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lt4276 1 4276fa for more information www.linear.com/lt4276 typical application features description ltpoe ++ /poe + /poe pd forward/flyback controller the lt ? 4276 is a pin-for-pin compatible family of ieee 802.3 and ltpoe ++ powered device (pd) controllers. it includes an isolated switching regulator controller capable of synchronous operation in both forward and flyback topologies with auxiliary power support. the lt4276 a employs the ltpoe ++ classification scheme, receiving 38.7w, 52.7w, 70w or 90w of power at the pd rj45 connector, and is backwards compatible with ieee 802.3. the lt4276 b is a fully 802. 3a t compliant, 25.5w type 2 (poe + ) pd. the lt4276 c is a fully 802. 3a f compli - ant, 13w type 1 (poe) pd. the lt4276 supports both for ward and flyback power supply topologies, configurable for a wide range of poe applications. the flyback topology supports no-opto feedback. auxiliary input voltage can be accurately sensed with just a resistor divider connected to the aux pin. the lt4276 utilizes an external, low r ds(on) n-channel mosfet for the hot swap function, maximizing power delivery and efficiency, reducing heat dissipation, and easing the thermal design. ltpoe ++ 70w power supply in a forward mode applications n ieee802.3af/at and ltpoe ++ ? 90w powered device (pd) with forward/flyback controller n lt4276a supports all of the following standards: n ltpoe ++ 38.7w, 52.7w, 70w and 90w n ieee 802.3at 25.5w compliant n ieee 802.3af up to 13w compliant n lt4276b is ieee 802.3at/af compliant n lt4276c is ieee 802.3af compliant n superior surge protection (100 v absolute maximum ) n wide junction temperature range (C40 c to 125 c) n auxiliary power support as low as 9v n no opto-isolator required for flyback operation n external hot swap ? n-channel mosfet for lowest power dissipation and highest system efficiency n >94% end - to - end efficiency with lt4321 ideal bridge n available in a 28-lead 4mm 5mm qfn package n high power wireless data systems n outdoor security camera equipment n commercial and public information displays n high temperature applications l , lt, ltc, ltm, ltpoe ++, linear technology and the linear logo are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners. lt4276 family max delivered power lt4276 grade a b c ltpoe ++ 90w l ltpoe ++ 70w l ltpoe ++ 52.7w l ltpoe ++ 38.7w l 25.5w l l 13w l l l ? ? v port vport r class auxr class ++ sw vcc v cc v in v cc 0.1f 10f bav19ws (t rr 50ns) 22f hs gate hs src ffs d ly pg sg ithb to microprocessor isen + isen C 4276 ta01 gnd fb31 rosc t2p ss 100h aux 37v-57v +C C + fmmt723 20m 5v13a +C 3.3k 10k 0.1f 100pf 10nf 100k lt4276a opto + downloaded from: http:///
lt4276 2 4276fa for more information www.linear.com/lt4276 pin configuration absolute maximum ratings vport, hssrc, v in voltages ..................... C0.3 to 100v hsgate current .................................................. 20ma v cc voltage .................................................... C0.3 to 8v rclass, rclass ++ voltages ................................. C0.3 to 8v (and vport) sfst, ffsdly, ithb, t2p voltages ...... C0.3 to v cc + 0.3v isen + , isen C voltages ........................................... 0.3v fb31 voltage .................................................. + 12v /C 30v rclass/rclass ++ current .............................. C 50ma aux current ........................................................ 1.4ma rosc current ..................................................... 100a rldcmp current ................................................ 500a t2p current ......................................................... C 2.5ma operating junction temperature range (note 3) lt4276 ai/ lt4276 bi/ lt4276 ci .............. C 40 c to 85 c lt4276 ah/ lt4276 bh/ lt4276 ch ....... C 40 c to 125 c storage temperature range .................. C 65 c to 150 c (notes 1, 2) 9 10 top view ufd package 28-lead (4mm 5mm) plastic qfn 11 12 13 28 27 26 25 24 14 23 6 5 4 3 2 1 gnd aux rclass ++ /nc* rclass t2p/nc** v cc v cc v cc dncv cc pggnd sg isen + isen C rldcmp vportnc hsgate hssrc v in swvcc v cc rosc sfst ffsdly ithb fb31 7 17 18 19 20 21 2216 8 15 29 gnd t jmax = 150c, jc = 3.4c/w exposed pad (pin 29) is gnd, must be soldered to pcb *rclass ++ is not connected in the lt4276b and lt4276c **t2p is not connected in the lt4276c order information lead free finish tape and reel part marking* max pd power package description temperature range lt4276aiufd#pbf lt4276aiufd#trpbf 4276a 90w 28-lead (4mm 5mm) plastic qfn C40c to 85c lt4276ahufd#pbf lt4276ahufd#trpbf 4276a 90w 28-lead (4mm 5mm) plastic qfn C40c to 125c lt4276biufd#pbf lt4276biufd#trpbf 4276b 25.5w 28-lead (4mm 5mm) plastic qfn C40c to 85c lt4276bhufd#pbf lt4276bhufd#trpbf 4276b 25.5w 28-lead (4mm 5mm) plastic qfn C40c to 125c lt4276ciufd#pbf lt4276ciufd#trpbf 4276c 13w 28-lead (4mm 5mm) plastic qfn C40c to 85c lt4276chufd#pbf lt4276chufd#trpbf 4276c 13w 28-lead (4mm 5mm) plastic qfn C40c to 125c consult ltc marketing for parts specified with wider operating temperature ranges. *the temperature grade is identified by a label on the shipping container. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel specifications, go to: http://www.linear.com/tapeandreel/ . some packages are available in 500 unit reels through designated sales channels with #trmpbf suffix. downloaded from: http:///
lt4276 3 4276fa for more information www.linear.com/lt4276 electrical characteristics symbol parameter conditions min typ max units vport, hssrc, v in operating voltage at vport pin l 60 v v sig vport signature range at vport pin l 1.5 10 v v class vport classification range at vport pin l 12.5 21 v v mark vport mark range at vport pin, after 1st classification event l 5.6 10 v vport aux range at vport pin, v aux 6.45v l 8 60 v signature/class hysteresis window l 1.0 v reset threshold l 2.6 5.6 v v hson hot swap turn-on voltage l 35 37 v v hsoff hot swap turn-off voltage l 30 31 v hot swap on/off hysteresis window l 3 v supply current vport, hssrc & v in supply current v vport = v hssrc = v vin = 60v l 2 ma vport supply current during classification v vport = 17.5v , rclass, rclass ++ open l 0.7 1.0 1.3 ma vport supply current during mark event v vport = v mark after 1st classification event l 0.4 2.2 ma signature and classification signature resistance v sig (note 4) l 23.6 24.4 25.5 k signature resistance during mark event v mark (note 4) l 5.2 8.3 11.4 k rclass/rclass ++ voltage C10ma i rclass C36ma l 1.36 1.40 1.43 v classification stability time v vport step to 17.5v, r cls = 35.7 l 2 ms digital interfacev auxt aux threshold v port = 17.5v, v in = v hssrc = 18.5v l 6.05 6.25 6.45 v i auxh aux pin current v aux = 6.05v, v port = 17.5v, v in = 9v, v cc = 0v l 3.3 5.3 7.3 a t2p output high v vcc - v t2p , C1ma load l 0.3 v t2p leakage v t2p = 0v l C1 1 a hot swap controli gpu hsgate pull up current v hsgate - v hssrc = 5v (note 5) l C27 C22 C18 a hsgate voltage C10a load, with respect to hssrc l 10 14 v hsgate pull down current v hsgate - v hssrc = 5v l 400 a v cc supply vccreg v cc regulation voltage l 7.2 7.6 8.0 v feedback amplifierv fb fb31 regulation voltage l 3.11 3.17 3.23 v fb31 pin bias current rldcmp open -0.1 a gm feedback amplifier average trans- conductance time average, C2a < i ithb < 2a l C52 C40 C26 a/v i sink ithb average sink current time average, v fb31 = 0v l 4.4 8.0 13.4 a soft-starti sfst charging current v sfst = 0.5v, 3.0v l C49 C42 C36 a the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t j = 25c. v vport = v hssrc = v vin = 40v, v vcc = vccreg, rosc, pg, and sg open, r ffsdly = 5.23k to gnd. aux connected to gnd unless otherwise specified. (note 2) downloaded from: http:///
