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19-3848; Rev 1; 10/08
KIT ATION EVALU BLE AVAILA
155Mbps to 2.5Gbps Burst-Mode Laser Driver
General Description
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 5A 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-and-hold 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. The MAX3643 burst-mode laser driver is packaged in a 4mm x 4mm, 24-pin thin QFN package. It operates from -40C to +85C. 10mA to 85mA Modulation Current 1mA to 70mA Bias Current Monitor Diode Sample and Hold 45ps Output Transition Time 2ns Turn-On/-Off Time Reference Voltage Generator LVPECL High-Speed Inputs (Data, Burst Enable)
Features
MAX3643
Ordering Information
PART MAX3643ETG MAX3643ETG+ TEMP RANGE -40C to +85C -40C to +85C PIN-PACKAGE 24 TQFN-EP* 24 TQFN-EP*
+Denotes a lead-free/RoHS-compliant package. *EP = Exposed paddle.
Applications
A/B/GPON ONT Modules up to 2.5Gbps 1.25Gbps IEEE EPON ONT Modules
Pin Configuration appears at end of data sheet.
Typical Application Circuit
+3.3V
0.1F 27nH 15 +3.3V FILTER VCC 24
OUT10 OUT+ 10 BIAS+ RCOMP CCOMP
IN+ IN-
MAX3643
BEN+ BENEN IMAX BCMON VREF VMSET MODSET VBSET BIASMDIN MDOUT BIASSET BENOUT GND
15 VCC
1k
3k
1k
1k
1k
ANALOG OUT ANALOG OUT ANALOG IN CONTROL
START CONVERT ANALOG IN ANALOG IN CONTINUOUS OPERATION
CONTROLLER
________________________________________________________________ Maxim Integrated Products
1
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.
155Mbps to 2.5Gbps Burst-Mode Laser Driver MAX3643
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, BIASMON ................-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 = +85C) 24-Pin TQFN, Multilayer Board (derate 27.8mW/C above +85C) ............................1807mW Operating Temperature Range ...........................-40C to +85C Storage Temperature Range ............................-55C to +150C Lead Temperature (soldering, 10s) .................................+300C
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 Supply Turn-On Time Ambient Temperature Data Rate Voltage at VMSET, VBSET Voltage at BIASMON Voltage at MDIN 0 0 0 SYMBOL 10% to 90% CONDITIONS MIN 0.001 -40 TYP MAX 1000 +85 2500 1.4 1.4 2.56 UNITS ms C Mbps V V V
ELECTRICAL CHARACTERISTICS
(VCC = +3.0V to +3.6V, TA = -40C to +85C. Typical values are at VCC = +3.3V, TA = +25C, IBIAS = 20mA, IMOD = 30mA, unless otherwise noted.) (Note 1)
PARAMETER Supply Current I/O SPECIFICATIONS LVPECL Differential Input Voltage LVPECL Common-Mode Input Voltage LVCMOS Output High Voltage LVCMOS Output Low Voltage BENOUT Propagation Delay LVCMOS Input Pullup Resistance LVCMOS Input Current LVCMOS Input High Voltage LVCMOS Input Low Voltage BIAS GENERATOR SPECIFICATIONS Bias Current Range Bias Current, Burst Off BIASSET Current Gain IBIAS IBIAS, OFF GBIAS VBIAS+, VBIAS- 0.6V BEN = low or EN = high 1mA IBIAS < 2mA, VBSET = VREF 2mA IBIAS < 10mA, VBSET = VREF 10mA IBIAS < 70mA, VBSET = VREF 70 82.5 1 5 88 88 88 110 94.5 mA/mA 70 50 mA A VIN = 0V or VIN = VCC 2.0 0.2 Td VIN VCM IOH = -100A IOL = 100A CL = 20pF, from BEN zero crossing to 67% CMOS level 75 50 VCC 0.8 30 VIN = (VIN+) - (VIN-) 200 VCC 1.49 VCC 0.2 0.2 VCC 1.32 1600 VCC VIN / 4 mVP-P V V V ns k A V V SYMBOL ICC CONDITIONS Excluding laser bias and mode currents, max at IMOD = 85mA, IBIAS = 70mA MIN TYP 32 MAX 51 UNITS mA
