VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control VSC7940 Features Applications • Power Supply: 5V ±5% • DC-Coupled to Laser Diode • Programmable Modulation Current: 5mA to 100mA • Programmable Bias Current: 1mA to 100mA • Enable/Disable Control • Automatic Optical Average Power Control • Modulation and Bias Current Monitors • SONET/SDH at 622Mb/s, 1.244Gb/s, 2.488Gb/s, 3.125Gb/s • Full-Speed Fibre Channel (1.062Gb/s) General Description The VSC7940 is a single 5V supply laser diode driver specially designed for SONET/SDH 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, 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 VSC7940 is available in die form or in a 32-pin TQFP package. Block Diagram VCC L AT C H IOUT+ IOUT- CF MUX DATA+ DATA- D RF SET Q VCC CLK+ CLK- CLR Q BIAS VCC VCC ENABLE MODMON BIASMON DISABLE APC MD FAIL 1nF MODSET G52357-0, Rev 3.2 05/11/01 BIASMAX CAPC 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 VSC7940 Electrical Characteristics Table 1: AC Specifications AC specifications are guaranteed by design and characterization. Typical values are for 5V operation. 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 TBD TBD ps 20% to 80% tF Output Fall Time TBD TBD 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 VSS Power Supply Voltage ICC Power Supply Current IBIAS Bias Current Range IBIAS-OFF Bias Off Current SBIAS Bias Current Stability Min Typ Max Units Conditions 4.75 5.0 5.25 V TBD 45 mA RBIASMAX=4.8kΩ IBIAS and IMOD excluded, VCC=5V 100 mA Voltage at BIAS pin=(VCC-1.6) 100 µA ENABLE=low or DISABLE=high(1) RMODSET=7.3kΩ 1 230 Bias Current Absolute Accuracy ±15 VRMD Monitor Diode Reverse Bias Voltage 1.5 IMD Monitor Diode Reverse Current Range 18 Monitor Diode Bias Setpoint Stability Monitor Diode Bias Absolute Accuracy IMOD Modulation Current Range -480 Page 2 % APC open loop. IBIAS=100mA APC open loop. IBIAS=1mA Refers to part-to-part variation V 1000 -50 480 90 µA ppm/°C IMD=1mA(2) IMD=18µA(2) -15 15 % 5 100 mA 200 µA ENABLE=low or DISABLE=high(1) % See Note 2 IMOD-OFF Modulation Off Current Modulation Current Absolute Accuracy ppm/°C 900 ±15 Refers to part-to-part variation © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com G52357-0, Rev 3.2 05/11/01 VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control VSC7940 Symbol Parameter Modulation Current Stability Min Typ Max -480 -50 480 Units ppm/°C 250 Conditions IMOD=60mA IMOD=5mA ABIAS BIASMON to IBIAS Gain 37 IBIAS/IBIASMON AMOD MODMON to IMON Gain 29 IMOD/IMODMON 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. Table 3: PECL and TTL/CMOS Input/Output Specifications Symbol VID Parameter Differential Input Voltage VICM Common-Mode Input Voltage Min Typ Max Units 1600 mVp-p (DATA+)-(DATA-) VCC 1.32 VCC VID/4 V PECL-compatible 10 mA 100 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) TTL Output High Voltage (FAIL) 2.4 TTL Output Low Voltage (FAIL) 0.1 Conditions 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 +7V 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 ............................................. -0.5V to +3.0V Voltage at OUT+, OUT- ..................................................................................................... -0.5V to (VCC + 1.5V) Voltage at BIAS .................................................................................................................. -0.5V to (VCC + 0.5V) Continuous 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).............................................................................................................................. +5V Negative Voltage Rail (GND) ............................................................................................................................ 