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19-1575; Rev 2; 7/02
KIT ATION EVALU ABLE IL AVA
+3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC
General Description Features
o o o o o o o o o +3.3V or +5.0V Single-Supply Operation 40mA Supply Current at +3.3V Programmable Bias Current from 1mA to 80mA Programmable Modulation Current from 5mA to 75mA Bias Current and Modulation Current Monitors 200ps Rise/Fall Time Automatic Average Power Control with Failure Monitor Complies with ANSI, ITU, and Bellcore SONET/SDH Specifications Enable Control
MAX3669
The MAX3669 is a complete, +3.3V laser driver with automatic power control (APC) circuitry for SDH/SONET applications up to 622Mbps. It accepts differential PECL inputs, provides bias and modulation currents, and operates over a temperature range from -40C to +85C. An APC feedback loop is incorporated to maintain a constant average optical power over temperature and lifetime. The wide modulation current range from 5mA to 75mA and bias current of 1mA to 80mA are easy to program, making this product ideal for use in various SDH/SONET applications. Two pins are provided to monitor the current levels in the laser: BIASMON with current proportional to laser bias current, and MODMON with current proportional to laser modulation. The MAX3669 also provides enable control and a failuremonitor output to indicate when the APC loop is unable to maintain the average optical power. The MAX3669 is available in 4mm x 4mm 24-pin thin QFN and 5mm x 5mm 32-pin TQFP packages as well as dice.
Ordering Information
PART MAX3669ETG MAX3669EHJ TEMP RANGE -40C to +85C -40C to +85C PIN-PACKAGE 24 Thin QFN (4mm x 4mm) 32 TQFP (5mm x 5mm)
Applications
622Mbps SDH/SONET Access Nodes Laser Driver Transmitters Section Regenerators
MAX3669E/D (Note A) Dice* Note A: Dice are designed to operate over a -40C to +140C junction temperature (Tj) range, but are tested and guaranteed at TA = +25C. *Contact factory for availability.
Pin Configurations appear at end of data sheet.
Typical Application Circuit
+3.3V +3.3V
LASER ENABLE FAIL VCC R6.3 OUTOUT+ R+ 20 RD 5 CD 1F
124
124 DATA+
MAX3693
4:1 SERIALIZER WITH CLOCK GEN
PECL DATA-
MAX3669
84.5 84.5
RFILT 20 CFILT 5pF
BIASMAX
MODSET
BIASMON MODMON
APCSET
BIAS CAPC GND MD
FERRITE BEAD CMD 100pF
0.1F +3.3V
________________________________________________________________ Maxim Integrated Products
1
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+3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC MAX3669
ABSOLUTE MAXIMUM RATINGS
Supply Voltage, VCC .............................................-0.5V to +7.0V Current into BIAS ............................................-20mA to +150mA Current into OUT+, OUT- ............................... -20mA to +100mA Current into MD....................................................-5mA to +5mA Voltage at DATA+, DATA-, ENABLE, FAIL, BIASMON, MODMON ..................-0.5V to (VCC + 0.5V) Voltage at OUT+, OUT- .............................+1.5V to (VCC + 1.5V) Voltage at MODSET, APCSET, BIASMAX, CAPC............................................................... -0.5V to +3.0V Voltage at BIAS .........................................+1.0V to (VCC + 0.5V) Continuous Power Dissipation (TA = +85C) 24-Lead Thin QFN (derate 20.8mW/C above +85C) ........................1354mW 32-Pin TQFP (derate 14.3mW/C above +85C).........929mW Operating Junction Temperature Range ...........-55C to +150C Processing Temperature (Die).........................................+400C Storage Temperature Range ............................ -65C to +165C 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.
