VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control VSC7938 Features Applications • SDH/SONET at 622Mb/s, 1.244Gb/s, 2.488Gb/s, 3.125Gb/s • Power Supply: 3.3V or 5V ±5% • AC-Coupled to Laser Diode • Programmable Modulation Current: 5mA to 60mA • Programmable Bias Current: 1mA to 100mA • Enable/Disable Control • Typical Rise/Fall Times of 60ps • Automatic Optical Average Power Control • Supply Current of 33mA at 3.3V • Full-Speed Fibre Channel (1.062Gb/s) General Description The VSC7938 is a single 3.3V or 5V supply laser diode driver specially designed for SDH/SONET applications up to 3.125Gb/s. External resistors set a wide range of bias and modulation currents for driving the laser. Data and clock inputs accept differential PECL signals. The automatic power control (APC) loop maintains a constant average optical power over temperature and lifetime. The dominant pole of the APC loop can be controlled with an external capacitor. Other features include enable/disable control, short-circuit protection for the modulation and bias inputs, short rise and fall times, programmable slow-start circuit to set laser turn-on delay, and failure-monitor output to indicate when the APC loop is unable to maintain the average optical power. The VSC7938 is available in die form or in a 48-pin TQFP package. Block Diagram 3.3V Operation VCC LP LATCH IOUT+ CD IOUT- CF MUX CLK+ CLK- RF LP DATA+ DATA- SET D Q VCC CLR Q BIAS ENABLE MD APC DISABLE FAIL SLWSTRT G52349-0, Rev 3.0 01/20/01 MODSET BIASMAX CAPC 1nF APCSET © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com Page 1 VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control VSC7938 Electrical Characteristics Table 1: AC Specifications AC specifications are guaranteed by design and characterization. Typical values are for 3.3V. Symbol Parameter Min Typ Max Units Conditions tSU Input Latch Setup Time 100 ps LATCH=high tH Input Latch Hold Time 100 ps LATCH=high Enable/Start-up Delay 250 ns tR Output Rise Time 60 80 ps 20% to 80% tF Output Fall Time 60 80 ps 20% to 80% PWD Pulse Width Distortion 10 50 ps See Notes 1, 2 CIDMAX Maximum Consecutive Identical Digits tJ Jitter Generation 80 bits 7 20 psp-p Jitter BW=12kHz to 20MHz, 0-1 pattern. NOTES:(1) Measured with 622Mb/s 0-1 pattern, LATCH=high. (2) PWD = (wider pulse - narrower pulse) / 2). Table 2: DC Specifications Symbol Parameter ICC Supply Current IBIAS Bias Current Range IBIAS-OFF Bias Off Current SBIAS Bias Current Stability VRMD Monitor Diode Reverse Bias Voltage IMD Monitor Diode Reverse Current Range Min TBD 1 Monitor Diode Bias Absolute Accuracy IMOD Modulation Current Range IMOD-OFF Modulation Off Current Conditions 45 mA 100 mA Voltage at BIAS pin=(VCC-1.6) 100 µA ENABLE=low or DISABLE=high(1) ppm/°C ±15 % 1.5 APC Open loop. IBIAS=100mA APC Open loop. IBIAS=1mA Refers to part-to-part variation V 18 -480 Units RMODSET=7.3kΩ RBIASMAX=4.8kΩ IBIAS and IMOD excluded VCC=5V 900 1000 -50 480 90 µA ppm/°C IMD=1mA(2) IMD=18µA(2) -15 15 % 5 60 mA 200 µA ENABLE=low or DISABLE=high(1) % See Note 2 Modulation Current Absolute Accuracy Modulation Current Stability Max 230 Bias Current Absolute Accuracy Monitor Diode Bias Setpoint Stability Typ ±15 -480 -50 250 480 ppm/°C Refers to part-to-part variation IMOD=60mA IMOD=5mA NOTES: (1) Both IBIAS and IMOD will turn off if any of the current set pins are grounded. (2) Assumes laser diode to monitor diode transfer function does not change with temperature. Page 2 © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com G52349-0, Rev 3.0 01/20/01 VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control VSC7938 Table 3: PECL and TTL/CMOS Inputs and Outputs Specifications Symbol Parameter Min VID Differential Input Voltage VICM Common-Mode Input Voltage VCC 1.49 IIN Clock and Data Input Current -1 VIH TTL Input High Voltage (ENABLE, LATCH) 2.0 VIL TTL Input Low Voltage (ENABLE, LATCH) Typ 100 TTL Output High Voltage (FAIL) 2.4 TTL Output Low Voltage (FAIL) 0.1 VCC 1.32 Max Units Conditions 1600 mVp-p (DATA+)-(DATA-) VCC VID/4 V PECL Compatible 10 µA V VCC 0.3 0.8 V VCC V Sourcing 50µA 0.44 V Sinking 100µA Absolute Maximum Ratings(1) Power Supply Voltage (VCC)............................................................................................................... -0.5V to 6V Current into BIAS.....................................................................................................................