.) (Note
PARAMETER POWER SUPPLY Power-Supply Current SPECIFICATIONS Differential Input Voltage Common-Mode Input Voltage Differential Input Resistance TX_DISABLE Input Pullup Resistance TX_DISABLE Input Current TX_DISABLE Input High Voltage TX_DISABLE Input Voltage TX_FAULT Output High Voltage TX_FAULT Output Voltage SHUTDOWN Output High Voltage SHUTDOWN Output Voltage BIAS GENERATOR Bias On-Current Range Bias Off-Current Bias Overshoot IBIAS IBIASOFF Current into BIAS Current into BIAS during TX_FAULT TX_DISABLE During module plugging (Notes IBC_MON External resistor defines voltage gain, IBIAS 1mA, RBC_MON 69.28k IBIAS 100mA, RBC_MON 693.25 Bias-Current Monitor Gain Stability IBIAS 100mA (Notes MAX3735 MAX3735A 10.0 11.5 13.5 13.5 100µA sourcing (Note sinking (Note 100µA sourcing 100µA sinking RPULL VHIGH VLOW GND, 3.3V, RPULL 7.4k -450 (VIN+) (VIN-), Figure 10.0 2400 mVP-P Excludes laser bias modulation currents (Note SYMBOL CONDITIONS UNITS
Bias-Current Monitor Gain
mA/A
2.7Gbps, Low-Power Laser Drivers
ELECTRICAL CHARACTERISTICS (continued)
(VCC +2.97V +3.63V, -40°C +85°C. Typical values +3.3V, IBIAS 20mA, IMOD 30mA, +25°C, unless otherwise noted.) (Note
PARAMETER Reverse Bias Voltage Average Current Range SYMBOL CONDITIONS 18µA 1500µA Average current into IBIAS (MAX3735) Average Power-Setting Stability closed loop (Notes IBIAS (MAX3735A) IBIAS 100mA Average Power Setting Accuracy Closed Loop IBIAS 100mA (Note External resistor defines voltage gain; 18µA, RPC_MON MAX3735 MAX3735A -880 -110 -650 0.95 1500 +880 +110 +650 1.23 1.05 ppm/°C UNITS
MAX3735/MAX3735A
AUTOMATIC POWER-CONTROL LOOP
MD-Current Monitor Gain
IPC_MON
1.5mA, RPC_MON MD-Current Monitor Gain Stability LASER MODULATOR Current into OUT+ pin; VOUT+, VOUT- 0.6V (DC-coupled) Current into OUT+ pin; 15_, VOUT+, VOUT- 2.0V (AC-coupled) Current into OUT+ during TX_FAULT TX_DISABLE IMOD 10mA IMOD 60mA 10mA IMOD 60mA (Note 80%, 10mA IMOD 60mA (Note 80%, 10mA IMOD 60mA (Note 10mA IMOD 60mA 2.67Gbps (Notes Deterministic Jitter 1.25Gbps (K28.5 pattern) 622Mbps (Note 155Mbps (Note Random Jitter 10mA IMOD 60mA (Note 18µA 1500µA (Notes MAX3735 MAX3735A
ppm/°C
Modulation On-Current Range
IMOD
Modulation Off-Current Modulation-Current Stability (Note Modulation-Current Absolute Accuracy Modulation-Current Rise Time Modulation-Current Fall Time
IMODOFF
-480 -255 11.5
+480 +255
psRMS
2.7Gbps, Low-Power Laser Drivers MAX3735/MAX3735A
ELECTRICAL CHARACTERISTICS (continued)
(VCC +2.97V +3.63V, -40°C +85°C. Typical values +3.3V, IBIAS 20mA, IMOD 30mA, +25°C, unless otherwise noted.) (Note
PARAMETER SAFETY FEATURES Excessive Bias-Current Comparator Threshold Range TX_FAULT always occurs VBC_MON 1.38V, TX_FAULT never occurs VBC_MON 1.22V TX_FAULT always occurs VPC_MON 1.38V, TX_FAULT never occurs VPC_MON 1.22V 1.22 1.30 1.39 SYMBOL CONDITIONS UNITS