DC ELECTRICAL CHARACTERISTICS
(VCC = +3.14V to +5.5V, TA = -40C to +85C, unless otherwise noted. Typical values are at VCC = +3.3V, TA = +25C.) (Note 1) PARAMETER Supply Current Bias Current Range Bias Off 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 DC Monitor Diode Current BIASMON to IBIAS Gain MODMON to IMOD Gain Monitor Diode Input Voltage (MD Pin) TTL Input High Voltage TTL Input Low Voltage TTL Output High Voltage (FAIL) TTL Output Low Voltage (FAIL) IMD ABIAS AMOD VMD VIH VIL VOH VOL Sourcing 50A Sinking 100A 2.4 0.1 VCC - 0.3 2 0.8 VCC 0.44 IBIAS/IBIASMON IMOD/IMODMON VID VICM IIN (Note 4) IMD = 1mA IMD = 18A (Note 5) -15 18 38 29 0.8 IBIAS SYMBOL (Note 2) VBIAS = VCC - 1.6V ENABLE = low (Note 3) APC open loop APC open loop Figure 1 PECL compatible IBIAS = 80mA IBIAS = 1mA -15 200 VCC 1.49 -1 -480 -50 35 +15 1000 VCC 1.32 255 815 +15 1600 VCC VID/4 +10 +480 1 CONDITIONS MIN TYP 40 MAX 60 80 100 UNITS mA mA A ppm/C % mVP-P V A ppm/C % A mA/mA mA/mA V V V V V
2
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+3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC MAX3669
AC ELECTRICAL CHARACTERISTICS
(VCC = +3.14V to +5.5V, load as shown in Figure 2, TA = -40C to +85C, unless otherwise noted. Typical values are at VCC = +3.3V, TA = +25C.) (Note 6) PARAMETER Modulation Current Range Modulation Off-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 at 622Mbps Note 1: Note 2: Note 3: Note 4: CID tR, tF 20% to 80%, RL = 10 | | 20 load (Note 8) (Notes 9, 10) Open loop 80 IMOD = 5mA IMOD = 75mA 70 10 250 IMOD = 5mA IMOD = 75mA SYMBOL IMOD (Note 7) ENABLE = low (Note 3) IMOD = 75mA IMOD = 5mA (Note 5) -15 100 230 -620 -165 205 +15 200 375 100 155 135 CONDITIONS MIN 5 TYP MAX 75 200 +620 UNITS mA A ppm/C % ps ps ps ns Bits
Dice are tested and guaranteed at TA = +25C only. Tested with RMODSET = 5.11k (IMOD 38mA), RBIASMAX = 4.56k (IBIAS 52mA), excluding IBIAS and IMOD. Both the bias and modulation currents will be disabled if any of the current set pins are shorted to ground. Guaranteed by design and characterization. This assumes that the laser to monitor diode transfer function does not change with temperature. Note 5: See the Typical Operating Characteristics for worst-case distributions. Note 6: AC characteristics are guaranteed by design and characterization. Note 7: Total IMOD out of OUT+. See the Design Procedure section for information regarding current delivered to the laser. Note 8: Input signal is a 622Mbps, 213 - 1 PRBS with eighty inserted 0s. Note 9: Input signal is a 622Mbps, 11110000 pattern. Note 10:PWD = (wider pulse - narrower pulse) / 2.
VCC
DATA+ DATA(DATA+) - (DATA-)
100mV MIN 800mV MAX OUT200mVP-P MIN 1600mVP-P MAX
20 1F
10 20
MAX3669
OUT+
1F
OSCILLOSCOPE
IOUT+ IMOD
IOUT+ BIAS 12.4 15 VCC 50
Figure 1. Required Input Signal and Output Polarity
Figure 2. Output Termination for Characterization 3
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+3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC MAX3669
Typical Operating Characteristics
(VCC = +3.3V, TA = +25C, unless otherwise noted.)
