View MAX3263_1397591.PDF datasheet online --- IC-ON-LINE

Datasheet File OCR Text:

________________general description the MAX3263 is a complete, easy-to-program, single +5v-powered, 155mbps laser diode driver with com- plementary enable inputs and automatic power control (apc). the MAX3263 accepts differential pecl inputs and provides complementary output currents. a tem- perature-stabilized reference voltage is provided to simplify laser current programming. this allows modu- lation current to be programmed up to 30ma and bias current to be programmed from up to 60ma with two external resistors. an apc circuit is provided to maintain constant laser power in transmitters that use a monitor photodiode. only two external resistors are required to implement the apc function. the MAX3263? fully integrated feature set includes a ttl-compatible laser failure indicator and a program- mable slow-start circuit to prevent laser damage. the slow-start is preset to 50ns and can be extended by adding an external capacitor. ________________________applications laser diode transmitters 155mbps sdh/sonet 155mbps atm ____________________________features rise times less than 1ns differential pecl inputs single +5v supply automatic power control temperature-compensated reference voltage complementary enable inputs _______________ordering information MAX3263 single +5v, fully integrated, 155mbps laser diode driver ________________________________________________________________ maxim integrated products 1 24 23 22 21 20 19 18 17 1 2 3 4 5 6 7 8 slwstrt ipin vcca gnda out+ gnda out- gnda ibiasout imodset ibiasset ibiasfb vref2 ipinset failout gndb vin+ vin- gndb vccb enb- enb+ vref1 osadj top view 16 15 14 13 9 10 11 12 ssop MAX3263 ___________________pin configuration 19-0432; rev 2; 5/01 part MAX3263cag 0? to +70? temp. range pin-package 24 ssop MAX3263 +5v 0.01 f 0.01 f +5v +5v +5v out+ ibiasout ipin pecl inputs out- failout ibiasfb osadj imodset ipinset ibiasset vcca vccb vin+ vin- enb+ gndb gnda enb- slwstrt vref1 vref2 laser 2.7k photo- diode ferrite bead _____________t ypical operating circuit for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com.
MAX3263 single +5v, fully integrated, 155mbps laser diode driver 2 _______________________________________________________________________________________ stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. t a = +25? (note 1) conditions ma 12 i ref available reference current v 3.15 3.3 3.55 v ref ma 60 i bias range of programmable laser bias current reference voltage v v il ttl low input ma 50 i vcc supply current v v cc - 1.165 v ih pecl input high v v cc - 1.475 v il pecl input low v 2 0.8 v ih ttl high input units min typ max symbol parameter minimum differential input swing is 1100mvp-p (note 3) conditions ma 30 i mod range of programmable modulation current units min typ max symbol parameter i bias = 25ma, i mod = 12ma, 4ns unit interval; measured from 10% to 90% ns 1 t r , t f modulation-current rise and fall time i mod = 12ma, t a = +25? % ?5 os aberrations, rising and falling edge i bias = 25ma, i mod = 12ma, 8ns period ps 100 pwd modulation-current pulse- width distortion absolute maximum ratings terminal voltage (with respect to gnd) supply voltages (v cc a, v cc b).............................-0.3v to +6v vin+, vin-, failout ................................................0v to v cc out+, out-, ibiasout ......................................+1.5v to v cc enb+, enb- ......................v cc or +5.5v, whichever is smaller differential input voltage ( | vin+ - vin- | ).........................+3.8v input current ibiasout ............................................................0ma to 75ma out+, out- ........................................................0ma to 40ma ibiasset ........................................................0ma to 1.875ma imodset...............................................................0ma to 2ma ipin, ipinset, osadj...........................................0ma to 2ma failout..............................................................0ma to 10ma ibiasfb................................................................-2ma to 2ma output current vref1, vref2.....................................................0ma to 20ma slwstrt ..............................................................0ma to 5ma continuous power dissipation (t a = +70?) ssop (derate 8mw/? above +70?) ..........................640mw operating temperature range...............................0? to +70? junction temperature ......................................................+150? storage temperature range .............................-55? to +175? dc electrical characteristics (v cc = v cc a = v cc b = +4.75v to +5.25v, t a = 0? to +70?, unless otherwise noted. typical values are at v cc = +5v and t a = +25?.) ac electrical characteristics (v cc = v cc a = v cc b = +4.75v to +5.25v, r load (at out+ and out-) = 25 ? connected to v cc , t a = 0? to +70?, unless other- wise noted. typical values are at v cc = +5v and t a = +25?.) (note 2) loaded with 2.7k ? pull-up resistor to v cc loaded with 2.7k ? pull-up resistor to v cc v 0.5 v ol failout output low v 4.5 v oh failout output high note 2: ac characteristics are guaranteed by design and characterization. note 3: an 1100mvp-p differential is equivalent to complementary 550mvp-p signals on vin+ and vin-. note 1: i vcc = i vcca + i vccb , i bias = 60ma, i mod = 30ma, and i pin = 140?.