lt4276 4 4276fa for more information www.linear.com/lt4276 symbol parameter conditions min typ max units gate outputs pg, sg output high level i = C1ma l v cc C0.1 v pg, sg output low level i = 1ma l 1 v pg rise time, fall time pg = 1000pf 15 ns sg rise time, fall time sg = 400pf 15 ns current sense/overcurrentv fault overcurrent fault threshold v isen + - v isen C l 125 140 155 mv v sense / v ithb current sense comparator threshold with respect to v ithb l C130 C111 C98 mv/v v ithb(os) v ithb offset l 3.03 3.17 3.33 v timingf osc default switching frequency rosc pin open l 200 214 223 khz switching frequency r osc = 45.3k to gnd l 280 300 320 khz f t2p ltpoe ++ signal frequency f sw /256 t min minimum pg on time l 175 250 330 ns d max maximum pg duty cycle l 63 66 70 % t pgdelay pg turn-on delay-flyback pg turn-on delay-forward 5.23k from ffsdl y to gnd 52.3k from ffsdly to gnd 10.5k from ffsdly to v cc 52.3k from ffsdly to v cc 45 171 92 391 ns ns ns ns t fbdly feedback amp enable delay time 350 ns t fb feedback amp sense interval 550 ns t pgsg pg falling to sg rising delay time-flyback pg falling to sg falling delay time- forward resistor from ffsdly to gnd 10.5k from ffsdl y to v cc 52.3k from ffsdly to v cc 20 67 301 ns ns ns t start start timer (note 6) delay after power good l 80 86 93 ms t fault fault timer (note 6) delay after overcurrent fault l 80 86 93 ms i mps mps current l 10 12 14 ma electrical characteristics the l denotes the specifications which apply over the full operating temperature range, otherwise specifications are at t j = 25c. v vport = v hssrc = v vin = 40v, v vcc = vccreg, rosc, pg, and sg open, r ffsdly = 5.23k to gnd. aux connected to gnd unless otherwise specified. (note 2) note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2. all voltages with respect to gnd unless otherwise noted. positive currents are into pins; negative currents are out of pins unless otherwise noted. note 3. this ic includes overtemperature protection that is intended to protect the device during momentary overload conditions. junction temperature can exceed 150c when overtemperature protection is active. continuous operation above the specified maximum operating junction temperature may impair device reliability. note 4. signature resistance specifications do not include resistance added by the external diode bridge which can add as much as 1.1k to the port resistance. note 5. i gpu available in poe powered operation. that is, available after v(vport) > v hson and v(aux) < v auxt , over the range where v(vport) is between v hsoff and 60v. note 6. guaranteed by design, not subject to test. downloaded from: http:///
lt4276 5 4276fa for more information www.linear.com/lt4276 typical performance characteristics v fb31 vs temperature feedback amplifier output current vs v fb31 switching frequency vs temperature current sense voltage vs duty cycle, i thb pg delay time vs temperature in flyback mode pg delay time vs temperature in forward mode input current vs input voltage 25k detection range signature resistance vs input voltage v cc current vs temperature vport voltage (v) 0 0 vport current (ma) 0.40.3 0.2 0.1 0.5 6 8 10 2 4 4276 g01 125c85c 25c C40c vport voltage (v) 1 23.75 signature resistance (k) 25.7525.25 24.75 24.25 26.25 6 5 8 7 9 2 4 3 4276 g02 125c85c 25c C40c temperature (c) C50 0 v cc current (ma) 10 86 4 2 12 50 25 100 75 125 0 C25 4276 g03 214khz 300khz temperature (c) C50 3.162 v fb31 (v) 3.1763.174 3.172 3.170 3.168 3.166 3.164 3.178 50 25 100 75 125 0 C25 4276 g04 fb31 voltage (v) 2.57 C15 ithb current (a) 10 5 C5 0 C10 15 3.17 3.37 3.57 3.77 2.77 2.97 4276 g05 125c85c 25c C40c temperature (c) C50 175 frequency (khz) 300275 250 225 200 325 50 25 100 75 125 0 C25 4276 g06 r osc = 45.3k rosc open v ithb = 1.8v v ithb = 2.3v v ithb = 2.6v v ithb = 2.9v duty cycle (%) 0 0 v (isen + - isenC) (mv) 140 80 100 120 6040 20 160 40 30 60 50 70 20 10 4276 g07 v ithb = 0.96v (fb31 = 0v) temperature (c) C50 0 pg delay time (ns) 200150 100 50 250 50 25 100 75 125 0 C25 4276 g08 r ffsdly = 5.23k r ffsdly = 52.3k t pgdelay , r ffsdly = 10.5k t pgsg , r ffsdly = 10.5k t pgsg , r ffsdly = 52.3k t pgdelay , r ffsdly = 52.3k temperature (c) C50 0 delay time (ns) 350200 250 300150 100 50 400 50 25 100 75 125 0 C25 4276 g09 downloaded from: http:///
lt4276 6 4276fa for more information www.linear.com/lt4276 pin functions gnd(pins 1, 19, exposed pad pin 29) : device ground. exposed pad must be electrically and thermally connected to pcb gnd and pin 19. rclass ++ (pin 3, lt4276 a only) : ltpoe ++ class select input. connect a resistor between rclass ++ to gnd per table 1. aux (pin 2) : auxiliary sense. assert aux via a resistive divider from the auxiliary power input to set the voltage at which the auxiliary supply takes over. asserting aux pulls down hsgate, disconnects the signature resistor and disables classification. the aux pin sinks i auxh when below its threshold voltage of v auxt to provide hysteresis. connect to gnd if not used. rclass (pin 4) : class select input. connect a resistor between rclass to gnd per table 1. t2p (pin 5, lt4276 a and lt4276 b only) : pse type indica - tor. low impedance to v cc indicates 2- event classification. alternating low/high impedance indicates ltpoe ++ clas - sification ( lt4276 a only, see applications information). high impedance indicates 1- event classification. this pin is not connected on the lt4276 c. see the applications information section for pin behavior when using the aux pin. dnc (pin 22): do not connect. leave pin open. rosc (pin 10) : programmable frequency adjustment. resistor to gnd programs operating frequency. leave open for default frequency of 214khz. sfst (pin 11) : soft-start. capacitor to gnd sets soft- start timing. ffsdly (pin 12) : forward/flyback select and primary gate delay adjustment. resistor to gnd adjusts gate drive delay for a flyback topology. resistor to v cc