EYE DIAGRAM (622Mbps, 1300nm LASER WITH 467MHz FILTER)
223 - 1 PRBS
MAX3669 TOC01
ELECTRICAL EYE DIAGRAM (IMOD = 35mA)
MAX3669 TOC02
ELECTRICAL EYE DIAGRAM (IMOD = 75mA)
622Mbps DATA RATE
MAX3669 TOC03
622Mbps DATA RATE
PATTERN = 213 - 1 + 80 CID IMOD = 35mA
PATTERN = 213 - 1 + 80 CID IMOD = 75mA
200ps/div
200ps/div
200ps/div
MONITOR DIODE CURRENT vs. APC SET RESISTOR
MAX3669 TOC04
BIAS CURRENT vs. MAXIMUM BIAS SET RESISTOR
MAX3669 TOC05
MODULATION CURRENT vs. MODULATION SET RESISTOR
MAX3669 TOC06
10
1000
100
1 IMD (mA) IBIAS (mA)
100 IMOD (mA) 10 1 1 10 RAPCSET (k) 100 0.1 1 10 RBIASMAX (k) 100 10
0.1
0.01
1 0.1 1 10 RMODSET (k) 100 1000
RANDOM JITTER vs. MODULATON CURRENT
MAX3669 TOC07
PULSE-WIDTH DISTORTION vs. MODULATION CURRENT
MAX3669 TOC08
SUPPLY CURRENT vs. TEMPERATURE
VCC = 5.0V 50 SUPPLY CURRENT (mA) 40 30 20 10 0 IBIAS = 48mA IMOD = 27mA -40 -15 10 35 60 85 VCC = 3.3V
MAX3669 TOC09
21 INCLUDES RANDOM JITTER DUE TO MEASUREMENT EQUIPMENT
50 45 40 35 PWD (ps)
60
20 RANDOM JITTER (psP-P)
19
30 25 20 15
18
17
10 5
16 0 20 40 IMOD (mA) 60 80
0 0 20 40 IMOD (mA) 60 80
TEMPERATURE (C)
4
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+3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC
Typical Operating Characteristics (continued)
(VCC = +3.3V, TA = +25C, unless otherwise noted.)
MAX3669
DISTRIBUTION OF MODULATION CURRENT STABILITY (WORST CASE)
TA = -40C TO +85C IMOD = 5mA
MAX3669-11
DISTRIBUTION OF MONITOR DIODE CURRENT STABILITY (WORST CASE)
TA = -40C TO +85C IMD = 18A 20 PERCENT OF UNITS (%)
MAX3669-12
35 30 25 UNITS (%) 20 15 10 5 0
25
15
10
5
-125
-25
75
175
275
375
475
575
0 -500
MODULATION CURRENT STABILITY (ppm/C)
-100 100 300 500 -300 MONITOR DIODE CURRENT STABILITY (ppm/C)
RATIO OF IMOD vs. IMODMON
MAX3669 toc13
RATIO OF IBIAS vs. IBIASMON
40 IBIAS/IBIASMON (mA/mA) 35 30 25 20 15 10 TA = +25C TA = -40C TA = +85C
MAX3669 toc14
35 TA = +85C 30 IMOD/IMODMON (mA/mA) 25 20 15 10 5 0 0 20 40 IMOD (mA) 60 TA = -40C TA = +25C
45
5 0 80 0 20 40 IBIAS (mA) 60 80
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+3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC MAX3669
Pin Description
PIN QFN 1, 13, 16, 19 2 3 4, 8, 11, 17, 22 5 6 7 9 10 12 14 15 18 20 TQFP 1, 2, 6, 15, 17, 20, 24 3 4 5, 10, 14, 21, 22, 30 7 8 9 11 12, 13, 26, 27, 28 16 18 19 23 25 NAME VCC DATA+ DATAGND BIASMON MODMON ENABLE FAIL N.C. BIAS OUT+ OUTMD CAPC Positive Supply Voltage Positive PECL Data Input Negative PECL Data Input Ground Sink Current Source. Proportional to the laser bias current. Sink Current Source. Proportional to the laser modulation current. TTL/CMOS Enable Input. High for normal operation, low to disable laser bias and modulation currents. Internally pulled high. TTL Output. Indicates APC failure when low. Internally pulled high through a 6k resistor. No Connection. Leave unconnected. Laser Bias Current Output. Isolate from laser with a ferrite bead. Positive Modulation Current Output. IMOD flows into this pad when the input signal is high. Connect this pad to AC-coupling network. Negative Modulation Current Output. IMOD flows into this pad when the input signal is low. Connect this pad to VCC through a 6.3 resistor. Monitor Photodiode Connection. Connect this pad to the monitor photodiode anode. A capacitor to ground is required to filter high-speed AC monitor photocurrent. APC Compensation Capacitor. A 0.1F capacitor connected from this pad to ground controls the dominant pole of the APC feedback loop. APC Set Resistor. A resistor connected from this pad to ground sets the desired average optical power. The resulting current is equal to the desired DC monitor diode current. Connect a 100k resistor from this pad to ground if APC is not used. Modulation Set Resistor. A resistor from this pad to ground sets the laser modulation current. Maximum Bias Set Resistor. A resistor from this pad to ground sets the maximum laser bias current. The APC function can subtract from this maximum value but cannot add to it. This resistor controls the bias-current level when the APC loop is not used. The exposed paddle must be soldered to ground. FUNCTION
