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sy88992l 3.3v, 4.25gbps vcsel driver january 2006 m9999 - 011306-a hbwhelp@micrel.com or (408) 955 - 1690 general description the sy88992l is a single supply 3.3v, low power consumption, small - form factor vcsel driver ideal for use in datacom applic a tions; ethernet, gbe (gigabit ethernet), and fc (fibre cha n nel) applications that operate from 100mbps up to 4 .25gbps. the modulation cu r rent is set by applying an external voltage at the im_set pin. the driver features an adjustable peaking option with variable ampl i tude and duration to improve vcsel edge response. the driver can deliver modulation current up to 25ma and a peaking cu r rent up to 35% of the modulation current. this device is intended to be used with micrel?s mic3001 optical transceiver manag e ment ic, which allows for both modulation and bias current co n trol and monitoring, apc (automatic power contr ol), and te m perature compensation. all support documentation can be found on micrel?s web site at: www.micrel.com . features ? up to 25ma modulation current ? operates from 100mbps to 4.25gbps ? peaking with variable durati on option for better vcsel r e sponse ? dual peaking, on the rise and falling edges ? peaking current proportional to modulation current ? easy modulation current setting ? fully controllable with micrel mic3001 ? small (3mm x 3mm) 16 pin qfn package applications ? mult irate lan, san applications up to 4.25gbps: ethernet, gbe, fc ? sff, sfp modules markets ? datacom ________________________________________________________________ typical application
micrel, inc. sy88992l january 2006 2 m9999 - 011306- a hbwhelp@micrel.com or (408) 955 - 1690 functional block diagram ordering information (1) part number pac kage type operating range package marking lead finish sy88992lmg qfn -16 indu s trial 992l with pb - free bar - line indicator nipdau pb - free sy88992lmgtr (2) qfn -16 indu s trial 992l with pb - free bar - line indicator nipdau pb - free notes: 1. contact factory for di e availability. dice are guaranteed at t a = +25c, dc electricals only. 2. tape and reel. pin configuration 16- pin qfn
micrel, inc. sy88992l january 2006 3 m9999 - 011306- a hbwhelp@micrel.com or (408) 955 - 1690 pin description pin number pin name pin function 2 din+ non - inverting input data. internally terminated with 50 ? to a reference vol t age. 3 din - inverting input data. internally terminated with 50 ? to a reference vol t age. 6 ip_set1 peaking current setting. connect this pin to gnd and keep pins 7 and 8 open to set peaking - to - modulation current ratio to 5%. combinations of the thre e pins, as shown in table below, will set different ratios up to 35%. 7 ip_set2 peaking current setting. connect this pin to gnd and keep pins 6 and 8 open to set peaking - to - modulation current ratio to 10%. combinations of the three pins, as shown in ta ble below, will set different ratios up to 35%. 8 ip_set3 peaking current setting. connect this pin to gnd and keep pins 6 and 7 open to set peaking - to - modulation current ratio to 20%. combinations of the three pins, as shown in table below, will set di fferent ratios up to 35%. 10 mod - inverted modulation current output. provides modulation current when input data is nega tive. 11 mod+ non - inverted modulation current output. provides modulation current when i n put data is positive. 13 im_set modulatio n current setting. the modulation current is set by applying a 0v to 1.2v voltage at this pin. 14 ipd_set peaking duration setting. the peaking current duration is set by installing a resistor b e tween this pin and ground. the plot on page 6 shows peaking duration versus the value of the resistor installed. 16 /en a low level signal applied to this pin will enable the output stage of the driver. i n ternally pulled down to ground with 75k ? resistor. 1, 4, 9, 12 gnd ground. ground and exposed pad must be con nected to the plane of the most negative potential. 5, 15 vcc supply voltage. bypass with a 0.1f//0.01f low esr capacitor as close to vcc pin as possible. truth table din+ din - /en mod+ (1) mod - vcsel output (2) l h l h l l h l l l h h x x h h h l notes: 1. i mod = 0 when mod+ = h. 2. assuming a common anode vcsel with its cathode tied to mod+. peaking current -to- modulation current ratio setting ip/i mod 0 % 5 % 10 % 15 % 20 % 25 % 30 % 35 % ip_set1 nc gnd nc gnd nc gnd nc gnd ip_set2 nc nc g nd gnd nc nc gnd gnd ip_set3 nc nc nc nc gnd gnd gnd gnd