adjusts gate drive delay for a forward topology. ithb (pin 13) : current threshold control. the voltage on this pin corresponds to the peak current of the external fet. note that the voltage gain from ithb to the input of the current sense comparator (v sense ) is negative. fb31 (pin 14) : feedback input. in flyback mode, connect external resistive divider from the third winding feedback. reference voltage is 3.17v . connect to gnd in forward mode.rldcmp (pin 15) : load compensation adjustment. op - tional resistor to gnd controls output voltage set point as a function of peak switching current. leave rldcmp open if load compensation is not needed.isen C (pin 16) : current sense, negative input. route as a dedicated trace to the current sense resistor. isen + (pin 17) : current sense, positive input. route as a dedicated trace to the current sense resistor. sg (pin 18) : secondary (synchronous) gate drive, output. pg (pin 20): primary gate drive, output. v cc (pins 6, 7, 8, 9, 21) : switching regulator controller supply voltage. connect a local 1f ceramic capacitor from v cc pin 21 to gnd pin 19 as close as possible to lt4276 as shown in table 2. swvcc(pin 23) : switch driver for v cc s buck regulator. this pin drives the base of a pnp in a buck regulator to generate v cc . v in (pin 24) : buck regulator supply voltage. usually separated from hssrc by a pi filter. hssrc (pin 25) : external hot swap mosfet source. connect to source of the external mosfet. hsgate (pin 26) : external hot swap mosfet gate con - trol, output. capacitance to gnd determines inrush time.nc (pin 27) : no connection. not internally connected. vport (pin 28) : pd interface supply voltage and external hot swap mosfet drain connection. downloaded from: http:///
lt4276 7 4276fa for more information www.linear.com/lt4276 block diagram C+ C+ C+ +C C+ C+ C+ +C +C slope comp osc tsd cp switching regulator controller pd interface controller start-up regulator internal buck controller 1.4v1.4v hsgate hssrc 11v vport vport swvcc v in v cc ithbsfst ffsdly rosc isen + isen C 4276 bd t2pgnd pg sg v cc vport rclass rclass ++ aux v auxt i auxh fb31 rldcmp feedback amp gm = C40a/v load comp current fault comparator current sense comparator v fb v fault a v = 10 a v = 1 v cc v sense v ithb(os) a v = ?v sense ?v ithb downloaded from: http:///
lt4276 8 4276fa for more information www.linear.com/lt4276 overview power over ethernet (poe) continues to gain popularity as products take advantage of dc power and high speed data available from a single r j45 connector. the lt4276a allows higher power while maintaining backwards compat - ibility with existing pse systems. the lt4276 combines a poe pd controller and a switching regulator controller capable of either flyback or for ward isolated power sup - ply operation.significant differences from previous products the lt4276 has several significant differences from pre - vious linear technology products. these differences are briefly summarized below. see applications information for more detail. ithb is inverted from the usual ith pin the ithb pin voltage has an inverse relationship to the cur - rent sense comparator threshold, v sense . furthermore, the ithb pin offset voltage, v ithb(os) , is 3.17v . see figure 1. duty-cycle based soft-start the lt4276 uses a duty cycle ramp soft-start that injects charge into ithb. this allows startup without appreciable overshoot and with inexpensive external components. the feedback pin (fb31) is 3.17v rather than 1.25v the error amp feedback voltage (v fb ) is 3.17v. applications information figure 1. v sense vs. v ithb flyback/forward mode is pin selectable the lt4276 operates in flyback mode if ffsdly is pulled down by a resistor to gnd. it operates in forward mode if ffsdly is pulled up by a resistor to v cc . the value of this resistor determines the t pgdelay and t pgsg . t2p pin polarity is reversedthe t2p pin pulls up to v cc when active rather than pull - ing down to gnd.v cc is powered by internally driven buck regulator the lt4276 includes a buck regulator controller that must be used to generate the v cc supply voltage. poe modes of operation the lt4276 has several modes of operation, depending on the input voltage sequence applied to the vport pin. v sense ?v sense ?v ithb v ithb v ithb(os) 4276 f01 table 1. classification codes, power levels and resistor selection class pd power available pd type nominal class current lt4276 grade capability resistor (1%) a b c r cls r cls ++ 0 13w type 1 0.7ma open open 1 3.84w type 1 10.5ma 150 open 2 6.49w type 1 18.5ma 80.6 open 3 13w type 1 28ma 52.3 open 4 25.5w type 2 40ma 35.7 open 4* 38.7w ltpoe ++ 40ma open 35.7 4* 52.7w ltpoe ++ 40ma 150 47.5 4* 70w ltpoe ++ 40ma 80.6 64.9 4* 90w ltpoe ++ 40ma 52.3 118 *an ltpoe ++ pd classifies as class 4 by an ieee 802.3 compliant pse. downloaded from: http:///
lt4276 9 4276fa for more information www.linear.com/lt4276 figure 2. type 1 detect/class signaling waveform figure 3. type 2 detect/class signaling waveform figure 4. ltpoe ++ detect/class signaling waveform applications information detectionduring detection, the pse looks for a 25k signature resistor which identifies the device as a pd. the lt4276 signature resistor is smaller than 25k to compensate for the additional series resistance introduced by the ieee required bridge. classification the detection/classification process varies depending on whether the pse is type 1, type 2, or ltpoe ++ . a type 1 pse, after a successful detection, may apply a classifica - tion probe voltage of 15.5v to 20.5v and measure current. in 2- event classification, a t ype 2 pse probes for power classification twice as shown in figure 3. the lt4276 a or lt4276 b recognizes this and pulls the t2p pin up to v cc to signal the load that type 2 power is available. otherwise it does not pull up on the t2p pin, indicating that only type 1 power is available. if an lt4276 a senses an ltpoe ++ pse it alternates between pulling t2p up and floating t2p at a rate of f t2p to indicate the ltpoe ++ power is available. ltpoe ++ classification the lt4276 a allows higher power allocation while main - taining backwards compatibility with existing pse systems by extending the classification signaling of ieee 802.3. linear technology pse controllers capable of ltpoe ++ are listed in the related parts section. ieee pses classify an ltpoe ++ pd as a type 2 pd. classification resistors (r cls and r cls ++ ) the r cls and r cls ++ resistors set the classification cur - rent corresponding to the pd power classification. select the value of r cls from table 1 and connect the resistor between the rclass pin and gnd. for ltpoe ++, use the lt4276 a and select the value of r cls ++ from table 1 in addition to r cls . the resistor tolerance must be 1% or better to avoid degrading the overall accuracy of the classification circuit. signature corrupt during mark during the mark state, the lt4276 presents <11k to the port as required by the ieee specification. 4276 f02 v port v hson v hsoff v classmin v sigmax v sigmin v reset detect class power on 4276 f03 v port v hson v hsoff v classmin v sigmax v sigmin v reset detect 1st class 1st mark 2nd mark 2nd class power on 4276 f04 v port v hson v hsoff v classmin v sigmax v sigmin v reset detect 1st class 1st mark 2nd mark 3rd mark 2nd class 3rd class power on downloaded from: http:///