21
29
APCSET
23
31
MODSET
24
32
BIASMAX Exposed Paddle
EP
--
6
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+3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC MAX3669
DATA+ IMOD DATAVCC 100k ENABLE IBIAS RBIASMON BIAS OUT+ OUT-
VCC
MAX3669
165X 5X
40X
VCC
IBIAS 38 RMODMON
MD
IMOD 29 FAILURE DETECTOR MODSET RMODSET BIASMAX FAIL RBIASMAX CAPC CAPC
IMD
APCSET RAPCSET
Figure 3. Functional Diagram
Detailed Description
The MAX3669 laser driver consists of three main parts: a high-speed modulation driver, a laser-biasing block with automatic power control (APC), and bias current and modulation current monitors. The circuit is optimized for low-voltage (+3.3V) operation. The output stage is composed of a high-speed differential pair and a programmable modulation current source. Since the modulation output drives a maximum current of 75mA into the laser with a 230ps edge speed, large transient voltage spikes can be generated due to the parasitic inductance. These transients and the laser forward voltage leave insufficient headroom for the proper operation of the laser driver if the modulation output is DC-coupled to the laser diode. To solve this problem, the MAX3669's modulation output is designed to be
AC-coupled to the cathode of a laser diode. A simplified functional diagram is shown in Figure 3. The MAX3669 modulation output is optimized for driving a 20 10 load; the minimum required voltage at OUT+ is 2.0V. Modulation current swings of 75mA are possible. To interface with the laser diode, a damping resistor (RD) is required for impedance matching. An RC shunt network may be used to compensate for the laser-diode parasitic inductance, thereby improving the optical output aberrations and duty-cycle distortion. At a 622Mbps data rate, any capacitive load at the cathode of a laser diode degrades the optical output performance. Since the BIAS output is directly connected to the laser cathode, minimize the parasitic capacitance associated with this pin by using an inductor to isolate the BIAS pin from the laser diode.
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+3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC MAX3669
Automatic Power Control
To maintain constant average optical power, the MAX3669 incorporates an APC loop to compensate for the changes in laser threshold current over temperature and lifetime. A back-facet photodiode mounted in the laser package is used to convert the optical power into a photocurrent. The APC loop adjusts the laser bias current so the monitor current is matched to a reference current set by RAPCSET. The time constant of the APC loop is determined by an external capacitor (CAPC). To eliminate the pattern-dependent jitter associated with the APC loop-time constant and to guarantee loop stability, the recommended value for CAPC is 0.1F. When the APC loop is functioning, the maximum allowable bias current is set by an external resistor, RBIASMAX. An APC failure flag (FAIL) is set low when the bias current can no longer be adjusted to achieve the desired average optical power. APC closed-loop operation requires the user to set three currents with external resistors connected between ground and BIASMAX, MODSET, and APCSET. Detailed guidelines for these resistor settings are described in the Design Procedure section.
Enable Control
The MAX3669 incorporates a laser driver enable function. When ENABLE is low, both the bias and modulation currents are off. The typical laser enable time is 250ns.
APC Failure Monitor
The MAX3669 provides an APC failure monitor (TTL/CMOS) to indicate an APC loop tracking failure. FAIL is set low when the APC loop can no longer adjust the bias current to maintain the desired monitor current. This output is internally pulled up to VCC through a 6k resistor.