MAX3263 single +5v, fully integrated, 155mbps laser diode driver _______________________________________________________________________________________ 3 0 02040 r biasset vs. bias current 5 MAX3263-01 i bias (ma) r biasset (k ? ) 60 3 1 4 2 6 7 8 0 0 5 10 15 20 25 r modset vs. modulation current 8 MAX3263-02 modulation current (map-p) r modset (k ? ) 30 6 4 2 10 12 differential input swing = 1100 mvp-p 100 0500 r pinset vs. monitor current MAX3263-03 monitor current ( a) r pinset ( ? ) 1000 10,000 1000 100,000 1,000,000 -10 -8 -6 -4 -2 0 2 4 6 8 10 02040 percent change in modulation current vs. temperature MAX3263-04 temperature (?) % change (w.r.t. +25?) 80 60 -2 -1 0 1 2 3 02040 percent change in bias current vs. temperature MAX3263-05 temperature ( c) % change (w.r.t. +25 c) 80 60 10 30 70 50 apc disabled 34 36 38 40 42 44 46 48 50 02040 supply current vs. temperature MAX3263-06 temperature ( c) supply current (ma) 80 60 0 0 5 10 15 20 25 allowable r osadj range vs. modulation current 8 MAX3263-07 modulation current (map-p) allowable r osadj (k ? ) 30 6 4 2 10 12 allowable range 0 0 400 800 1200 1600 maximum modulation current vs. minimum differential input signal amplitude 25 MAX3263-08 minimum differential input signal amplitude (mvp-p) maximum modulation current (map-p) 2000 20 15 10 5 30 35 40 r modset = 1.2k ? r osadj = 2k ? __________________________________________typical operating characteristics (MAX3263cag loads at out+ and out- = 25 ? , v cc = v cc a = v cc b = +5v, t a = +25?, unless otherwise noted.)