lt4276 10 4276fa for more information www.linear.com/lt4276 applications information inrush and powered ononce the pse detects and optionally classifies the pd, the pse then powers on the pd. when the port voltage rises above the v hson threshold, it begins to source i gpu out of the hsgate pin. this current flows into an external capacitor (c gate in figure 5) that causes a voltage to ramp up the gate of the external mosfet. the external mosfet acts as a source follower and ramps the voltage up on the output bulk capacitor (c port in figure 5), thereby determining the inrush current (i inrush in figure 5). to meet ieee requirements, design i inrush to be ~100ma. the lt4276 internal charge pump provides an n-channel mosfet solution, eliminating a larger and more costly p-channel fet. the low r ds(on) mosfet also maximizes power delivery and efficiency, reduces power and heat dissipation, and eases thermal design. figure 5. programming i inrush figure 6. v cc buck regulator external v cc supply the external v cc supply must be configured as a buck regulator shown in figure 6. to optimize the buck regulator, use the external component values in table 2 correspond - ing to the v in operating range. this buck regulator runs in discontinuous mode with the inductor peak current considerably higher than average load current on v cc . thus, the saturation current rating of the inductor must exceed the values shown in table 2. place the capacitor, c, as close as possible to v cc pin 21 and gnd pin 19. for optimal performance, place the external components as close as possible to the lt4276. lt4276 hsgate gnd 4276 f05 vport hssrc c gate i gpu 3.3k + c port vport i inrush i inrush = i gpu ? c port c gate delay start after the hsgate charges up to approximately 7v above hssrc, fully enhancing the external hot swap mosfet, the switching regulator controller operates after a delay of t start . during this delay, the lt4276 draws i mps from vport to ensure that the pse does not dc disconnect the pd due to maintain power signature requirements. v in r e v cc v in v cc gnd swvcc lt4276 fmmt723pbss9110t l(h) c(f) 4276 f06 auxiliary supply override if the aux pin is held above v auxt , the lt4276 enters auxiliary power supply override mode. in this mode the signature resistor is disconnected, classification is dis - abled, and hsgate is pulled down. the t2p pin pulls up to v cc on the lt4276 b (or the lt4276 a when no r cls ++ resistor is present). the t2p pin alternates between pulling up and floating at f t2p on the lt4276 a when the r cls ++ resistor is present. the aux pin allows for setting the auxiliary supply turn on (v auxon ) and turn off (v auxoff ) voltage thresholds. the auxiliary supply hysteresis voltage (v auxhys ) is set by sinking current (i auxh ) only when the aux pin voltage is table 2 . buck regulator component selection v in c l i s at r e 9v-57v poe 22f 10f 22h 100h 1.2a 300ma 1 20 downloaded from: http:///
lt4276 11 4276fa for more information www.linear.com/lt4276 applications information figure 7. aux threshold and hysteresis calculation lt4276 gnd 4276 f08a aux r1 v aux +C r2 r1 = v auxon ? v auxoff i auxh = v auxhys i auxh r2 = r1 v auxoff v auxt ? 1 ?? ? ?? ? r1 v aux(max) ? v auxt 1.4ma switching regulator controller operation the switching regulator controller portion of the lt4276 is a current mode controller capable of implementing either a flyback or a forward power supply. when used in flyback mode, no opto-isolator is required for feedback because the output voltage is sensed via the transformer s third winding.flyback mode the lt4276 is programmed into flyback mode by placing a resistor r ffsdly from the ffsdly pin to gnd. this resis - tor must be in the range of 5.23k to 52.3k . if using a potentiometer to adjust r ffsdly , ensure the adjustment of the potentiometer does not exceed 52.3k .the value of r ffsdly determines t pgdelay according to the following equations: t pgdelay 2.69ns / k ? r ffsdly + 30ns t pgsg 20ns the pg and sg relationships in flyback mode are shown in figure 8. the sg pin must be connected to the secondary side mosfet through a gate drive transformer as shown in figure 9. add a schottky diode from pg to gnd as shown in figure 9 to prevent pg from going negative. figure 8: pg and sg relationship in flyback mode figure 9: example pg and sg connections in flyback mode pgsg 4276 f07 t pgdelay t pgon t pgsg ? ? ? ? pg sg gnd lt4276 4276 f08 ffsdly r ffsdly isen + isen C + forward mode the lt4276 is programmed into forward mode by placing a resistor r ffsdly from the ffsdly pin to v cc . the r ffsdly resistor must be in the range of 10.5k to 52.3k . if using a potentiometer to adjust r ffsdly ensure the adjustment of the potentiometer does not exceed 52.3k.the value of r ffsdly determines t pgdelay and t pgsg ac - cording to the following equations: t pgdelay 7.16ns/k ? r ffsdly + 17ns t pgsg 5.60ns/k ? r ffsdly + 7.9ns the pg and sg relationships in forward mode are shown in figure 10. less than v auxt . use the following equations to set v auxon and v auxoff via r1 and r2 in figure 7. a capacitor up to 1000pf may be placed between the aux pin and gnd to improve noise immunity. v auxon must be lower than v hsoff . downloaded from: http:///
lt4276 12 4276fa for more information www.linear.com/lt4276 applications information figure 10: pg and sg relationship in forward mode in forward mode, the sg pin has the correct polarity to drive the active clamp p-channel mosfet through a simple level shifter as shown in figure 11. add a schottky diode from the pg to gnd as shown in figure 11 to prevent pg from going negative. feedback amplifier in the flyback mode, the feedback amplifier senses the output voltage through the transformer s third winding as shown in figure 12. the amplifier is enabled only during the fixed interval, t fb , as shown in figure 13. this eliminates the opto-isolator in isolated designs, thus greatly improving the dynamic response and stability over lifetime. since t fb is a fixed interval, the time-averaged transconductance, gm, varies as a function of the user-selected switching frequency. pgsg 4276 f09 t pgdelay t pgsg figure 11: example pg and sg connections in forward mode ? ? pg v cc v cc sg gnd lt4276 4276 f10 ffsdly r ffsdly isen + isen C +C +C +C ? ? ? feedback fb31 lt4276 third primary 4276 f11 secondary ithb pg isen + isen C rldcmp r fb2 v in v out r sense v fb r fb1 r ldcmp a v = 10 figure 12: feedback and load compensation connection figure 13: feedback amplifier timing diagram pg fb31 voltage gnd sg 4276 f09 t fb t fbdly v fb feedback amplifier output, ithb as shown in the block diagram, v sense is the input of the current sense comparator. v sense is derived from the output of a linear amplifier whose input is the voltage on the ithb pin, v ithb . this linear amplifier inverts its input, v ithb , with a gain, v sense /v ithb , and with an offset voltage of v ithb(os) to yield its output, v sense . this relationship is shown graphically in figure 1. note the slope v sense /v ithb is a negative number and is provided in the electrical characteristics table. v ithb = v ithb(os) + v sense ? v sense v ithb ?? ? ?? ? ?1 downloaded from: http:///