micrel, inc. sy88992l january 2006 4 m9999 - 011306- a hbwhelp@micrel.com or (408) 955 - 1690 absolute maximum ratings (1) supply voltage (v in ) ........................... ? 0.5v to +4.0v cml input voltage (v in ) .......... v cc ? 1.2v to v cc +0.5v ttl control input voltage (v in ) ................... 0v to v cc lead temperature (soldering, 20sec.) ........... +260 c storage temperature (t s ) ............... ? 65c to +150c operating ratings (2) supply voltage (v cc ) .......................... +3.0v to +3.6v ambient temperature (t a ) ................ ? 40c to +85c package thermal resistance (3) qfn ( ja ) still - air .............................................. 60c/w ( jb ) ......................................................... 33c/w dc electrical characteristics t a = - 40c to 85c and v cc = 3.0v to 3.6v, unless otherwise noted. typical values are at: v cc = 3.3v, t a = 25c, i mod = 13ma (4) symbol parameter condition min typ max units i cc power suppl y current peaking not used 57 95 ma maximum peaking used 70 110 ma i mod (4) modulation current ac - coupled 3 25 ma i mod_off modulation off current current at mod+ and mod - when the part is disabled 100 a v mod_min minimum voltage required at the d river output (headroom) for proper operation 1.5 v r in input resistance (din+ -to - din -) 90 100 110 ? v id differential input voltage swing 200 2400 mv pp vi m_set voltage range on i m_set i mod range 3ma ? 25ma (4) 1.2 v v il /en input low 0.8 v v ih /en input high 2 v input impedance at /en 75 k ? notes: 1. permanent device damage may oc cur if absolute maximum ratings are exceeded. this is a stress rating only and functional operation is not implied at conditions other than those detailed in the operational sections of this data sheet. exposure to absolute maxi mum ratings conditions for e xtended periods may affect device reliability. 2. the data sheet limits are not guaranteed if the device is operated beyond the operating ratings. 3. package thermal resistance assumes exposed pad is soldered (or equivalent) to the devices most negative po tential on the pcb. jb uses a 4 - layer and ja in still air unless otherwise stated. 4. i mod is defined as the current at the output of the driver. that current splits between the pull - up network at the output and the vcsel. for a nominal pull - up resistor of 75 ? at the output of the driver and a nominal 50 ? vcsel equivalent resistor, 60% of that current goes to the vcsel.
micrel, inc. sy88992l january 2006 5 m9999 - 011306- a hbwhelp@micrel.com or (408) 955 - 1690 ac electrical characteristics t a = - 40c to +80c and v cc = 3.0 to 3.6v, unless otherwise noted. typical values are at v cc = 3.3v, t a = 25 c, i mod = 13ma (5) , and ac - coupled 50 ? load to ground with 75? pull - up (see figure below). symbol parameter condition min typ max units data rate nrz 0.1 4.25 gbps t off (6) turn off time 50 ? load 1 1.5 ns t on (7) turn on time 50 ? load 1.8 2.5 ns t r o utput current rise time 20% to 80%, i mod = 13ma, no peaking, 50 ? load 65 95 ps 20% to 80%, i mod = 13ma, i p /i mod =20%, r ipd =1.5k ? 60 75 ps t f output current fall time 20% to 80%, i mod = 13ma, no peaking, 50 ? load 65 95 ps 20% to 80%, i mod = 13ma, i p /i mod =20%, r ipd =1.5k ? 60 75 ps total jitter @ 2.5gbps data rate, 50 ? load 30 ps pp pulse - width distortion 50 ? load 20 ps (i p / i mod ) max maximum peaking current -to - modulation current ratio 35 % t p peaking current duration (8) i mod = 13ma, r i pd_set = 0 ? 150 ps notes: 5. i mod is defined as the current at the output of the driver. that current splits between the pull - up network at the output and the vcsel. for a nominal pull - up resistor of 75 ? at the output of the driver and a nominal 50 ? vcs el equivalent resistor, 60% of that current goes to the vcsel. 6. turn - off time is defined as the delay between the time the signal at /en rises to 50% of its amplitude and the time when the outpu t of the driver reaches 10% of its steady - state amplitude. 7. t urn - on time is defined as the delay between the time the signal at /en falls to 50% of its amplitude and the time when the output of the driver reaches 90% of its steady - state amplitude. 8. the peaking current duration is the time between the start of the pea king current, which is the same as the start of the modulation current transition, and the time when the peaking current reaches its maximum, i.e., the top of the peak. test circuit
micrel, inc. sy88992l january 2006 6 m9999 - 011306- a hbwhelp@micrel.com or (408) 955 - 1690 typical operating characteristics t a = +25c and v cc = 3.3v, unless otherwise noted. i mod = 0ma r ipd_set (k ?)