MAX3263 single +5v, fully integrated, 155mbps laser diode driver 4 _______________________________________________________________________________________ ______________________________________________________________pin description name function pin 10 enb+ noninverting enable ttl input. output currents are enabled only when enb+ is high and enb- is low. 1 vref2 temperature-compensated reference output. vref2 is internally connected to vref1. 12 osadj overshoot-adjust input. connect to internal voltage reference through a resistor to adjust the overshoot of the modulation output signal (see typical operating characteristics ). 11 vref1 temperature-compensated reference output. vref1 is internally connected to vref2. 13 ibiasfb bias-feedback current output. output from automatic power-control circuit. connect to i biasset when using apc. 14 ibiasset laser bias current-programming input. connect to internal voltage reference through a resis- tor to set bias current (see typical operating characteristics ). i biasout = 40 x (i biasset + i biasfb ). 15 imodset laser modulation current-programming input. connect to internal voltage reference through a resistor to set modulation current (see typical operating characteristics ). i mod = 20 x i modset . 16 ibiasout laser bias current output. connect to laser cathode through an r-l filter network (see the bias network compensation section). 17, 19, 21 gnda ground for bias and modulation current drivers 22 vcca +5v supply voltage for bias and modulation current drivers. connect vcca to the same potential as vccb, but provide separate bypassing for vcca and vccb. 20 out+ modulation output. when vin+ is low and vin- is high, out+ sinks i mod . 9 enb- inverting enable ttl input. output currents are enabled only when enb+ is high and enb- is low. 8 vccb +5v supply voltage for voltage reference and automatic power-control circuitry. connect vccb to the same potential as vcca, but provide separate bypassing for vcca and vccb. 6 vin- inverting pecl data input 5 vin+ noninverting pecl data input 4, 7 gndb ground for voltage reference and automatic power-control circuitry 3 failout failout output. active-low, open-collector ttl output indicates if automatic power-control loop is out of regulation due to insufficient monitor-diode current (when vpin is below the 2.6v threshold). connect failout to vcc through a 2.7k ? pull-up resistor. 2 ipinset monitor photodiode programming input. connect inpinset to vref1 or vref2 through a resistor to set the monitor current when using automatic power control (see typical operating characteristics ). 18 out- modulation output. when vin+ is high and vin- is low, out- sinks i mod . 23 ipin monitor photodiode current input. connect ipin to photodiode? anode. 24 slwstrt slow-start capacitor input. connect capacitor to ground or leave unconnected to set start-up time, t startup = 25.4k ? (c slwstrt + 2pf).
MAX3263 single +5v, fully integrated, 155mbps laser diode driver _______________________________________________________________________________________ 5 _______________detailed description the MAX3263 laser driver has three main sections: a reference generator with temperature compensation, a laser bias block with automatic power control, and a modulation driver (figure 1). the reference generator provides temperature-com- pensated biasing and a voltage-reference output. the voltage reference is used to program the current levels of the high-speed modulation driver, laser diode, and pin (p+, intrinsic, n-) monitor diode. the laser bias block sets the bias current in the laser diode and maintains it above the threshold current. a current-controlled current source (current mirror) pro- grams the bias, with ibiasset as the input. the mirror? gain is approximately 40 over the MAX3263? input range. keep the output voltage of the bias stage above 2.2v to prevent saturation. the modulation driver consists of a high-speed input buffer and a common-emitter differential output stage. the modulation current mirror sets the laser modulation current in the output stage. this current is switched between the out+ and out- ports of the laser driver. the modulation current mirror has a gain of approximately 20. keep the voltages at out+ and out- above 2.2v to prevent saturation. MAX3263 vccb v cc 20 x i modset 40 x i biasset i biasout ipin ipinset r pinset 1 x i pinset ibiasset ibiasfb r biasset imodset r modset r osadj iosadj vin+ vin- enb+ gnda enb- slwstrt vref1, vref2 laser photo- diode loop- stability capacitor 0.1 f gndb vcca out+ out- failout +2.6v comparator v cc x 3/5 transconductance amplifier main bias generator bandgap reference bias compen- sation figure 1. functional diagram
