+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control
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+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control
MAX3668 complete, +3.3V laser driver with automatic power control (APC) circuitry SDH/SONET applications 622Mbps. accepts differential PECL inputs, provides bias modulation currents, operates over temperature range -40°C +85°C. feedback loop incorporated maintain constant average optical power over temperature lifetime. wide modulation current range 75mA bias current 80mA easy program, making this product ideal various SDH/SONET applications. MAX3668 also provides enable control failuremonitor output indicate when loop unable maintain average optical power. MAX3668 available 32-pin TQFP package well dice. Single +3.3V +5.0V Operation 38mA Supply Current +3.3V Programmable Modulation Current from 75mA Programmable Bias Current from 80mA Rise/Fall Time <200ps Automatic Average Power Control with Failure Monitor Complies with ANSI, ITU, Bellcore SONET/SDH Specifications Enable Control
Features
MAX3668
Ordering Information
PART MAX3668EHJ MAX3668E/D TEMP. RANGE -40°C +85°C (see Note) PIN-PACKAGE TQFP (5mm 5mm) Dice*
Applications
622Mbps SDH/SONET Access Nodes Laser Driver Transmitters Section Regenerators
Note: Dice designed operate over -40°C +140°C junction temperature (Tj) range, tested guaranteed +25°C. *Contact factory availability. Configuration appears data sheet.
Typical Operating Circuit
+3.3V +3.3V LASER ENABLE FAIL R6.3 OUTOUT+ 1.0µF
DATA+
MAX3693
SERIALIZER WITH CLOCK
PECL DATA-
MAX3668
RFILT CFILT
BIASMAX
MODSET
APCSET
BIAS CAPC
FERRITE BEAD 1000pF
0.1µF
Covered U.S. Patent numbers 5,802,089 5,883,910
Maxim Integrated Products
free samples latest literature, visit www.maxim-ic.com phone 1-800-998-8800. small orders, phone 1-800-835-8769.
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control MAX3668
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, .-0.5V +7.0V Current into BIAS .-20mA +150mA Current into OUT+, OUT- -20mA +100mA Current into MD.-5mA +5mA Voltage DATA+, DATA-, ENABLE, FAIL .-0.5V (VCC 0.5V) Voltage OUT+, OUT- .+1.5V (VCC 1.5V) Voltage MODSET, APCSET, BIASMAX, CAPC. -0.5V +3.0V Voltage BIAS .+1.0V (VCC 0.5V) Continuous Power Dissipation +85°C) 32-Pin TQFP (derate 14.3mW/°C above +85°C). 929mW Operating Junction Temperature Range .-55°C +150°C Processing Temperature (Die).+400°C Storage Temperature Range -65°C +165°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 +3.14V +5.5V, -40°C +85°C, unless otherwise noted. Typical values +3.3V, +25°C.) (Note PARAMETER Supply Current Bias Current Range Bias Current Bias Current Stability Bias Current Absolute Accuracy Differential Input Voltage Common-Mode Input Voltage DATA+, DATA- Input Current Monitor Diode Current Stability Monitor Diode Current Absolute Accuracy Monitor Diode Current Monitor Diode Input Voltage Pin) Input High Voltage Input Voltage Output High Voltage (FAIL) Output Voltage (FAIL) Sourcing 50µA Sinking 100µA 0.44 VICM (Note 18µA (Note IBIAS SYMBOL (Note VBIAS 1.6V ENABLE (Note open loop open loop Figure PECL compatible IBIAS 80mA IBIAS 1.49 -480 1000 1.32 1600 VID/4 CONDITIONS UNITS ppm/°C mVp-p ppm/°C
