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VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7940
Features
SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control
Applications
* SONET/SDH at 622Mb/s, 1.244Gb/s, 2.488Gb/s, 3.125Gb/s * Full-Speed Fibre Channel (1.062Gb/s)
* 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
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+ IOUTMUX DATA+ DATACLK+ CLKCLR Q BIAS SET Q
CF RF VCC
D
VCC
ENABLE DISABLE
VCC
MODMON BIASMON APC MD FAIL 1nF MODSET BIASMAX CAPC APCSET
G52357-0, Rev 3.2 05/11/01
(c) VITESSE SEMICONDUCTOR CORPORATION * 741 Calle Plano * Camarillo, CA 93012 Tel: (800) VITESSE * FAX: (805) 987-5896 * Email: prodinfo@vitesse.com Internet: www.vitesse.com
Page 1
VITESSE
SEMICONDUCTOR CORPORATION
SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control
Preliminary Data Sheet
VSC7940
Electrical Characteristics
Table 1: AC Specifications
AC specifications are guaranteed by design and characterization. Typical values are for 5V operation.
Symbol
tSU tH
Parameter
Input Latch Setup Time Input Latch Hold Time Enable/Start-up Delay
Min
100 100
Typ
Max
Units
ps ps
Conditions
LATCH=high LATCH=high
250 TBD TBD 10 80 7 20 TBD TBD 50
ns ps ps ps bits psp-p Jitter BW=12kHz to 20MHz, 0-1 pattern. 20% to 80% 20% to 80% See Notes 1, 2
tR tF PWD CIDMAX tJ
Output Rise Time Output Fall Time Pulse Width Distortion Maximum Consecutive Identical Digits Jitter Generation
NOTES: (1) Measured with 622Mb/s 0-1 pattern, LATCH=high. (2) PWD = (wider pulse - narrower pulse) / 2).
Table 2: DC Specifications Symbol
VSS ICC IBIAS IBIAS-OFF SBIAS
Parameter
Power Supply Voltage Power Supply Current Bias Current Range Bias Off Current Bias Current Stability Bias Current Absolute Accuracy
Min
4.75
Typ
5.0 TBD
Max
5.25 45 100 100
Units
V
Conditions
RMODSET=7.3k mA mA A ppm/C % V 1000 -50 90 -15 5 15 100 200 15 480 A ppm/C % mA A % ENABLE=low or DISABLE=high(1) See Note 2 IMD=1mA(2) IMD=18A(2) Refers to part-to-part variation RBIASMAX=4.8k IBIAS and IMOD excluded, VCC=5V Voltage at BIAS pin=(VCC-1.6) ENABLE=low or DISABLE=high(1) APC open loop. IBIAS=100mA APC open loop. IBIAS=1mA Refers to part-to-part variation
1
230 900 15 1.5 18 -480
VRMD IMD
Monitor Diode Reverse Bias Voltage Monitor Diode Reverse Current Range Monitor Diode Bias Setpoint Stability Monitor Diode Bias Absolute Accuracy
IMOD
Modulation Current Range
IMOD-OFF Modulation Off Current Modulation Current Absolute Accuracy
Page 2
(c) VITESSE SEMICONDUCTOR CORPORATION * 741 Calle Plano * Camarillo, CA 93012 Tel: (800) VITESSE * FAX: (805) 987-5896 * Email: prodinfo@vitesse.com Internet: www.vitesse.com
G52357-0, Rev 3.2 05/11/01
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7940
Symbol Parameter
Modulation Current Stability ABIAS AMOD BIASMON to IBIAS Gain MODMON to IMON Gain
SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control
Min
-480
Typ
-50 250 37 29
Max
480
Units
ppm/C
Conditions
IMOD=60mA IMOD=5mA IBIAS/IBIASMON 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 VICM IIN VIH VIL
Parameter
Differential Input Voltage Common-Mode Input Voltage Clock and Data Input Current TTL Input High Voltage (ENABLE, LATCH) TTL Input Low Voltage (ENABLE, LATCH) TTL Output High Voltage (FAIL) TTL Output Low Voltage (FAIL)
Min
100 VCC 1.49 -1 2.0
Typ
VCC 1.32
Max
1600 VCC VID/4 10 0.8
Units
mVp-p V mA V V V V
Conditions
(DATA+)-(DATA-) PECL-compatible
2.4 0.1
VCC 0.3
