sy88982l 3.3v, 2.7gbps high - current, lo w - power laser driver for fp/dfb lasers december 2009 1 m9999 - 121009- a hbwhelp@micrel.com or (408) 955 - 1690 general description the sy88982l is a single 3.3v supply, low power consumption, small form factor driver for telecom/datacom applications using fp/dfb lasers at data rates up to 2.7gbps. the driver can deliver modulation current up to 90ma, and the high compliance voltage if offers, makes the part suitable for high - current operation (with the laser ac - or dc - coupled to it). this device is intended to be used with micrel?s mic3003 optical transceiver management ic, which allows for both modulation and bia s current control and monitoring, automatic power control, and temperature compensation. all support documentation can be found on micrel?s web site at: www.micrel.com . features ? 2.4v minimum laser compliance voltage for high - current dc - coupled applications ? 48ma power supply current typical ? operation up to 2.7gbps ? modulation current up to 90ma ? des igned for use with the mic3003 ? laser may be dc - or ac - coupled ? small form factor 16 - pin (3mm x 3mm) qfn package applications ? multi - rate lan, man applications up to 2.7gbps: fc, gbe, sonet oc3/12/24/48 and sdh stm1/4/8/16 ? sff, sfp modules markets ? telecom, datacom ________________________________________________________________ typical application laser dc - coupled to the driver laser ac - coupled to the driver
micrel, inc. sy88982l december 2009 2 m9999 - 121009- a hbwhelp@micrel.com or (408) 955 - 1690 functional block diagram ordering information (1) part number package type operating range package marking lead finish sy88982lmg qfn -16 indu s trial 982l with pb - free bar - line indicator nipdau pb - free sy88982lmgtr (2) qfn -16 indu s trial 982l with pb - free bar - line indicator nipdau pb - free notes: 1. contact factory for die availability. dice are guaranteed at t a = +25c, dc electrical s only. 2. tape and reel. pin configuration 16- pin qfn
micrel, inc. sy88982l december 2009 3 m9999 - 121009- a hbwhelp@micrel.com or (408) 955 - 1690 pin description pin numb er pin name pin function 1, 4, 7, 8, 13 gnd ground. ground and exposed pad must be connected to the plane of the most negative potential. 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. 5, 6 vcc supply voltage. bypass with a 0.1f//0.01f low esr capacitor as close to vcc pin as possible. 9, 10 mod - inverted modulation current output. provides modulation current when input data is nega tive. 11, 12 mod+ non - inverted modulation current output. provides modulation current when i n put data is positive. 14 vref reference voltage. install a 0.1f capacitor between vref and vcc. 15 im_set modulation current setting and control. the volt age applied to this pin will set the modulation current. to be connected to the mic3003 pin 24 (vmod+). input impedance 25k ?. 16 /en a high level signal applied to this pin will disable the output stage of the driver. i n ternally pulled down with 25k ? resi stor. truth table din+ din - /en mod+ (1) mod - laser 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 mo d+ = h. 2. assuming that the laser is tied to mod+.
micrel, inc. sy88982l december 2009 4 m9999 - 121009- 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.) ........... +260c st orage 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 85 c and v cc = +3.0v to +3.6v, unless otherwise noted. typical values are v cc = +3.3v, t a = 25c, i mod = 60ma. symbol parameter condition min typ max units i cc power supply current modulation current excluded 48 65 (4) ma v mod_min minimum voltage required at the driver output (headroom) for proper operation 0.6 v r in(data) input resistance (din+, din -) 45 50 55 ? v id differential input voltage swing 200 2400 mv pp /en low 0.8 v /en high 2 v r in (imod_set) i m_set input resistance 25 k ? v im_set voltage range on i m_set pin i mod range 10ma ? 90ma 1.2 v ac electrical characteristics t a = - 40c to 8 5c and v cc = +3.0v to +3.6v, unless otherwise noted. typical values are v cc = +3.3v, t a = 25c, i mod = 60ma. symbol parameter condition min typ max units data rate nrz 0.155 2.7 gbps i mod modulation current (5) ac - coupled 10 90 ma dc- coupled 10 70 (6) ma i mod_off modulation off current current at mod+ when the device is disabled. 750 a t r output current rise time 20% to 80%, i mod = 60ma, 15 load 55 80 ps t f output current fall time 20% to 80%, i mod = 60ma, 15 load 55 80 ps total jitter @2.5gbps data rate 20 ps pp pulse - width distortion i mod range 10ma ? 90ma 20 ps notes: 1. permanent device damage may occur if absolute maximum r atings 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 extended periods may affec t 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 potential on the pcb. jb uses a 4 - layer and ja in still air unless otherwise stated. 4. i cc = 48ma for worst - case conditions with i mod = 90ma, t a = +85c, v cc = 3.6. 5. load = 15. 6. assuming vcc = 3.0v, laser bandgap voltage = 1v, laser package inductance = 1nh, laser equivalent ser ies resistor = 5, and damping resistor = 10.