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control MAX3668
ELECTRICAL CHARACTERISTICS
(VCC +3.14V +5.5V, load shown Figure -40°C +85°C, unless otherwise noted. Typical values +3.3V, +25°C.) (Note PARAMETER Modulation Current Range Modulation Current Modulation Current Stability Modulation Current Absolute Accuracy Output Rise/Fall Time Jitter Generation (peak-to-peak) Pulse-Width Distortion (peak-to-peak) Enable/Start-Up Delay Maximum Consecutive Identical Digits 622Mbps tR/tF 80%, load (Note (Notes Open loop IMOD IMOD 75mA IMOD IMOD 75mA SYMBOL IMOD (Note ENABLE (Note IMOD 75mA IMOD (Note -620 CONDITIONS UNITS ppm/°C Bits
Note Characteristics -40°C guaranteed design characterization. Dice tested +25°C only. Note Tested with RMODSET 5.11k (IMOD 38mA), RBIASMAX 4.56k (IBIAS 52mA), excluding IBIAS IMOD. Note Both bias modulation currents will disabled current pins shorted ground. Note This assumes that laser monitor diode transfer function does change with temperature. Note Typical Operating Characteristics worst-case distributions. Note characteristics guaranteed design characterization. Note Total IMOD OUT+. Refer Design Procedure information regarding current delivered laser. Note Input signal 622Mbps, 213- PRBS with inserted zeros. Note Input signal 622Mbps, 11110000 pattern. Note 10:PWD (wider pulse narrower pulse)
DATA+ DATA(DATA+) (DATA-)
100mV 800mV 200mVp-p OUT-
1.0µF
1600mVp-p IOUT+ IMOD
MAX3668
OUT+ BIAS
1.0µF
OSCILLOSCOPE
12.4
Figure Required Input Signal Output Polarity
Figure Output Termination Characterization
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control MAX3668
Typical Operating Characteristics
(VCC +3.3V, +25°C, unless otherwise noted.)
DIAGRAM (622Mbps, 1300nm LASER WITH 467MHz FILTER)
MAX3668 TOC01
DIAGRAM (IMOD 35mA)
MAX3668 TOC02
DIAGRAM (IMOD 75mA)
622Mbps
MAX3668 TOC03
PRBS
622Mbps
PATTERN IMOD 35mA
PATTERN IMOD 75mA
193ps/div
200ps/div
200ps/div
MONITOR DIODE CURRENT RESISTOR
MAX3668 TOC04
BIAS CURRENT MAXIMUM BIAS RESISTOR
MAX3668 TOC05
MODULATION CURRENT MODULATION RESISTOR
MAX3688 TOC06
1000
IBIAS (mA) (mA)
IMOD (mA) RAPCSET RBIASMAX
0.01
RMODSET 1000
RANDOM JITTER MODULATON CURRENT
MAX3668 TOC07
PULSE-WIDTH DISTORTION MODULATION CURRENT
(ps)
MAX3668 TOC08
SUPPLY CURRENT TEMPERATURE
MAX3668 TOC09
INCLUDES RANDOM JITTER MEASUREMENT EQUIPMENT
RANDOM JITTER p-p)
SUPPLY CURRENT (mA) +5.0V +3.3V
IBIAS 48mA IMOD 33mA IMOD (mA) TEMPERATURE (°C)
IMOD (mA)
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control
Typical Operating Characteristics (continued)
(VCC +3.3V, +25°C, unless otherwise noted.)
