EVALUATION KIT AVAILABLE MAX3669 +3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC General Description Features 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. +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 Ordering Information PART Applications 622Mbps SDH/SONET Access Nodes TEMP RANGE PIN-PACKAGE MAX3669ETG -40C to +85C 24 TQFN-EP* MAX3669ETG+ -40C to +85C 24 TQFN-EP* MAX3669EHJ -40C to +85C 32 TQFP MAX3669EHJ+ -40C to +85C 32 TQFP +Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad. Laser Driver Transmitters Section Regenerators Pin Configurations appear at end of data sheet. Typical Application Circuit +3.3V +3.3V 124 124 FAIL ENABLE LASER VCC R6.3 DATA+ RD 5 OUT- PECL 84.5 OUT+ MAX3669 DATA4:1 SERIALIZER WITH CLOCK GEN CD 1F 84.5 RFILT 20 CFILT 5pF BIAS GND CAPC MODMON MODSET BIASMON BIASMAX FERRITE BEAD APCSET MAX3693 R+ 20 MD CMD 100pF 0.1F +3.3V For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim Integrated's website at www.maximintegrated.com. 19-1575; Rev 6; 1/13 MAX3669 +3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC 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) TQFN (derate 20.8mW/C above +85C) .................1354mW TQFP (derate 14.3mW/C above +85C) ....................929mW Operating Junction Temperature Range ...........-55C to +150C 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.) PARAMETER SYMBOL Supply Current Bias Current Range CONDITIONS (Note 1) IBIAS ENABLE = low (Note 2) Bias Current Stability APC open loop Bias Current Absolute Accuracy APC open loop VID Common-Mode Input Voltage VICM DATA+, DATA- Input Current IIN Monitor Diode Current Stability 1 IBIAS = 80mA 255 IBIAS = 1mA 815 -15 Figure 1 200 VCC 1.49 PECL compatible VCC 1.32 -1 (Note 3) Monitor Diode Current Absolute Accuracy DC Monitor Diode Current TYP 40 VBIAS = VCC - 1.6V Bias Off Current Differential Input Voltage MIN IMD = 1mA -480 IMD = 18A (Note 4) -50 UNITS 60 mA 80 mA 100 A ppm/C +15 % 1600 mVP-P VCC VID/4 V +10 A +480 35 -15 IMD MAX +15 18 1000 ppm/C % A BIASMON to IBIAS Gain ABIAS IBIAS/IBIASMON 38 mA/mA MODMON to IMOD Gain AMOD IMOD/IMODMON 29 mA/mA 0.8 V Monitor Diode Input Voltage (MD Pin) VMD TTL Input High Voltage VIH TTL Input Low Voltage VIL TTL Output High Voltage (FAIL) VOH Sourcing 50A 2.4 TTL Output Low Voltage (FAIL) VOL Sinking 100A 0.1 2 2 V VCC - 0.3 0.8 V VCC V 0.44 V Maxim Integrated MAX3669 +3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC 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 5) PARAMETER Modulation Current Range SYMBOL IMOD Modulation Off-Current CONDITIONS MIN (Note 6) UNITS 75 mA 200 A 5 IMOD = 75mA -620 -165 IMOD = 5mA (Note 4) +620 205 Modulation Current Absolute Accuracy -15 tR, tF Jitter Generation (Peak-to-Peak) 20% to 80%, RL = 10 | | 20 load +15 IMOD = 5mA 100 200 IMOD = 75mA 230 375 IMOD = 5mA 70 155 IMOD = 75mA 10 135 (Note 7) Pulse-Width Distortion (Peak-to-Peak) (Notes 8, 9) Enable/Start-Up Delay Open loop Maximum Consecutive Identical Digits at 622Mbps MAX ENABLE = low (Note 2) Modulation Current Stability Output Rise/Fall Time TYP 100 250 CID ppm/C % ps ps ps ns 80 Bits Note 1: Tested with RMODSET = 5.11k (IMOD 38mA), RBIASMAX = 4.56k (IBIAS 52mA), excluding IBIAS and IMOD. Note 2: Both the bias and modulation currents will be disabled if any of the current set pins are shorted to ground. Note 3: Guaranteed by design and characterization. This assumes that the laser to monitor diode transfer function does not change with temperature. Note 4: See the Typical Operating Characteristics for worst-case distributions. Note 5: AC characteristics are guaranteed by design and characterization. Note 6: Total IMOD out of OUT+. See the Design Procedure section for information regarding current delivered to the laser. Note 7: Input signal is a 622Mbps, 213 - 1 PRBS with eighty inserted 0s. Note 8: Input signal is a 622Mbps, 11110000 pattern. Note 9: PWD = (wider pulse - narrower pulse) / 2. VCC DATA+ 100mV MIN DATA- 800mV MAX 20 1F OUT- (DATA+) - (DATA-) 200mVP-P MIN 1600mVP-P MAX 10 MAX3669 20 1F OSCILLOSCOPE OUT+ IOUT+ IMOD IOUT+ BIAS 12.4 50 15 VCC Figure 1. Required Input Signal and Output Polarity Maxim Integrated Figure 2. Output Termination for Characterization 3 MAX3669 +3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC Typical Operating Characteristics (VCC = +3.3V, TA = +25C, unless otherwise