micrel, inc. sy88992l january 2006 7 m9999 - 011306- a hbwhelp@micrel.com or (408) 955 - 1690 typical waveforms
micrel, inc. sy88992l january 2006 8 m9999 - 011306- a hbwhelp@micrel.com or (408) 955 - 1690 peaking variation with i p /i mod ratio and peaking duration as it can be seen on the set of electrical waveforms below, the amplitude of the peak increases with the peaking - to - modulation current r atio and the width of the peak increases with peaking duration. increasing peaking duration increasing peaking percentage
micrel, inc. sy88992l january 2006 9 m9999 - 011306- a hbwhelp@micrel.com or (408) 955 - 1690 input and output stages figure 1a. simplified input stage figure 1b. simplified output stage interfacing the input to different logic drivers figure 2a. ac - coupling to lvpecl driver figure 2b. ac - coupling to cml driver
micrel, inc. sy88992l january 2006 10 m9999 - 011306- a hbwhelp@micrel.com or (408) 955 - 1690 driver?s special features the sy88992l features a peaking current of programmable amplitude and duration on both the rising and the falling edges. the amplitude of the peaking current is adjustable in steps of 5% of the modulation current from 0% to 35%. as shown in the table on page 3, the ratio between the peaking current and the modulation current (i p /i mod ) can be programmed by connecting pin 6 (ip_set1) and/or pin 7 (ip_set2) and/or pin 8 (ip_set3) to ground. when all these three pins are left open, there is no peaking (ratio 0%). when they?re all connected to ground the ratio is maximum (35%). for each family of vcsels used with the driver, the user must try many co mbinations in order to get the best response for the vcsel. the peaking current duration can be tuned by installing a resistor between pin 14 and ground; 0 ? provides maximum duration and 3k ? or higher provides the minimum duration. the combined features wi ll improve the vcsel response for a better optical signal quality. the electrical eye diagrams on page 8 show how the signal changes as the peaking - to - modulation current varies. application hints the typical application section on the front page shows how to connect the driver to the vcsel single - ended. to improve transition time and vcsel response, the vcsel can be driven differentially, as shown in figure 3. driving the vcsel differentially will also minimize the cross talk with the rest of the circuitry on the board, especially with the receiver. the driver is always ac - coupled to the vcsel and the headroom of the driver is determined by the pull - up network at the output. in figure 3, the modulation current out of the driver is split between the pull - up network and the vcsel. if, for example, the total pull - up resistor is twice the sum of the damping resistor and vcsel equivalent series resistance, only two thirds (2/3) of the modulation current will be used by the vcsel. therefore, to maximize the modula tion current going through the vcsel, the total pull - up resistors should be kept as high as possible. one solution consists of using an inductor alone as pull - up, creating a high impedance path for the modulation current and zero ohm (0 ? ) path for the dc c urrent. this offers a headroom equal to vcc for the driver and almost all the modulation current goes into the vcsel. however, using the inductor alone will cause signal distortion. to avoid this, a combination of resistors and inductors can be used, as sh own on figure 3. in this case, the headroom of the driver is v cc ? r1 x i mod , where i mod is the portion of the modulation current that goes through the pull - up network. for instance, if a modulation current out of the driver of 25ma is considered, with a p ull - up resistor of 75 ? , and the vcsel with the damping resistor total resistance is 50 ? , then the modulation current will split; 10ma to the pull - up resistor and 15ma to the laser. the headroom for the driver will be v cc ? 75 x 10 = v cc ? 750mv which is way hi gher than the minimum voltage required for the output stage of the driver to operate properly. the coupling capacitor creates a low - frequency cutoff in the circuit. therefore, a proper coupling capacitor value must be chosen to acc ommodate different data rates in the application. if the value of the capacitor is too high, it may cause problems in high data rate applications. if its value is too small, it won?t be able to hold a constant charge between the first bit and the last bit in a long string of identical bits in low data rate application. both cases lead to higher pattern - dependent jitter in the transmitter signal. 0.1 f is found to be good for applications from 155mbps to 4.25gbps . figure 3. driving a common anode vcsel differentially
micrel, inc. sy88992l january 2006 m9999 - 011306-a hbwhelp@micrel.com or (408) 955 - 1690 package information 16- pin (3mm x 3mm) qfn micrel, inc. 2180 fortune d rive san jose, ca 95131 usa tel +1 (408) 944 - 0800 fax +1 (408) 474 - 1000 web http://www.micrel.com the information furnished by micrel in this data sheet is believed to be accurate and reliable. however, no responsibility is assumed by micrel for it s use. micrel reserves the right to change circuitry and specifications at any time without notification to the customer. micrel products are not designed or authorized for use as components in life support appliances, devices or systems where mal function of a product can reasonably be expected to result in personal injury. life support devices or systems are devices or systems that (a) are intended for surgical implant into the body or (b) support or sustain life, and whose failure to perform can be reaso nably expected to result in a significant injury to the user. a purchaser?s use or sale of micrel products for use in life support appliances, devices or systems is a purchaser?s own risk and purchaser agrees to fully indemnify micrel for any damages resul ting from such use or sale. ? 2006 micrel, incorporated.

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