2
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155Mbps to 2.5Gbps Burst-Mode Laser Driver
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.0V to +3.6V, TA = -40C to +85C. Typical values are at VCC = +3.3V, TA = +25C, IBIAS = 20mA, IMOD = 30mA, unless otherwise noted.) (Note 1)
PARAMETER BIASSET Current Gain Stability BIASSET Current Gain Linearity Bias Current Overshoot Bias Current Monitor Gain Bias Current Monitor Gain Stability BIASSET Resistor MODULATOR SPECIFICATIONS Modulation Current Range Modulation Current Off Instantaneous Voltage at OUT+ MODSET Current Gain MODSET Current Gain Stability MODSET Current Gain Linearity MODSET, BIASSET Gain Matching (Note 15) Modulation Current Rise Time Modulation Current Fall Time Deterministic Jitter Random Jitter MODSET Resistor MODSET, BIASSET Voltage Range Voltage Error Input Leakage TURN-OFF/-ON SPECIFICATIONS Burst-Enable Time Burst-Disable Time (Notes 2, 6, 7) (Notes 2, 6, 8) 2.3 2.0 ns ns (Note 5) VMSET and VBSET pins 0.1 RMOD tR tF GMOD IMOD IMOD, OFF BEN = low or EN = high or VIN = low 10mA IMOD < 60mA 60mA IMOD 85mA 10mA < IMOD < 85mA, VMSET = VREF (Note 13) (Note 14) IBIASSET = 0.15mA, IMODSET = 0.7mA IMODSET = IBIASSET = 0.15mA IMODSET = IBIASSET = 0.4mA IMODSET = IBIASSET = 0.55mA 20% to 80% 20% to 80% (Note 3) (Note 4) 40 45 45 17 0.8 50 0.6 0.75 82.5 -4.4 -2.2 0.5 1.7 1 1 85 85 45 1.4 60 ps ps psP-P psRMS % 88 94.5 +4.4 +2.2 10 5 85 120 mA A V mA/mA % % RBIAS GBSM SYMBOL CONDITIONS 5mA IBIAS 70mA (Note 13) 5mA IBIAS 70mA (Note 14) VCC turn-on/-off < 1s 2mA IBIAS 70mA, VBSET = VREF 1mA IBIAS < 5mA 5mA IBIAS 70mA -5 40 50 11 14 4 +5 60 MIN -4.4 -3.75 TYP MAX +4.4 +3.75 10 17 UNITS % % % mA/A %
MAX3643
MODSET, BIASSET OPERATIONAL AMPLIFIER SPECIFICATIONS 0.005 1.4 5 1.5 V mV A
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155Mbps to 2.5Gbps Burst-Mode Laser Driver MAX3643
ELECTRICAL CHARACTERISTICS (continued)
(VCC = +3.0V to +3.6V, TA = -40C to +85C. Typical values are at VCC = +3.3V, TA = +25C, IBIAS = 20mA, IMOD = 30mA, unless otherwise noted.) (Note 1)
PARAMETER SAMPLE/HOLD SPECIFICATIONS MDIN Voltage Range MDOUT Settling Sample/Hold Droop Sampling Error Relative to final value at 3s, CL < 20pF After 100s (Note 9) Final value measured after 10s (MDOUT - MDIN), burst width > 576ns RL > 10k, CL < 50pF 5mA < IBIAS, 10mA < IMOD (Note 10) (Notes 2, 11) 3 RIMAX = 3k IBIAS+IMOD RIMAX = 5k RIMAX = 10k 1.25Gbps (Note 12) 155 100 50 33 150 75 % mA 1.175 3 0.05 2.56 1 2.56 14 V mV mV mV SYMBOL CONDITIONS MIN TYP MAX UNITS
BANDGAP VOLTAGE REFERENCE SPECIFICATIONS VREF Output MODULATION/BIAS CURRENT DISABLE Enable Time Disable Time RIMAX Range Current Limit (Tested with IBIAS = IMOD) OPTICAL EVALUATION Eye Margin 5.5 375 15 s ns k 1.235 1.295 V
Note 1: DC parameters are production tested at TA = +25C, guaranteed by design and characterization at TA = -40C. 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 10M. 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 SXT5731-Q laser. Note 13: Current gain stability = [(Gain - nominal Gain) / nominal Gain], nominal Gain at VCC = 3.3V, TA = +25C. Note 14: Gain linearity = (Gainmax - Gainmin), Gainavg = Gainmax - Gainmin Gainavg/2 2 Note 15: Gain matching = Gain mod / Gainbias - Gain mod nom / Gainbiasnom nominal at VCC = 3.3V, TA = +25C.