-20mA to +150mA Current into OUT+, OUT- ...............................................................................................................................TBD Current into MD .............................................................................................................................-5mA to +5mA Current into FAIL ......................................................................................................................... -10mA to 30mA Voltage at DATA+, DATA-, CLK+, CLK-, ENABLE, LATCH......................................... -0.5V to (VCC + 0.5V) Voltage at APCFILT, MODSET, BIASMAX, APCSET, MD, FAIL, SLWSTRT.......................... -0.5V to +3.0V Voltage at OUT+, OUT- ..................................................................................................... -0.5V to (VCC + 1.5V) Voltage at BIAS .................................................................................................................. -0.5V to (VCC + 0.5V) Continouous Power Dissipation (TA = +85°C, TQFP derate 20.8mW/°C above +85°C) .......................1350mW Operating Junction Temperature Range ...................................................................................... -55°C to +150°C Storage Temperature Range ........................................................................................................ -65°C to +165°C NOTE: (1) CAUTION: Stresses listed under “Absolute Maximum Ratings” may be applied to devices one at a time without causing permanent damage. Functionality at or above the values listed is not implied. Exposure to these values for extended periods may affect device reliability. Recommended Operating Conditions Positive Voltage Rail (VCC)..................................................................................................... +3.135V to +5.25V Negative Voltage Rail (GND) ............................................................................................................................0V Modulation Current (IMOD)(1) .......................................................................................................................30mA Ambient Temperature Range (TA)................................................................................................. -40°C to +85°C NOTE: (1) VCC = 3.3V, IBIAS = 60mA. G52349-0, Rev 3.0 01/20/01 © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com Page 3 VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control VSC7938 Bare Die Descriptions Figure 1: Pad Assignments 1773µm (0.0698") Pad 11 VCC1 2233µm (0.0879") Pad 10 CLK- Pad 9 CLK+ Pad 8 VCC1 Pad 7 GND1 Pad 6 VCC1 Pad 5 DATA- Pad 4 DATA+ Pad 3 VCC1 Pad 2 GND1 Pad 12 GND1 Pad 1 GND2 Pad 13 LATCH Pad 48 VCC2 Pad 14 ENABLE Pad 47 BIASMAX Pad 15 DISABLE Pad 46 MODSET Pad 16 GND1 Pad 45 GND2 Pad 17 SLWSTRT Pad 44 APCSET Pad 18 VCC1 Pad 43 AUTSEL VSC7938 Pad 19 FAIL Pad 42 GND2 Pad 20 GND4 Pad 41 PB_GND Pad 21 PB_GND Pad 40 GND3 Pad 22 APCFILT Pad 39 PB_GND Pad 23 GND4 Pad 38 CAPC Pad 24 VCC4 Pad 37 VCC3 Pad 25 BIAS Pad 36 GND3 Pad 26 PB_GND Pad 27 VCC4 Pad 28 DB_OUT+ Pad 29 OUT+ Pad 30 OUT- Pad 31 DB_OUT- Pad 32 VCC4 Pad 33 GND4 Pad 34 GND3 Pad 35 MD Die Size: Die Thickness: Pad Pitch: Pad Size: 1773µm x 2233µm (0.0698" x 0.0879") 625µm (0.0246") 115µm (0.0045") 95µm x 95µm (0.0037" x 0.0037") Pad to Pad Clearance: 20µm (0.0008") Pad Passivation Opening: 95µm x 95µm (0.0037" x 0.0037") Scribe Size: 75µm (0.0030") Page 4 20µm (0.0008") © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com 75µm (0.0030") G52349-0, Rev 3.0 01/20/01 VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control VSC7938 Table 4: Pad Coordinates Signal Name Pad Number Coordinates (µm) X Y Signal Name Pad Number Coordinates (µm) X Y GND2 1 1613.55 1863.475 BIAS 25 159.45 368.475 GND1 2 1414.525 2073.55 PB_GND 26 369.525 159.45 VCC1 3 1289.525 2073.55 VCC4 27 484.525 159.45 DATA+ 4 1174.525 2073.55 DB_OUT+ 28 599.525 159.45 DATA- 5 1059.525 2073.55 OUT+ 29 714.525 159.45 VCC1 6 944.525 2073.55 OUT- 30 829.525 159.45 GND1 7 829.525 2073.55 DB_OUT- 31 944.525 159.45 VCC1 8 714.525 2073.55 