Short-Circuit Protection
The MAX3669 provides short-circuit protection for the modulation, bias, and monitor current sources. If either BIASMAX, MODSET, or APCSET is shorted to ground, the bias and modulation outputs will be turned off.
Design Procedure
When designing a laser transmitter, the optical output is usually expressed in terms of average power and extinction ratio. Table 1 gives the relationships that are helpful in converting between the optical average power and the modulation current. These relationships are valid if the average duty cycle of the optical waveform is 50%.
Bias and Modulation Monitors
The MAX3669 includes pins to monitor the output levels of bias and modulation current. BIASMON and MODMON sink current proportional to laser bias current and modulation current, respectively. By monitoring the current through RMODMON and RBIASMON, it is possible to monitor the levels of bias and modulation current in the laser (Figure 3).
Programming the Modulation Current
In addition to being a function of RMODSET, the modulation current delivered to the laser (IMODL) also depends on the values of the series damping resistor (RD), the shunt compensation resistance (RFILT), and the laser diode's resistance (see Typical Operating Circuit). The modulation current (assuming CFILT<Open-Loop Operation
If necessary, the MAX3669 is fully operational without APC. In this case, the laser current is directly set by two external resistors connected from ground to BIASMAX and MODSET. Connect a 100k resistor from APCSET to ground and leave MD open for open-loop operation.
Table 1. Optical Power Definition
PARAMETER Average Power Extinction Ratio Optical Power High Optical Power Low Optical Amplitude Laser Slope Efficiency Laser Modulation Current 8 SYMBOL PAVG re P1 P0 PP-P IMOD RELATION PAVG = (P0 + P1) / 2 re = P1 / P0 P1 = 2PAVG x re / (re + 1) P0 = 2PAVG / (re + 1) PP-P = 2PAVG (re - 1) / (re + 1) = PP-P / IMODL IMODL = PP-P /
Programming the Bias Current
When using the MAX3669 in open-loop operation, the bias current is determined by the RBIASMAX resistor. To select this resistor, determine the required bias current at +25C. See the Bias Current vs. Maximum Bias Set
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+3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC
Resistor graph in the Typical Operating Characteristics and select the value of R BIASMAX that corresponds to the required current at +25C. When using the MAX3669 in closed-loop operation, the RBIASMAX resistor sets the maximum bias current available to the laser diode over temperature and life. The APC loop can subtract from this maximum value but cannot add to it. See the Bias Current vs. Maximum Bias Set Resistor graph in the Typical Operating Characteristics and select the value of RBIASMAX that corresponds to the end-of-life bias current at +85C. Referring to Figure 4, the droop resulting from long time periods without transitions can be represented by the following equation: (100% - DROOP) = e AC-coupling of IMOD results in a discharge level for that is equal to PAVG. An overall droop of 6% relative to P p-p equates to a 12% droop relative to P AVG . To ensure a droop of less than 12% (6% relative to Pp-p), this equation can be solved for as follows: = -t = 7.8t ln(1 - 0.12)
-t
MAX3669
Programming the APC Loop
When the MAX3669's APC feature is used, program the average optical power by adjusting the APCSET resistor. To select this resistor, determine the desired monitor current to be maintained over temperature and life. See the Monitor Diode Current vs. APC Set Resistor graph in the Typical Operating Characteristics and select the value of RAPCSET that corresponds to the required current.
Interfacing with the Laser Diode
To minimize optical output aberrations due to the laser parasitic inductance, an RC shunt network may be used (see Typical Operating Circuit). If RL represents the laser diode resistance, the recommended total resistance for RD + RL is 10. Starting values for coaxial lasers are RFILT = 20 and CFILT = 5pF. RFILT and CFILT should be experimentally adjusted to optimize the output waveform. A bypass capacitor should also be placed as close to the laser anode as possible for best performance.
If t1 equals 80 consecutive unit intervals without a transition, the time constant associated with the DC blocking capacitor needs to be longer than: AC RACCD = 7.8 (80 bits) (1.6ns/bit) = 1.0s RFILT can be ignored for CFILT<< CD; therefore, the estimated value of RAC is: RAC = 20 (RD + rLASER) Assuming RD = 5, and rLASER = 5: RAC = 6.7 with CD = 1F, AC = 6.7s.