Excessive MD-Current Comparator Threshold Range TIMING REQUIREMENTS TX_DISABLE Assert Time t_off
1.22
1.30
1.39
Time from rising edge TX_DISABLE IBIAS IBIASOFF IMOD IMODOFF (Note Time from falling edge TX_DISABLE IBIAS IMOD steady state when TX_FAULT before reset CAPC 2.7nF, MAX3735 (Note MAX3735A (Note
0.14
TX_DISABLE Negate Time
t_on
TX_DISABLE Negate Time During FAULT Recovery TX_FAULT Reset Time PowerOn Time TX_FAULT Assert Time TX_DISABLE Reset
Time from falling edge TX_DISABLE t_onFAULT IBIAS IMOD steady state when TX_FAULT before reset (Note t_init t_fault From power-on negation TX_FAULT using TX_DISABLE (Note Time from fault TX_FAULT CFAULT 20pF, RFAULT 4.7k (Note Time TX_DISABLE must held high reset TX_FAULT (Note
Note Note Note Note Note Note Note Note Note Note
Specifications -40°C guaranteed design characterization. Dice tested +25°C only. Maximum value specified IMOD 60mA, IBIAS 100mA. TX_FAULT open-collector output must pulled with 4.7k resistor. Guaranteed design characterization. turn-on time must 0.8s, DC-coupled interface. Gain stability defined digital diagnostic document (SFF-8472, rev. 9.0) over temperature supply variation. Assuming that laser diode photodiode transfer function does change with temperature. Accuracy refers part-to-part variation. Deterministic jitter measured using PRBS equivalent pattern. Broadband noise filtered through network shown Figure capacitor, 0.47µF, 0603 ferrite bead inductor added (optional). This supply voltage filtering reduces hotplugging inrush current. supply noise must 100mVP-P 2MHz. Note CAPC values chosen shown Table (MAX3735A).
2.7Gbps, Low-Power Laser Drivers MAX3735/MAX3735A
VOLTAGE VIN+ VIN(100mV min, 1200mV max)
MAX3735 MAX3735A
OUT30 0.5pF
(VIN+) (VIN-)
(200mVP-P min, 2400mVP-P max)
CURRENT IOUT+ IMOD
OUT+ OUT+
IOUT+ OSCILLOSCOPE
TIME
Figure Required Input Signal Output Polarity
Figure Output Termination Characterization
HOST BOARD FILTER DEFINED SOURCE NOISE VOLTAGE SUPPLY 0.1µF 10µF 0.1µF
MODULE LASER DRIVER
OPTIONAL
OPTIONAL
Figure Supply Filter
2.7Gbps, Low-Power Laser Drivers MAX3735/MAX3735A
Typical Operating Characteristics
(VCC +3.3V, CAPC 0.01µF, IBIAS 20mA, IMOD 30mA, +25°C, unless otherwise noted.)
OPTICAL
MAX3735 toc01
OPTICAL
MAX3735 toc02
8.2dB, 2.7Gbps, 2.3GHz FILTER PRBS, 1310nm LASER
8.2dB, 1.25Gbps, 900MHz FILTER K28.5 PATTERN, 1310nm LASER
54ps/div
115ps/div
OPTICAL
MAX3735 toc03
ELECTRICAL
MAX3735 toc04
12dB, 155Mbps, 117MHz FILTER PRBS, 1310nm LASER
2.7Gbps, PRBS, 30mA MODULATION
85mV/div
919ps/div
58ps/div
SUPPLY CURRENT TEMPERATURE
EXCLUDES IBIAS IMOD
MAX3735 toc05
BIAS-CURRENT MONITOR GAIN TEMPERATURE
MAX3735 toc06
SUPPLY CURRENT (mA)
GAIN (mA/A)
TEMPERATURE (°C)
TEMPERATURE (°C)
2.7Gbps, Low-Power Laser Drivers
Typical Operating Characteristics (continued)
(VCC +3.3V, CAPC 0.01µF, IBIAS 20mA, IMOD 30mA, +25°C, unless otherwise noted.)