lt4276 13 4276fa for more information www.linear.com/lt4276 the block diagram shows v sense is compared against the voltage across the current sense resistor, v(isen + )- v(isen C ) modified by the internal slope compensation voltage discussed subsequently. load compensation as can be seen in figure 13, the voltage on the fb31 pin droops slightly during the flyback period. this is mostly caused by resistances of components of the secondary side such as : the secondary winding, r ds(on) of the syn - chronous mosfet, esr of the output capacitor, etc. these resistances cause a feedback error that is proportional to the current in the secondary loop at the time of feedback sample window . to compensate for this error, the lt4276 places a voltage proportional to the peak current in the primary winding on the rldcmp pin. determining feedback and load compensation resistors because the resistances of components on the secondary side are generally not well known, an empirical method must be used to determine the feedback and load com - pensation resistor values. initially set r fb2 = 2k r fb1 r fb2 v out v fb n third n secondary ?r fb2 connect the resistor r ldcmp between the rldcmp pin and gnd. r ldcmp must be at least 10k . adjust r ldcmp for minimum change of v out over the full input and output load range. a potentiometer in series with 10k may be initially used for r ldcmp and adjusted. the potentiometer+ 10k may then be removed, measured, and replaced with the equivalent fixed resistor. the resulting v out differs from the desired v out due to offset injected by load compensa - tion. the change to r fb2 to correct this is predicted by: r fb2 = v out v fb n third n secondary r fb2 2 r fb1 applications information where: v out is the desired change to v out r fb2 is the required change to r fb2 n third /n secondary is the transformer third winding to secondary winding opto-isolator feedback for forward mode operation, the flyback voltage cannot be sensed across the transformer. thus, opto-isolator feed - back must be used. when using opto-isolator feedback, connect the fb31 pin to gnd and leave the rldcmp pin open. in this condition, the feedback amplifier sinks an average current of i sink into the ithb pin. an example for feedback connections is shown in figure 14. note that since i sink is time-averaged over the switching period, the sink current varies as a function of the user-selected switching frequency. figure 14: opto-isolator feedback connections in the forward mode lt4276 ithb 4276 f13 v cc v out c x r x fb31 gnd soft-start in poe applications, a proper soft-start design is required to prevent the pd from drawing more current than the pse can provide. the soft-start time, t sfst , is approximately the time in which the power supply output voltage, v out , is charg - ing its output capacitance, c out . this results in an inrush current at the port of the pd, iport_inrush . care must be taken in selecting t sfst to prevent the pd from drawing more current than the pse can provide. downloaded from: http:///
lt4276 14 4276fa for more information www.linear.com/lt4276 applications information in the absence of an output load current, the iport_inrush, is approximated by the following equation: iport_inrush (c out ? v out 2 )/( ? t sfst ? v in ) where is the power supply efficiency, v in is the input voltage of the pd iport_inrush plus the port current due to the load current must be below the current the pse can provide. note that the pse current capability depends on the pse operating standard. the lt4276 contains a soft-start function that controls t sfst by connecting an external capacitor, c sfst , between the sfst pin and gnd. the sfst pin is pulled up with i sfst when the lt4276 begins switching. the voltage ramp on the sfst pin is proportional to the duty cycle ramp for pg.for flyback mode, the soft-start time is: t sfst = 600a nf c sfst i sfst ?? ? ?? ? t pgon + t pgdelay ? t min ( ) where t pgon is the time when pg is high as shown in figure 8 once the power supply is in steady-state. in for ward mode, each of the back page applications sche - matics provides a chart with t sfst vs. c sfst . select the application and choose a value of c sfst that corresponds to the desired soft-start time. current sense comparator the lt4276 uses a differential current sense comparator to reduce the effects of stray resistance and inductance on the measurement of the primary current. isen + and isen C must be kelvin connected to the sense resistor pads. like most switching regulator controllers, the current sense comparator begins sensing the current t min after pg turns on. then, the comparator turns pg off after the voltage across isen + and isen C exceeds the current sense comparator threshold, v sense . note that the voltage across isen + and isen C is modified by lt4276 s internal slope compensation. slope compensation the lt4276 incorporates current slope compensation. slope compensation is required to ensure current loop stability when the duty cycle is greater than or near 50%. the slope compensation of the lt4276 does not reduce the maximum peak current at higher duty cycles. control loop compensation in flyback mode, loop frequency compensation is per - formed by connecting a resistor/capacitor network from the output of the feedback amplifier (ithb pin) to gnd as shown in figure 12. in forward mode, loop compensation is performed by varying r x and c x in figure 14. adjustable switching frequency the lt4276 has a default switching frequency, f osc , of 214 khz when the rosc pin is left open. if a higher switching frequency, f sw , is desired (up to 300 khz), a resistor no smaller than 45.3k may be added between the rosc pin to gnd. the resistor can be calculated below: r osc = 3900k ? khz f sw ? f osc ( ) k ( ) short circuit response if the power supply output voltage is shorted, overloaded, or if the soft-start capacitor is too small, an overcurrent fault event occurs when the voltage across the sense pins exceeds v fault (after the blanking period of t min ). this begins the internal fault timer t fault . for the duration of t fault , the lt4276 turns off pg and sg and pulls the sfst pin to gnd. after t fault expires, the lt4276 initi - ates soft-start.the fault and soft-start sequence repeats as long as the short circuit or overload conditions persist. this condition is recognized by the pg waveform shown in figure 15 re peating at an interval of t fault . figure 15: pg waveform with output shorted t fault 4276 f14 downloaded from: http:///