VCC4 32 1059.525 159.45 CLK+ 9 599.525 2073.55 GND4 33 1174.525 159.45 CLK- 10 484.525 2073.55 GND3 34 1289.525 159.45 VCC1 11 369.525 2073.55 MD 35 1404.525 159.45 GND1 12 159.45 1863.475 GND3 36 1613.55 368.475 LATCH 13 159.45 1748.475 VCC3 37 1613.55 483.475 ENABLE 14 159.45 1633.475 CAPC 38 1613.55 598.475 DISABLE 15 159.45 1518.475 PB_GND 39 1613.55 713.475 GND1 16 159.45 1403.475 GND3 40 1613.55 828.475 SLWSTRT 17 159.45 1288.475 PB_GND 41 1613.55 943.475 VCC1 18 159.45 1058.475 GND2 42 1613.55 1058.475 FAIL 19 159.45 1058.475 AUTSEL 43 1613.55 1173.475 GND4 20 159.45 828.475 APCSET 44 1613.55 1288.475 PB_GND 21 159.45 828.475 GND2 45 1613.55 1403.475 APCFILT 22 159.45 598.475 MODSET 46 1613.55 1518.475 GND4 23 159.45 598.475 BIASMAX 47 1613.55 1633.475 VCC4 24 159.45 483.475 VCC2 48 1613.55 1748.475 G52349-0, Rev 3.0 01/20/01 © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com Page 5 VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control VSC7938 Package Pin Descriptions VCC BIASMAX MODSET GND APCSET RESERVED GND NC GND NC CAPC VCC 48 47 46 45 44 43 42 41 40 39 38 37 Figure 2: Pin Diagram GND 1 36 GND GND 2 35 MD VCC 3 34 GND DATA+ 4 33 GND DATA- 5 32 VCC 31 NC 30 OUT- VCC 6 GND 7 VCC 8 29 OUT+ CLK+ 9 28 NC CLK- 10 27 VCC VCC 11 26 NC GND 12 25 BIAS Page 6 14 15 16 17 18 19 20 21 22 23 24 ENABLE DISABLE GND SLWSTRT VCC FAIL GND NC APCFILT GND VCC LATCH 13 VSC7938 © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com G52349-0, Rev 3.0 01/20/01 VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control VSC7938 Table 5: Pin Identifications Pin Name Pin Number GND 1, 2, 7, 12, 16, 20, 23, 33, 34 36, 40, 42, 45 VCC 3, 6, 8, 11, 18, 24, 27, 32, 37, 48 Description Ground Power Supply DATA+ 4 Positive Data Input (PECL) DATA- 5 Negative Data Input (PECL) CLK+ 9 Positive Clock Input (PECL). Connect to VCC if data retiming is not used. CLK- 10 Negative Clock Input (PECL). Leave unconnected if data retiming is not used. LATCH 13 Latch Input (TTL/CMOS). Connect to VCC for data retiming and GND for direct data. ENABLE 14 Enable Input (TTL/CMOS). If used, connect DISABLE to GND. Connect to VCC for normal operation and GND to disable laser bias and modulation currents. DISABLE 15 Disable Input (TTL/CMOS). If used, leave ENABLE pin floating. Connect to GND for normal operation and VCC to disable laser bias and modulation currents. SLWSTRT 17 Connect capacitor to GND to delay turn on time of bias and modulation currents. 19 Output (TTL/CMOS). When low, it indicates APC failure. FAIL NC 21, 26, 28, 31, 39, 41 No Connection. Leave these pins unconnected. APCFILT 22 No effect on device operation. BIAS 25 Laser Bias Current Output OUT+ 29 Positive Modulation-Current Output. IMOD flows when input data is high. OUT- 30 Negative Modulation-Current Output. IMOD flows when input data is low. MD 35 Monitor Diode Input. Connect to monitor photodiode anode. Connect capacitor to GND to filter high-speed AC monitor photocurrent. CAPC 38 Capacitor to GND sets dominant pole of the APC feedback loop. RESERVED 43 Do not connect. APCSET 44 Resistor to GND sets desired average optical power. If APC is not used connect 100kΩ resistor to GND. MODSET 46 Connect resistor to GND to set desired modulation current. BIASMAX 47 Connect resistor to GND to set maximum bias current. The APC function can subtract from this value, but it cannot add to it. G52349-0, Rev 3.0 01/20/01 © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com Page 7 VITESSE SEMICONDUCTOR CORPORATION SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control Preliminary Data Sheet VSC7938 Detailed Description The VSC7938 is a high-speed laser driver with Automatic Power Control. The device is designed to operate up to 3.125Gb/s with a 3.3V or 5V supply. The data and clock inputs support PECL inputs as well as other inputs that meet the common-mode voltage and differential voltage swing specifications. The differential pair output stage is capable of sinking up to 60mA from the laser with typical rise and fall times of 60ps. This output may be DC-coupled for 5V operation. To allow for larger output swings during 3.3V operation, the VSC7938 was designed to be AC-coupled to the laser cathode with a pull-up inductor for DC-biasing. This configuration will