0V Ambient Temperature Range (TA).................................................................................................. -40°C to +85°C G52357-0, Rev 3.2 05/11/01 © 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 VSC7940 Bare Die Pad Descriptions Figure 1: Pad Assignments 1773µm (0.0698") Pad 10 GND1 Pad 9 VCC1 Pad 8 CLK- Pad 7 CLK+ (Pin 7) (Pin 6) (Pin 5) Pad 11 LATCH (Pin 8) Pad 12 ENABLE (Pin 9) Pad 6 VCC1 Pad 5 GND1 Pad 4 VCC1 Pad 3 DATA- Pad 2 DATA+ Pad 1 VCC1 (Pin 4) (Pin 3) (Pin 2) (Pin 1) Pad 48 GND1 Pad 47 GND2 Pad 46 VCC2 (Pin 32) Pad 13 (Pin 10) DISABLE (Pin 31) Pad 45 BIASMAX (Pin 30) Pad 44 MODSET Pad 14 GND1 2233µm (0.0879") Pad 43 GND2 Pad 15 (Pin 11) BIASMON (Pin 29) Pad 42 APCSET Pad 16 (Pin 12) MODMON (Pin 28) Pad 41 RESERVED Pad 17 VSC7940 FAIL Pad 40 GND2 Pad 18 GND4 Pad 39 PB_GND (Pin 13) Pad 19 PB_GND (Pin 27) Pad 38 GND3 Pad 37 PB_GND Pad 20 APCFILT (Pin 14) Pad 21 GND4 (Pin 15) (Pin 26) Pad 36 CAPC Pad 22 VCC4 (Pin 16) (Pin 25) Pad 35 VCC3 Pad 23 BIAS (Pin 17) Pad 34 GND3 (Pin 18) Pad 24 PB_GND1 Die Size: Die Thickness: Pad Pitch: Pad to Pad Clearance: Pad Passivation Opening: Page 4 20µm (0.0008") Pad 25 VCC4 Pad 26 DB_OUT+ (Pin 19) (Pin 20) Pad 27 OUT+ Pad 28 OUT- Pad 29 DB_OUT- (Pin 21) (Pin 22) (Pin 23) (Pin 24) Pad 30 VCC4 Pad 31 GND4 Pad 32 GND3 Pad 33 MD 1773µm x 2233µm (0.0698" x 0.0879") 625µm (0.0246") 115µm (0.0045") 20µm (0.0008") 95µm x 95µm (0.0037" x 0.0037") µ © 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") G52357-0, Rev 3.2 05/11/01 VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control VSC7940 Table 4: Pad Coordinates Signal Name VCC1 Pad No. 1 Coordinates (µm) X Y (Pin 1) 1211.025 1995.05 Signal Name VCC4 Coordinates (µm) Pad No. 25 X Y (Pin 18) 406.025 80.95 521.025 80.95 636.025 80.95 DATA+ 2 (Pin 2) 1096.025 1995.05 DB_OUT+ 26 DATA- 3 (Pin 3) 981.025 1995.05 OUT+ 27 (Pin 19) VCC1 4 (Pin 4) 866.025 1995.05 OUT– 28 (Pin 20) GND1 5 751.025 1995.05 DB_OUT– 29 VCC1 6 636.025 1995.05 VCC4 30 CLK+ 7 (Pin 5) 521.025 1995.05 GND4 31 751.025 80.95 866.025 80.95 (Pin 21) 981.025 80.95 (Pin 22) 1096.025 80.95 CLK- 8 (Pin 6) 406.025 1995.05 GND3 32 (Pin 23) 1211.025 80.95 VCC1 9 (Pin 7) 291.025 1995.05 MD 33 (Pin 24) 1326.025 80.95 GND1 10 80.95 1784.975 GND3 34 1535.05 289.975 LATCH 11 (Pin 8) 80.95 1669.975 VCC3 35 (Pin 25) 1535.05 404.975 ENABLE 12 (Pin 9) 80.95 1554.975 CAPC 36 (Pin 26) 1535.05 519.975 DISABLE 13 (Pin 10) 80.95 1439.975 PB_GND 37 1535.05 634.975 GND1 14 80.95 1324.975 GND3 38 BIASMON 15 (Pin 11) 80.95 1209.975 PB_GND 39 (Pin 27) 1535.05 749.975 1535.05 864.975 MODMON 16 (Pin 12) 80.95 1094.975 GND2 40 1535.05 979.975 FAIL 17 (Pin 13) 80.95 979.975 RESERVED 41 (Pin 28) 1535.05 1094.975 GND4 18 80.95 864.975 APCSET 42 (Pin 29) 1535.05 1209.975 PB_GND 19 80.95 749.975 GND2 43 1535.05 1324.975 APCFILT 20 (Pin 14) 80.95 634.975 MODSET 44 (Pin 30) 1535.05 1439.975 GND4 21 (Pin 15) 80.95 519.975 BIASMAX 45 (Pin 31) 1535.05 1554.975 (Pin 32) VCC4 22 (Pin 16) 80.95 404.975 VCC2 46 1535.05 1669.975 BIAS 23 (Pin 17) 80.95 289.975 GND2 47 1535.05 1784.975 PB_GND 24 291.025 80.95 GND1 48 1336.025 1995.05 G52357-0, Rev 3.2 05/11/01 © 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 VSC7940 Package Pin Description VCC BIASMAX MODSET APCSET RESERVED GND CAPC VCC 32 31 30 29 28 27 26 25 Figure 2: Pin Diagram VCC 1 24 MD DATA+ 2 23 GND DATA- 3 22 GND 21 VCC 20 OUT- VCC 4 CLK- 5 CLK+ 6 19 OUT+ VCC 7 18 VCC LATCH 8 17 BIAS Page 6 10 11 12 13 14 15 16 DISABLE BIASMON MODMON FAIL APCFILT GND VCC ENABLE 9 VSC7940 © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com G52357-0, Rev 3.2 05/11/01 VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet VSC7940 SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control Table 5: Pin Identifications Pin Name Pin Number GND 10, 15, 