PHOTOCURRENT MONITOR GAIN TEMPERATURE
MAX3735 toc07
MAX3735/MAX3735A
MODULATION CURRENT RMODSET
MAX3735 toc08
MONITOR DIODE CURRENT RAPCSET
(mA)
MAX3735 toc09
GAIN (A/A)
IMOD (mA)
RMODSET
RAPCSET
TEMPERATURE (°C)
EDGE TRANSITION TIME MODULATION CURRENT
MAX3735 toc10
DETERMINISTIC JITTER MODULATION CURRENT
MAX3735 toc11
RANDOM JITTER MODULATION CURRENT
MAX3735 toc12
FALL TIME
(psP-P) (INCLUDING PWD)
RANDOM JITTER (psRMS)
EDGE TRANSITION TIME (ps)
RISE TIME
IMOD (mA)
IMOD (mA)
IMOD (mA)
PLUG WITH TX_DISABLE
MAX3735 toc13
STARTUP WITH SLOW RAMPING SUPPLY
MAX3735 toc14
TRANSMITTER ENABLE
MAX3735 toc15
3.3V FAULT
3.3V
3.3V
FAULT TX_DISABLE
HIGH
FAULT
t_on 44µs
TX_DISABLE LASER OUTPUT
t_init 60ms
TX_DISABLE LASER OUTPUT
LASER OUTPUT 20ms/div 12µs/div
20ms/div
2.7Gbps, Low-Power Laser Drivers MAX3735/MAX3735A
Typical Operating Characteristics (continued)
(VCC +3.3V, CAPC 0.01µF, IBIAS 20mA, IMOD 30mA, +25°C, unless otherwise noted.)
TRANSMITTER DISABLE
MAX3735 toc16
RESPONSE FAULT
MAX3735 toc17
3.3V VPC_MON
EXTERNALLY FORCED FAULT t_fault 0.9µs
FAULT TX_DISABLE
t_off 134ns
FAULT TX_DISABLE
HIGH
HIGH
LASER OUTPUT
LASER OUTPUT
40ns/div
1µs/div
FAULT RECOVERY TIME
MAX3735 toc18
FREQUENT ASSERTION TX_DISABLE
MAX3735 toc19
VPC_MON
EXTERNAL FAULT REMOVED HIGH HIGH t_init 60ms
VPC_MON EXTERNALLY FORCED FAULT FAULT
FAULT
TX_DISABLE LASER OUTPUT
TX_DISABLE
LASER OUTPUT
100ms/div
4µs/div
2.7Gbps, Low-Power Laser Drivers
Description
NAME INPC_MON BC_MON SHUTDOWN TX_FAULT MODSET BIAS OUT+ OUTMD APCFILT1 APCFILT2 APCSET TX_DISABLE Exposed +3.3V Supply Voltage Noninverted Data Input Inverted Data Input Photodiode Current Monitor Output. Current this develops ground-referenced voltage across external resistor that proportional monitor diode current. Bias Current Monitor Output. Current this develops ground-referenced voltage across external resistor that proportional bias current. Ground Shutdown Driver Output. Voltage output control external transistor optional shutdown circuitry. Open-Collector Transmit Fault Indicator (Table resistor connected from this ground sets desired modulation current. Laser Bias Current Output Noninverted Modulation Current Output. Connect pins externally minimize parasitic inductance package. IMOD flows into this when input data high. Inverted Modulation Current Output. IMOD flows into this when input data low. Monitor Diode Input. Connect this anode monitor photodiode. capacitor ground required filter high-speed monitor photocurrent. Connect capacitor (CAPC) between (APCFILT1) (APCFILT2) dominant pole feedback loop. APCFILT1 resistor connected from this ground sets desired average optical power. Transmitter Disable, TTL. Laser output disabled when TX_DISABLE asserted high left unconnected. laser output enabled when this asserted low. Ground. Must soldered circuit board ground proper thermal electrical performance (see Exposed Package section). FUNCTION
MAX3735/MAX3735A
Detailed Description
MAX3735/MAX3735A laser drivers consist three parts: high-speed modulation driver, laser-biasing block with automatic power control (APC), safety circuitry (Figure circuit design optimized high-speed low-voltage (+3.3V) operation.