isolate laser forward voltage from the output circuitry and will allow the output at OUT+ to swing above and below the supply voltage VCC. The key features of the VSC7938 are Automatic Power Control, low power supply current, and fast rise and fall times. The VSC7939 and VSC7940 are other Vitesse laser drivers with similar features in a 32-pin TQFP package. These devices also have pins for monitoring modulation and bias currents. The VSC7940 is a special version of the VSC7939 designed to drive 100mA into a DC-coupled load with a 5V supply. Automatic Power Control To ensure constant average optical power, the device utilizes an Automatic Power Control loop. A photodiode mounted in the laser package provides optical feedback to compensate for changes in average laser output power due to changes that affect laser performance such as temperature and laser lifetime. The laser bias current is adjusted by the APC loop according to the reference current set at APCSET by an external resistor. An external capacitor at CAPC controls the time constant for the APC feedback loop. The recommended value for CAPC is 0.1µF. This value reduces pattern-dependent jitter associated with the APC feedback loop and guarantees stability. Because the APC loop noise is internally filtered, APCFILT is not internally connected and does not need to be connected to any external components. The device’s performance will not be affected if a capacitor is connected to APCFILT. If the APC loop cannot adjust the bias current to track the desired monitor current, FAIL is set low. The device may be operated with or without APC. To utilize APC, a capacitor must be connected at CAPC (0.1µF) and a resistor must be connected at APCSET to set the average optical power. For open-loop operation (no APC), a 100kΩ resistor should be connected between APCSET and GND. CAPC has no effect on openloop operation. In both modes of operation, resistors to ground should be placed at BIASMAX and MODSET to set the bias and modulation currents. Data Retiming The VSC7938 provides inputs for differential PECL clock signals for data retiming to minimize jitter at high speeds. To incorporate this function, LATCH should be connected to VCC. If this function is unused, CLK+ should be connected to VCC, CLK- should be left unconnected, and LATCH should be connected to GND. Short-Circuit Protection If BIASMAX or MODSET are shorted to ground, the output modulation and bias currents will be turned off. Page 8 © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com G52349-0, Rev 3.0 01/20/01 VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet VSC7938 SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control Enable/Disable Two pins are provided to allow either ENABLE or DISABLE control. If ENABLE is used, connect DISABLE to ground. Is DISABLE is used, leave ENABLE floating. Both modulation and bias currents are turned off when ENABLE is low or DISABLE is high. Typically, ENABLE or DISABLE responds within approximately 250ns. Slow-Start For laser safety, the VSC7938 offers a slow-start mechanism via the SLWSTRT pin which provides delay for enabling the laser diode. To disable Slow-Start, leave SLWSTRT open. An external capacitor to ground sets the delay by the following equation: τENABLE(ns) = CSLWSTRT(pF) * 20 + 250ns Controlling the Modulation Current The output modulation current may be determined from the following equation where Pp-p is the peak-topeak optical power, PAVE is the average power, re is the extinction ratio, and η is the laser slope efficiency: IMOD = Pp-p / η= 2 * PAVE * (re-1) / (re+1) / η A resistor at MODSET controls the output bias current. Graphs of IMODSET vs. RMODSET in Typical Operating Characteristics for both 3.3V and 5V operation describe the relationship between the resistor at MODSET and the output modulation current at 25°C. After determining the desired output modulation current, use the graph to determine the appropriate resistor value at MODSET. Controlling the Bias Current A resistor at BIASMAX should be used to control the output bias current. Graphs of IBIASMAX vs. RBIASMAX in Typical Operating Characteristics for both 3.3V and 5V operation describe the relationship between the resistor at BIASMAX and the output bias current