AVAILABLE BIAS CURRENT MAXIMUM BIAS RESISTOR
MAX3668 TOC10
MAX3668
DISTRIBUTION MODULATION CURRENT STABILITY (WORST CASE)
MAX3668-11
DISTRIBUTION MONITOR DIODE CURRENT STABILITY (WORST CASE)
-40°C +85°C 18µA PERCENT UNITS
MAX3668-12
1000 +3.3V, BIAS CURRENT (mA)
-40°C +85°C IMOD PERCENT UNITS
CLOSED-LOOP OPERATION
+3.3V RBIAS
MODULATION DIODE CURRENT STABILITY (ppm/°C)
MONITOR DIODE CURRENT STABILITY (ppm/°C)
Description
NAME DATA+ DATAGND ENABLE FAIL N.C. BIAS OUT+ OUTMD CAPC APCSET MODSET BIASMAX Positive Supply Voltage Positive PECL Data Input Negative PECL Data Input Ground TTL/CMOS Enable Input. High normal operation, disable laser bias modulation currents. Internally pulled high. Output. Indicates failure when low. Internally pulled high through resistor. Connection. Leave unconnected. Laser Bias Current Output. Isolate from laser with ferrite bead. Positive Modulation Current Output. IMOD flows into this when input signal high. Connect this coupling network. Negative Modulation Current Output. IMOD flows into this when input signal low. Connect this through resistor. Monitor Photodiode Connection. Connect this monitor photodiode anode. capacitor ground required filter high-speed monitor photocurrent. Compensation Capacitor. 0.1µF capacitor connected from this ground controls dominant pole automatic power control (APC) feedback loop. Resistor. resistor connected from this ground sets desired average optical power. resulting current equal desired monitor diode current. Connect 100k resistor from this ground used. Modulation Resistor. resistor from this ground sets laser modulation current. Maximum Bias Resistor. resistor from this ground sets maximum laser bias current. function subtract from this maximum value cannot This resistor controls bias-current level when loop used. FUNCTION
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control MAX3668
DATA+ OUT+ OUTVCC 100k ENABLE IBIAS BIAS
DATA-
165X
MAX3668
FAILURE DETECTOR MODSET RMODSET BIASMAX FAIL RBIASMAX CAPC RAPCSET CAPC APCSET
Figure Functional Diagram
Detailed Description
MAX3668 laser driver consists main parts: high-speed modulation driver laser-biasing block with Automatic Power Control (APC). circuit optimized low-voltage (+3.3V) operation. output stage composed high-speed differential pair programmable modulation current source. Since modulation output drives maximum current 75mA into laser with 230ps edge speed, large transient voltage spikes generated parasitic inductance. These transients laser forward voltage leave insufficient headroom proper operation laser driver modulation output DC-coupled laser diode. solve this problem, MAX3668's modulation output designed
AC-coupled cathode laser diode. simplified functional diagram shown Figure MAX3668 modulation output optimized driving load; minimum required voltage OUT+ 2.0V. Modulation current swings 75mA possible. interface with laser diode, damping resistor (RD) required impedance matching. shunt network used compensate laser-diode parasitic inductance, thereby improving optical output aberrations duty-cycle distortion. 622Mbps data rate, capacitive load cathode laser diode degrades optical output performance. Since BIAS output directly connected laser cathode, minimize parasitic capacitance associated with this using inductor isolate BIAS from laser cathode.
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control
Automatic Power Control
maintain constant average optical power, MAX3668 incorporates 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 monitor current matched reference current RAPCSET. time constant loop determined external capacitor (CAPC). eliminate pattern-dependent jitter associated with loop-time constant guarantee loop stability, recommended value CAPC 0.1µF. When loop functioning, maximum allowable bias current external resistor, RBIASMAX. failure flag (FAIL) when bias current longer adjusted achieve desired average optical power. closed-loop operation requires user three currents with external resistors connected between ground BIASMAX, MODSET, APCSET. Detailed guidelines these resistor settings described Design Procedure section.
Short-Circuit Protection
MAX3668 provides short-circuit protection modulation, bias, monitor current sources. either BIASMAX, MODSET, APCSET shorted ground, bias modulation outputs will turned off.
MAX3668
Design Procedure
When designing laser transmitter, optical output usually expressed terms average power extinction ratio. Table gives relationships that helpful converting between optical average power modulation current. These relationships valid average duty cycle optical waveform 50%.
Programming Modulation Current
addition being function RMODSET, modulation current delivered laser (IMODL) also depends values series damping resistor (RD), shunt compensation resistance (RFILT), laser diode's resistance (see Typical Operating Circuit). modulation current (assuming CFILT<<CD) into laser diode represented following: IMODL IMOD LASER Assuming rLASER this equation simplified IMODL IMOD(0.67) laser resistance approximately refer Modulation Current Modulation Resistor graph Typical Operating Characteristics select value RMODSET that corresponds required current +25°C.