VCC 0.44
Sourcing 50A Sinking 100A
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 = +85C, TQFP derate 20.8mW/C above +85C) .........................1350mW Operating Junction Temperature Range ...................................................................................... -55C to +150C Storage Temperature Range ........................................................................................................ -65C to +165C
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).................................................................................................. -40C to +85C
G52357-0, Rev 3.2 05/11/01
(c) VITESSE SEMICONDUCTOR CORPORATION * 741 Calle Plano * Camarillo, CA 93012 Tel: (800) VITESSE * FAX: (805) 987-5896 * Email: prodinfo@vitesse.com Internet: www.vitesse.com
Page 3
VITESSE
SEMICONDUCTOR CORPORATION
SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control
Preliminary Data Sheet
VSC7940
Bare Die Pad Descriptions
Figure 1: Pad Assignments
1773m (0.0698")
Pad 9 VCC1 Pad 10 GND1 Pad 11 LATCH Pad 12 ENABLE (Pin 7)
Pad 8 CLK(Pin 6)
Pad 7 CLK+ (Pin 5)
Pad 6 VCC1
Pad 5 GND1
Pad 4 VCC1 (Pin 4)
Pad 3 DATA(Pin 3)
Pad 2 DATA+ (Pin 2)
Pad 1 VCC1 (Pin 1)
Pad 48 GND1 Pad 47 GND2 Pad 46 VCC2 Pad 45 BIASMAX Pad 44 MODSET Pad 43 GND2 (Pin 29) Pad 42 APCSET Pad 41 RESERVED Pad 40 GND2 Pad 39 PB_GND (Pin 27) Pad 38 GND3 Pad 37 PB_GND (Pin 26) Pad 36 CAPC Pad 35 VCC3 Pad 34 GND3
(Pin 8)
(Pin 32)
20m (0.0008")
(Pin 9)
(Pin 31)
Pad 13 (Pin 10) DISABLE Pad 14 GND1 Pad 15 (Pin 11) BIASMON Pad 16 (Pin 12) MODMON
(Pin 30)
(Pin 28)
2233m (0.0879")
VSC7940
Pad 17 FAIL Pad 18 GND4 Pad 19 PB_GND
(Pin 13)
Pad 20 APCFILT (Pin 14) Pad 21 GND4 Pad 22 VCC4 Pad 23 BIAS (Pin 15)
(Pin 16)
(Pin 25)
(Pin 17) (Pin 18) Pad 24 PB_GND1 Pad 25 VCC4 Pad 26 DB_OUT+ (Pin 19) Pad 27 OUT+ (Pin 20) Pad 28 OUTPad 29 DB_OUT(Pin 21) Pad 30 VCC4 (Pin 22) Pad 31 GND4 (Pin 23) Pad 32 GND3 (Pin 24) Pad 33 MD
Die Size: Die Thickness: Pad Pitch: Pad to Pad Clearance: Pad Passivation Opening:
1773m x 2233m (0.0698" x 0.0879") 625m (0.0246") 115m (0.0045") 20m (0.0008") 95m x 95m (0.0037" x 0.0037")
75m (0.0030")
Page 4
(c) VITESSE SEMICONDUCTOR CORPORATION * 741 Calle Plano * Camarillo, CA 93012 Tel: (800) VITESSE * FAX: (805) 987-5896 * Email: prodinfo@vitesse.com Internet: www.vitesse.com
G52357-0, Rev 3.2 05/11/01
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7940
Table 4: Pad Coordinates Signal Name
VCC1 DATA+ DATAVCC1 GND1 VCC1 CLK+ CLKVCC1 GND1 LATCH ENABLE DISABLE GND1 BIASMON MODMON FAIL GND4 PB_GND APCFILT GND4 VCC4 BIAS PB_GND 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 (Pin 14) (Pin 15) (Pin 16) (Pin 17) (Pin 11) (Pin 12) (Pin 13) (Pin 8) (Pin 9) (Pin 10) (Pin 5) (Pin 6) (Pin 7)
SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control
Pad No.
(Pin 1) (Pin 2) (Pin 3) (Pin 4)
Coordinates (m) X
1211.025 1096.025 981.025 866.025 751.025 636.025 521.025 406.025 291.025 80.95 80.95 80.95 80.95 80.95 80.95 80.95 80.95 80.95 80.95 80.95 80.95 80.95 80.95 291.025
Y
1995.05 1995.05 1995.05 1995.05 1995.05 1995.05 1995.05 1995.05 1995.05 1784.975 1669.975 1554.975 1439.975 1324.975 1209.975 1094.975 979.975 864.975 749.975 634.975 519.975 404.975 289.975 80.95
Signal Name
VCC4 DB_OUT+ OUT+ OUT- DB_OUT- VCC4 GND4 GND3 MD GND3 VCC3 CAPC PB_GND GND3 PB_GND GND2 RESERVED APCSET GND2 MODSET BIASMAX VCC2 GND2 GND1 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48
Pad No.