at 25°C. If the APC is not used, the appropriate resistor value at BIASMAX is determined by first selecting the desired output bias current, and then using the graph to determine the appropriate resistor value at BIASMAX. When using APC, BIASMAX sets the maximum allowed bias current. After determining the maximum end-of-life bias current at 85°C for the laser, refer to the graph of IBIASMAX vs. RBIASMAX in Typical Operating Characteristics to select the appropriate resistor value. Controlling the APC Loop To select the resistor at APCSET, use the graph of IMD vs. RAPCSET in Typical Operating Characteristics. The graph relates the desired monitor current to the appropriate resistance value at APCSET. IMD may be calculate from the desired optical average power, PAVE,, and the laser-to-monitor transfer, ρMON, for a specific laser using the following equation: IMD = PAVE * ρMON G52349-0, Rev 3.0 01/20/01 © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com Page 9 VITESSE SEMICONDUCTOR CORPORATION SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control Preliminary Data Sheet VSC7938 Laser Diode Interface An RC shunt network should be placed at the laser output interface. The sum of the resistor placed at the output and the laser diode resistance should be 25Ω. For example, if the laser diode has a resistance of 5Ω, a 20Ω resistor should be placed in series with the laser. For optimal performance, a bypass capacitor should be placed close to the laser anode. A “snubber network” consisting of a capacitor CF and resistor RF should be placed at the laser output to minimize reflections from the laser (see Block Diagram). Suggested values for these components are 80Ω and 2pF, respectively. However, these values should be adjusted until an optical output waveform is obtained. Reducing Pattern-Dependent Jitter Three design values significantly affect pattern-dependent jitter; the capacitor at CAPC, the pull-up inductor at the output (LP), and the AC-coupling capacitor at the output (CD). As previously stated, the recommended value for the capacitor at CAPC is 0.1µF. This results in a 10kHz loop bandwidth which makes the patterndependent jitter from the APC loop negligible. For 2.5Gb/s data rates, the recommended value for CD is 0.056µF. The time constant at the output is dominated by LP. The variation in the peak voltage should be less that 12% of the average voltage over the maximum consecutive identical digit (CID) period. The following equation approximates this time constant for a CID period, t, of 100UI = 40ns: τLP = -t / ln(1-12%) = 7.8t = LP / 25Ω Therefore, the inductor LP should be a 7.8µH SMD ferrite bead inductor for this case. Input/Output Considerations Although the VSC7938 is PECL compatible, this is not required to drive the device. The inputs must only meet the common-mode voltage and differential voltage swing specifications. Power Consumption The following equation provides the device supply current (IS) in terms of quiescent current (IQ), modulation current (IMOD), and bias current (IBIAS): IS = IQ + 0.47 * IMOD + 0.15 * IBIAS For 3.3V operation, IQ is 15mA. For 5V operation, IQ is 20mA. This equation may be used to determine the estimated power dissipation: PDIS = VCC * IS For example, if the device were operated at 3.3V with a 30mA modulation current and a 10mA bias current, the supply current would be: IS = 15mA + 0.47 * 30mA + 0.15 * 10mA = 31 This corresponds to a power dissipation of 3.3V * 31mA = 102mW. Page 10 © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com G52349-0, Rev 3.0 01/20/01 VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet VSC7938 SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control Typical Operating Characteristics G52349-0, Rev 3.0 01/20/01 IMODSET vs. RMODSET IMODSET vs. RMODSET T=25°C VCC = 3.3V T=25°C VCC = 5V IBIASMAX vs. RBIASMAX IBIASMAX vs. RBIASMAX T=25°C, VCC = 3.3V T=25°C, VCC = 5V © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com Page 11 VITESSE SEMICONDUCTOR CORPORATION SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control IMD vs. RAPCSET, T=25°C, VCC = 3.3V Rise and Fall Times T=85°C, V=3.3V Page 12 Preliminary Data Sheet VSC7938 IMD vs. RAPCSET, T=25°C, VCC = 5V Monte Carlo Simulation of ICC © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com G52349-0, Rev 3.0 01/20/01 VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control VSC7938 Applications Information The following is a typical design example for the VSC7938 assuming 3.3V operation with APC. Select a Laser The Table 5 provides specifications for a typical communication-grade laser capable of operating at 2.5Gb/s. Table 6: Typical Laser Characteristics Symbol Parameter Value Units λ PAVE Wavelength Average Optical Output Power 1310 6 nm mW Ith ρMON Threshold Current Laser to Monitor Transfer 6 0.04 mA mA/mW η TC Laser Slope Efficiency Operating Temperature Range 0.4 -40 to +85 mW/mA °C Select Resistor for APCSET The monitor diode current is estimated by IMD = PAVE * ρMON = 6mW * 0.04mA/mW = 0.24mA. The IMD vs. RAPCSET in Typical Operating Characteristics shows the resistor at APCSET should be 5kΩ. Select Resistor for MODSET To ensure some minimum extinction ratio over temperature and lifetime, assume an optimal extinction ratio of 20 (13dB) at 25°C. The modulation current may be calculated from the following equation: IMOD = Pp-p / η= 2 * PAVE * (re-1) / (re+1) / η = 2 * 6mA * (20-1) / (20 + 1) / 0.4 = 27.1mA The graph of IMODSET vs. RMODSET in Typical Operating Characteristics shows the resistor for MODSET should be 8.5kΩ. Select Resistor for BIASMAX The maximum threshold current at +85°C and end of life must be determined. A graph of a typical laser’s Ith versus TC reveals a maximum threshold current of 30mA at 85 °C. Therefore, the maximum bias can be approximated by: IBIASMAX = ITH-MAX + IMOD / 2 = 30mA + 27.1mA / 2 = 43.6mA The graph of IBIASMAX vs. RBIASMAX in Typical Operating Characteristics shows the resistor for BIASMAX should be 5kΩ. Wire Bonding For best performance, gold ball-bonding techniques are recommended. Wedge bonding is not recommended. For best performance and to minimize inductance keep wire bond lengths short. PCB Layout Guidelines Use high frequency PCB layout techniques with solid ground planes to minimize crosstalk and EMI. Keep high speed traces as short as possible for signal integrity. The output traces to the laser diode must be short to minimize inductance. Short output traces will provide best performance. G52349-0, Rev 3.0 01/20/01 © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com Page 13 VITESSE SEMICONDUCTOR CORPORATION SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control Preliminary Data Sheet VSC7938 Package Information - 48 Pin TQFP 1. All dimensioning and tolerancing conform to ANSI Y14.5-1982. 2. Controlling dimension: millimeter. 3. This outline conforms to JEDEC Publication 95 Registration MS-026. Page 14 © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com G52349-0, Rev 3.0 01/20/01 VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet VSC7938 SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control Ordering Information The order number for this product is formed by a combination of the device type and package type. VSC7938 xx Device Type SONET/SDH 3.125Gb/s Laser Diode Driverwith Automatic Power Control Package RO: 48-Pin TQFP, 7x7x1.4mm W: Dice Waffle Pack Notice Vitesse Semiconductor Corporation (“Vitesse”) provides this document for informational purposes only. This document contains pre-production information about Vitesse products in their concept, development and/or testing phase. All information in this document, including descriptions of features, functions, performance, technical specifications and availability, is subject to change without notice at any time. Nothing contained in this document shall be construed as extending any warranty or promise, express or implied, that any Vitesse product will be available as described or will be suitable for or will accomplish any particular task. Vitesse products are not intended for use in life support appliances, devices or systems. Use of a Vitesse product in such applications without written consent is prohibited. G52349-0, Rev 3.0 01/20/01 © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com Page 15 VITESSE SEMICONDUCTOR CORPORATION SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control Page 16 Preliminary Data Sheet © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com VSC7938 G52349-0, Rev 3.0 01/20/01