noted.) ELECTRICAL EYE DIAGRAM (IMOD = 75mA) 223 - 1 PRBS MAX3669 TOC02 MAX3669 TOC01 ELECTRICAL EYE DIAGRAM (IMOD = 35mA) 622Mbps DATA RATE 622Mbps DATA RATE PATTERN = 213 - 1 + 80 CID IMOD = 75mA PATTERN = 213 - 1 + 80 CID IMOD = 35mA 200ps/div 200ps/div 200ps/div MONITOR DIODE CURRENT vs. APC SET RESISTOR BIAS CURRENT vs. MAXIMUM BIAS SET RESISTOR MODULATION CURRENT vs. MODULATION SET RESISTOR IMD (mA) IBIAS (mA) IMOD (mA) 100 1 10 10 0.1 1 0.01 1 10 1 0.1 100 1 10 100 0.1 1 100 10 RAPCSET (k) RBIASMAX (k) RMODSET (k) RANDOM JITTER vs. MODULATON CURRENT PULSE-WIDTH DISTORTION vs. MODULATION CURRENT SUPPLY CURRENT vs. TEMPERATURE 35 PWD (ps) 19 18 30 25 20 15 MAX3669 TOC09 40 VCC = 5.0V 50 SUPPLY CURRENT (mA) 20 45 1000 60 MAX3669 TOC08 INCLUDES RANDOM JITTER DUE TO MEASUREMENT EQUIPMENT 50 MAX3669 TOC07 21 RANDOM JITTER (psP-P) 100 MAX3669 TOC06 1000 MAX3669 TOC05 MAX3669 TOC04 10 40 VCC = 3.3V 30 20 10 17 10 5 0 16 0 20 40 IMOD (mA) 4 MAX3669 TOC03 EYE DIAGRAM (622Mbps, 1300nm LASER WITH 467MHz FILTER) 60 80 0 20 40 IMOD (mA) 60 80 IBIAS = 48mA IMOD = 27mA 0 -40 -15 10 35 60 85 TEMPERATURE (C) Maxim Integrated MAX3669 +3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC Typical Operating Characteristics (continued) (VCC = +3.3V, TA = +25C, unless otherwise noted.) DISTRIBUTION OF MODULATION CURRENT STABILITY (WORST CASE) MAX3669-12 TA = -40C TO +85C IMOD = 5mA 30 25 MAX3669-11 35 DISTRIBUTION OF MONITOR DIODE CURRENT STABILITY (WORST CASE) TA = -40C TO +85C IMD = 18A PERCENT OF UNITS (%) 20 20 15 10 15 10 5 5 0 -125 -25 75 175 275 375 475 0 -500 575 -100 100 300 500 -300 MONITOR DIODE CURRENT STABILITY (ppm/C) MODULATION CURRENT STABILITY (ppm/C) RATIO OF IBIAS vs. IBIASMON RATIO OF IMOD vs. IMODMON TA = +85C TA = +25C 20 TA = -40C 15 10 TA = +85C 40 IBIAS/IBIASMON (mA/mA) IMOD/IMODMON (mA/mA) 30 25 45 MAX3669 toc13 35 MAX3669 toc14 UNITS (%) 25 35 TA = +25C 30 TA = -40C 25 20 15 10 5 5 0 0 0 Maxim Integrated 20 40 IMOD (mA) 60 80 0 20 40 60 80 IBIAS (mA) 5 MAX3669 +3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC Pin Description PIN 6 NAME FUNCTION TQFN-EP TQFP 1, 13, 16, 19 1, 2, 6, 15, 17, 20, 24 VCC 2 3 DATA+ Positive PECL Data Input 3 4 DATA- Negative PECL Data Input 4, 8, 11, 17, 22 5, 10, 14, 21, 22, 30 GND Positive Supply Voltage Ground 5 7 BIASMON Sink Current Source. Proportional to the laser bias current. 6 8 MODMON Sink Current Source. Proportional to the laser modulation current. 7 9 ENABLE TTL/CMOS Enable Input. High for normal operation, low to disable laser bias and modulation currents. Internally pulled high. 9 11 FAIL TTL Output. Indicates APC failure when low. Internally pulled high through a 6k 10 12, 13, 26, 27, 28 N.C. No Connection. Leave unconnected. 12 16 BIAS Laser Bias Current Output. Isolate from laser with a ferrite bead. 14 18 OUT+ Positive Modulation Current Output. IMOD flows into this pad when the input signal is high. Connect this pad to AC-coupling network. 15 19 OUT- 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. 18 23 MD Monitor Photodiode Connection. Connect this pad to the monitor photodiode anode. A capacitor to ground is required to filter high-speed AC monitor photocurrent. 20 25 CAPC APC Compensation Capacitor. A 0.1F capacitor connected from this pad to ground controls the dominant pole of the APC feedback loop. 21 29 APCSET 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. 23 31 MODSET Modulation Set Resistor. A resistor from this pad to ground sets the laser modulation current. 24 32 BIASMAX 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. -- -- EP Exposed Pad (TQFN only). The exposed paddle must be soldered to ground. Maxim Integrated MAX3669 +3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC DATA+ IMOD OUT+ OUT- DATAVCC 100k VCC ENABLE IBIAS RBIASMON 165X VCC BIAS MAX3669 40X 5X IBIAS 38 MD RMODMON IMD IMOD 29 FAILURE DETECTOR MODSET CAPC BIASMAX APCSET FAIL RMODSET RBIASMAX CAPC 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 Maxim Integrated 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. 7 MAX3669 +3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC Automatic Power Control Enable 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. 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 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. 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). 