lt4276 15 4276fa for more information www.linear.com/lt4276 applications information overtemperature protection the ieee 802.3 specification requires a pd to withstand any applied voltage from 0v to 57v indefinitely. during classification, however, the power dissipation in the lt4276 may be as high as 1.5w . the lt4276 can easily tolerate this power for the maximum ieee classification timing but overheats if this condition persists abnormally. the lt4276 includes an over-temperature protection feature which is intended to protect the device during momentary overload conditions. if the junction temperature exceeds the over-temperature threshold, the lt4276 pulls down hsgate pin, disables classification, and disables the switching regulator operation. maximum duty cycle the maximum duty cycle of the pg pin is modified by the chosen t pgdelay and f sw . it is calculated below: max power supply duty cycle = d max ? t pgdelay ? f sw for an appropriate margin during transient operation, the forward or flyback power supply should be designed so that its maximum steady-state duty cycle should be about 10% lower than the lt4276 maximum power supply duty cycle calculated above. external interface and component selection poe input diode bridge pds are required to polarity-correct its input voltage. when diode bridges are used, the diode forward voltage drops affect the voltage at the vport pin. the lt4276 is designed to tolerate these voltage drops. the voltage parameters shown in the electrical characteristics are specified at the lt4276 package pins. for high efficiency applications, the lt4276 supports an lt4321 -based poe ideal diode bridge that reduces the forward voltage drop from 0.7v to nearly 20mv per diode in normal operation, while maintaining ieee 802.3 compliance. auxiliary input diode bridge some pds are required to receive ac or dc power from an auxiliary power source. a diode bridge is typically required to handle the voltage rectification and polarity correction. in high efficiency applications, the voltage drop across the rectifier cannot be tolerated. the lt4276 can be configured with an lt4320 -based ideal diode bridge to recover the diode voltage drop and ease thermal design.input capacitor a 0.1f capacitor is needed from vport to gnd to meet the input impedance requirement in ieee 802.3 and to properly bypass the lt4276 . this capacitor must be placed as close as possible to the vport and gnd pins. transient voltage suppressor the lt4276 specifies an absolute maximum voltage of 100v and is designed to tolerate brief overvoltage events due to ethernet cable surges. to protect the lt4276 , install a unidirectional transient voltage suppressor (tvs) such as an sma j58 a between the vport and gnd pins. this tvs must be placed as close as possible to the vport and gnd pins of the lt4276. for pd applications that require an auxiliary power input, install a tvs between v in and gnd as close as possible to the lt4276.for extremely high cable discharge and surge protection contact linear technology applications. downloaded from: http:///
lt4276 16 4276fa for more information www.linear.com/lt4276 typical applications + v out 5v at 2.3a Cv out q1 l1: coilcraft, do1813p-181hc l2: coilcraft, do1608c-103 l4: coilcraft, do1608c-104 c2: 22f, 6.3v, murata grm31cr70j226ke19 c5: 47f, 6.3v, panasonic 6svp47m c7: 2.2f, 100v, murata grm32er72a225ka35 t1: wrth, 750313109 q1: psmn075-100mse t2: pca epa4271ge or pulse pe-68386nl vport gnd l2 10h l1 180nh l4 100h 10f100v 10nf100v 3.3k 10f 10v hssrc swvcc fb31 pgsg ithb rosc sfst ffsdly rclass gnd vport lt4276c hsgate isen + isen C v in v cc c72.2f fdn86246 bat54ws bat46ws t2 4276 ta02 psmn4r2-30mld mmbt3906 mmbt3904 t1 1nf 1f 6.04k 20 2k 2701/4w 11 1/4w 60m1/4w 15 100 1f 330pf 0.1f 107k 5.23k 52.3 8.2 ptvs58vp1utp 4.7nf 2.2nf 2kv 20k 10k 2.2nf c222f c547f 6.3v 47pf630v 0.1f 100v 2.2nf 2kv bav19ws ? ? ? ? ? fmm t 723 13w (type 1) poe power supply in flyback mode with 5v, 2.3a output efficiency vs load current output regulation vs load current load current (a) 0.2 76 efficiency (%) 9088 86 84 82 80 78 92 1.2 1.0 1.6 1.8 2.0 2.2 1.4 2.4 0.4 0.8 0.6 4276 ta02a vport = 37v vport = 48v vport = 57v load current (a) 0.2 4.80 v out (v) 5.155.10 5.05 5.00 4.95 4.90 4.85 5.20 1.2 1.0 1.6 1.8 2.0 2.2 1.4 2.4 0.4 0.8 0.6 4276 ta02b vport = 37v vport = 48v vport = 57v downloaded from: http:///
lt4276 17 4276fa for more information www.linear.com/lt4276 typical applications + v out 5v at 4.7a Cv out q1 l1: coilcraft, do1813p-181hc l2: coilcraft, do1608c-103 l4: coilcraft, do1608c-104 c2, c3: 22f, 6.3v, murata grm31cr70j226ke19 c5: 47f, 6.3v, panasonic 6svp47m c7: 2.2f, 100v, murata grm32er72a225ka35 t1: wrth, 750313082 or pca epc3409g q1-q9: psmn075-100mse t2: pca epa4271ge or pulse pe-68386nl l2 10h l1 180nh l4 100h 10f100v 10nf100v 3.3k 24v 8.2 10f 10v hssrc swvcc fb31 pgsg t2p ithb rosc sfst ffsdly rclass gnd vport lt4276b hsgate isen + isen C v in v cc c72.2f bsz520n15ns3g bat54ws bat46ws to microprocessor 4276 ta03 psmn2r4-30mld mmbt3906 mmbt3904 t1 1nf 1f 5.90k 20 2k 160||1601/4w 5.1 1/4w 40m1/4w 15 100 1f 220pf 0.1f 107k 7.50k 35.7 ptvs58vp1utp 3.3nf 2.2nf 2kv 20k 10k 2.2nf c2, c322f || 22f c547f 100pf100v 47nf100v 2.2nf 2kv opto bg36 lt4321 bg12 tg12 tg36 tg78 tg45 bg45 bg78 outp outn enen in12 t2 q2 q3 q4 q5 q6 q7 q8 q9 1 data pairs spare pairs 23 6 4 5 7 8 in36in45 in78 47nf100v bav19ws ?? ? ? ? fmmt723 25.5w (type 2) poe + power supply in flyback mode with 5v, 4.7a output efficiency vs load current v out vs load current load current (a) 0.5 78 efficiency (%) 9290 88 86 84 82 80 94 2.0 1.5 3.0 3.5 4.0 4.5 2.5 5.0 1.0 4276 ta03a vport = 42.5v vport = 50v vport = 57v load current (a) 0.5 4.80 v out (v) 5.155.10 5.05 5.00 4.95 4.90 4.85 5.20 2.0 1.5 3.0 3.5 4.0 4.5 2.5 5.0 1.0 4276 ta03b vport = 42.5v vport = 50v vport = 57v downloaded from: http:///
