19-1570; Rev 0; 12/99 KIT ATION EVALU E L B AVAILA +3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC Features ♦ Single +3.3V or +5V Power Supply ♦ 64mA Supply Current at +3.3V ♦ Programmable Bias Current from 1mA to 100mA ♦ Programmable Modulation Current from 5mA to 60mA An automatic power control (APC) feedback loop is incorporated to maintain a constant average optical power over temperature and lifetime. The wide modulation current range of 5mA to 60mA and bias current of 1mA to 100mA are easy to program, making this product ideal for use in various SDH/SONET applications. The MAX3869 also provides enable control, two current monitors that are directly proportional to the laser bias and modulation currents, and a failure-monitor output to indicate when the APC loop is unable to maintain the average optical power. The MAX3869 is available in a small 32-pin TQFP package as well as dice. ♦ Bias Current and Modulation Current Monitors ♦ 87ps Rise/Fall Time ♦ Automatic Average Power Control with Failure Monitor ♦ Complies with ANSI, ITU, and Bellcore SDH/SONET Specifications ♦ Enable Control Ordering Information PART Applications SONET/SDH Transmission Systems Add/Drop Multiplexers TEMP. RANGE PIN-PACKAGE MAX3869EHJ -40°C to +85°C 32 TQFP-EP* MAX3869E/D -40°C to +85°C Dice** *EP = Exposed Paddle. **Dice are designed to operate over this range, but are tested and guaranteed at TA = +25°C only. Contact factory for availability. Pin Configuration appears at end of data sheet. Digital Cross-Connects Section Regenerators 2.5Gbps Optical Transmitters Typical Application Circuit +3.3V 124Ω FAIL 124Ω ENABLE 124Ω LATCH 124Ω +3.3V DATA+ LD FERRITE BEAD OUT- DATA- MAX3890 25Ω 0.01µF 23Ω OUT+ 0.056µF SERIALIZER WITH CLOCK GEN. MAX3869 CLK+ BIAS CLKBIASMON CAPC APCFILT 84.5Ω APCSET 84.5Ω MODSET 84.5Ω BIASMAX MD 84.5Ω 1000pF MODMON +3.3V ________________________________________________________________ Maxim Integrated Products 1 For free samples & the latest literature: http://www.maxim-ic.com, or phone 1-800-998-8800. For small orders, phone 1-800-835-8769. MAX3869 General Description The MAX3869 is a complete, single +3.3V laser driver for SDH/SONET applications up to 2.5Gbps. The device accepts differential PECL data and clock inputs and provides bias and modulation currents for driving a laser. A synchronizing input latch can be used (if a clock signal is available) to reduce jitter. MAX3869 +3.3V, 2.5Gbps 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-, CLK+, CLK-, ENABLE, LATCH, FAIL, BIASMON, MODMON .....-0.5V to (VCC + 0.5V) Voltage at APCFILT, CAPC, MODSET, BIASMAX, APCSET ...........................................-0.5V to +3.0V Voltage at OUT+, OUT-.............................+1.5V to (VCC + 1.5V) Voltage at BIAS .........................................+1.0V to (VCC + 0.5V) Continuous Power Dissipation (TA = +85°C) 32-Pin TQFP-EP (derate 22.2mW/°C above +85°C) ..1444mW Storage Temperature Range .............................-65°C to +165°C Operating Junction Temperature Range ...........-55°C to +150°C Processing Temperature (die) .........................................+400°C Lead Temperature (soldering, 10s) .................................+300°C 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 = -40°C to +85°C. Typical values are at VCC = +3.3V, IMOD = 30mA, IBIAS = 60mA, TA = +25°C, unless otherwise noted.) (Note 1) PARAMETER Supply Current Bias Current Range Bias Off-Current SYMBOL (Note 2) IBIAS (Note 3) IBIAS-OFF Bias-Current Stability Bias-Current Absolute Accuracy Differential Input Voltage CONDITIONS ICC VID 100 µA 900 ppm/°C APC open loop -15 15 % Figure 1 200 1600 mVp-p VCC VID/4 V 10 µA 2.0 TTL Input Low Voltage ENABLE, LATCH TTL Output High Voltage FAIL Sourcing 50µA 2.4 TTL Output Low Voltage FAIL Sinking 100µA 0.1 VCC 1.32 -1 Monitor-Diode Reverse Bias Voltage Monitor-Diode DC Current Range mA IBIAS = 1mA ENABLE, LATCH IIN mA 100 230 TTL Input High Voltage Clock and Data Input Current UNITS 112 IBIAS = 100mA VCC 1.49 VICM MAX 64 ENABLE = low (Note 4) PECL compatible Common-Mode Input Voltage TYP 1 APC open loop (Note 5) MIN V VCC - 0.3 0.8 V VCC V 0.44 V 1.5 V 18 IMD Monitor-Diode Bias Setpoint