19-4769; Rev 0a; 9/98 KIT ATION EVALU E L B AVAILA +3.3V, 2.5Gbps SDH/SONET Laser Driver with Automatic Power Control Features The MAX3867 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. The synchronizing input latch can be bypassed if a clock signal is not available. 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 MAX3867 also provides enable control, a programmable slow-start circuit to set the laser turn-on delay, and a failure-monitor output to indicate when the APC loop is unable to maintain the average optical power. The MAX3867 is available in a small 48-pin TQFP package as well as dice. ♦ Single +3.3V or +5V Power Supply ♦ 62mA Supply Current at +3.3V ♦ Programmable Modulation Current from 5mA to 60mA ♦ Programmable Bias Current from 1mA to 100mA ♦ Rise/Fall Time < 90ps ♦ Automatic Average Power Control with Failure Monitor ♦ Complies with ANSI, ITU, and Bellcore SDH/SONET Specifications ♦ Enable Control Ordering Information Applications SONET/SDH Transmission Systems Add/Drop Multiplexers PART TEMP. RANGE PIN-PACKAGE MAX3867ECM -40°C to +85°C 48 TQFP MAX3867E/D -40°C to +85°C Dice* *Dice are designed to operate over this range, but are tested and guaranteed at TA = +25°C only. Contact factory for availability. Digital Cross-Connects Section Regenerators Pin Configuration appears at end of data sheet. 2.5Gbps Optical Transmitters Typical Operating Circuit +3.3V 124Ω FAIL 124Ω ENABLE 124Ω LATCH 124Ω +3.3V DATA+ LD *FERRITE BEAD OUT- DATA- MAX3890 25Ω 20Ω OUT+ 0.056µF SERIALIZER WITH CLOCK GEN. MAX3867 CLK+ BIAS CLKCAPC APCFILT 84.5Ω APCSET 84.5Ω MODSET 84.5Ω BIASMAX MD 84.5Ω 1000pF ________________________________________________________________ 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. MAX3867 General Description MAX3867 +3.3V, 2.5Gbps SDH/SONET Laser Driver with Automatic Power Control 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, SLWSTRT.........-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) Current into FAIL ...............................................-10mA to +30mA Continuous Power Dissipation (TA = +85°C) TQFP (derate 20.8mW/°C above +85°C) ...................1354mW 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, 10sec) .............................+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, and 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 (Note 5) VID Common-Mode Input Voltage VICM Clock and Data Input Current IIN MIN TYP MAX UNITS 62 105 mA 100 mA 100 µA 1 ENABLE = low (Note 4) APC open loop, IBIAS = 100mA 230 APC open loop, IBIAS = 1mA 900 APC open loop -15 15 % Figure 1 200 1600 mVp-p VCC VID/4 V 10 µA PECL compatible VCC 1.49 VCC 1.32 -1 TTL Input High Voltage (ENABLE, LATCH) 2.0 V TTL Input Low Voltage (ENABLE, LATCH) TTL Output High Voltage FAIL Sourcing 50µA 2.4 TTL Output Low Voltage FAIL Sinking 100µA 0.1 Monitor-Diode Reverse Bias Voltage Monitor-Diode DC Current Range V VCC V 0.44 V V 18 IMD (Note 6) Monitor-Diode Bias Absolute Accuracy (Note 5) 2 VCC - 0.3 0.8 1.5 Monitor-Diode Bias Setpoint Stability Note 1: Note 2: Note 3: Note 4: Note 5: Note 6: ppm/°C IMD = 1mA -480 1000 50 480 90 IMD = 18µA -15 Characteristics at -40°C guaranteed by design and characterization. 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. _______________________________________________________________________________________ 15 µA ppm/°C % +3.3V, 2.5Gbps SDH/SONET Laser Driver with Automatic Power Control (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, and 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 Modulation-Off Current 5 IMOD IMOD-OFF ENABLE = low (Note 4) -480 IMOD = 60mA Modulation-Current Stability -15 (Note 6) Output Rise Time tR 20% to 80% (Note 8) Output Fall Time tF 20% to 80% (Note 8) Output Aberrations 79 MAX3867C/D 69 MAX3867ECM 88 MAX3867C/D 79 Enable/Start-Up Delay Maximum Consecutive Identical Digits Jitter Generation µA 480 15 MAX3867ECM (Note 8) Pulse-Width Distortion mA 250 IMOD = 5mA Modulation-Current Absolute Accuracy -50 60 200 % ps (Note 10) ps ±15 % 250 ns 80 PWD ppm/°C bits (Notes 8, 9) 9 50 ps Jitter BW = 12kHz to 20MHz, 0-1 pattern 7 20 psp-p 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. _______________________________________________________________________________________ 3 MAX3867 AC ELECTRICAL CHARACTERISTICS MAX3867 +3.3V, 2.5Gbps SDH/SONET Laser Driver with Automatic Power Control DATA+ 100mV MIN DATA- 800mV MAX 200mVp-p MIN 1600mVp-p MAX (DATA+) - (DATA-) IOUT+ IMOD Figure 1. Required Input Signal and Output Polarity VCC tCLK = 402ps A A A, B ARE SMD FERRITE BEADS B = BLM11A601S MURATA ELECTRONICS A = BLM21A102S MURATA ELECTRONICS CLK tSU B tH 25Ω B MAX3867 DATA 0.056µF OUT0.5pF * OSCILLOSCOPE OUT+ Figure 3. Setup/Hold Time Definition 0.056µF BIAS 15Ω 50Ω 50Ω VCC * TO COMPENSATE PACKAGE LEADS, NOT USED FOR DIE. Figure 2. Output Termination for Characterization 4 _______________________________________________________________________________________ +3.3V, 2.5Gbps SDH/SONET Laser Driver with Automatic Power Control (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 PERCENT IN UNITS (%) 40 30 20 MEAN = 88ps σ = 3.0ps 48-TQFP IMOD = 30mA VCC = +3.14V TA = +85°C 35 PERCENT IN UNITS (%) 48-TQFP IMOD = 30mA 50 40 MAX3867-02a MAX3867-01 60 30 25 20 15 MEAN = 111.6ps σ = 2.9ps 10 10 5 0 0 50ps/div 80 84 92 88 96 106 108 110 112 114 116 118 120 122 FALL TIME (ps) 100 FALL TIME (ps) RANDOM JITTER vs. IMOD ELECTRICAL EYE DIAGRAM PATTERN = 213 - 1 + 80 CID IMOD = 60mA 48-TQFP PATTERN = 213 - 1 + 80 CID IMOD = 30mA 48-TQFP 0.020 RANDOM JITTER (UIp-p) 55mV /div MAX3867 toc05 0.022 MAX3867-05a MAX3867-04a ELECTRICAL EYE DIAGRAM 26mV /div MAX3867-03a EYE DIAGRAM (2.488Gbps, 1300nm FP LASER, 1.87GHz FILTER, 48-TQFP) 0.018 0.016 0.014 JITTER BW = 12kHz to 20MHz 1-0 PATTERN 0.012 0.010 50ps/div 4 50ps/div 11 18 25 32 39 46 53 60 IMOD (mA) 90 1.1 1.0 0.9 80 70 60 40 60 IMD (mA) 80 50 40 20 0.1 0 1 100 10 RBIASMAX (kΩ) 300 0.6 0.5 0.2 10 0 0.8 0.7 0.4 0.3 30 20 MAX3867-08 1.2 MAX3867-07 MAX3867-06 100 IMOD (mA) IBIASMAX (mA) 100 IMD vs. RAPCSET IMOD vs. RMODSET IBIASMAX vs. RBIASMAX 120 0 1 10 RMODSET (kΩ) 100 0.1 1 10 100 RAPCSET (kΩ) _______________________________________________________________________________________ 5 MAX3867 Typical Operating Characteristics Typical Operating Characteristics (continued) (VCC = +3.3V, load as shown in Figure 2, TA = +25°C, unless otherwise noted.) PULSE-WIDTH DISTORTION vs. IMOD SUPPLY CURRENT vs. TEMPERATURE (EXCLUDE IBIAS, IMOD, 25Ω LOAD) VCC = +5V MAX3867-10 90 80 25 MAX3867-09 100 20 70 VCC = +3.3V 60 PWD (ps) ICC (mA) MAX3867 +3.3V, 2.5Gbps SDH/SONET Laser Driver with Automatic Power Control 50 40 15 10 VCC = +3.3V 30 VCC = +5V IMOD = 30mA IBIAS = 45mA 20 5 10 0. 0 -40 -15 10 35 60 85 5 10 20 30 40 50 60 IMOD (mA) TEMPERATURE (°C) Pin Description 6 PIN NAME FUNCTION 1, 42, 45 GND2 Ground for internal reference 2, 7, 12, 15, 16, GND1 Ground for digital circuits 3, 6, 8, 11, 18 VCC1 Power supply for digital circuits 4 DATA+ Positive PECL Data Input 5 DATA- Negative PECL Data Input 9 CLK+ Positive PECL Clock Input. Connect to VCC if latch function is not used. 10 CLK- Negative PECL Clock Input. Leave unconnected if latch function is not used. 13 LATCH 14 ENABLE 17 SLWSTRT 19 FAIL TTL/CMOS output. Indicates APC failure when low. 21, 26, 28, 31, 39, 41, 43 N.C. No Connection. Leave unconnected. 22 APCFILT 20, 23, 33 GND4 Ground for output circuitry 24, 27, 32 VCC4 Power Supply for output circuitry TTL/CMOS Latch Input. High for latched data, low for direct data. TTL/CMOS Enable Input. High for normal operation, low to disable laser bias and modulation currents. A capacitor from this pad to ground delays the turn-on time of laser bias and modulation currents. 