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 SYMBOL PAVG RELATION PAVG = (P0 + P1) / 2 Extinction Ratio re re = P1 / P0 Optical Power High P1 P1 = 2PAVG x re / (re + 1) Optical Power Low P0 P0 = 2PAVG / (re + 1) Optical Amplitude PP-P Laser Slope Efficiency Laser Modulation Current 8 PP-P = 2PAVG (re - 1) / (re + 1) = PP-P / IMODL IMOD IMODL = PP-P / 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 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<<CD) into the laser diode can be represented by the following: 20 IMODL = IMOD 20 + (RD + rLASER ) Assuming RD = 5 and rLASER = 5, this equation is simplified to: IMODL = IMOD(0.67) For RD = 5.0 and a laser resistance of approximately 5, see the Modulation Current vs. Modulation Set Resistor graph in the Typical Operating Characteristics and select the value of RMODSET that corresponds to the required current at +25C. 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 Maxim Integrated MAX3669 +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: -t (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: = 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. Pattern-Dependent Jitter (PDJ) 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. 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. Maxim Integrated -t = 7.8t ln(1 - 0.12) = AC DROOP << AC Pp-p PAVG t1 t Figure 4. Droop 9 MAX3669 +3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC 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 typi- 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: cal laser forward voltage. ABIAS RBIASMON 1.6V IBIASMAX 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: TH = 22mA at +25C Threshold Temperature Coefficient: TH = 1.3%/C Laser to Monitor Transfer: MON = 0.2A/W Laser Slope Efficiency: = 0.05mW/mA at +25C 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. 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. 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 10 where IBIASMAX is the maximum current expected for the application. 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 I MOD Modulation Currents Exceeding 50mA 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. VCC 10 FERRITE BEADS LD OUTOUT+ CD 1F MAX3669 BIAS RFILT RD 5 CFILT FERRITE BEAD MD 100pF Figure 5. Output Termination for Maximum Modulation Current Maxim Integrated MAX3669 +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. Layout Considerations To minimize inductance, keep the connections between the MAX3669 output pins and LD as close as possible. 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. 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. Pin Configurations VCC 2 23 MD DATA+ 3 22 GND DATA- 4 GND 5 20 VCC VCC 6 19 OUT- BIASMON 7 18 OUT+ MODMON 8 17 VCC + 24 VCC MAX3669 21 GND VCC 1 CAPC VCC 24 23 22 21 20 19 VCC 1 18 MD DATA+ 2 17 GND DATA- 3 16 VCC GND 4 15 OUT- BIASMON 5 14 OUT+ MODMON 6 13 VCC MAX3669 EP 13 14 15 16 N.C. GND VCC BIAS TQFP (5mm x 5mm) Maxim Integrated ENABLE 12 N.C. GND 11 FAIL 10 ENABLE 7 9 8 9 10 11 12 GND 25 BIAS CAPC 26 APCSET N.C. 27 N.C. N.C. 28 GND N.C. 29 FAIL APCSET 30 MODSET GND 31 BIASMAX MODSET 32 + GND BIASMAX TOP VIEW THIN QFN (4mm x 4mm) 11 MAX3669 +3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC Chip Information SUBSTRATE CONNECTED TO GND Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a "+", "#", or "-" in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE 12 PACKAGE CODE OUTLINE NO. LAND PATTERN NO. TQFP H32+2F 21-0110 90-0149 TQFN-EP T2444+3 21-0139 90-0021 Maxim Integrated MAX3669 +3.3V, 622Mbps SDH/SONET Laser Driver with Current Monitors and APC Revision History REVISION NUMBER REVISION DATE 6 1/13 DESCRIPTION Removed dice option from data sheet; removed the Chip Topography section; added the Package Information table PAGES CHANGED 1, 2, 3, 11, 12 Maxim Integrated cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim Integrated product. No circuit patent licenses are implied. Maxim Integrated reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000 (c) 2013 Maxim Integrated Products, Inc. 13 Maxim Integrated and the Maxim Integrated logo are trademarks of Maxim Integrated Products, Inc. Mouser Electronics Authorized Distributor Click to View Pricing, Inventory, Delivery & Lifecycle Information: Maxim Integrated: MAX3669EHJ+ MAX3669EHJ+T MAX3669ETG+ MAX3669ETG+T MAX3669EHJ MAX3669EHJ-T