Stability (Note 6) Monitor-Diode Bias Absolute Accuracy (Note 5) IMD = 1mA -480 1000 50 480 90 IMD = 18µA -15 15 µA ppm/°C % BIASMON to IBIAS Gain ABIAS IBIAS/IBIASMON 37 A/A MODMON to IMOD Gain AMOD IMOD/IMODMON 29 A/A 2 _______________________________________________________________________________________ +3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC (VCC = +3.14V to +5.5V, load as shown in Figure 2, TA = -40°C to +85°C. Typical values are at VCC = +3.3V, IMOD = 30mA, TA = +25°C.) (Note 7) PARAMETER SYMBOL CONDITIONS MIN TYP MAX UNITS Input Latch Setup Time tSU LATCH = high, Figure 3 100 ps Input Latch Hold Time tH LATCH = high, Figure 3 100 ps Modulation-Current Range 5 IMOD Modulation-Off Current IMOD-OFF ENABLE = low (Note 4) -480 IMOD = 60mA Modulation-Current Stability -15 (Note 5) Output Rise Time tR 20% to 80% (Note 8) Output Fall Time tF 20% to 80% (Note 8) Output Aberrations µA 480 15 MAX3869EHJ 78 MAX3869E/D 69 MAX3869EHJ 87 MAX3869E/D 79 (Note 8) Enable/Start-Up Delay Maximum Consecutive Identical Digits Pulse-Width Distortion mA 300 IMOD = 5mA Modulation-Current Absolute Accuracy -8 60 200 PWD % ps (Note 10) ps ±15 % 250 ns 80 Jitter Generation ppm/°C bits (Notes 8, 9) 14 50 ps Jitter BW = 12kHz to 20MHz, 0-1 pattern 7 20 psp-p Dice are tested at TA = +25°C only. Tested at RMODSET = 2.49kΩ, RBIASMAX = 1.69kΩ, excluding IBIAS and IMOD. Voltage on BIAS pin is (VCC - 1.6V). Both the bias and modulation currents will be switched off if any of the current set pins are grounded. Accuracy refers to part-to-part variation. Assuming that the laser to monitor-diode transfer function does not change with temperature. Guaranteed by design and characterization. Note 7: AC characteristics are guaranteed by design and characterization. Note 8: Measured with 622Mbps 0-1 pattern, LATCH = high. Note 9: PWD = (wider pulse - narrower pulse) / 2. Note 10: See Typical Operating Characteristics for worst-case distribution. Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: DATA+ 100mV MIN DATA- 800mV MAX 200mVp-p MIN (DATA+) - (DATA-) 1600mVp-p MAX IOUT+ IMOD Figure 1. Required Input Signal and Output Polarity _______________________________________________________________________________________ 3 MAX3869 AC ELECTRICAL CHARACTERISTICS MAX3869 +3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC VCC tCLK = 402ps A A A, B ARE SMD FERRITE BEADS: B = BLM11A601S MURATA ELECTRONICS A = BLM21A102S MURATA ELECTRONICS CLK tSU B 25Ω B tH DATA MAX3869 0.056µF OUTIOUT+ Figure 3. Setup/Hold Time Definition OSCILLOSCOPE OUT+ 0.056µF BIAS 15Ω 50Ω 50Ω VCC Figure 2. Output Termination for Characterization Typical Operating Characteristics (VCC = +3.3V, load as shown in Figure 2, TA = +25°C, unless otherwise noted.) DISTRIBUTION OF FALL TIME (WORST-CASE CONDITIONS) TYPICAL DISTRIBUTION OF FALL TIME 35 MAX3869-02 MAX3869-01 25 32 TQFP-EP IMOD = 30mA 32 TQFP-EP IMOD = 60mA VCC = 3.14V TA = +85°C 30 15 MEAN = 87.3ps σ = 1.6ps 10 PERCENT OF UNITS (%) PERCENT OF UNITS (%) 20 25 MAX3869-03 EYE DIAGRAM (2.488Gbps, 1300nm FP LASER, 1.87GHz FILTER, 32 TQFP-EP) 20 MEAN = 119.1ps σ = 2.0ps 15 10 5 5 0 0 48ps/div 83 84 85 86 87 88 89 FALL TIME (ps) 90 91 92 113 114.5 116 117.5 119 120.5 122 123.5 125 126.5 FALL TIME (ps) MITSUBISHI ML725C8F LASER DIODE 4 _______________________________________________________________________________________ +3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC (VCC = +3.3V, load as shown in Figure 2, TA = +25°C, unless otherwise noted.) RANDOM JITTER vs. IMOD 8.0 7.5 RANDOM JITTER (psp-p) 7.0 400mV/div 250mV/div MAX3869-05 MAX3869-04 ELECTRICAL EYE DIAGRAM (IMOD = 60mA, 213-1 +80 CID, 32 TQFP-EP) MAX3869-06 ELECTRICAL EYE DIAGRAM (IMOD = 30mA, 213-1 +80 CID, 32 TQFP-EP) 6.5 6.0 5.5 5.0 4.5 4.0 3.5 3.0 100ps/div 50 40 0.8 0.7 0.6 0.5 0.1 0 0 1 300 10 RBIASMAX (kΩ) 100 1 IBIAS = 100mA, IMOD = 50mA GAIN (IBIAS/IBIASMON) 40 70 VCC = +3.14V 50 40 30 20 MAX3869-11 50 VCC = +5.5V 60 100 BIAS-CURRENT MONITOR GAIN vs. TEMPERATURE MAX3869-10 90 10 RAPCSET (kΩ) SUPPLY CURRENT vs. TEMPERATURE (EXCLUDE IBIAS, IMOD, 25Ω LOAD) SUPPLY CURRENT (mA) 0.1 RMODSET (kΩ) 100 50 0.2 10 100 45 0.4 0.3 20 0 40 MAX3869-09 MAX3869-08 60 30 20 