lt4276 18 4276fa for more information www.linear.com/lt4276 typical applications q1 10nf100v 3.3k l4 100h 10f 10v bav19ws fmmt723 8.2 ptvs58vp1utp 0.1f 100v l1 2.2h c5100f ( 2) c8100f 6hva100m + + l2 4.9h 22f100v hssrc swvcc ffsdly pgsg ithb rosc sfst rclass ++ rclass gnd fb31 t2p vport lt4276a hsgate isen + isen C v in v cc v cc +v out +v out +5v at 13a v cc c72.2f ( 2) bat54ws bsc190n12ns3 4276 ta04 20m1/4w 1001206 10nf250v 5 100nf250v 750 330 240 4.7n zr431 10k 10.0k 10.0k 1k 10 10 cmmsh1-40l bsc054n04ns bsc054n04ns cmmsh1-40l t1 cmmsh1-40l 8.2v cmhz4694 18vcmhz5248b 18vcmhz5248b 2.2nf 2kv 33nf 0.1f 0.1f 10k 0.1f fdmc2523p cmmsh1-40l m0c207m mmbt3904 vport gnd 13k 20 80.6 64.9 0.47f 100pf 100k 107k ?? l1: coilcraft, xal-1010-222me l2: wrth, 744314490 l4: coilcraft, do1608c-104 c5, 100f, 6.3v, suncon 6hva100m c7: 2.2f, 100v, murata grm32er72a225ka35l c8: 100f, 6.3v, suncon 6hva100m t1: wrth, 750313095 q1: psmn040-100mse to microprocessor opto 10nf efficiency vs load current v out vs load current 70w ltpoe ++ power supply in forward mode with 5v, 13a output load current (a) 1 76 efficiency (%) 9290 88 86 84 82 80 78 94 76 9 10 11 12 8 13 32 54 4276 ta04a vport = 41v vport = 50v vport = 57v load current (a) 1 4.80 v out (v) 5.155.10 5.05 5.00 4.95 4.90 4.85 5.20 76543 9 10 11 12 8 13 2 4276 ta04b vport = 41v vport = 50v vport = 57v c sfst (f) t sfst (ms) 0.10 1.2 0.33 3.8 1.0 12 3.3 38 downloaded from: http:///
lt4276 19 4276fa for more information www.linear.com/lt4276 efficiency vs load current v out vs load current + l2 6.5h 22f100v hssrc swvcc ffsdly pgsg ithb rosc sfst rclass ++ rclass gnd fb31 t2p vport lt4276a hsgate isen + isen C v in v cc v cc +v out +v out +12v at 7a v cc c72.2f ( 2) bat54ws bsc190n12ns3 4276 ta05 15m1/4w 1001206 33nf250v 0.22f250v 750 820 20k zr431 10k 10.0k 100pf 38.3k 13k 10 cmmsh1-60 bsc123n08s3 bsc123n08s3 t1 cmmsh1-100 cmmsh1-100 13v cmhz4700 7.5v cmhz5236b 2.2nf 2kv 6.8nf 0.1f 0.1f 10k 0.1f fdmc2523p cmmsh1-40l m0c207m mmbt3904 29.4k v cc bg36 lt4321 bg12 tg12 tg36 tg78 tg45 bg45 bg78 outp outn enen in12 t2 q2 q3 q4 q5 q6 q7 q8 q9 1 data pairs spare pairs 23 6 4 5 7 8 in36in45 in78 76.8 64.9 1f 100pf* 100pf 100k 107k 330pf 20 ?? 7.5 q1 10nf100v 47nf100v 3.3k l4 100h 10f 10v 8.2 ptvs58vp1utp 47nf 100v l1 8.2h 22f 16v ( 2) 100f16v 16hva100m l1: coilcraft, xal-1010-822me l2: wrth, 744314650 l4: coilcraft, do1608c-104 c5, 100f, 6.3v, tdk c3225x5r0j107m c7: 2.2f, 100v, murata grm32er72a225ka35l c8: 100f, 16v, suncon 16hva100m t1: pca epc3577g-lf t2: wrth, 749022016 q1: psmn040-100mse q2-q9: psmn075-100mse to microprocessor opto fmmt723 820pf 100pf +v out +v out 7.5vcmhz5236b 5.1k fmmt624 fmmt624 5.1k 100pf bav19ws typical applications 90w ltpoe ++ power supply in forward mode with 12v, 7a output load current (a) 0.7 76 efficiency (%) 9492 90 88 86 84 82 80 78 96 2.8 2.1 4.2 4.9 5.6 6.3 3.5 7.0 1.4 4276 ta05a vport = 41v vport = 50v vport = 57v load current (a) 0.7 11.5 v out (v) 12.412.3 12.2 12.1 12.0 11.9 11.8 11.7 11.6 12.5 2.8 2.1 1.4 4.2 4.9 5.6 6.3 3.5 7.0 4276 ta05b vport = 41v vport = 50v vport = 57v c sfst (f) t sfst (ms) 0.10 1.5 0.33 4.9 1.0 15 3.3 48 downloaded from: http:///
lt4276 20 4276fa for more information www.linear.com/lt4276 typical applications 38.7w ltpoe ++ power supply in flyback mode with 5v, 7a output + v out 5v at 7a Cv out q1 l1: coilcraft, do1813p-181hc l2: coilcraft, do1608c-103 l4: coilcraft, do1608c-104 c2, c3: 47f, 6.3v, grm31cr60j476me19l c5: 47f, 6.3v, panasonic 6svp47m c7: 2.2f, 100v, murata grm32er72a225ka35l t1: wrth, 750314783 or pca epc3586g q1-q9: psmn075-100mse t2: pca epa4271ge or pulse pe-68386nl l2 10h l1 180nh l4 100h 10f100v 10nf100v 47nf100v 3.3k 24v 8.2 10f 10v hssrc swvcc fb31 pgsg t2p ithb rosc sfst ffsdly r class ++ gnd vport lt4276a hsgate isen + isen C v in v cc c72.2f bsz900n20 ns3g bat54ws bat46ws to microprocessor 4276 ta06 psmn2r4-30mld mmbt3906 mmbt3904 t1 1nf 1f 5.90k2.00k 801/4w 5.1 1/4w 40m1/4w 15 100 20 1f 220pf 0.1f 107k 7.50k rldcmp 51k 35.7 ptvs58vp1utp 3.3nf 2.2nf 2kv 20k 10k 2.2nf c2, c347f || 47f c547f 100pf100v 47f100v 2.2nf 2kv opto bg36 lt4321 bg12 tg12 tg36 tg78 tg45 bg45 bg78 outp outn enen in12 t2 q2 q3 q4 q5 q6 q7 q8 q9 1 data pairs spare pairs 23 6 4 5 7 8 in36in45 in78 bav19ws ?? ? ? ? fmmt723 efficiency vs load current output regulation vs load current load current (a) 0.5 78 efficiency (%) 9290 88 86 84 82 80 94 4.03.5 5.0 5.5 6.0 6.5 4.5 7.0 3.02.52.01.51.0 4276 ta06a vport = 50v vport = 57v load current (a) 0.5 4.80 v out (v) 5.155.10 5.05 5.00 4.95 4.90 4.85 5.20 4.03.5 5.0 5.5 6.0 6.5 4.5 7.0 3.02.52.01.51.0 4276 ta06b vport = 50v vport = 57v downloaded from: http:///
lt4276 21 4276fa for more information www.linear.com/lt4276 typical applications 25.5w (type 2) poe + and 9v-57v auxiliary input power supply in flyback mode with 12v, 1.9a output efficiency vs load current output regulation vs load current + v out 12v at 1.9a Cv out q1 l1: coilcraft, do1813p-561ml l2: wrth, 7443330820 l3: murata, lqm31pn2r2m00l l4: coilcraft, do1813h-223 c2, c3: 10f, 16v, murata grm31cr61c106ka88 c5: 33f, 20v, kemet, t494v336m020as c7, c8: 3.3f, 100v, tdk c3225x7s2a335m t1: pca epc3601g or wrth 750315422 q1: psmn075-100mse q1-q9:psmn075-100mse t2: pca epa4271ge or pulse pe-68386nl l2 8.2h l3 2.2h 1f 680f63v l1 560nh l4 22h 10f100v 68nf100v 0.1f 3.3k 158k931k 24v 47nf100v 8.2 22f 10v pmeg10010elr hssrc swvcc fb31 pgsg t2p ithb rosc sfst ffsdly rclass gnd vport aux lt4276b hsgate isen + isen C v in v cc c7, c83.3f fdmc86160 bat54ws bat46ws to microprocessor 4276 ta08 bsz900nf20ns3 cmlt7820g cmlt3820g t1 220pf 1f 4.75k2.00k 621/4w 82||82 1/4w 15m1/4w 15 100 1f 220pf 0.1f 107k 9.31k rldcmp 51k 35.7 ptvs58vp1utp 4.7nf 2.2nf 2kv 43k 10k 2.2nf c2, c310f || 10f c533f 100pf100v 47nf100v 2.2nf 2kv opto bg36 lt4321 bg12 tg12 tg36 tg78 tg45 bg45 bg78 outp outn enen in12 tg2tg1 outp outn in1in2 bg2 bg1 t2 q2 q3 q4 q5 q6 q7 q8 q9 1 data pairs spare pairs 23 6 4 5 7 8 in36in45 in78 lt4320 bsz110n06ns3 x4 mmsd4148 x3 v aux 9v to 57vdc or 24vac 1 ?? ? ? ? + fmmt723 load current (a) 0.2 70 efficiency (%) 9290 88 86 84 82 80 78 76 74 72 94 1.2 1.6 1.8 1.4 2.0 1.0 0.8 0.6 0.4 4276 ta08a v aux = 57v v aux = 42.5v v aux = 24v v aux = 9v load current (a) 0.2 11.5 v out (v) 12.412.3 12.2 12.1 12.0 11.9 11.8 11.7 11.6 12.5 1.2 1.6 1.8 1.4 2.0 1.0 0.8 0.6 0.4 4276 ta08b v aux = 57v v aux = 42.5v v aux = 24v v aux = 9v downloaded from: http:///
lt4276 22 4276fa for more information www.linear.com/lt4276 typical applications 25.5w (type 2) poe + power supply in flyback mode with 3.3v, 6.8a output efficiency vs load current output regulation vs load current + v out 3.3v at 6.8a Cv out q1 l1: coilcraft, do1813p-181hc l2: coilcraft, do1608c-103 l4: coilcraft, do1608c-104 c2, c3: 22f, 6.3v, murata grm31cr70j226ke19 c5: 68f, 4v, 4svpa68maa c7: 2.2f, 100v, murata grm32er72a225ka35 t1: wrth, 750310743 or pca epc3408g q1-q9: psmn075-100mse t2: pca epa4271ge or pulse pe-68386nl l2 10h l1 180nh l4 100h 10f100v 10nf100v 47nf100v 3.3k 24v 8.2 10f 10v hssrc swvcc fb31 pgsg t2p ithb rosc sfst ffsdly rclass gnd vport lt4276b hsgate isen + isen C v in v cc c72.2f bsz900n20ns3 bat54ws bat46ws to microprocessor 4276 ta09 psmn2r4-30mld mmbt3906 mmbt3904 t1 1nf 47 1f 6.49k2k 1001/4w 5.1 1/4w 40m1/4w 15 100 1f 470pf 0.1f 107k 6.81k 35.7 ptvs58vp1utp 4.7nf 2.2nf 2kv 8.25k 10k 2.2nf c2, c322f || 22f c568f 100pf100v 47nf100v 2.2nf 2kv opto bg36 lt4321 bg12 tg12 tg36 tg78 tg45 bg45 bg78 outp outn enen in12 t2 q2 q3 q4 q5 q6 q7 q8 q9 1 data pairs spare pairs 23 6 4 5 7 8 in36in45 in78 b0540ws bav19ws 20 ?? ? ? ? fmmt723 load current (a) 0.7 72 efficiency (%) 9088 86 84 82 80 78 76 74 92 4.2 5.6 6.3 4.9 7.0 3.5 2.8 2.1 1.4 4276 ta09a vport = 57v vport = 50v vport = 42.5v load current (a) 0.7 3.1 v out (v) 3.53.4 3.3 3.2 3.6 4.2 5.6 6.3 4.9 7.0 3.5 2.8 2.1 1.4 4276 ta09b vport = 57v vport = 50v vport = 42.5v downloaded from: http:///