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 Automatic Power Control PIN NAME FUNCTION 25 BIAS Laser Bias Current Output 29 OUT+ Positive Modulation-Current Output. IMOD flows through this pad when input data is high. 30 OUT- Negative Modulation-Current Output. IMOD flows through this pad when input data is low. 35 MD 34, 36, 40 GND3 Ground for APC 37 VCC3 Power Supply for APC 38 CAPC A capacitor connected from this pad to ground controls the dominant pole of the APC feedback loop. (CAPC = 0.1µF) 44 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. 46 MODSET A resistor connected from this pad to ground sets the desired modulation current. 47 BIASMAX A resistor connected from this pad to ground sets the maximum bias current. The APC function can subtract from this maximum value, but can not add to it. 48 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. Power Supply for internal reference _______________Detailed Description The MAX3867 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 MAX3867’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 MAX3867 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 (R D) is required for impedance matching. An RC shunt network is also 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 MAX3867 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 MAX3867 Pin Description (continued) MAX3867 +3.3V, 2.5Gbps SDH/SONET Laser Driver with Automatic Power Control VCC LATCH LP MAX3867 CD OUT+ IMOD 0 DATA D Q 1 RD MUX CF OUT- CLK LP 25Ω RF VCC ENABLE IBIAS 172X BIAS 40X 5X MD 1000pF IMD 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 aver8 age optical power. To filter out the APC loop noise, use 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 MAX3867 is fully operational without APC. In this case, the laser current is directly set by two external resistors connected from ground to BIASMAX _______________________________________________________________________________________ +3.3V, 2.5Gbps SDH/SONET Laser Driver with Automatic Power Control 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. Enable Control The MAX3867 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. Slow-Start For laser safety reasons, the MAX3867 incorporates a slow-start circuit which provides a programmable delay time for enabling a laser diode. An external capacitor (CSLWSTRT) connected from this pad to ground programs the delay by the equation: tENABLE ≅ 100kΩ · (CSLWSTRT + 2.5pF) APC Failure Monitor The MAX3867 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 MAX3867 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 average duty cycle of optical waveform is 50% Programming the Modulation Current For a given laser power PAVE, slope efficiency η, and extinction ration re, the modulation current can be calculated by Table 1. Refer to 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 MAX3867 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. Refer to 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. When using the MAX3867 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. Refer to 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. Programming the APC Loop When the MAX3867’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. Refer to the IMD vs. RAPCSET 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 is required (Figure 4). If RL represents the laser diode resistance, the recommended total resistance for RD + RL is 25Ω. Starting values for coaxial lasers are RF = 75Ω and C F = 3.3pF. R F and C F should be experimentally adjusted until the optical output waveform is optimized. A bypass capacitor should also be placed as close to the laser anode as possible, for the best performance. Pattern-Dependent Jitter (PDJ) When transmitting NRZ data with long strings of consecutive identical digits (CID), LF droop can occur and contribute to pattern-dependent jitter. To minimize this Table 1. Optical Power Definition PARAMETER Average Power SYMBOL PAVE RELATION PAVE = (P0 + P1) / 2 Extinction Ratio re re = P1 / P0 Optical Power High P1 P1 = 2PAVE · re / (re + 1) Optical Power Low P0 P0 = 2PAVE / (re + 1) Optical Amplitude Pp-p Laser Slope Efficiency Modulation Current η IMOD Pp-p = 2PAVE (re - 1) / (re + 1) η = Pp-p / IMOD IMOD = Pp-p /η _______________________________________________________________________________________ 9 MAX3867 and MODSET. See the Design Procedure section for more details on open-loop operation. MAX3867 +3.3V, 2.5Gbps SDH/SONET Laser Driver with Automatic Power Control pattern-dependent jitter, three external components must be properly chosen: capacitor CAPC, which dominates the APC loop time constant; pull-up inductor LP; and AC-coupling 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 pattern-dependent jitter associated with an APC loop time constant can be ignored. The time constant associated with the output pull-up inductor (LP), and the AC-coupling capacitor (CD), will also impact the pattern-dependent jitter. 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 The MAX3867 data and clock inputs are PECL-compatible. However, it is not necessary to drive the MAX3867 with a standard PECL signal. As long as the specified common-mode voltage and the differential voltage swings are met, the MAX3867 will operate properly. Calculate Power Consumption The junction temperature of the MAX3867 dice must be kept below +150°C at all times. The total power dissipation of the MAX3867 can be estimated by the following: P = VCC · VCC + (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. Applications Information The following is an example of how to set up the MAX3867. Select Laser A communication-grade laser should be selected for 2.488Gbps applications. Assume the laser output average power is PAVE = 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: ΙTH = 22mA at +25°C Threshold Temperature Coefficient: βTH = 1.3%/°C Laser to Monitor Transfer: ρMON = 0.2A/W Laser Slope Efficiency: η = 0.05mW/mA at +25°C Determine RAPCSET The desired monitor diode current is estimated by IMD = PAVE · 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. 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. Junction temperature = P(W) · 48 (°C/W) 10 ______________________________________________________________________________________ +3.3V, 2.5Gbps SDH/SONET Laser Driver with Automatic Power Control Laser Safety and IEC 825 Using the MAX3867 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. Wire Bonding Die For high current density and reliable operation, the MAX3867 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) mils. Layout Considerations To minimize inductance, keep the connections between the MAX3867 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. Chip Topography VCC3 CAPC N.C. GND3 N.C. GND2 CLK- VCC1 VCC1 DATA+ GND1 N.C. APCSET GND2 MODSET VCC2 TOP VIEW BIASMAX Pin Configuration VCC1 CLK+ GND1 DATA- VCC1 48 47 46 45 44 43 42 41 40 39 38 37 GND1 GND2 LATCH VCC2 GND2 1 36 GND3 GND1 2 35 MD VCC1 3 34 GND3 DATA+ 4 33 GND4 GND1 GND1 SLWSTRT DATA- 5 32 VCC4 VCC1 VCC1 6 31 N.C. GND1 7 30 OUT- FAIL GND4 VCC1 8 29 OUT+ CLK+ MAX3867 28 N.C. 9 CLK- 10 27 VCC4 VCC1 11 26 N.C. GND1 12 25 BIAS VCC4 GND4 APCFILT N.C. GND4 FAIL VCC1 SLWSTRT GND1 GND1 LATCH ENABLE 13 14 15 16 17 18 19 20 21 22 23 24 BIASMAX ENABLE MODSET GND2 APCSET 0.083" N.C. (2.108mm) GND2 N.C. N.C. GND3 APCFILT GND4 N.C. CAPC VCC4 VCC3 BIAS GND3 N.C. N.C. OUT- VCCA GND3 VCC4 OUT+ N.C. GND4 MD 0.070" (1.778mm) TQFP ______________________________________________________________________________________ 11 MAX3867 Modulation Current More than 60mA At +5V power supply, the headroom voltage for the MAX3867 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 MAX3867 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. +3.3V, 2.5Gbps SDH/SONET Laser Driver with Automatic Power Control TQFPPO.EPS MAX3867 Package Information 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. 12 ____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600 © 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.