22, 23, 27 VCC 1, 4, 7, 16, 18, 21, 25, 32 Description Ground Power Supply DATA+ 2 Positive Data Input (PECL) DATA- 3 Negative Data Input (PECL) CLK+ 5 Positive Clock Input (PECL). Connect to VCC if LATCH function is not used. CLK- 6 Negative Clock Input (PECL). Leave unconnected if LATCH function is not used. LATCH 8 Latch Input (TTL/CMOS). Connect to VCC for data retiming and GND for direct data. ENABLE 9 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 10 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. BIASMON 11 Bias Current Monitor. Sink current source that is proportional to the laser bias current. MODMON 12 Modulation Current Monitor. Sink current source that is proportional to the laser modulation current. FAIL 13 Output (TTL/CMOS). When low, indicates APC failure. APCFILT 14 No effect on device operation. BIAS 17 Laser Bias Current Output OUT+ 19 Positive Modulation-Current Output. IMOD flows when input data is high. OUT- 20 Negative Modulation-Current Output. IMOD flows when input data is low. MD 24 Monitor Diode Input. Connect to monitor photodiode anode. Connect capacitor to GND to filter high-speed AC monitor photocurrent. CAPC 26 Capacitor to GND sets dominant pole of the APC feedback loop. RESERVED 28 Do not connect. APCSET 29 Resistor to GND sets desired average optical power. If APC is not used, connect 100kΩ resistor to GND. MODSET 30 Connect resistor to GND to set desired modulation current. BIASMAX 31 Connect resistor to GND to set maximum bias current. The APC function can subtract from this value, but cannot add to it. G52357-0, Rev 3.2 05/11/01 © 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 VSC7940 Detailed Description The VSC7940 is a high-speed laser driver with Automatic Power Control. The device is designed to operate up to 3.125Gb/s with a 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 100mA into the laser with typical rise and fall times of 60ps. The VSC7940 is designed to be DC-coupled. The key features of the VSC7940 are its Automatic Power Control, low power supply current, and fast rise and fall times. The VSC7938 and VSC7939 are similar Vitesse laser drivers designed for 60mA maximum output modulation currents. These laser drivers may be powered from a 3.3V or 5V supply and may be AC- or DC-coupled to the laser diode. The VSC7939 is available in the same 32-pin TQFP package as the VSC7940. The VSC7938 is available in a 48-pin TQFP package. Automatic Power Control To ensure constant average optical power, the VSC7940 utilizes an Automatic Power Control (APC) 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 VSC7940 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. Modulation and Bias Current Monitors The VSC7940 provides monitoring of the modulation and bias currents vias BIASMON and MODMON. These pins sink a current proportional to the actual modulation and bias currents. MODMON sinks approximately 1/29th of the amount of modulation current and BIASMON sink approximately 1/37th of the amount of the bias current. These pins should be tied through a pull-up resistor to VCC. The resistors must be chosen such that the voltage at MODMON is greater than VCC - 1.0V and the voltage at BIASMON is greater than VCC 1.6V. 