(Pin 18) (Pin 19) (Pin 20) (Pin 21) (Pin 22) (Pin 23) (Pin 24) (Pin 25) (Pin 26) (Pin 27)
Coordinates (m) X
406.025 521.025 636.025 751.025 866.025 981.025 1096.025 1211.025 1326.025 1535.05 1535.05 1535.05 1535.05 1535.05 1535.05 1535.05
Y
80.95 80.95 80.95 80.95 80.95 80.95 80.95 80.95 80.95 289.975 404.975 519.975 634.975 749.975 864.975 979.975 1094.975 1209.975 1324.975 1439.975 1554.975 1669.975 1784.975 1995.05
(Pin 28) (Pin 29) (Pin 30) (Pin 31) (Pin 32)
1535.05 1535.05 1535.05 1535.05 1535.05 1535.05 1535.05 1336.025
G52357-0, Rev 3.2 05/11/01
(c) VITESSE SEMICONDUCTOR CORPORATION * 741 Calle Plano * Camarillo, CA 93012 Tel: (800) VITESSE * FAX: (805) 987-5896 * Email: prodinfo@vitesse.com Internet: www.vitesse.com
Page 5
VITESSE
SEMICONDUCTOR CORPORATION
SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control
Preliminary Data Sheet
VSC7940
Package Pin Description
Figure 2: Pin Diagram
RESERVED
BIASMAX
MODSET
APCSET
CAPC 26
GND
VCC
32
31
30
29
28
27
VCC DATA+ DATAVCC CLKCLK+ VCC LATCH
1 2 3 4 5 6 7 8
25
VCC
24 23 22 21
MD GND GND VCC OUTOUT+ VCC BIAS
VSC7940
20 19 18 17
9
10
11
12
13
14
15 GND
MODMON
FAIL
ENABLE
DISABLE
BIASMON
Page 6
(c) VITESSE SEMICONDUCTOR CORPORATION * 741 Calle Plano * Camarillo, CA 93012 Tel: (800) VITESSE * FAX: (805) 987-5896 * Email: prodinfo@vitesse.com Internet: www.vitesse.com
APCFILT
VCC
16
G52357-0, Rev 3.2 05/11/01
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7940
Table 5: Pin Identifications Pin Name
GND VCC DATA+ DATACLK+ CLKLATCH ENABLE DISABLE BIASMON MODMON FAIL APCFILT BIAS OUT+ OUTMD CAPC RESERVED APCSET MODSET BIASMAX
SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control
Pin Number
10, 15, 22, 23, 27 1, 4, 7, 16, 18, 21, 25, 32 2 3 5 6 8 9 10 11 12 13 14 17 19 20 24 26 28 29 30 31 Ground Power Supply Positive Data Input (PECL) Negative Data Input (PECL)
Description
Positive Clock Input (PECL). Connect to VCC if LATCH function is not used. Negative Clock Input (PECL). Leave unconnected if LATCH function is not used. Latch Input (TTL/CMOS). Connect to VCC for data retiming and GND for direct data. 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 Input (TTL/CMOS). If used, leave ENABLE pin floating. Connect to GND for normal operation and VCC to disable laser bias and modulation currents. Bias Current Monitor. Sink current source that is proportional to the laser bias current. Modulation Current Monitor. Sink current source that is proportional to the laser modulation current. Output (TTL/CMOS). When low, indicates APC failure. No effect on device operation. Laser Bias Current Output Positive Modulation-Current Output. IMOD flows when input data is high. Negative Modulation-Current Output. IMOD flows when input data is low. Monitor Diode Input. Connect to monitor photodiode anode. Connect capacitor to GND to filter high-speed AC monitor photocurrent. Capacitor to GND sets dominant pole of the APC feedback loop. Do not connect. Resistor to GND sets desired average optical power. If APC is not used, connect 100k resistor to GND. Connect resistor to GND to set desired modulation current. 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
(c) VITESSE SEMICONDUCTOR CORPORATION * 741 Calle Plano * Camarillo, CA 93012 Tel: (800) VITESSE * FAX: (805) 987-5896 * Email: prodinfo@vitesse.com 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 0.1F. 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 (0.1F) and a resistor must be connected at APCSET to set the average optical power. For open-loop operation (no APC), a 100k 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
(c) VITESSE SEMICONDUCTOR CORPORATION * 741 Calle Plano * Camarillo, CA 93012 Tel: (800) VITESSE * FAX: (805) 987-5896 * Email: prodinfo@vitesse.com 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 is the laser slope efficiency:
IMOD = Pp-p / = 2 * PAVE * (re-1) / (re+1) / 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 25C. 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 25C. 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 85C 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, MON, for a specific laser using the following equation: IMD = PAVE * MON 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 25. For example, if the laser diode has a resistance of 5, a 20 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 80 and 2pF, respectively, however, these values should be adjusted until an optical output waveform is obtained.
