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?on-bright electronics confidential - 1 - ob_doc_ds_79a0 OB2279 current mode pwm c ontroller f r e q shuffling w i th latc h shu tdow n general descri ption OB2279 is a highl y integ r ated current m ode pwm control ic optim ized fo r high perform ance, low standby pow er and cost effe ctive offline fly b ac k converter applications. pwm switching frequenc y at norm a l operation is externally pr ogrammable and trimmed to tigh t range . at no load or light load condition, t h e i c operates in extended ?bu r st m ode? to m i nim i ze switching loss. lower stan db y p o wer and high er conversion efficiency is thus achieved. vdd low st artup current and low operating curre nt contribute to a reliable po wer on startu p design with OB2279. a l a rge value resistor could t hus be used i n the startup circuit for reduc ed power loss. the internal slope com p ensation im p roves sy stem large signal stability and reduces the possible sub- harm onic oscillation at high pwm dut y cy cle output . leading-edge blankin g on current sense input rem oves the signal glitch du e to snubber circuit diode reverse r eco very and greatly reduces the external co m ponent count an d s y stem cost in the design. OB2279 offers co m p rehensiv e protection coverage including cy cle-by -cy c le current li m iting(ocp), vdd under voltage lockout(uvlo), vdd over voltage protection(ovp), vdd cl a m p, gate cla m p, over load protection(olp) and over tem p e ratur e protection (otp), etc. different latch shutdown optio ns are offered on OB2279 in d ifferent device version. v version has ovp latch shutdown . t v e rsion supp orts both ovp and otp latch shutdown. l version pro v ides all ovp, otp and olp latch shutd o wn control. excellent emi perform ance is achieved with on- bright pr opr ietary freq u e ncy shuffli ng techni qu e together with soft switching control at t h e totem pole gate drive out put. tone energ y at below 20khz is minim ized in operation. c onsequentl y , audio no ise is elim inated during operation. OB2279 is of fered in sop-8 and dip-8 packages. features on-bright proprietary frequency shuffling technolog y for im proved emi performance power on soft start extended burst mode control for im proved efficiency and minim u m s tandby power design audio noise free operatio n external p r ogrammable pwm switching frequency internal sy nchronized slope co m p ensati on low vin/v dd startup current(3ua) and low operating current (2.3m a ) leading edge blanking on current sense input co m p lete protection coverage with selectiv e protections fo r latch shutd o wn o vdd ov er voltage protection(ovp) ? latch shutdown o over tem p erature protection(otp) ? auto recovery or l a tch shutdow n o over load p r otection. (o lp) ? aut o r ecovery or latch shut down o vdd under voltage lockout with hysteresis (uvlo) o gate output voltage clamp (16. 5v) o built-in ocp com p ensation to achieve minim u m opp variation over universal ac input range. appl icat ions offline ac/dc flyback converter for adaptor notebook ad aptor lcd monitor /tv/pc/set-top box p o wer supplies open-frame smps printer power ty pic al ap pli ca t ion on-bright confidential to bona fide (?) http://
?on-bright electronics confidential - 2 - ob_doc_ds_79a0 OB2279 current mode pwm c ontroller f r e q shuffling w i th latc h shu tdow n general information pin configu r ation the pin map of OB2279 in dip8 and sop8 package is shown as below. orde ring information part numbe r desc ription OB2279ap-v dip8, v version with ovp latch OB2279ap-t dip8, t version with ovp/otp latch OB2279ap-l dip8, l version with ovp/otp/olp latch OB2279cp-v sop8, v version with ovp latch OB2279cp-t sop8, t version with ovp/otp latch OB2279cp-l sop8, l version with ovp/otp/olp latch note: all devices are offer ed in pb-free package if not other w i se noted. package dissipation rati ng package r ja ( c/w) dip8 90 sop8 150 abso lute ma x i mum ra ti ng s paramete r value vdd clamp voltage 35 v vdd cl a m p continuous current 10 ma v fb input voltage -0.3 to 7v v sense input voltage to sense pin -0.3 to 7v v rt input voltage to rt pin -0.3 to 7v v ri input voltage to ri pin -0.3 to 7v min/max op erating junction te m p erature t j -20 to 150 o c min/max storage te m p er a ture t st g -55 to 150 o c lead te m p er ature (soldering, 10secs) 260 o c note: stresses beyond those listed under ?absolute maximum ratings? ma y cau s e permanent d amage to the de vice. these are stress ratings only , fu nctional operat ion of the de vice at these or an y othe r conditions bey o nd those indicated under ?recommende d operating con ditions? is not implied. exposure to absolute maximum-rate d conditi ons for extende d periods ma y affect device r e li ability . on-bright confidential to bona fide (?)