35 1.0 0.9 IMD (mA) IMOD (mA) 40 30 1.1 70 60 25 IMD vs. RAPCSET 90 80 80 20 1.2 80 10 15 IMOD (mA) 100 MAX3869-07 100 1 10 IMOD vs. RMODSET IBIASMAX vs. RBIASMAX 120 IBIASMAX (mA) 5 100ps/div IBIAS = 10mA, IMOD = 10mA 30 20 10 10 0 0 -40 -15 10 35 TEMPERATURE (°C) 60 85 -40 -15 10 35 60 85 TEMPERATURE (°C) _______________________________________________________________________________________ 5 MAX3869 Typical Operating Characteristics (continued) Typical Operating Characteristics (continued) (VCC = +3.3V, load as shown in Figure 2, TA = +25°C, unless otherwise noted.) MODULATION-CURRENT MONITOR GAIN vs. TEMPERATURE PULSE-WIDTH DISTORTION vs. IMOD 35 IBIAS = 100mA, IMOD = 50mA 30 20 VCC = +3.3V IBIAS = 10mA, IMOD = 10mA PWD (ps) 25 MAX3869-13 25 MAX3869-12 40 GAIN (IMOD/IMODMON) MAX3869 +3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC 20 15 10 15 VCC = +5V 10 5 5 0. 0 -40 -15 10 35 60 85 TEMPERATURE (°C) 5 10 20 30 40 50 60 IMOD (mA) Pin Description 6 PIN NAME FUNCTION 1, 4, 7 VCC1 2 DATA+ Noninverting PECL Input 3 DATA- Inverting PECL Input 5 CLK+ Positive PECL Clock Input. Connect to VCC if latch function is not used. 6 CLK- Negative PECL Clock Input. Leave unconnected if latch function is not used. 8 LATCH TTL/CMOS Latch Input. High for latched data, low for direct data. Internal 100kΩ pull-up to VCC. 9 ENABLE TTL/CMOS Enable Input. High for normal operation, low to disable laser bias and modulation current. Internal 100kΩ pull-up to VCC. 10, 15 GND1 11 BIASMON Bias Current Monitor. Sink current source that is proportional to the laser bias current. 12 MODMON Modulation Current Monitor. Sink current source that is proportional to the laser modulation current. 13 FAIL 14 APCFILT 16, 18, 21 VCC4 Power Supply for Output Circuitry 17 BIAS Laser Bias Current Output 19 OUT+ Positive Modulation-Current Output. IMOD flows through this pad when input data is high. Power Supply for Digital Circuits Ground for Digital Circuits TTL/CMOS Failure Output. Indicates APC failure when low. Connect a capacitor (CAPCFILT = 0.1µF) from this pad to ground to filter the APC noise. _______________________________________________________________________________________ +3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC PIN NAME FUNCTION 20 OUT- Negative Modulation-Current Output. IMOD flows through this pad when input data is low. 22 GND4 Ground for Output Circuitry 23 GND3 Ground for APC 24 MD 25 VCC3 Power Supply for APC 26 CAPC A capacitor connected from this pad to ground controls the dominant pole of the APC feedback loop (CAPC = 0.1µF). 27 GND2 Ground for Internal Reference 28 N.C. 29 APCSET A resistor connected from this pad to ground sets the desired average optical power. Connect 100kΩ from this pad to ground if APC is not used. 30 MODSET A resistor connected from this pad to ground sets the desired modulation current. 31 BIASMAX A resistor connected from this pad to ground sets the maximum bias current. The APC function can subtract from this maximum value, but cannot add to it. 32 VCC2 Monitor Diode Input. Connect this pad to a monitor photodiode anode. A capacitor to ground is required to filter high-speed AC monitor photocurrent. No Connection. Leave unconnected. Power Supply for Internal Reference _______________Detailed Description The MAX3869 laser driver consists of two main parts: a high-speed modulation driver and a laser-biasing block with automatic power control (APC). The circuit design is optimized for both high-speed and low-voltage (+3.3V) operation. To minimize the pattern-dependent jitter of the input signal at speeds as high as 2.5Gbps, the device accepts a differential PECL clock signal for data retiming. When LATCH is high, the input data is synchronized by the clock signal. When LATCH is low, the input data is directly applied to the output stage. 