lt4276 23 4276fa for more information www.linear.com/lt4276 typical applications 25.5w (type 2) poe + power supply in flyback mode with 24v, 1a output efficiency vs load current v out vs load current + v out 24v at 1a Cv out q1 l2: coilcraft, do1608c-103 l4: coilcraft, do1608c-104 c2: 4.7f, 50v, murata grm31cr71h475m012 c5: 22f, 35v, panasonic eeh-za1v220r c7: 2.2f, 100v, murata grm32er72a225ka35 t1: wrth, 750314782 or pca epc3603g q1-q9: psmn075-100mse t2: pca epa4271ge or pulse pe-68386nl l2 10h l4 100h 10f100v 10nf100v 3.3k 24v 8.2 10f 10v hssrc swvcc fb31 pgsg t2p ithb rosc sfst ffsdly rclass gnd vport lt4276b hsgate isen + isen C v in v cc c72.2f bsz520n15ns3g bat54ws bat46ws to microprocessor 4276 ta10 bsz12dn20ns3 mmbt3906 mmbt3904 t1 150pf 0.1f 6.49k2.00k 20 1001/4w 120||120 1/4w 40m1/4w 15 100 1f 10pf 0.47f 107k 5.23k rldcmp 24k 35.7 ptvs58vp1utp 3.3nf 2.2nf 2kv 160k 10k 2.2nf c2, c34.7f 50v c522f 47pf100v 47nf100v 2.2nf 2kv opto bg36 lt4321 bg12 tg12 tg36 tg78 tg45 bg45 bg78 outp outn enen in12 t2 q2 q3 q4 q5 q6 q7 q8 q9 1 data pairs spare pairs 23 6 4 5 7 8 in36in45 in78 47nf100v bav19ws ?? ? ? ? fmmt723 load current (a) 0.1 74 efficiency (%) 9290 88 86 84 82 80 78 76 94 0.6 0.8 0.9 0.7 1.0 0.5 0.4 0.3 0.2 4276 ta10a vport = 57v vport = 50v vport = 42.5v load current (a) 0.1 23.0 v out (v) 24.624.4 24.824.2 24.0 23.8 23.6 23.4 23.2 25.0 0.6 0.8 0.9 0.7 1.0 0.5 0.4 0.3 0.2 4276 ta10b vport = 57v vport = 50v vport = 42.5v downloaded from: http:///
lt4276 24 4276fa for more information www.linear.com/lt4276 package description please refer to http://www.linear.com/product/lt4276#packaging for the most recent package drawings. 4.00 0.10 (2 sides) 2.50 ref 5.00 0.10 (2 sides) note: 1. drawing proposed to be made a jedec package outline mo-220 variation (wxxx-x). 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package pin 1top mark (note 6) 0.40 0.10 27 28 12 bottom viewexposed pad 3.50 ref 0.75 0.05 r = 0.115 typ r = 0.05 typ pin 1 notch r = 0.20 or 0.35 45 chamfer 0.25 0.05 0.50 bsc 0.200 ref 0.00 C 0.05 (ufd28) qfn 0506 rev b recommended solder pad pitch and dimensions apply solder mask to areas that are not soldered 0.70 0.05 0.25 0.05 0.50 bsc 2.50 ref 3.50 ref 4.10 0.05 5.50 0.05 2.65 0.05 3.10 0.05 4.50 0.05 package outline 2.65 0.10 3.65 0.10 3.65 0.05 ufd package 28-lead plastic qfn (4mm 5mm) (reference ltc dwg # 05-08-1712 rev b) downloaded from: http:///
lt4276 25 4276fa for more information www.linear.com/lt4276 information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representa - tion that the interconnection of its circuits as described herein will not infringe on existing patent rights. revision history rev date description page number a 12/15 changed diode type of diode between swvcc and v cc from schottky to regular (bav19ws) on all applicable schematics.added additional conditions to v auxt and i auxh parameters. revised graph: pg delay time vs temperature in flyback mode. added t2 transformer part number recommendation to all flyback schematics. updated parts list for 25.5w (12v/1.9a) flyback schematic. 1, 10, 16-20, 22, 23 35 16, 17, 19- 23, 26 21 downloaded from: http:///
lt4276 26 4276fa for more information www.linear.com/lt4276 ? linear technology corporation 2015 lt 1215 rev a ? printed in usa linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax : (408) 434-0507 www.linear.com/lt4276 related parts typical application part number description comments ltc4267/ ltc4267-1/ ltc4267-3 ieee 802.3af pd interface with integrated switching regulator internal 100v, 400ma switch, programmable class, 200/300khz constant frequency pwm ltc4269-1 ieee 802.3af pd interface with integrated flyback switching regulator 2-event classification, programmable class, synchronous no-opto flyback controller, 50khz to 250khz, aux support ltc4269-2 ieee 802.3af pd interface with integrated forward switching regulator 2-event classification, programmable class, synchronous forward controller, 100khz to 500khz, aux support lt4275a/b/c ltpoe ++ /poe + /poe pd controller external switch, ltpoe ++ support ltc4278 ieee 802.3af pd interface with integrated flyback switching regulator 2-event classification, programmable class, synchronous no-opto flyback controller, 50khz to 250khz, 12v aux support ltc4290/ltc4271 8-port poe/poe + /ltpoe ++ pse controller transformer isolation, supports ieee 802.3af, ieee 802.3at and ltpoe ++ pds lt4320/lt4320-1 ideal diode bridge controller 9v - 72v ,dc to 600hz input. controls 4- nmosfets, voltage rectification without diode drops lt4321 poe ideal diode bridge controller controls 8-nmosfets for ieee-required pd voltage rectification without diode drops 25.5w (type 2) poe + power supply in flyback mode with 12v, 1.9a output efficiency vs load current output regulation vs load current + v out 12v at 1.9a Cv out q1 c5: 22f, 16v, panasonic 16svp22m c7: 2.2f, 100v, murata grm32er72a225ka35 t1: wrth, 750310742 or pca epc3410g q1-q9: psmn075-100mse t2: pca epa4271ge or pulse pe-68386nl l2 10h l1 180nh l4 100h 10f100v 10nf100v 3.3k 24v 8.2 10f 10v hssrc swvcc fb31 pgsg t2p ithb rosc sfst ffsdly rclass gnd vport lt4276b hsgate isen + isen C v in v cc c72.2f bsz520n15ns3g bat54ws bat46ws moc207m v out to microprocessor 4276 ta11 fdmc86160 mmbt3906 mmbt3904 t1 470pf 1f 6.49k2.00k 150v1/4w 13 1/4w 40m1/4w 15 100 1f 220pf 0.1f 107k 5.23k 35.7 ptvs58vp1utp 3.3nf 2.2nf 2kv 26.1k 10k 2.2nf c210f c522f 47pf630v 47nf100v 2.2nf 2kv bg36 lt4321 bg12 tg12 tg36 tg78 tg45 bg45 bg78 outp outn enen in12 t2 q2 q3 q4 q5 q6 q7 q8 q9 1 data pairs spare pairs 23 6 4 5 7 8 in36in45 in78 47nf100v l1: coilcraft, do1813p-181hc l2: coilcraft, do1608c-103 l4: coilcraft, do1608c-104 c2: 10f, 16v, murata grm31cr61c106ka88 bav19ws 10k 47k 20 ?? ? ? ? fmmt723 load current (a) 0.2 70 efficiency (%) 9088 86 84 82 80 78 76 74 72 92 1.2 1.6 1.8 1.4 2.0 1.0 0.8 0.6 0.4 4276 ta11a vport = 57v vport = 50v vport = 42.5v load current (a) 0.2 11.5 v out (v) 12.312.2 12.1 12.0 11.9 11.8 11.7 11.6 12.512.4 1.2 1.6 1.8 1.4 2.0 1.0 0.8 0.6 0.4 4276 ta11b vport = 57v vport = 50v vport = 42.5v downloaded from: http:///

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