Open-Loop Operation
necessary, MAX3668 fully operational without APC. this case, laser current directly external resistors connected from ground BIASMAX MODSET. Connect 100k resistor from APCSET ground leave open open-loop operation.
Enable Control
MAX3668 incorporates laser driver enable function. When ENABLE low, both bias modulation currents off. typical laser enable time 250ns.
Failure Monitor
MAX3668 provides failure monitor (TTL/CMOS) indicate loop tracking failure. FAIL when loop longer adjust bias current maintain desired monitor current. This output internally pulled through resistor.
Programming Bias Current
When using MAX3668 open-loop operation, bias current determined RBIASMAX resistor. select this resistor, determine required bias current +25°C. Refer Bias Current Maximum Bias Resistor graph Typical Operating Characteristics select value BIASMAX that corresponds required current +25°C. When using MAX3668 closed-loop operation, RBIASMAX resistor sets maximum bias current available laser diode over temperature life. loop subtract from this maximum value cannot Refer Bias Current Maximum Bias Resistor graph Typical Operating Characteristics select value RBIASMAX that corresponds end-of-life bias current +85°C.
Table Optical Power Definition
PARAMETER Average Power Extinction Ratio Optical Power High Optical Power Optical Amplitude Laser Slope Efficiency Modulation Current SYMBOL PAVE Pp-p IMOD RELATION PAVE 2PAVE 2PAVE Pp-p 2PAVE Pp-p IMOD IMOD Pp-p
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control MAX3668
Programming Loop
When MAX3668's feature used, program average optical power adjusting APCSET resistor. select this resistor, determine desired monitor current maintained over temperature life. Refer Monitor Diode Current Resistor graph Typical Operating Characteristics select value RAPCSET that corresponds required current. equals consecutive unit intervals without transition, time constant associated with blocking capacitor needs longer than: RACCD bits) (1.6ns/bit) 1.0µs RFILT ignored CFILT<< therefore estimated value rLASER) Assuming rLASER with 1.0µF, 6.7µs.
Interfacing with Laser Diode
minimize optical output aberrations laser parasitic inductance, shunt network used (see Typical Operating Circuit). represents laser diode resistance, recommended total resistance Starting values coaxial lasers RFILT CFILT 5pF. RFILT CFILT should experimentally adjusted optimize output waveform. bypass capacitor should also placed close laser anode possible best performance.
Input Termination Requirement
MAX3668 data inputs PECL-compatible. However, necessary drive MAX3668 with standard PECL signal. long specified common-mode voltage differential voltage swings met, MAX3668 will operate properly.
Calculate Power Consumption
total power dissipation MAX3668 estimated following: (VCC IBIAS IMOD (VCC IMOD where IBIAS maximum bias current RBIASMAX, IMOD modulation current, typical laser forward voltage.
Pattern-Dependent Jitter (PDJ)
When transmitting data with long strings consecutive identical digits (CID), droop contribute pattern-dependent jitter. minimize this pattern-dependent jitter, external components must properly chosen: capacitor CAPC, which dominates loop time constant; AC-coupling capacitor filter noise effects guarantee loop stability, recommended value CAPC 0.1µF. This results loop bandwidth 20kHz. Consequently, pattern-dependent jitter associated with loop time constant ignored. time constant associated with blocking capacitor will have effect PDJ. important that this time constant produce minimum droop long consecutive streams. Referring Figure droop resulting from long time periods without transitions represented following equation: (100% DROOP) coupling IMOD results discharge level that equal PAVG. overall droop relative equates droop relative ensure droop less than relative Pp-p), this equation solved follows: 7.8t ln(1 0.12)
Applications Information
following example MAX3668.