Gain mod nom / Gainbiasnom
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155Mbps to 2.5Gbps Burst-Mode Laser Driver
Typical Operating Characteristics
(Typical values are at VCC = +3.3V, TA = +25C, data pattern = 27-1 PRBS + 80 ones + 27-1 PRBS + 80 zeros, unless otherwise noted.)
OPTICAL EYE DIAGRAM (1.25Gbps, 933MHz FILTER, PATTERN 213-1 + 80 CID)
MAX3643 toc01
MAX3643
SUPPLY CURRENT vs. TEMPERATURE (IBIAS = 20mA, IMOD = 30mA)
55 50 45 DJ (psP-P) ICC (mA) 40 35 30 25 20 15 10 EXCLUDES BIAS AND MODULATION CURRENT
MAX3643 toc02
DETERMINISTIC JITTER vs. MODULATION AMPLITUDE
27 24 21 18 15 12 9 6 3 0
MAX3643 toc03
60
30
EXCELIGHT SXT5731-Q LASER AVERAGE OPTICAL POWER = 3dBm EXTINCTION RATIO = 15dB GbE MASK MARGIN = 33% 1.2 1.1 1.0 RANDOM JITTER (psRMS) 0.9
-40
-20
0
20
40
60
80
10
20
30
TEMPERATURE (C)
50 60 40 IMOD (mA)
70
80
RANDOM JITTER vs. MODULATION AMPLITUDE
MAX3643 toc04
IMOD vs. IMODSET
80 70 60 IMOD (mA) 50 40 30 20 10 0
MAX3643 toc05
90
0.8 0.7 0.6 0.5 0.4 0.3 0.2 10 20 30 40 50 60 70 80 IMOD (mA)
0
200
400
600
800
1000
IMODSET (A)
IBIAS vs. IBIASSET
MAX3643 toc06
IMOD vs. VMSET (RMODSET = 1k)
80 70 IMOD (mAP-P) 60 50 40 30 20 10 0
MAX3643 toc07
90 80 70 60 IBIAS (mA) 50 40 30 20 10 0 0 200 400 600 800
90
1000
0
0.2
0.4
0.6 VMSET (V)
0.8
1.0
1.2
IBIASSET (A)
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155Mbps to 2.5Gbps Burst-Mode Laser Driver MAX3643
Typical Operating Characteristics (continued)
(Typical values are at VCC = +3.3V, TA = +25C, data pattern = 27-1 PRBS + 80 ones + 27-1 PRBS + 80 zeros, unless otherwise noted.)