the overshoot mirror sets the bias in the input buffer stage (figure 2). reducing this current slows the input stage and reduces overshoot in the modulation signal. at the same time, the peak-to-peak output swing of the input buffer stage is reduced. careful design must be used to ensure that the buffer stage can switch the out- put stage completely into the nonlinear region. the input swing required to completely switch the output stage depends on both r osadj and the modulation current. see allowable r osadj range vs. modulation current and maximum modulation current vs. minimum differential input signal amplitude graphs in the typical operating characteristics . for the output stage, the width of the linear region is a function of the desired modulation current. increasing the modulation current increases the linear region. therefore, increases in the modulation current require larger output levels from the first stage. failure to ensure that the output stage switches com- pletely results in a loss of modulation current (and extinction ratio). in addition, if the modulation port does not switch completely off, the modulation current will contribute to the bias current, and may complicate module assembly. automatic power control the automatic power control (apc) feature allows an optical transmitter to maintain constant power, despite changes in laser efficiency with temperature or age. the apc requires the use of a monitor photodiode. the apc circuit incorporates the laser diode, the monitor photodiode, the pin set current mirror, a transconduc- tance amplifier, the bias set current mirror, and the laser fail comparator (figure 1). light produced by the laser diode generates an average current in the monitor pho- todiode. this current flows into the MAX3263? ipin input. the ipinset current mirror draws current away from the ipin node. when the current into the ipin node equals the current drawn away by ipinset, the node voltage is set by the v cc x 3/5 reference of the transcon- ductance amplifier. when the monitor current exceeds ipinset, the ipin node voltage will be forced higher. if the monitor current decreases, the ipin node voltage is decreased. in either case, the voltage change is ampli- fied by the transconductance amplifier, and results in a feedback current at the ibiasfb node. under normal apc operation, ibiasfb is summed with ibiasset, and the laser bias level is adjusted to maintain constant out- put power. this feedback process continues until the monitor-diode current equals ipinset. if the monitor-diode current is sufficiently less than ipin- set (i.e., the laser stops functioning), the voltage on the ipin node drops below 2.6v. this triggers the failout comparator, which provides a ttl signal indicating laser failure. the failout output asserts only if the monitor- diode current is low, not in the reverse situation where the monitor current exceeds ipinset. failout is an open-collector output that requires an external pull-up resistor of 2.7k ? to v cc . the transconductance amplifier can source or sink cur- rents up to approximately 1ma. since the laser bias gen- erator has a gain of approximately 40, the apc function has a limit of approximately 40ma (up or down) from the initial set point. to take full advantage of this adjustment range, it may be prudent to program the laser bias cur- rent slightly higher than required for normal operation. however, do not exceed the i biasout absolute maxi- mum rating of 75ma. to maintain apc loop stability, a 0.1? bypass capaci- tor may be required across the photodiode. if the apc function is not used, disconnect the ibiasfb pin. enable inputs the MAX3263 provides complementary enable inputs (enb+, enb-). the laser is disabled by reducing the ref- erence voltage outputs (vref1, vref2). only one logic state enables laser operation (figure 3 and table 1). MAX3263 single +5v, fully integrated, 155mbps laser diode driver 6 _______________________________________________________________________________________ v cc outputs 280 ? 280 ? 9 ? 400 ? 9 ? 2(i osadj ) i mod 2(i osadj ) input buffer output stage inputs MAX3263 figure 2. MAX3263 modulation driver (simplified)
temperature considerations the MAX3263 output currents are programmed by cur- rent mirrors. these mirrors each have a 2v be temperature coefficient. the reference voltage (v ref ) is adjusted 2v be so these changes largely cancel, resulting in output cur- rents that are very stable with respect to temperature (see typical operating characteristics ). __________________design procedure interfacing suggestions use high-frequency design techniques for the board layout of the MAX3263 laser driver. adding some damp- ing resistance in series with the laser raises the load impedance and helps reduce power consumption (see reducing power consumption section). minimize any series inductance to the laser, and place a bypass capacitor as close to the laser? anode as possible. power connections labeled vcca are used to supply the laser modulation and