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vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control g52350-0, rev 3.2 page 1 02/26/01 ? vitesse semiconductor corporation ? 741 calle plano camarillo, ca 93012 tel: (800) vitesse fax: (805) 987-5896 email: prodinfo@vitesse.com internet: www.vitesse.com features applications general description the vsc7939 is a single 3.3v or 5v supply laser diode driver specially designed for sonet/sdh applica- tions 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 con- trolled 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 vsc7939 is available in die form or in a 32-pin tqfp package. block diagram ? 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 3.3v operation q set clr q d mux apc bias iout+ iout- md modset biasmax capc apcset fail latch 1nf modmon biasmon data + data - clk+ clk- enable disable c d l p l p v cc v cc v cc v cc c f r f sonet/sdh at 622mb/s, 1.244gb/s, 2.488gb/s, 3.125gb/s full-speed fibre channel (1.062gb/s)
vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control page 2 g52350-0, rev 3.2 02/26/01 ? vitesse semiconductor corporation 741 calle plano camarillo, ca 93012 tel: (800) vitesse fax: (805) 987-5896 email: prodinfo@vitesse.com internet: www.vitesse.com electrical characteristics table 1: ac specifications ac specifications are guaranteed by design and characterization. typical values are for 3.3v. notes: (1) measured with 622mb/s 0-1 pattern, latch=high. (2) pwd = (wider pulse - narrower pulse) / 2). table 2: dc specifications symbol parameter min typ max units conditions t su input latch setup time 100 ps latch=high t h input latch hold time 100 ps latch=high enable/start-up delay 250 ns t r output rise time 60 80 ps 20% to 80% t f output fall time 60 80 ps 20% to 80% pwd pulse width distortion 10 50 ps see notes 1, 2 cid max maximum consecutive identical digits 80 bits t j jitter generation 7 20 ps p-p jitter bw=12khz to 20mhz, 0-1 pattern. symbol parameter min typ max units conditions i cc supply current tbd 45 ma r modset =7.3k ? r biasmax =4.8k ? i bias and i mod excluded v cc =5v i bias bias current range 1 100 ma voltage at bias pin=(v cc -1.6) i bias-off bias off current 100 a enable=low or disable=high (1) s bias bias current stability 230 ppm/ c apc open loop. i bias =100ma 900 apc open loop. i bias =1ma bias current absolute accuracy 15 % refers to part-to-part variation vr md monitor diode reverse bias voltage 1.5 v i md monitor diode reverse current range 18 1000 a monitor diode bias setpoint stability -480 -50 480 ppm/ c i md =1ma (2) 90 i md =18 a (2) monitor diode bias absolute accuracy -15 15 % refers to part-to-part variation i mod modulation current range 5 60 ma i mod-off modulation off current 200 a enable=low or disable=high (1)
vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control g52350-0, rev 3.2 page 3 02/26/01 ? vitesse semiconductor corporation 741 calle plano camarillo, ca 93012 tel: (800) vitesse fax: (805) 987-5896 email: prodinfo@vitesse.com internet: www.vitesse.com notes: (1) both i bias and i mod will turn off if any of the current set pins are grounded. (2) assumes laser diode to monitor diode transfer func- tion does not change with temperature. table 3: pecl and ttl/cmos inputs and outputs specifications modulation current absolute accuracy 15 % see note 2 modulation current stability -480 -50 480 ppm/ c i mod =60ma 250 i mod =5ma a bias biasmon to i bias gain 37 a/a i bias /i biasmon a mod modmon to i mon gain 29 a/a i mod /i modmon symbol parameter min typ max units conditions v id differential input voltage 100 1600 mv p-p (data+)-(data-) v icm common-mode input voltage v cc - 1.49 v cc - 1.32 v cc - v id /4 v pecl-compatible i in clock and data input current -1 10 a v ih ttl input high voltage (enable, latch) 2.0 v v il ttl input low voltage (enable, latch) 0.8 v ttl output high voltage (fail )2.4 v cc - 0.3 v cc v sourcing 50a ttl output low voltage (fail ) 0.1 0.44 v sinking 100a symbol parameter min typ max units conditions
vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control page 4 g52350-0, rev 3.2 02/26/01 ? vitesse semiconductor corporation 741 calle plano camarillo, ca 93012 tel: (800) vitesse fax: (805) 987-5896 email: prodinfo@vitesse.com internet: www.vitesse.com absolute maximum ratings (1) power supply voltage (v cc )............................................................................................................. -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 (v cc + 0.5v) voltage at apcfilt, modset, biasmax, apcset, md, fail ............................................. -0.5v to +3.0v voltage at out+, out- ..................................................................................................... -0.5v to (v cc + 1.5v) voltage at bias ................................................................................................................ .. -0.5v to (v cc + 0.5v) continouous power dissipation (t a = +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 caus- ing 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 (v cc )..................................................................................................... +3.135v to +5.25v negative voltage rail (gnd) .................................................................................................... ........................0v modulation current (i mod ) (1) .......................................................................................................................30ma ambient temperature range (t a )................................................................................................. -40 c to +85 c note: (1) v cc = 3.3v, i bias = 60ma.
vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control g52350-0, rev 3.2 page 5 02/26/01 ? vitesse semiconductor corporation 741 calle plano camarillo, ca 93012 tel: (800) vitesse fax: (805) 987-5896 email: prodinfo@vitesse.com internet: www.vitesse.com bare die pad descriptions figure 1: pad assignments vsc7939 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 1 gnd2 pad 48 vcc2 pad 47 biasmax 20 m (0.0008") 1773 m (0.0698") (pin 1) (pin 2) (pin 3) (pin 4) (pin 5) (pin 6) (pin 18) (pin 19) (pin 20) (pin 21) (pin 22) (pin 23) (pin 24) (pin 25) (pin 26) (pin 27) (pin 28) (pin 29) (pin 31) (pin 30) (pin 32) (pin 7) (pin 8) (pin 9) (pin 10) (pin 11) (pin 12) (pin 13) (pin 14) (pin 15) (pin 16) (pin 17) pad 46 modset pad 45 gnd2 pad 44 apcset pad 43 reserved pad 42 gnd3 pad 41 pb_gnd pad 40 gnd3 pad 39 pb_gnd pad 38 capc pad 37 vcc3 pad 36 gnd3 pad 12 gnd1 pad 13 latch pad 14 enable pad 15 disable pad 16 gnd1 pad 17 biasmon pad 18 modmon pad 19 fail pad 20 gnd4 pad 21 pb_gnd pad 22 apcfilt pad 23 gnd4 pad 24 vcc4 pad 25 bias pad 11 vcc1 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 pad 26 pb_gnd1 die size: 1773m x 2233m (0.0698" x 0.0879") die thickness: 625 m (0.0246 " ) pad pitch: 115 m (0.0045 " ) pad size: 95m x 95m (0.0037 " x 0.0037 " ) pad to pad clearance: 20m (0.0008 " ) pad passivation opening: 95m x 95m (0.0037 " x 0.0037 " ) scribe size: 75m (0.0030 " ) 2233 m (0.0879") 75 m (0.0030")
vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control page 6 g52350-0, rev 3.2 02/26/01 ? vitesse semiconductor corporation 741 calle plano camarillo, ca 93012 tel: (800) vitesse fax: (805) 987-5896 email: prodinfo@vitesse.com internet: www.vitesse.com table 4: pad coordinates signal name pad no. coordinates (m) signal name pad no. coordinates (m) x y x y gnd2 1 1613.55 1863.475 bias 25 (pin 17) 159.45 368.475 gnd1 2 1414.525 2073.55 pb_gnd 26 369.525 159.45 vcc1 3 (pin 1) 1289.525 2073.55 vcc4 27 (pin 18) 484.525 159.45 data+ 4 (pin 2) 1174.525 2073.55 db_out+ 28 599.525 159.45 data- 5 (pin 3) 1059.525 2073.55 out+ 29 (pin 19) 714.525 159.45 vcc1 6 (pin 4) 944.525 2073.55 out ? 30 (pin 20) 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 (pin 21) 1059.525 159.45 clk+ 9 (pin 5) 599.525 2073.55 gnd4 33 (pin 22) 1174.525 159.45 clk- 10 (pin 6) 484.525 2073.55 gnd3 34 (pin 23) 1289.525 159.45 vcc1 11 (pin 7) 369.525 2073.55 md 35 (pin 24) 1404.525 159.45 gnd1 12 159.45 1863.475 gnd3 36 1613.55 368.475 latch 13 (pin 8) 159.45 1748.475 vcc3 37 (pin 25) 1613.55 483.475 enable 14 (pin 9) 159.45 1633.475 capc 38 (pin 26) 1613.55 598.475 disable 15 (pin 10) 159.45 1518.475 pb_gnd 39 1613.55 713.475 gnd 16 159.45 1403.4 gnd3 40 (pin 27) 1613.55 828.475 biasmon 17 (pin 11) 159.45 1288.475 pb_gnd 41 1613.55 943.475 modmon 18 (pin 12) 159.45 1058.475 gnd3 42 1613.55 1058.475 fail 19 (pin 13) 159.45 1058.475 reserved 43 (pin 28) 1613.55 1173.475 gnd4 20 159.45 943.475 apcset 44 (pin 29) 1613.55 1288.475 pb_gnd 21 159.45 828.475 gnd2 45 1613.55 1403.475 apcfilt 22 (pin 14) 159.45 713.475 modset 46 (pin 30) 1613.55 1518.475 gnd4 23 (pin 15) 159.45 598.475 biasmax 47 (pin 31) 1613.55 1633.475 vcc4 24 (pin 16) 159.45 483.475 vcc2 48 (pin 32) 1613.55 1748.475
vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control g52350-0, rev 3.2 page 7 02/26/01 ? vitesse semiconductor corporation 741 calle plano camarillo, ca 93012 tel: (800) vitesse fax: (805) 987-5896 email: prodinfo@vitesse.com internet: www.vitesse.com package pin description figure 2: pin diagram 1 2 3 4 5 6 7 8 vcc data + data - vcc clk- clk+ vcc latch md gnd gnd vcc out- out+ vcc bias 9 10 11 12 13 14 15 16 enable disable biasmon modmon fail apcfilt gnd vcc vcc biasmax modset apcset reserved gnd capc vcc 32 31 30 29 28 27 26 25 24 23 22 21 20 19 18 17 vsc7939
vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control page 8 g52350-0, rev 3.2 02/26/01 ? vitesse semiconductor corporation 741 calle plano camarillo, ca 93012 tel: (800) vitesse fax: (805) 987-5896 email: prodinfo@vitesse.com internet: www.vitesse.com table 5: pin identifications pin name pin number description gnd 15, 22, 23, 27 ground v cc 1, 4, 7, 16, 18, 21, 25, 32 power supply data+ 2 positive data input (pecl) data- 3 negative data input (pecl) clk+ 5 positive clock input (pecl). connect to v cc 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 v cc for data retiming and gnd for direct data. enable 9 enable input (ttl/cmos). if used, connect disable to gnd. connect to v cc 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 v cc 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. i mod flows when input data is high. out- 20 negative modulation-current output. i mod 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 100k ? 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.
vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control g52350-0, rev 3.2 page 9 02/26/01 ? vitesse semiconductor corporation 741 calle plano camarillo, ca 93012 tel: (800) vitesse fax: (805) 987-5896 email: prodinfo@vitesse.com internet: www.vitesse.com detailed description the vsc7939 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 vsc7939 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 v cc . the key features of the vsc7939 are automatic power control, low power supply current, and fast rise and fall times. the vsc7938 is another vitesse laser drivers with similar features in a 48-pin tqfp package. the vsc7938 does not have monitoring for modulation and bias currents. the vsc7940 is a modified version of the vsc7939 capable of 100ma output currents. automatic power control to ensure constant average optical power, the vsc7939 utilizes an automatic power control loop. a pho- todiode mounted in the laser package provides optical feedback to compensate for changes in average laser out- put 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 0.1 f. 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 (0.1 f) 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 open- loop 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 vsc7939 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 v cc . if this function is unused, clk+ should be connected to v cc , 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.
vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control page 10 g52350-0, rev 3.2 02/26/01 ? vitesse semiconductor corporation 741 calle plano camarillo, ca 93012 tel: (800) vitesse fax: (805) 987-5896 email: prodinfo@vitesse.com internet: www.vitesse.com modulation and bias current monitors the vsc7939 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 approxi- mately 1/28th of the amount of modulation current and biasmon sink approximately 1/35th of the amount of the bias current. these pins should be tied through a pull-up resistor to v cc . the resistors must be chosen such that the voltage at modmon is greater than v cc - 1.0v and the voltage at biasmon is greater than v cc - 1.6v. enable/disable two pins are provided to allow either enable or disable control. if enable is used, connect dis- able 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 approxi- mately 250ns. controlling the modulation current the output modulation current may be determined from the following equation where p p-p is the peak-to- peak optical power, p av e is the average power, r e is the extinction ratio, and is the laser slope efficiency: i mod = p p-p / = 2 * p av e * (r e -1) / (r e +1) / a resistor at modset controls the output bias current. graphs of i modset vs. r modset in typical operat- ing 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 i biasmax vs. r biasmax 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 deter- mine 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 i biasmax vs. r biasmax in typical operating characteristics to select the appropriate resistor value. controlling the apc loop to select the resistor at apcset, use the graph of i md vs. r apcset in typical operating characteristics. the graph relates the desired monitor current to the appropriate resistance value at apcset. i md may be calcu- late from the desired optical average power, p av e , , and the laser-to-monitor transfer, mon , for a specific laser using the following equation: i md = p av e * mon
vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control g52350-0, rev 3.2 page 11 02/26/01 ? vitesse semiconductor corporation 741 calle plano camarillo, ca 93012 tel: (800) vitesse fax: (805) 987-5896 email: prodinfo@vitesse.com internet: www.vitesse.com 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 c f and resistor r f 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. reducing pattern-dependent jitter three design values significantly affect pattern-dependent jitter; the capacitor at capc, the pull-up induc- tor at the output (l p ), and the ac-coupling capacitor at the output (c d ). as previously stated, the recommended value for the capacitor at capc is 0.1 f. this results in a 10khz loop bandwidth which makes the pattern- dependent jitter from the apc loop negligible. for 2.5gb/s data rates, the recommended value for c d is 0.056 f. the time constant at the output is domi- nated by l p . 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 = l p / 25 ? therefore, the inductor l p should be a 7.8 h smd ferrite bead inductor for this case. input/output considerations although the vsc7939 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 (i s ) in terms of quiescent current (i q ), modula- tion current (i mod ), and bias current (i bias ): i s = i q + 0.47 * i mod + 0.15 * i bias for 3.3v operation, i q is 15ma. for 5v operation, i q is 20ma. this equation may be used to determine the estimated power dissipation: p dis = v cc * i s 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: i s = 15ma + 0.47 * 30ma + 0.15 * 10ma = 31 this corresponds to a power dissipation of 3.3v * 31ma = 102mw.
vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control page 12 g52350-0, rev 3.2 02/26/01 ? vitesse semiconductor corporation 741 calle plano camarillo, ca 93012 tel: (800) vitesse fax: (805) 987-5896 email: prodinfo@vitesse.com internet: www.vitesse.com typical operating characteristics i modset vs. r modset t= 25 c v cc = 3.3v i modset vs. r modset t= 25 c v cc = 5v i biasmax vs. r biasmax t= 25 c, v cc = 3.3v i biasmax vs. r biasmax t= 25 c, v cc = 5v
vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control g52350-0, rev 3.2 page 13 02/26/01 ? vitesse semiconductor corporation 741 calle plano camarillo, ca 93012 tel: (800) vitesse fax: (805) 987-5896 email: prodinfo@vitesse.com internet: www.vitesse.com i md vs. r apcset , t= 25 c, v cc = 3.3v i md vs. r apcset , t= 25 c, v cc = 5v rise and fall times t=8 5 c, v=3.3v monte carlo simulation of i cc
vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control page 14 g52350-0, rev 3.2 02/26/01 ? vitesse semiconductor corporation 741 calle plano camarillo, ca 93012 tel: (800) vitesse fax: (805) 987-5896 email: prodinfo@vitesse.com internet: www.vitesse.com applications information the following is a typical design example for the vsc7939 assuming 3.3v operation with apc. select a laser the table 7 provides specifications for a typical communication-grade laser capable of operating at 2.5gb/s. table 6: typical laser characteristics select resistor for apcset the monitor diode current is estimated by i md = p av e * mon = 6mw * 0.04ma/mw = 0.24ma. the i md vs. r apcset 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 25 c . the modulation current may be calculated from the following equation: i mod = p p-p / = 2 * p av e * (r e -1) / (r e +1) / = 2 * 6ma * (20-1) / (20 + 1) / 0.4 = 27.1ma the graph of i modset vs. r modset in typical operating characteristics shows the resistor for modset should be 8.5k ? . 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 i th versus t c reveals a maximum threshold current of 30ma at 85 c . therefore, the maximum bias can be approximated by: i biasmax = i th-max + i mod / 2 = 30ma + 27.1ma / 2 = 43.6ma the graph of i biasmax vs. r biasmax in typical operating characteristics shows the resistor for biasmax should be 5k ? . 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: r modmon = 1v * 28 / 120ma = 233 ? r biasmon = 1.6v * 35 / 120ma = 467 ? symbol parameter valu e units wavelength 1310 nm p av e average optical output power 6 mw i th threshold current 6 ma mon laser to monitor transfer 0.04 ma/mw laser slope efficiency 0.4 mw/ma t c operating temperature range -40 to +85 c
vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control g52350-0, rev 3.2 page 15 02/26/01 ? vitesse semiconductor corporation 741 calle plano camarillo, ca 93012 tel: (800) vitesse fax: (805) 987-5896 email: prodinfo@vitesse.com internet: www.vitesse.com standard values for these values are r modmon = 232 ? and r biasmon = 464 ? . a voltage of 4.8v at modmon would indicate a modulation current of: i mod = (5.2v - 4.8v) * 28 / 232ma = 48ma wire bonding for best performance, gold ball-bonding techniques are recommended. wedge bonding is not recom- mended. 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.
vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control page 16 g52350-0, rev 3.2 02/26/01 ? vitesse semiconductor corporation 741 calle plano camarillo, ca 93012 tel: (800) vitesse fax: (805) 987-5896 email: prodinfo@vitesse.com internet: www.vitesse.com 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
vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control g52350-0, rev 3.2 page 17 02/26/01 ? vitesse semiconductor corporation 741 calle plano camarillo, ca 93012 tel: (800) vitesse fax: (805) 987-5896 email: prodinfo@vitesse.com internet: www.vitesse.com ordering information the order number for this product is formed by a combination of the device type and package type. vsc7939 xx device type package sonet/sdh 3.125gb/s laser diode driver with automatic power control rp: 32-pin tqfp 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 descript ions of features, functions, performance, technical specifications and availability, is subject to change without notice at any time. nothing contained in t his 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 su itable 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 appl ications without written consent is prohibited.
vitesse semiconductor corporation preliminary data sheet vsc7939 sonet/sdh 3.125gb/s laser diode driver with automatic power control page 18 g52350-0, rev 3.2 02/26/01 ? 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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