IBIAS vs. VBSET (RBIASSET = 1k)
MAX3643 toc08
BIAS CURRENT MONITOR GAIN (IBCMON/IBIAS) vs. TEMPERATURE
MAX3643 toc09
TIMING DIAGRAM, BURST-ON (933MHz FILTER ON OUT+)
MAX3643 toc10
90 80 70 60 IBIAS (mA) 50 40 30 20 10 0 0 0.2 0.4 0.6 0.8
17
VOUT+
16 GAIN (mA/A)
15
VBIAS+
14 VBEN+ 13
12 1.0 -40 -20 0 20 40 60 80 500ps/div VBSET (V) TEMPERATURE (C)
TIMING DIAGRAM, BURST-OFF (933MHz FILTER ON OUT+)
MAX3643 toc11
SAMPLE/HOLD (10M LOAD, 2.8s SAMPLE AND 100s HOLD, MDIN = 1.56V)
MAX3643 toc12
IBIAS + IMOD CURRENT THRESHOLD vs. RIMAX
140 CURRENT THRESHOLD (mA)
MAX3643 toc13
160
VOUT+ 1.56V MDOUT VBIAS+ 1.22V
120 100 80 60 40 20 0 0 5 10 R 15 (k) 20 25 30
BEN+ VBEN+
500ps/div
20s/div
ELECTRICAL EYE DIAGRAM (2.5Gbps, IMOD = 30mA, PATTERN = PRBS 27 - 1 + 80 CID)
MAX3643 toc14
100ps/div
6
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155Mbps to 2.5Gbps Burst-Mode Laser Driver
Pin Description
PIN 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15, 18 16 17 19 20 21 22 23 24 EP NAME VCCA IN+ INVCCS BEN+ BENBENOUT EN BCMON IMAX MDOUT MDIN BIASBIAS+ VCCO OUT+ OUTGND MODSET VMSET VREF VBSET BIASSET EP Analog Supply Voltage Noninverted Data Input, LVPECL Compatible Inverted Data Input, LVPECL Compatible Signal Supply Voltage Noninverted Burst-Enable Input, LVPECL Compatible Inverted Burst-Enable Input, LVPECL Compatible Burst-Enable Output, LVCMOS. Signal replicates BEN input. Enable Input LVCMOS. Active low enables BIAS and MOD 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. Monitor Diode In. Analog Input for sample/hold. Connect BIAS- to VCC Through a 15 Resistor (or 5 Resistor and Switching Diode) Laser Bias Current Output. Modulation current flows into this pin when BEN input is high. Output Supply Voltage Laser Modulation Current Output. Modulation current flows into this pin when both BEN and IN inputs are high. Connect OUT- to VCC Through a 15 Resistor (or 5 Resistor and Switching Diode) Supply Ground. This pin must be connected to ground. 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. FUNCTION
MAX3643
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7
155Mbps to 2.5Gbps Burst-Mode Laser Driver MAX3643
VCC
0.1F 27nH 24
15 OUT+ 10
MAX3643
IN+ LVPECL INBEN+ LVPECL BENCMOS
OUTBIAS+
10
RCOMP CCOMP
VCC BIAS15
BENOUT IMAX VCC VCC MDIN CMOS EN I1 IM = 88 x I1 I2 IB = 88 x I2 MDOUT VCC LIMIT LIMIT
IBCMON = IB x 0.014 1.2V RMOD RBIAS
VREF
VMSET
MODSET VBSET
BIASSET BCMON
Figure 1. Functional Diagram
8
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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. tion current output OUT+ is optimized to drive a 15 load, and must be DC-coupled. A damping resistor, RD, provides impedance matching to the laser diode. The combined value of the series damping resistor and the laser diode equivalent series resistance should be close to 15. An RC shunt network, RCOMP/CCOMP, should also be provided to reduce optical output aberrations and duty-cycle distortion. The values of RCOMP and CCOMP can be adjusted to match the laser and PC board layout characteristics for optimal optical eye performance. The OUT- pin is normally connected through a 15 resistor to VCC or through a switching diode and series resistor to VCC. With some laser diodes, the use of a switching diode at OUT can improve the optical output eye by better matching the laser characteristics. The bias current ranges from 1mA to 70mA, as set by the current through BIASSET. Current in the BIAS output also 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 must also be connected through a 15 resistor or through a switching diode and series resistor 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.
MAX3643
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 1k resistor from BCMON to ground gives the following relationship: VBCMON = IBIAS x GBSM x 1k The voltage at BCMON must be below 1.4V for proper operation.
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.