?on-bright electronics confidential - 3 - ob_doc_ds_79a0 OB2279 current mode pwm c ontroller f r e q shuffling w i th latc h shu tdow n marking information termi n al assignments pin num pin name i/o description 1 gnd p ground 2 fb i feedback input pin. pwm duty cycle is determined by voltage level into this pin and current-sense signal level at pin 6. 3 vin i connected through a large value resistor to rectified line input for startup and line voltage sensing. 4 ri i internal oscillator frequency setting pin. a resistor connected between ri and gnd sets the pwm frequency. 5 rt i dual function pin. either connected through a ntc resistor to gnd for over temperature shutdown control or used as latch shutdown control input. 6 sense i current sense input pin. connected to mosfet current sensing resistor node. 7 vdd p dc power supply pin. 8 gate o totem-pole gate drive output for power mosfet. on-bright confidential to bona fide (?)
?on-bright electronics confidential - 4 - ob_doc_ds_79a0 OB2279 current mode pwm c ontroller f r e q shuffling w i th latc h shu tdow n block diagram recommended oper ating condi tion symbol parameter min max unit vdd vdd supply voltage 11.5 25 v ri ri resistor value 100 133 kohm t a operating am bient tem p erature -20 85 o c on-bright confidential to bona fide (?)
?on-bright electronics confidential - 5 - ob_doc_ds_79a0 OB2279 current mode pwm c ontroller f r e q shuffling w i th latc h shu tdow n el ect r ical characterist ics (t a = 25 o c if not ot herwise noted) symbol parameter test conditi ons min typ max unit supply voltage (vdd) i_vdd_start up vdd start up current vdd =15v, ri=100k measure curr ent into vdd 3 20 ua i_vdd_ops operation current vdd =16v, ri=100kohm, v fb =3v 2.3 ma uvlo(enter ) vdd under voltage lockout e n ter 8.8 9.8 10.8 v uvlo(exit) vdd under voltage lockout e x it (startup) 15.5 16.5 17.5 v ovp(latch) vdd over v o ltage latch trigger 26.5 28 29.5 v ovp(d e-lat c h) vdd lat c h relea se voltage threshold 7.5 v i(vdd)_latch vdd bleedin g current at latch shutdown when vdd = 9v 45 ua t d _ovp vdd ovp debounce time ri = 100koh m 80 usec v dd _clam p v dd zener clam p voltage ri = 100 koh m , i(v dd ) = 5 m a 35 v t_softstart soft start ti me 3 msec feedback input section(fb pin) a vcs pwm input gain v fb / v cs 2.8 v/v v fb_ open v fb open voltage vdd = 16v 6.2 v i fb _short fb pin short circuit current short fb pin to gnd, mea s ure curr ent 0.75 ma v th _0d zero duty cycle fb threshold voltage vdd = 16v, ri=100kohm 0.95 v v th _bm burst mode fb threshold vo ltage 1.6 v v th _pl power li m iti ng fb threshold vo ltage 4.4 v t d _pl power li m iting debounce time vdd = 16v, ri=100kohm 80 msec z fb _in input im pedance 9.0 kohm current s e n se input(sen se pin) t_blankin g sense input l eading edge blanking time ri = 100koh m 300 nsec z sense _in sense input im pedance 30 kohm t d _oc over current detection and control delay cl=1nf at gate, ri=100kohm 70 nsec v th _oc_0 current lim i ting threshold at no compensation vdd = 16v, i(vin) = 0ua, ri=100 kohm 0.85 0.90 0.95 v on-bright confidential to bona fide (?)
?on-bright electronics confidential - 6 - ob_doc_ds_79a0 OB2279 current mode pwm c ontroller f r e q shuffling w i th latc h shu tdow n v th _oc_1 current lim i ting threshold at co m p ensation vdd = 16v, i(vin) = 150ua, ri=1 00kohm 0.80 v oscillator f osc nor m al o scil lation frequency ri = 100kohm 60 65 70 khz ? f_tem p central frequency tem p erature stability vdd = 16v, ri=100kohm, -20 o c to 100 o c 3 % ? f_vdd central frequency voltage stabilit y vdd = 12-28v, ri=100kohm 3 % ri_range operating ri range 50 100 250 kohm v_ri_open ri open volta ge vdd = 16v 2.0 v f_bm burst mode base frequency vdd = 16v, ri=100kohm 20 khz gate drive output vol output low level vdd = 16v, io = 20 m a 0.3 v voh output high level vdd = 16v, io = 20 m a 11 v vg_clam p output clamp voltage level 16.5 v t_r output rising time vdd = 16v, cl = 1nf 120 nsec t_f output falling time vdd = 16v, cl = 1nf 50 nsec over temperature protection i_rt output curre nt of rt pin vdd = 16v, ri=100kohm 70 ua v th _otp otp threshold voltage vdd = 16v, ri=100kohm 1.01 5 1 .06 5 1.11 5 v v th _otp_off (version v o n ly ) otp recovery threshold vo ltage vdd = 16v, ri=100kohm 1.16 5 v v th _rt_latch (version v o n ly ) rt input lat c h threshold vo ltage 0.6 v t d _otp otp de-bounce ti m e vdd = 16v, ri=100kohm 100 usec v_rt_open rt pin open voltage vdd = 16v, ri=100kohm 3.7 v frequency s huffling ? f_osc frequency modulatio n r a nge /base fr equency ri=100kohm -3 3 % freq_shuffli ng shuffling frequenc y ri = 100koh m 32 hz on-bright confidential to bona fide (?)