G52357-0, Rev 3.2 05/11/01
(c) VITESSE SEMICONDUCTOR CORPORATION * 741 Calle Plano * Camarillo, CA 93012 Tel: (800) VITESSE * FAX: (805) 987-5896 * Email: prodinfo@vitesse.com 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 0.1F. 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 0.056F. 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: LP = -t / ln(1-12%) = 7.8t = LP / 25
Therefore, the inductor LP should be a 7.8H 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
(c) VITESSE SEMICONDUCTOR CORPORATION * 741 Calle Plano * Camarillo, CA 93012 Tel: (800) VITESSE * FAX: (805) 987-5896 * Email: prodinfo@vitesse.com Internet: www.vitesse.com
G52357-0, Rev 3.2 05/11/01
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7940
IBIASMAX vs. RBIASMAX
T=25C, VCC = 5V
SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control
Typical Operating Characteristics
IMOD vs. RMODSET
T=25C VCC = 5V
IMD vs. RAPCSET, T=25C, VCC = 5V
G52357-0, Rev 3.2 05/11/01
(c) VITESSE SEMICONDUCTOR CORPORATION * 741 Calle Plano * Camarillo, CA 93012 Tel: (800) VITESSE * FAX: (805) 987-5896 * Email: prodinfo@vitesse.com 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
PAVE Ith MON TC Wavelength Average Optical Output Power Threshold Current Laser to Monitor Transfer Laser Slope Efficiency Operating Temperature Range
Parameter
Value
1310 6 6 0.04 0.4 -40 to +85
Units
nm mW mA mA/mW mW/mA C
Select Resistor for APCSET The monitor diode current is estimated by IMD = PAVE * MON = 6mW * 0.04mA/mW = 0.24mA. The IMD vs. RAPCSET in Typical Operating Characteristics shows the resistor at APCSET should be 5k. Select Resistor for MODSET To ensure some minimum extinction ratio over temperature and lifetime, assume an optimal extinction ratio of 20 (13dB) at 25C. The modulation current may be calculated from the following equation:
IMOD = Pp-p / = 2 * PAVE * (re-1) / (re+1) / = 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 8.5k.
Select Resistor for BIASMAX The maximum threshold current at +85C 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 85C. 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 5k.
Page 12
(c) VITESSE SEMICONDUCTOR CORPORATION * 741 Calle Plano * Camarillo, CA 93012 Tel: (800) VITESSE * FAX: (805) 987-5896 * Email: prodinfo@vitesse.com 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
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 = 233 RBIASMON = 1.6V * 35 / 120mA = 467 Standard values for these values are RMODMON = 232 and RBIASMON = 464. 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
(c) VITESSE SEMICONDUCTOR CORPORATION * 741 Calle Plano * Camarillo, CA 93012 Tel: (800) VITESSE * FAX: (805) 987-5896 * Email: prodinfo@vitesse.com Internet: www.vitesse.com
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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
(c) VITESSE SEMICONDUCTOR CORPORATION * 741 Calle Plano * Camarillo, CA 93012 Tel: (800) VITESSE * FAX: (805) 987-5896 * Email: prodinfo@vitesse.com Internet: www.vitesse.com
G52357-0, Rev 3.2 05/11/01
VITESSE
SEMICONDUCTOR CORPORATION
Preliminary Data Sheet
VSC7940
Ordering Information
SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control
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
(c) VITESSE SEMICONDUCTOR CORPORATION * 741 Calle Plano * Camarillo, CA 93012 Tel: (800) VITESSE * FAX: (805) 987-5896 * Email: prodinfo@vitesse.com Internet: www.vitesse.com
Page 15
VITESSE
SEMICONDUCTOR CORPORATION
SONET/SDH 3.125Gb/s Laser Diode Driver with Automatic Power Control
Preliminary Data Sheet
VSC7940
Page 16
(c) VITESSE SEMICONDUCTOR CORPORATION * 741 Calle Plano * Camarillo, CA 93012 Tel: (800) VITESSE * FAX: (805) 987-5896 * Email: prodinfo@vitesse.com Internet: www.vitesse.com
G52357-0, Rev 3.2 05/11/01

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