High-Speed Modulation Driver
output stage composed high-speed differential pair programmable modulation current source. MAX3735/MAX3735A optimized driving load; minimum instantaneous voltage required OUT+ 0.6V. Modulation current swings 60mA possible when laser diode DC-coupled driver 85mA when laser diode AC-coupled driver.
interface with laser diode, damping resistor (RD) required impedance matching. combined resistance series damping resistor equivalent series resistance laser diode should equal reduce optical output aberrations duty-cycle distortion caused laser diode parasitic inductance, shunt network might necessary. Refer Maxim Application Note HFAN 02.0: Interfacing Maxim's Laser Drivers Laser Diodes more information. data rates 2.7Gbps, capacitive load cathode laser diode degrades optical output performance. Because BIAS output directly connected laser cathode, minimize parasitic capacitance associated with using inductor isolate BIAS parasitics from laser cathode.
2.7Gbps, Low-Power Laser Drivers MAX3735/MAX3735A
SHUTDOWN INVCC PC_MON IMOD ENABLE IBIAS ENABLE RPC_MON IBIAS BC_MON X270 SAFETY LOGIC POWER DETECTOR (4.7k 10k) IAPCSET RAPCSET APCSET INPUT BUFFER
MAX3735 MAX3735A
DATA PATH IMOD
OUTOUT+ BIAS IBIAS
RBC_MON MODSET RMODSET TX_FAULT
APCFILT1 TX_DISABLE SHUTDOWN CAPC
APCFILT2
Figure Functional Diagram
Laser-Biasing
maintain constant average optical power, MAX3735/MAX3735A incorporate loop compensate changes laser threshold current over temperature lifetime. back-facet photodiode mounted laser package used convert optical power into photocurrent. loop adjusts laser bias current that monitor current matched reference current RAPCSET. time constant loop determined external capacitor (CAPC). possible CAPC values, Applications Information section.
response various single-point failures. transmit fault condition latched until reset toggle TX_DISABLE VCC. laser driver offers redundant laser diode shutdown through optional shutdown circuitry (see Typical Applications Circuit). TX_FAULT should pulled high with 4.7k resistor required MSA. Safety Circuitry Current Monitors MAX3735/MAX3735A feature monitors (BC_MON, PC_MON) bias current (IBIAS) photo current (IMD). monitors realized mirroring fraction currents developing voltages across external resistors connected ground. Voltages greater than 1.38V PC_MON BC_MON result fault state. example, connecting resistor ground each monitor output gives following relationships: VBC_MON (IBIAS VPC_MON
Safety Circuitry
safety circuitry contains input disable (TX_DISABLE), latched fault output (TX_FAULT), fault detectors (Figure This circuitry monitors operation laser driver forces shutdown fault detected (Table single-point fault short GND. Table view circuit
2.7Gbps, Low-Power Laser Drivers MAX3735/MAX3735A
COUNTER t_init
MAX3735 MAX3735A
IMOD ENABLE
TX_DISABLE COUNTER t_onfault PC_MON COMP RPC_MON IBIAS BC_MON MODSET SHORTCIRCUIT DETECTOR COMP LATCH 100ns DELAY
IBIAS ENABLE
SHUTDOWN CMOS TX_FAULT OPEN COLLECTOR
RBC_MON
Figure Safety Circuitry
Table Typical Fault Conditions
pins shorted (singlepoint failure, Table bias current photocurrent exceed programmed threshold. End-of-life (EOL) condition laser diode. bias current and/or photocurrent exceed programmed threshold. Laser cathode grounded photocurrent exceeds programmed thresholds. feedback loop (broken interconnection, defective monitor photodiode), bias current exceeds programmed threshold.
section, select value RMODSET that corresponds required current +25°C.
Programming Loop
Program average optical power adjusting -RAPCSET. select resistance, determine desired monitor current maintained over temperature lifetime. Monitor Diode Current RAPCSET graph Typical Operating Characteristics section, select value RAPCSET that corresponds required current.