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 60mA into the laser with an edge speed of 100ps, 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 MAX3869’s modulation output is designed to be AC-coupled to the cathode of a laser diode. An external pull-up inductor is necessary to DC-bias the modulation output at VCC. Such a configuration isolates laser forward voltage from the output circuitry and allows the output at OUT+ to swing above and below the supply voltage VCC. A simplified functional diagram is shown in Figure 4. The MAX3869 modulation output is optimized for driving a 25Ω load; the minimum required voltage at OUT+ is 2.0V. Modulation current swings of 80mA are possible, but due to minimum power-supply and jitter requirements at 2.5Gbps, the specified maximum modulation current is limited to 60mA. To interface with the laser diode, a damping resistor (RD) is required for impedance matching. An RC shunt network may also be necessary to compensate for the laser-diode parasitic inductance, thereby improving the optical output aberrations and duty-cycle distortion. At the data rate of 2.5Gbps, any capacitive load at the cathode of a laser diode will degrade 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 cathode. Automatic Power Control To maintain constant average optical power, the MAX3869 incorporates an APC loop to compensate for the changes in laser threshold current over temperature and lifetime. A back-facet photodiode mounted in the _______________________________________________________________________________________ 7 MAX3869 Pin Description (continued) MAX3869 +3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC VCC LP2 LATCH LP1 RP MAX3869 RD OUT+ IMOD 0 CD MUX DATA D Q 1 OUT- CLK 25Ω VCC ENABLE IBIAS BIASMON 165x IBIAS 37 BIAS 40x 5x MD MOBMON 1000pF IMD IMOD 29 FAILURE DETECTOR MODSET BIASMAX RMODSET RBIASMAX CAPC APCSET FAIL CAPC RAPCSET Figure 4. Functional Diagram laser package is used to convert the optical power into a photocurrent. The APC loop adjusts the laser bias current so that 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 0.1µF. 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. To filter out the APC loop noise, use 8 an external capacitor at APCFILT with a recommended value of 0.1µF. 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. Open-Loop Operation If necessary, the MAX3869 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. See the Design Procedure section for more details on open-loop operation. _______________________________________________________________________________________ +3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC Enable Control The MAX3869 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, and the typical disable time is 25ns. Current Monitors Programming the Modulation Current For a given laser power PAVG, slope efficiency η, and extinction ration re, the modulation current can be calculated using Table 1. See the IMOD vs. RMODSET graph in the Typical Operating Characteristics and select the value of RMODSET that corresponds to the required current at +25°C. Programming the Bias Current When using the MAX3869 in open-loop operation, the bias current is determined by the RBIASMAX resistor. To select this resistor, determine the required bias current at +25°C. See the IBIASMAX vs. RBIASMAX graph in the Typical Operating Characteristics and select the value of RBIASMAX that corresponds to the required current at +25°C. The MAX3869 features bias- and modulation-current monitor outputs. The BIASMON output sinks a current equal to 1/37 of the laser bias current (IBIAS / 37). The MODMON output sinks a current equal to 1/29 of the laser modulation current (IMOD / 29). BIASMON and MODMON should be connected through a pull-up resistor to VCC. Choose a pull-up resistor value that ensures a voltage at BIASMON greater than VCC - 1.6V and a voltage at MODMON greater than VCC - 1.0V. When using the MAX3869 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 IBIASMAX vs. RBIASMAX graph in the Typical Operating Characteristics and select the value of RBIASMAX that corresponds to the end-of-life bias current at +85°C. Slow-Start When the MAX3869’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 I MD vs. R APCSET graph in the Typical Operating Characteristics and select the value of RAPCSET that corresponds to the required current. For laser safety reasons, the MAX3869 incorporates a slow-start circuit that provides a delay of 250ns for enabling a laser diode. APC Failure Monitor The MAX3869 