laser bias circuits. vccb connec- tions supply the bias-generator and automatic-power control circuits. for optimum operation, isolate these sup- plies from each other by independent bypass filtering. gnda and gndb have multiple pins. connect all pins to optimize the MAX3263? high-frequency perfor- mance. ground connections between signal lines (vin+, vin-, out+, out-) improve the quality of the signal path by reducing the impedance of the intercon- nect. multiple connections, in general, reduce induc- tance in the signal path and improve the high-speed signal quality. gnd pins should be tied to the ground plane with short runs and multiple vias. avoid ground loops, since they are a source of high-frequency inter- ference. the MAX3263 data inputs accept pecl input signals, which require 50 ? termination to (v cc - 2v). figure 4 shows alternative termination techniques. when a ter- mination voltage is not available, use the thevenin- equivalent termination. when interfacing with a non-pecl signal source, use one of the other alterna- tive termination methods shown in figure 4. bias network compensation for best laser transmitter performance, add a filter to the circuit. most laser packages (to-46 or dil) have a sig- nificant amount of package inductance (4nh to 20nh), which limits their usable data rate. the MAX3263 out pin has about 1pf of capacitance. these two parasitic components can cause high-frequency ringing and aberrations on the output signal. if ringing is present on the transmitter output, try adding a shunt rc filter to the laser cathode. this limits the bandwidth of the transmitter to usable levels and reduces ringing dramatically (figure 5). l = laser inductance c = shunt filter capacitance r = shunt filter resistance a good starting point is r = 25 ? and c = l / 4r. increase c until aberrations are reduced. the ibiasout pin has about 4pf of parasitic capaci- tance. when operating at bias levels over 50ma, the impedance of the bias output may be low enough to decrease the rise time of the transmitter. if this occurs, the impedance of the ibiasout pin can be increased by adding a large inductor in series with the pin. reducing power consumption the laser driver typically consumes 40ma of current for internal functions. typical load currents, such as 12ma of modulation current and 20ma of bias current, bring the total current requirement to 72ma. if this were dissipated entirely in the laser driver, it would generate 360mw of MAX3263 single +5v, fully integrated, 155mbps laser diode driver _______________________________________________________________________________________ 7 table 1. MAX3263 truth table enb- enb+ 0 0 0 1 1 0 1 1 vref off on off off enb+ data out (load = 1300nm laser at out-) 2 s/div figure 3. enable/disable operation
MAX3263 single +5v, fully integrated, 155mbps laser diode driver 8 _______________________________________________________________________________________ this symbol represents a transmission line with characteristic impedance z o = 50 ? . MAX3263 5v 120 ? 82 ? 82 ? 5v pecl signal source vin+ vin- 120 ? a) thevenin-equivalent termination MAX3263 68 ? 50 ? 50 ? 50 ? 5v non-pecl signal source vin+ vin- 180 ? c) single-ended non-pecl termination MAX3263 1.8k 680 ? 50 ? 5v non-pecl signal source vin+ vin- 5v 1.8k 680 ? 50 ? b) differential non-pecl termination MAX3263 5v 3.6k 1.3k 1.3k 0v ecl signal source -2v vin+ vin- 3.6k 50 ? 50 ? -2v d) ecl termination figure 4. alternative pecl data-input terminations
heat. fortunately, a substantial portion of this power is dissipated across the laser diode. a typical laser diode drops approximately 1.6v when forward biased. this leaves 3.4v at the MAX3263? out- terminal. it is safe to reduce the output terminal voltage even further with a series damping resistor. terminal voltage levels down to 2.2v can be used without degrading the laser driver? high-frequency performance. power dissipation can be further reduced by adding a series resistor on the laser driver? out+ side. select the series resistor so the out+ terminal voltage does not drop below 2.2v with the maximum modulation current. _____________ applications information programming the MAX3263 laser driver programming the MAX3263 is best explained by an example. assume the following laser diode characteris- tics: wavelength 1300nm threshold current i th 20ma at +25?(+0.35ma/ ? temperature variation) monitor responsivity mon 0.1a/w (monitor current / average optical power into the fiber) modulation efficiency 0.1mw/ma (worst case) now assume the communications system has the fol- lowing requirements: average power p ave 0dbm (1mw) extinction ratio er 6db (er = 4) temperature range tr 0? to +70? 1) determine the value of ipinset: the desired monitor-diode current is (p ave )( mon ) = (1mw)(0.1a/w) = 100?. the r pinset vs. monitor current graph in the typical operating characteristics show that r pinset should be 18k ? . 