Interfacing with Laser Diodes
minimize optical output aberrations caused signal reflections electrical interface laser diode, series-damping resistor required (Figure Additionally, MAX3735/MAX3735A outputs optimized load. Therefore, series combination where represents laser-diode resistance, should equal Typical values best performance, place bypass capacitor (0.01µF typ) close possible anode laser diode. shunt network between laser cathode ground minimizes optical output aberrations. Starting values most coaxial lasers RCOMP series with CCOMP 8pF. Adjust these values experimentally until optical output waveform optimized. Refer Maxim Application Note: HFAN 02.0: Interfacing Maxim's Laser Drivers Laser Diodes more information.
Design Procedure
When designing laser transmitter, optical output usually expressed terms average power extinction ratio. Table shows relationships helpful converting between optical average power modulation current. These relationships valid mark density duty cycle optical waveform 50%.
Programming Modulation Current
given laser power (PAVG), slope efficiency extinction ratio (re), modulation current calculated using Table Modulation Current RMODSET graph Typical Operating Characteristics
2.7Gbps, Low-Power Laser Drivers MAX3735/MAX3735A
Table Circuit Responses Various Single-Point Faults
NAME TX_FAULT TX_DISABLE CIRCUIT RESPONSE OVERVOLTAGE SHORT Does affect laser power. Modulation bias currents disabled. optical average power increases fault occurs VPC_MON exceeds threshold. loop responds decreasing bias current. optical average power decreases loop responds increasing bias current. fault state occurs VBC_MON exceeds threshold voltage. Disables bias current. fault state occurs. Does affect laser power. shutdown circuitry used, laser current disabled fault state* occurs. this condition, laser forward voltage light emitted. circuit responds increasing bias current until fault detected, then fault state* occurs. Does affect laser power. Fault state* occurs. Fault state* occurs. IBIAS increases until VBC_MON exceeds threshold voltage. IBIAS increases until VBC_MON exceeds threshold voltage. Does affect laser power. Does affect laser power. CIRCUIT RESPONSE UNDERVOLTAGE SHORT GROUND Does affect laser power. Normal condition circuit operation. optical average power decreases loop responds increasing bias current. fault state occurs VBC_MON exceeds threshold voltage. optical average power increases fault occurs VPC_MON exceeds threshold. loop responds decreasing bias current. circuit responds increasing bias current until fault detected, then fault state* occurs. Does affect laser power. Fault state* occurs. shutdown circuitry used, laser current disabled. Fault state* occurs. shutdown circuitry used, laser current disabled. Does affect laser power. Does affect laser power. Does affect laser power. IBIAS increases until VBC_MON exceeds threshold voltage. IBIAS increases until VBC_MON exceeds threshold voltage. Fault state* occurs. Fault state* occurs.
SHUTDOWN BIAS OUT+ OUTPC_MON BC_MON APCFILT1 APCFILT2 MODSET APCSET
fault state asserts TX_FAULT pin, disables modulation bias currents, asserts SHUTDOWN pin.
Table Optical Power Definitions
PARAMETER Average Power Extinction Ratio Optical Power High Optical Power Optical Amplitude Laser Slope Efficiency Modulation Current SYMBOL PAVG PP-P IMOD RELATION PAVG 2PAVG 2PAVG PP-P PP-P IMOD IMOD PP-P
Pattern-Dependent Jitter
minimize pattern-dependent jitter associated with loop time constant, guarantee loop stability, connect capacitor between APCFILT1 APCFILT2 (see Applications Information section more information about choosing values). capacitor attached photodiode anode (CMD) also recommended filter transient currents that originate from photodiode. maintain stability proper phase margin associated with poles created should greater than MAX3735. CAPC should greater than MAX3735A.
2.7Gbps, Low-Power Laser Drivers
Input Termination Requirements
MAX3735/MAX3735A data inputs compliant. On-chip differential input impedance provided optimal termination (Figure Because on-chip biasing network, MAX3735/MAX3735A inputs self-bias proper operating point accommodate AC-coupling.
Determine RAPCSET
desired monitor diode current estimated PAVG 200µA. Monitor Diode RAPCSET graph Typical Operating Characteristics section shows that RAPCSET should value also estimated using equation below: 1.23 RAPCSET)
MAX3735/MAX3735A
Optional Shutdown Output Circuitry
SHUTDOWN control output features extended safety when laser cathode grounded. external transistor required implement this circuit (Figure event fault, SHUTDOWN asserts high, placing optional shutdown transistor cutoff mode thereby shutting laser current.