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. Short-Circuit Protection The MAX3869 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 output 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 mark density and duty cycle of the optical waveform are 50%. Programming the APC Loop Interfacing with Laser Diodes To minimize optical output aberrations caused by signal reflections at the electrical interface to the laser diode, a series damping resistor (RD) is required (Figure 4). Additionally, the MAX3869 outputs are optimized for a 25Ω load. Therefore, the series combination of RD and RL (where RL represents the laser-diode resistance) Table 1. Optical Power Definition PARAMETER SYMBOL RELATION Average Power PAVG Extinction Ratio re re = P1 / P0 Optical Power High P1 P1 = 2PAVG · re / (re + 1) Optical Power Low P0 P0 = 2PAVG / (re + 1) Optical Amplitude Pp-p Laser Slope Efficiency Modulation Current PAVG = (P0 + P1) / 2 Pp-p = 2PAVG (re - 1) / (re + 1) η η = Pp-p / IMOD IMOD IMOD = Pp-p / η _______________________________________________________________________________________ 9 MAX3869 Optional Data Input Latch To minimize input data pattern-dependent jitter, the differential clock signal should be connected to the data input latch, which is selected by an external LATCH control. If LATCH is high, the input data is retimed by the rising edge of CLK+. If LATCH is low, the input data is directly connected to the output stage. When this latch function is not used, connect CLK+ to VCC and leave CLK- unconnected. MAX3869 +3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC should equal 25Ω. Typical values for RD are 18Ω to 23Ω. For best performance, a bypass capacitor (0.01µF typical) should be placed as close as possible to the anode of the laser diode. Depending on the exact characteristics of the laser diode and PC board layout, a resistor (RP) of 20Ω to 70Ω in parallel with pull-up inductor LP1 can be useful in damping overshoot and ringing in the optical output. In some applications (depending on laser-diode parasitic inductance characteristics), an RC shunt network between the laser cathode and ground will help minimize optical output aberrations. Starting values for most coaxial lasers are R = 75Ω in series with C = 3.3pF. These values should be experimentally adjusted until the optical output waveform is optimized. Pattern-Dependent Jitter When transmitting NRZ data with long strings of consecutive identical digits (CIDs), LF droop can occur and contribute to pattern-dependent jitter (PDJ). To minimize this PDJ, three external components must be properly chosen: capacitor CAPC, which dominates the APC loop time constant; pull-up inductor LP; and ACcoupling capacitor CD. To filter out noise effects and guarantee loop stability, the recommended value for CAPC is 0.1µF. This results in an APC loop bandwidth of 10kHz or a time constant of 16µs. As a result, the PDJ associated with an APC loop time constant can be ignored. The time constant associated with the output pull-up inductor (LP ≈ LP2), and the AC-coupling capacitor (CD) will also impact the PDJ. For such a second-order network, the PDJ due to the low frequency cutoff will be dominated by LP. For a data rate of 2.5Gbps, the recommended value for CD is 0.056µF. During the maximum CID period t, it is recommended to limit the peak voltage droop to less than 12% of the average (6% of the amplitude). The time constant can be estimated by: -t/τ 12% = 1 - e LP τLP = 7.8t If τLP = LP / 25Ω, and t = 100UI = 40ns, then LP = 7.8µH. To reduce the physical size of this element (LP), use of SMD ferrite beads is recommended (Figure 2). Input Termination Requirement Calculating Power Consumption The junction temperature of the MAX3869 dice must be kept below +150°C at all times. The total power dissipation of the MAX3869 can be estimated by the following: P = VCC · ICC + (VCC - Vf) · IBIAS + IMOD (VCC - 25Ω · 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. Junction Temperature = P(W) · 45 (°C/W) ___________Applications Information An example of how to set up the MAX3869 follows. Select Laser A communication-grade laser should be selected for 2.488Gbps applications. Assume