Output Drivers
The modulation current ranges from 10mA to 85mA, as set by the current through MODSET. The laser modula-
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9
155Mbps to 2.5Gbps Burst-Mode Laser Driver MAX3643
BURST-ENABLE (BEN) IN
125s FOR BPON/GPON
INTERNAL MDIN VOLTAGE SAMPLER
BENOUT OUTPUT
3s MDOUT < 2.56mV 1.2V 100s
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: IMOD = 1.2V x 88 RMODSET + RMOD
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 3k IMAX. 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:
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 x 88 RMODSET + RMOD
10
______________________________________________________________________________________
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. Laser diode bias current is set in the same manner as modulation current.
130 ZO = 50 LVPECL ZO = 50 82 82 IN-/BEN-
MAX3643
VCC
130
MAX3643
IN+/BEN+
LVPECL Data/Burst-Enable Inputs
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.
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 mux input as shown in the Typical Applications Circuit. 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 2k, 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
IN+ INVCMBEN + (100mV to 800mV) VCMBEN VCMBEN - (100mV to 800mV) BEN+ 3.3V BENR1 = 1.65k
MAX3643
VCMBEN = +2.0V R2 = 2.54k
Figure 4. Single-Ended Biasing for Burst Enable
mux is in the on-state, the capacitance at the input is typically 10pF to 20pF. 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.
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11
155Mbps to 2.5Gbps Burst-Mode Laser Driver MAX3643
Applications Information
Running Burst-Enable Single-Ended
See Figure 5 for setting up the single-ended LVTTL or LVCMOS biasing for burst enable.
R3 = 5k VCC IN+ IN-
Layout Considerations
To minimize inductance, keep the connections between the MAX3643 output pins and laser diode as close as possible. Optimize the laser diode performance by placing a bypass capacitor as close as possible to the laser anode. Take extra care to minimize stray parasitic capacitance on the BIAS and MD pins. Use good high-frequency layout techniques and multilayer boards with uninterrupted ground planes to minimize EMI and crosstalk.
LVTTL OR LVCMOS HIGH
BEN+ LVTTL OR LVCMOS LOW R4 = 3k VCC BENR5 = 5k
MAX3643
R6 = 9k
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 5k
16k
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 HFAN-08.1: Thermal Considerations for QFN and Other Exposed-Paddle Packages for additional information.
IN+/BEN+
VCC 5k IN-/BEN-
24k
MAX3643
Figure 6. Simplified Input Circuit Schematic
12
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155Mbps to 2.5Gbps Burst-Mode Laser Driver
Pin Configuration
TOP VIEW
BIAS+ VCCO BIASOUT+ VCCO OUT-
Chip Information
TRANSISTOR COUNT: 2771 PROCESS: SiGe BiPOLAR
MAX3643
18 GND 19 MODSET 20 VMSET 21 VREF 22 VBSET 23 BIASSET 24
17
16
15
14
13 12 MDIN 11 MDOUT 10 IMAX
Package Information
For the latest package outline information and land patterns, go to www.maxim-ic.com/packages. PACKAGE TYPE 24 TQFN-EP PACKAGE CODE T2444-3 DOCUMENT NO. 21-0139
MAX3643
*EP
9 8
BCMON EN BENOUT
+
1 VCCA 2 IN+ 3 IN4 VCCS 5 BEN+ 6 BEN-
7
THIN QFN (4mm x 4mm)
*THE EXPOSED PAD MUST BE CONNECTED TO GROUND FOR PROPER THERMAL AND ELECTRICAL PERFORMANCE.
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13
155Mbps to 2.5Gbps Burst-Mode Laser Driver MAX3643
Revision History
REVISION NUMBER 0 REVISION DATE 11/05 Initial release. Added "155Mbps to 2.5Gbps" to the data sheet/part title. Updated the Applications section. 1 10/08 In the Operating Conditions table, changed the data rate from 1250Mbps to 2500Mbps. In the Typical Operating Characteristics, added the ELECTRICAL EYE DIAGRAM graph. DESCRIPTION PAGES CHANGED -- All 1 2 6
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.
14 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2008 Maxim Integrated Products is a registered trademark of Maxim Integrated Products, Inc.

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