Determine RMODSET
achieve minimum extinction ratio (re) over temperature lifetime, calculate required extinction ratio +25°C. Assuming results calculation +25°C, peak-to-peak optical power 1.81mW, according Table required modulation current 1.81mW (0.05mW/mA) 36.2mA. Modulation Current RMODSET graph Typical Operating Characteristics section shows that RMODSET should 9.5k. value also estimated using equation below: IMOD 1.23 (0.0037 RMODSET)
Applications Information
example MAX3735/MAX3735A follows: Select communications-grade laser 2.488Gbps. Assume that laser output average power PAVG 0dBm, operating temperature -40°C +85°C, minimum extinction ratio (8.2dB), laser diode following characteristics: Wavelength: 1.3µm Threshold current: 22mA +25°C Threshold temperature coefficient: 1.3% Laser-to-monitor transfer: 0.2A/W Laser slope efficiency: 0.05mW/mA +25°C
Determine CAPC
order meet timing requirements minimize pattern-dependent jitter, CAPC capacitor value determined laser-to-monitor transfer other variables. following equations table used choose CAPC values MAX3735 MAX3735A, respectively. equations table assume DC-coupled laser. Refer Maxim Application Note HFDN 23.0: Choosing Loop
MAX3735 MAX3735A
PACKAGE 0.11pF 0.97nH
MAX3735 MAX3735A
PACKAGE 0.81nH 0.11pF OUT-
0.99nH 0.11pF
OUT+
IN0.11pF 0.97nH
0.99nH OUT+
0.11pF
Figure Simplified Input Structure
Figure Simplified Output Structure
2.7Gbps, Low-Power Laser Drivers MAX3735/MAX3735A
Capacitors Used with MAX3735/MAX3735A Module Designs more information choosing CAPC DCand AC-coupled laser interfaces. MAX3735 following equation find CAPC value when using MAX3735: CAPC 4.04 10-9 t_on (29.3 20.6 0.22 ITH2) (1947 IMOD 7.78 IMOD2 0.103 IMOD3) where units are: CAPC ITH, IMOD then chosen approximately smaller than CAPC MAX3735. MAX3735A Table choose CAPC when using MAX3735A. CAPC should chosen according highest gain lasers (generally cold temperature). CAPC selection assumes reduction gain lasers +85°C from cold (-40°C) values. isolates laser forward voltage from output circuitry allows output OUT+ swing above below supply voltage (VCC). When AC-coupled, MAX3735/MAX3735A modulation current programmed from 10mA 85mA. Refer Maxim Application Note HFAN 02.0: Interfacing Maxim's Laser Drivers Laser Diodes more information ACcoupling laser drivers laser diodes.
Interface Models
Figures show simplified input output circuits MAX3735/MAX3735A laser driver. dice used, replace package parasitic elements with bondwire parasitic elements.
Wire Bonding
MAX3735 uses gold metalization with thickness (typ). Maxim characterized this circuit with gold wire ball bonding (1-mil diameter wire). Die-pad size (2388µm) square, thickness (381µm). Refer Maxim Application Note HFAN-08.0.1: Understanding Bonding Coordinates Physical Size additional information.
Table MAX3735A CAPC Selection
LASER GAIN (A/A) 0.005 0.007 0.010 0.020 0.030 0.040 CAPC (µF) 0.039 0.047 0.068 0.100 0.120 0.120
Layout Considerations
minimize inductance, keep connections between MAX3735 output pins laser diode close possible. Optimize laser diode performance placing bypass capacitor close possible laser anode. good high-frequency layout techniques multiple-layer boards with uninterrupted ground planes minimize crosstalk.