Input Termination Requirement
The MAX3669 data inputs are PECL compatible. However, it is not necessary to drive the MAX3669 with a standard PECL signal. As long as the specified common-mode voltage and differential voltage swings are met, the MAX3669 will operate properly.
Pattern-Dependent Jitter (PDJ)
When transmitting NRZ data with long strings of consecutive identical digits (CIDs), LF droop can contribute to PDJ. To minimize this PDJ, two external components must be properly chosen: capacitor CAPC, which dominates the APC loop time constant, and AC-coupling capacitor CD. To filter out noise effects and guarantee loop stability, the recommended value for CAPC is 0.1F. This results in an APC loop bandwidth of 20kHz. Consequently, the PDJ associated with an APC loop time constant can be ignored. The time constant associated with the DC blocking capacitor on I MOD will have an effect on PDJ. It is important that this time constant produce minimum droop for long consecutive bit streams.
= AC << AC Pp-p PAVG DROOP
t1
t
Figure 4. Droop
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+3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC MAX3669
Calculate Power Consumption
The total power dissipation of the MAX3669 can be estimated by the following: P = VCC x ICC + (VCC - Vf) x IBIAS + IMOD (VCC - 20 x IMOD / 2) where IBIAS is the maximum bias current set by RBIASMAX, IMOD is the modulation current, and Vf is the typical laser forward voltage. In this example, IBIAS = 68.1mA. The Bias Current vs. Maximum Bias Set Resistor graph in the Typical Operating Characteristics shows that RBIASMAX should be 3k.
Determine RBIASMON To avoid saturating the current mirror of BIASMON, the voltage at this pin should not drop below (VCC - 1.6V). The resulting condition is:
ABIAS RBIASMON 1.6V IBIASMAX where IBIASMAX is the maximum current expected for the application.
Applications Information
The following is an example of how to set up the MAX3669.
Select Laser
A communication-grade laser should be selected for 622Mbps applications. Assume the laser output average power is PAVG = 0dBm, the minimum extinction ratio is re = 6.6 (8.2dB), the operating temperature is -40C to +85C, and the laser diode has the following characteristics: Wavelength: = 1.3m Threshold Current: Threshold Temperature Coefficient: Laser to Monitor Transfer: Laser Slope Efficiency: TH = 22mA at +25C
Determine RMODMON To avoid saturating the current mirror of MODMON, the voltage at this pin should not drop below (VCC - 1V). The resulting condition is:
A RMODMON 1V MOD IMOD
Modulation Currents Exceeding 50mA
TH = 1.3%/C MON = 0.2A/W = 0.05mW/mA at +25C To drive modulation currents greater than 50mA at 3.3V, external pullup inductors (Figure 5) should be used to DC-bias the modulation output at VCC. Such a configuration isolates the laser forward voltage from the output circuitry and allows the output at OUT+ to swing above and below the supply voltage VCC.
Determine RAPCSET
The desired monitor diode current is estimated by IMD = PAVG x MON = 200A. The Monitor Diode Current vs. APC Set Resistor graph in the Typical Operating Characteristics shows that RAPCSET should be 6k.
VCC
Determine RMODSET
To achieve a minimum extinction ratio (re) of 6.6dB over temperature and lifetime, calculate the required extinction ratio at +25C. Assuming re = 20, the peak-to-peak optical power Pp-p = 1.81mW, according to Table 1. The required modulation current is 1.81(mW) / 0.05(mW/mA) = 36.2mA. The Modulation Current vs. Modulation Set Resistor graph (see Typical Operating Characteristics) shows that RMODSET should be 5k.