the laser output average power is PAVG = 0dBm, minimum extinction ratio is re = 6.6 (8.2dB), the operating temperature is -40°C to +85°C, and the laser diode has the following characteristics: Wavelength: λ = 1.3µm Threshold Current: Threshold Temperature Coefficient: Laser to Monitor Transfer: Laser Slope Efficiency: ΙTH = 22mA at +25°C βTH = 1.3%/°C ρMON = 0.2A/W η = 0.05mW/mA at +25°C Determine RAPCSET The desired monitor diode current is estimated by IMD = PAVG · ρMON = 200µA. The IMD vs. RAPCSET graph in the Typical Operating Characteristics shows that RAPCSET should be 6.0kΩ. Determine RMODSET To achieve a minimum extinction ratio (re) of 6.6dB over temperature and lifetime, calculate the required extinction ratio at +25°C. 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 IMOD vs. RMODSET graph in the Typical Operating Characteristics shows that RMODSET should be 4.8kΩ. The MAX3869 data and clock inputs are PECL compatible. However, it is not necessary to drive the MAX3869 with a standard PECL signal. As long as the specified common-mode voltage and the differential voltage swings are met, the MAX3869 will operate properly. 10 ______________________________________________________________________________________ +3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC Layout Considerations To minimize inductance, keep the connections between the MAX3869 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. Modulation Currents Exceeding 60mA Using the MAX3869 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 customer 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. With a +5V power supply, the headroom voltage for the MAX3869 is significantly improved. In this case, it is possible to achieve a modulation current of more than 60mA with AC-coupling, if the junction temperature is kept below 150°C. The MAX3869 can also be DC-coupled to a laser diode when operating with a +5V supply; the voltage at OUT+ should be ≥ 2.0V for proper operation. Wire Bonding Die For high current density and reliable operation, the MAX3869 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 (100µm) square, and die thickness is 12 mils (300µm) square. Laser Safety and IEC 825 Chip Information TRANSISTOR COUNT: 1561 SUBSTRATE CONNECTED TO GND ______________________________________________________________________________________ 11 MAX3869 Determine RBIASMAX Calculate the maximum threshold current (ITH(MAX)) at T A = +85°C and end of life. Assuming I TH(MAX) = 50mA, the maximum bias current should be: IBIASMAX = ITH(MAX) + IMOD/2 In this example, IBIASMAX = 68.1mA. The IBIASMAX vs. RBIASMAX graph in the Typical Operating Characteristics shows that RBIASMAX should be 3.2kΩ. MAX3869 +3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC Pin Configuration Chip Topography CLK- TOP VIEW VCC1 VCC2 BIASMAX MODSET APCSET N.C. GND2 CAPC VCC3 VCC1 32 31 30 29 28 27 26 25 1 24 MD LATCH VCC2 ENABLE BIASMAX GND1 MODSET 2 23 GND3 DATA- 3 22 GND4 MODMON CLK+ 5 CLK- 21 VCC4 MAX3869 6 N.C. 19 OUT+ APCFILT CAPC VCC3 GND3 7 18 VCC4 LATCH 8 17 BIAS BIAS GND3 N.C. 16 VCC4 15 GND1 14 APCFILT 13 FAIL 12 MODMON BIASMON GND1 ENABLE 11 N.C. 20 OUT- VCC1 10 GND2 APCSET 0.083" GND3 (2.108mm) N.C. FAIL GND4 GND4 VCC4 9 12 GND2 DATA+ 4 VCC1 DATA+ GND1 GND1 GND1 BIASMON VCC1 VCC1 CLK+ GND1 DATA- VCC1 N.C. N.C. OUT- VCC4 GND3 VCC4 OUT+ N.C. GND4 MD 0.070" (1.778mm) ______________________________________________________________________________________ +3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC 32L,TQFP.EPS ______________________________________________________________________________________ 13 MAX3869 Package Information +3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC MAX3869 Package Information (continued) 14 ______________________________________________________________________________________ +3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC MAX3869 NOTES ______________________________________________________________________________________ 15 MAX3869 +3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC NOTES 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 © 1999 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.