Select Laser
communication-grade laser should selected 622Mbps applications. Assume laser output average power PAVE 0dBm, minimum extinction
Pp-p PAVG DROOP
Figure Droop
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control
ratio (8.2dB), operating temperature -40°C +85°C, laser diode following characteristics: Wavelength: Threshold Current: Threshold Temperature Coefficient: Laser Monitor Transfer: Laser Slope Efficiency: 1.3µm 22mA +25°C 1.3%/°C 0.2A/W 0.05mW/mA +25°C
Wire Bonding
high current density reliable operation, MAX3668 uses gold metalization. Make connections with gold wire only, using ball-bonding techniques. Wedge bonding recommended. Die-pad size mils (100µm) square, thickness mils (300µm) mils.
MAX3668
Layout Considerations
minimize inductance, keep connections between MAX3668 output pins close possible. Optimize laser diode performance placing bypass capacitor close possible laser anode. good high-frequency layout techniques multilayer boards with uninterrupted ground planes minimize crosstalk.
Determine RAPCSET
desired monitor diode current estimated PAVE 200µA. Monitor Diode Current Resistor graph Typical Operating Characteristics shows that RAPCSET should
Laser Safety
Using MAX3668 laser driver alone does ensure that transmitter design compliant with 825. entire transmitter circuit component selections must considered. Customers must determine level fault tolerance required their application, recognizing that Maxim products designed authorized components systems intended surgical implant into body, applications intended support sustain life, other application where failure Maxim product could create situation where personal injury death occur.
Determine RMODSET
achieve minimum extinction ratio (re) over temperature lifetime, calculate required extinction ratio +25°C. Assuming peak-to-peak optical power Pp-p 1.81mW according Table required modulation current 1.81(mW) 0.05(mW/mA) 36.2mA. Modulation Current Modulation Resistor graph (see Typical Operating Characteristics) shows that RMODSET should
Determine RBIASMAX
Calculate maximum threshold current (ITH(MAX)) +85°C life. Assuming TH(MAX) 50mA, maximum bias current should IBIAS ITH(MAX) IMOD this example, IBIAS 68.1mA. Bias Current Maximum Bias Resistor graph Typical Operating Characteristics shows that RBIASMAX should
FERRITE BEADS 1.0µF
Modulation Current More than 50mA
drive modulation currents greater than 50mA 3.3V, external pull-up inductors (Figure should used DC-bias modulation output VCC. Such configuration isolates laser forward voltage from output circuitry allows output OUT+ swing above below supply voltage VCC. power supply, headroom voltage MAX3668 significantly improved. this case, possible achieve modulation current more than 50mA (using resistor pull-ups shown Typical Operating Circuit). MAX3668 also DC-coupled laser diode when operating supply; voltage OUT+ should 2.0V proper operation.
OUTOUT+
RFILT CFILT
MAX3668
BIAS 1000pF FERRITE BEAD
Figure Output Termination Maximum Modulation Current
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control MAX3668
Configuration
Chip Topography
N.C. DATADATA+ BIASMAX MODSET APCSET N.C. 0.083" (2.10mm) N.C. N.C. CAPC
VIEW
BIASMAX MODSET APCSET CAPC N.C. N.C. N.C.
DATA+ DATAGND ENABLE
MAX3668
OUT18 OUT+
ENABLE N.C. N.C. FAIL N.C. N.C. BIAS
FAIL
N.C.
N.C.
BIAS
TQFP
N.C. OUT+ OUTN.C. 0.070" (1.78mm)
N.C.
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control
Package Information
32L,TQFP.EPS (Package information continues next page.)
MAX3668
+3.3V, 622Mbps SDH/SONET Laser Driver with Automatic Power Control MAX3668
Package Information (continued)
Maxim makes warranty, representation guarantee regarding suitability products particular purpose, does Maxim assume liability arising application product circuit specifically disclaims liability, including without limitation consequential incidental damages. "Typical" parameters vary different applications. operating parameters, including "typicals" must validated each customer application customer's technical experts. Maxim products designed, intended authorized components systems intended surgical implant into body, other applications intended support sustain life, other application which failure Maxim product could create situation where personal injury death occur.
_Maxim Integrated Products, Gabriel Drive, Sunnyvale, 94086 408-737-7600 2000 Maxim Integrated Products Printed registered trademark Maxim Integrated Products.
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