10 FERRITE BEADS LD
OUTOUT+ CD 1F FERRITE BEAD 100pF RD 5 RFILT CFILT
MAX3669
BIAS MD
Determine RBIASMAX
Calculate the maximum threshold current (ITH(MAX)) at T A = +85C and end of life. Assuming I TH(MAX) = 50mA, the maximum bias current should be: IBIAS = ITH(MAX) + IMOD / 2
Figure 5. Output Termination for Maximum Modulation Current
10
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+3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC
At +5V power supply, the headroom voltage for the MAX3669 is significantly improved. In this case, it is possible to achieve a modulation current of more than 50mA (using resistor pullups as shown in the Typical Operating Circuit). The MAX3669 can also be DC-coupled to a laser diode when operating at +5V supply; the voltage at OUT+ should be 2.0V for proper operation. Optimize the laser diode performance by placing a bypass capacitor as close as possible to the laser anode. Use good high-frequency layout techniques and multilayer boards with uninterrupted ground planes to minimize EMI and crosstalk.
MAX3669
Laser Safety and IEC 825
Using the MAX3669 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. Customers must determine the level of fault tolerance required by their application, recognizing that Maxim products are not designed or authorized for use as components in systems intended for surgical implant into the body, for applications intended to support or sustain life, or for any other application where the failure of a Maxim product could create a situation where personal injury or death may occur.
Wire Bonding Die
For high current density and reliable operation, the MAX3669 uses gold metalization. Make connections to the die with gold wire only, using ball-bonding techniques. Wedge bonding is not recommended. Die-pad size is 4 mils (100m) square, and die thickness is 12 mils (300m).
Layout Considerations
To minimize inductance, keep the connections between the MAX3669 output pins and LD as close as possible.
Pin Configurations
TOP VIEW
BIASMAX MODSET APCSET CAPC
BIASMAX
GND
N.C.
N.C.
N.C.
MODSET
APCSET
CAPC 20
GND
32 VCC VCC DATA+ DATAGND VCC BIASMON MODMON 1 2 3 4 5 6 7 8 9 ENABLE
31
30
29
28
27
26
25 24 VCC 23 MD 22 GND 21 GND VCC
24
23
22
21
19 18 17 16
1 2 3 4 5 6 10 11 12
VCC
MD GND
VCC
DATA+ DATAGND BIASMON MODMON
MAX3669
20 VCC 19 OUT18 OUT+ 17 VCC
MAX3669
15 14 13
OUTOUT+
VCC
7
8 GND
ENABLE
GND
FAIL
N.C.
FAIL
GND
VCC
BIAS
GND
N.C.
N.C.
THIN QFN
TQFP
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BIAS
10
11
12
13
14
15
16
9
11
+3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC MAX3669
Chip Topography
TRANSISTOR COUNT: 1525
MODMON BIASMON VCC GND VCC DATADATA+ VCC GND GND
Chip Information
SUBSTRATE CONNECTED TO GND
GND VCC
GND ENABLE GND GND N.C. VCC FAIL GND N.C. N.C. GND VCC BIAS
VCC BIASMAX MODSET GND APCSET N.C. 0.083" GND (2.10mm) N.C. GND N.C. CAPC VCC GND
12
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N.C. VCC N.C. OUT+ OUTN.C. VCC GND GND MD 0.070" (1.78mm)
+3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC
Package Information
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.) 32L,TQFP.EPS ______________________________________________________________________________________ 13
MAX3669
+3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC MAX3669
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
14
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+3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
MAX3669
PACKAGE OUTLINE 12,16,20,24L QFN THIN, 4x4x0.8 mm
21-0139
A
______________________________________________________________________________________
15
+3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC MAX3669
Package Information (continued)
(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information, go to www.maxim-ic.com/packages.)
PACKAGE OUTLINE 12,16,20,24L QFN THIN, 4x4x0.8 mm
21-0139
A
Maxim makes no warranty, representation, or guarantee regarding the suitability of its products for any particular purpose, nor does Maxim assume any liability arising out of the application or use of any product or circuit and specifically disclaims any and all liability, including without limitation consequential or incidental damages. "Typical" parameters can and do vary in different applications. All operating parameters, including "typicals" must be validated for each customer application by customer's technical experts. Maxim products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the Maxim product could create a situation where personal injury or death may occur.
16 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 (c) 2002 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

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