Exposed-Pad Package
exposed 24-pin provides very thermal resistance path heat removal from also electrical ground MAX3735/ MAX3735A must soldered circuit board ground proper thermal electrical performance. Refer Maxim Application Note HFAN-08.1: Thermal Considerations Other Exposed-Pad Packages additional information.
where Gain IMD/(IBIAS IMOD) DC-coupled lasers. then chosen approximately smaller than CAPC MAX3735A
Using MAX3735/MAX3735A with Digital Potentiometers
more information using MAX3735/MAX3735A with Dallas DS1858/DS1859 controller, refer Maxim Application Note HFAN 2.3.3: Optimizing Resolution Laser Driver Setting Using Linear Digital Potentiometers more information.
Laser Safety
Using MAX3735/MAX3735A laser driver alone does ensure that transmitter design compliant with 825. entire transmitter circuit component selections must considered. Each user must determine level fault tolerance required application, recognizing that Maxim products neither designed authorized components systems intended surgical implant into body, applications intended support sustain life, other application which failure Maxim product could create situation where personal injury death occur.
Modulation Currents Exceeding 60mA
applications requiring modulation current greater than 60mA, headroom insufficient proper operation laser driver laser DC-coupled. avoid this problem, MAX3735/MAX3735A's modulation output AC-coupled cathode laser diode. external pullup inductor necessary DCbias modulation output VCC. Such configuration
2.7Gbps, Low-Power Laser Drivers
MAX3735 Chip Topography
0.079" (2.007mm) TX_DISABLE APCSET APCFILT2 APCFILT1
MAX3735/MAX3735A
OUT-
OUT0.060" (1.524mm) OUT+
OUT+
PC_MON
BC_MON INDEX SHUTDOWN TX_FAULT MODSET
BIAS
2.7Gbps, Low-Power Laser Drivers MAX3735/MAX3735A
Bonding Coordinates
TX_DISABLE
Configuration
APCFILT2
Table MAX3735 Bondpad Locations
16** 17** 18** 19** NAME BC_MON PC_MON ININ+ TX_DISABLE APCSET APCFILT2 APCFILT1 OUTOUTOUT+ OUT+ BIAS MODSET TX_FAULT SHUTDOWN COORDINATES 1008 1193 1383 1567 1758 1758 1758 1758 1758 1758 1758 1578 1401 1205 1016 1063 1149 1149 1149 1149 1149 1149 1149 1149 1032
INVCC PC_MON BC_MON
VIEW
APCFILT1
APCSET
OUTOUT+ OUT+ BIAS
MAX3735 MAX3735A
SHUTDOWN
TX_FAULT
MODSET
Thin QFN* (4mm 4mm)
*THE EXPOSED MUST CONNECTED CIRCUIT BOARD GROUND PROPER THERMAL ELECTRICAL PERFORMANCE.
Chip Information
TRANSISTOR COUNT: SUBSTRATE CONNECTED SIZE: mils mils PROCESS: SiGe Bipolar
*Index pad. Orient with this lower-left corner. **Bond both pairs OUT- OUT+ minimize series inductance.
2.7Gbps, Low-Power Laser Drivers
Package Information
(The package drawing(s) this data sheet reflect most current specifications. latest package outline information, www.maxim-ic.com/packages.)
12,16,20, QFN.EPS
MAX3735/MAX3735A
PACKAGE OUTLINE 12,16,20,24L QFN, 4x4x0.90
21-0106
PACKAGE OUTLINE 12,16,20,24L QFN, 4x4x0.90
21-0106
2.7Gbps, Low-Power Laser Drivers MAX3735/MAX3735A
Package Information
(The package drawing(s) this data sheet reflect most current specifications. latest package outline information, www.maxim-ic.com/packages.)
THIN.EPS
PACKAGE OUTLINE THIN QFN, 4x4x0.8mm
21-0139
PACKAGE OUTLINE THIN QFN, 4x4x0.8mm
21-0139
Maxim cannot assume responsibility circuitry other than circuitry entirely embodied Maxim product. circuit patent licenses implied. Maxim reserves right change circuitry specifications without notice time.
_Maxim Integrated Products, Gabriel Drive, Sunnyvale, 94086 408-737-7600 2004 Maxim Integrated Products Printed registered trademark Maxim Integrated Products.

2.7Gbps, Low-Power Laser Drivers Reference Design Available Fully

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