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 G52357-0, Rev 3.2 05/11/01 VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet VSC7940 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 to within approximately 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 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 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 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. G52357-0, Rev 3.2 05/11/01 © 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 VSC7940 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 VSC7940 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 = 19mA + 0.4 * IMOD + 0.16 * IBIAS This equation may be used to determine the estimated power dissipation: PDIS = VCC * IS For example, if the device were operated at 5V with a 30mA modulation current and a 10mA bias current, the supply current would be: IS = 19mA + 0.4 * 30mA + 0.16 * 10mA = 33mA This corresponds to a power dissipation of 5V * 33mA = 165mW.P 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 G52357-0, Rev 3.2 05/11/01 VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet VSC7940 SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control Typical Operating Characteristics IBIASMAX vs. RBIASMAX IMOD vs. RMODSET T=25°C, VCC = 5V T=25°C VCC = 5V IMD vs. RAPCSET, T=25°C, VCC = 5V G52357-0, Rev 3.2 05/11/01 © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com Page 11 VITESSE SEMICONDUCTOR CORPORATION SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control Preliminary Data Sheet VSC7940 Applications Information The following is a typical design example for the VSC7940 assuming 5V operation with APC. Select a Laser The Table 8 provides specifications for a typical communication-grade laser capable of operating at 2.5Gb/s. Table 6: Typical Laser Characteristics Symbol Parameter Value Units 1310 nm λ Wavelength PAVE Average Optical Output Power 6 mW Ith Threshold Current 6 mA ρMON Laser to Monitor Transfer 0.04 mA/mW η Laser Slope Efficiency 0.4 mW/mA TC Operating Temperature Range -40 to +85 °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. Page 12 © VITESSE SEMICONDUCTOR CORPORATION • 741 Calle Plano • Camarillo, CA 93012 Tel: (800) VITESSE • FAX: (805) 987-5896 • Email: [email protected] Internet: www.vitesse.com G52357-0, Rev 3.2 05/11/01 VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control VSC7940 Select Resistors for MODMON and BIASMON Assuming the modulation and bias currents never exceed 120mA, the following equations provide values for the resistor at MODMON, RMODMON, and the resistor at BIASMON, RBIASMON: RMODMON = 1V * 28 / 120mA = 233Ω RBIASMON = 1.6V * 35 / 120mA = 467Ω Standard values for these values are RMODMON = 232Ω and RBIASMON = 464Ω. A voltage of 4.8V at MODMON would indicate a modulation current of: IMOD = (5.2V - 4.8V) * 28 / 232mA = 48mA 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. G52357-0, Rev 3.2 05/11/01 © 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 VSC7940 Package Information - 32 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 G52357-0, Rev 3.2 05/11/01 VITESSE SEMICONDUCTOR CORPORATION Preliminary Data Sheet SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control VSC7940 Ordering Information The order number for this product is formed by a combination of the device type and package type. VSC7940 Device Type SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control xx Package RP: 32-Pin TQFP W: Dice Waffle Pack otice itesse Semiconductor Corporation (“Vitesse”) provides this document for informational purposes only. This document contains pre-production information bout Vitesse products in their concept, development and/or testing phase. All information in this document, including descriptions of features, functions, erformance, technical specifications and availability, is subject to change without notice at any time. Nothing contained in this document shall be construed s 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 ny particular task. itesse products are not intended for use in life support appliances, devices or systems. Use of a Vitesse product in such applications without written consent s prohibited. G52357-0, Rev 3.2 05/11/01 © 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 VSC7940 G52357-0, Rev 3.2 05/11/01