2) determine r modset : the average power is defined as (p1 + p0) / 2, where p1 is the average amplitude of a transmitted ?ne?and p0 is the average amplitude of a transmitted ?ero. the extinction ratio is p1/p0. combining these equa- tions results in p1 = (2 x p ave x er) / (er + 1) and p0 = (2 x p ave ) / (er + 1). in this example, p1 = 1.6mw and p0 = 0.4mw. the optical modulation is 1.2mw. the modulation current required to produce this output is 1.2mw / = (1.2mw) / (0.1ma/mw) = 12ma. the typical operating characteristics show that r modset = 3.9k ? yields the desired modulation current. 3) determine the value of r osadj : using the allowable r osadj range vs. modulation current graph in the typical operating characteristics , a 5.6k ? resistor is chosen for 12ma of modulation cur- rent. the maximum r osadj values given in the graph minimize aberrations in the waveform and ensure that the driver stage operates fully limited. 4) determine the value of r biasset : the automatic power control circuit can adjust the bias current 40ma from the initial setpoint. this feature makes the laser driver circuit reasonably insensitive to variations of laser threshold from lot to lot. the bias set- ting can be determined using one of two methods: a) set the bias at the laser threshold. b) set the bias at the midpoint of the highest and low- est expected threshold values. method a is straightforward. in the second method, it is assumed that the laser threshold will increase with age. the lowest threshold current occurs at 0? when the laser is new. the highest threshold current occurs at +70? at the end of the product? life. assume the laser is near the end of life when its threshold reaches two- times its original value. lowest bias current: i th + ? i th = 20ma + (0.35ma/?)(-25?) = 11.25ma highest bias current: 2 x i th + ? i th = 40ma + (0.35ma/?)(+45?) = 55.8ma MAX3263 single +5v, fully integrated, 155mbps laser diode driver _______________________________________________________________________________________ 9 MAX3263 +5v out+ out- ipin 0.1 f ibiasout 25 ? 18 ? 18 ? ferrite bead laser shunt rc photo- diode 0.01 f as close to the laser anode as possible as close to the laser cathode as possible c 10 h figure 5. typical laser interface with bias compensation
MAX3263 single +5v, fully integrated, 155mbps laser diode driver 10 ______________________________________________________________________________________ ______________________________________________________________________ package information in this case, set the initial bias value to 34ma (which is the midpoint of the two extremes). the 40ma adjust- ment range of the MAX3263 maintains the average laser power at either extreme. the typical operating characteristics show that r biasset = 1.8k ? delivers the required bias current. laser safety and iec 825 using the MAX3263 laser driver alone does not ensure that a transmitter design is compliant with iec 825 safe- ty requirements. the entire transmitter circuit and com- ponent selections must be considered. each customer must determine the level of fault tolerance required by their application, recognizing that maxim products are not designed or authorized for use as components in systems intended for surgical implant into the body, for applications intended to support or sustain life, or for any other application where the failure of a maxim product could create a situation where personal injury or death may occur. ssop.ep s
MAX3263 single +5v, fully integrated, 155mbps laser diode driver ______________________________________________________________________________________ 11 notes
MAX3263 single +5v, fully integrated, 155mbps laser diode driver notes maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 12 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ? 2001 maxim integrated products printed usa is a registered trademark of maxim integrated products. maxim makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does maxim assume any lia- bility arising out of the application or use of any product or circuit and specifically disclaims any and all liability, includ ing without limitation consequential or incidental damages. ?ypical?parameters can and do vary in different applications. all operating parameters, including ?yp icals?must be validated for each customer application by customer? technical experts. maxim products are not designed, intended or authorized for use as c omponents in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other applic ation in which the failure of the maxim product could create a situation where personal injury of death may occur.

▲Up To Search▲

Price & Availability of MAX3263

	To Download MAX3263 Datasheet File
If you can't view the Datasheet, Please click here to try to view without PDF Reader .