micrel, inc. sy88982l december 2009 5 m9999 - 121009- a hbwhelp@micrel.com or (408) 955 - 1690 typical operating characteristics test circuit
micrel, inc. sy88982l december 2009 6 m9999 - 121009- a hbwhelp@micrel.com or (408) 955 - 1690 functional characteristics
micrel, inc. sy88982l december 2009 7 m9999 - 121009- a hbwhelp@micrel.com or (408) 955 - 1690 input and output stages figure 1a. simplified input stage figure 1b. simplified outpu t stage interfacing the input to different logic drivers figure 2a. dc - coupling to lvpecl driver figure 2b. ac - coupling to lvpecl driver figure 2c. ac - coupling to cml driver figure 2d. ac - coupling to lvds driver
micrel, inc. sy88982al december 2009 8 m9999 - 121009- a hbwhelp@micrel.com or (408) 955 - 1690 application informati on the typical applications diagram on the first page shows how to connect the driver to the laser, single ended. to improve transition time and laser response, the laser can be driven differentially as shown in figures 3 and 4. driving the laser different ially will also minimize the crosstalk with the rest of the circuitry on the board, especially the receiver. dc- coupling in addition to the low power consumption and high modulation current, the sy88982l offers a high compliance voltage. as can be seen in the ?typical operating characteristics? section (i mod vs. v mod curves), the minimum voltage needed at the output of the driver for proper operation is less than 600mv, leaving a large headroom, v cc - 600mv, to the laser with the damping resistor. to show the importance of this high compliance voltage, consider the voltage drops along the path from v cc to ground through the laser, damping resistor, and driver: v cc = driver headroom + v rd + v laser v rd = rd x i mod v laser = v band - gap + r laser x i mod + ldi/dt v ba nd - gap + r laser x i mod = 1.6v at maximum for a fabry perrot or a dfb laser. ldi/dt is the voltage drop due to the laser parasitic inductance during i mod transitions. assuming l = 1nh, t f = t f = 80ps (measured between 20% and 80% of i mod ), and i mod = 70ma ( 42ma from 20% to 80%), then ldi/dt will be equal to 525mv. this number can be minimized by making the laser leads as short as possible and using and rc compensation network between the cathode of the laser and ground or across the laser driver outputs as s hown in figure 3. to be able to drive the laser dc - coupled with a high current, it is necessary to keep the damping resistor as small as possible. for example, if the drop due to parasitic inductance of the laser is neglected (compensated for) and the maxi mum drop across the laser (1.6v) considered while keeping a minimum of 600mv headroom for the driver, then the maximum damping resistor that allows a 70ma modulation current into the laser is: r dmax = (v cc - 0.6v - 1.6v)/0.07a the worst case will be with v cc = 3.0v, leading to r dmax = 11.4 ? on the other hand, the small is the value of r d , the higher is the overshoot/undershoot on the optical signal from the laser. in the circuit shown in figure 3, the rc compensation network across the driver outputs (mod+ and mod - ) allows the user r d = 10 ?. the optical eye diagrams at data rates of 155mbps/622mbps/1.25gbps/2.5gbps, shown in ?functional characteristics? section, are all obtained with the same circuit using r d = 10 ?, r comp = 100 ?, and c comp = 3pf. the compensation network may change fr om one board to another and from one type of laser to another. an additional compensation network (rc) can be added at the laser cathode for further compensation and eye smoothing. figure 3. laser dc - coupled ac - coupling when trying to ac couple the lase r to the driver, the headroom of the driver is no longer a problem since it is dc isolated from the laser with the coupling capacitor. at the output, the headroom of the driver is determined by the pull - up network. in figure 4, the modulation current out o f the driver is split between the pull - up network and the laser. if, for example, the total pull - up resistor is twice the sum of the damping resistor and laser equivalent series resistance, only two thirds (2/3) of the modulation current will be used by th e laser. so, to keep most of the modulation current going through the laser, the total pull - up resistor must be kept as high as possible. one solution consists in using an inductor alone as pull - up, presenting a high impedance path for the modulation curre nt and zero ohm (0 ?) path for the dc current offering a headroom of the driver equal to v cc and almost all the modulation current goes into the laser. the inductor alone will cause signal distortion, and, to improve that, a combination of resistors and ind uctors can be used (as shown on figure 4). 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. when the laser is ac - coupled to the driver, the coupling capa citor creates a low - frequency cutoff in the circuit, and its value must be chosen as large as
micrel, inc. sy88982l december 2009 9 m9999 - 121009- a hbwhelp@micrel.com or (408) 955 - 1690 possible. if the value of the cap is too high, it will slow down the fast signals edges, and, if its value is too small, it won?t be able to hold a constant chang e between the first bit and the last bit of a long string of identical bits in a low data rate application. this leads to higher pattern - dependent jitter in the transmitter signal. 0.1f is found to be good for all applications from 155mbps to 2.7gbps. ac - coupling the laser to the driver brings a solution to the driver headroom problem at the expense of extra components, loss of part of the modulation current wasted in the pull - up network, and additional power consumption. figure 4. laser ac - coupled
micrel, inc. sy88982l december 2009 10 m9999 - 121009- a hbwhelp@micrel.com or (408) 955 - 1690 package information 16- pin (3mm x 3mm) qfn micrel, inc. 2180 fortune drive 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 mic rel for its use. micrel reserves the right to change circuitry and specifications at any time without notification to the custome r. micrel products are not designed or authorized for use as components in life support appliances, devices or systems where m alfunction 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 ca n be reasonably 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 dam ages resulting from such use or sale. ? 2005 micrel, incorporated.
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