?on-bright electronics confidential - 7 - ob_doc_ds_79a0 OB2279 current mode pwm c ontroller f r e q shuffling w i th latc h shu tdow n characterizati on plots vdd startup current vs. vdd 0 2 4 6 8 10 12 14 16 18 20 0 2 4 6 8 1 01 21 4 1 6 v dd( v) i_vdd(u a ) i_ vd d st ar tu p vs . t em pe ra tu re 0 2 4 6 8 - 20 0 20 4 0 6 0 80 100 120 te mp ( c) i _vdd (u a) vdd uvlo and ops current 0 0. 5 1 1. 5 2 2. 5 3 0 4 8 1 2 1 62 02 4 2 8 vd d (v ) i_ vd d (m a) v d d o per a t i o n c u r r en t v s . lo a d 1 2 3 4 5 6 0 500 100 0 1500 2000 gatedrive load ing (pf) i(v dd ) (m a) fosc 50khz fosc 65khz fosc 100khz uv lo (e nt er ) vs . te mp 9. 3 9. 4 9. 5 9. 6 9. 7 9. 8 9. 9 -2 0 0 2 0 40 6 0 8 0 10 0 1 20 temp (c) uv lo (en te r) ( v) uvlo(exi t) v s. te mp 1 5.8 1 5.9 16 1 6.1 1 6.2 1 6.3 1 6.4 1 6.5 1 6.6 -2 0 0 20 40 6 0 8 0 100 120 t emp (c) uv lo (e xi t) ( v ) on-bright confidential to bona fide (?)
?on-bright electronics confidential - 8 - ob_doc_ds_79a0 OB2279 current mode pwm c ontroller f r e q shuffling w i th latc h shu tdow n fosc vs. ri 0 20 40 60 80 100 120 140 50 70 9 0 110 13 0 150 17 0 190 210 2 30 250 ri (koh m) fosc (khz) fo sc vs . t em per at ure 64 64 .5 65 65 .5 66 66 .5 67 67 .5 -2 0 0 20 40 60 80 1 00 1 20 t emp (c) fo sc (k hz ) vth_oc(v) v s iv in(ua) 0.6 0. 7 0. 8 0. 9 1. 0 0 50 100 150 200 250 300 iv i n ( u a ) vth_oc ( v) i_ rt v s. t e mp 69 69 .2 69 .4 69 .6 69 .8 70 70 .2 70 .4 70 .6 - 20 0 2 0 40 60 80 10 0 12 0 temp (c) i _rt (ua) w/ ri=100kohm i vdd_ l a c t h( ua ) vs v d d( v ) 30. 0 35. 0 40. 0 45. 0 50. 0 7. 5 7. 8 8. 1 8. 4 8. 7 9 . 0 v dd( v ) i vdd_l a c t h ( um a on-bright confidential to bona fide (?)
?on-bright electronics confidential - 9 - ob_doc_ds_79a0 OB2279 current mode pwm c ontroller f r e q shuffling w i th latc h shu tdow n operat ion descript ion OB2279 is a highl y integr ated pwm controller ic optim ized for offline fl yback converter applications with requirement in latch shutdow n or auto recovery . th e extended burst m ode co ntrol greatl y reduces the standby powe r consum ption and helps the design easily meet the international power conservation requirem e nts. z startup current and start up control startup current of ob227 9 is designed to be ver y low so that vdd could be charged up above uvlo(exit) threshold lev e l and device starts up quickly . a large value startup resistor can therefore be used to mini m ize the power loss y e t reliable startup in application. for a typical ac/ d c adaptor with universal input range design, a 2 m ? , 1/8 w startup resist or could be used together with a vdd capacitor to provide a fast startup a nd y e t low power dissipation design so lution. z operating c u rrent the operating current of OB2279 is lo w at 2.3ma. good efficiency is achieved with OB2279 low operating cu rrent together with extended burst m ode control sche m es. z frequency shuffling for emi improv ement the frequency shuffli ng/jittering (switching frequency m odulatio n) is im plem ented in OB2279 . the oscillation frequenc y is m odulated with a internally gen e rated random source so that the tone energy is eve n ly spread out. the spread spectru m minim izes the conduction band emi a nd therefore ease s the sy ste m design i n meeting str ingent emi requirem e nt. z burst mode operation at zero load or light load condition, m o st of the power dissipation in a switching mode power suppl y is from switching loss on the mosfet transistor, the core loss of the transformer and the loss on t h e snubber cir c uit. the m a gnitude of power loss is in propor tion to t h e num ber of switching events within a fixed period of tim e. reducing switching event s leads to th e reduction on the power loss and thus conserves the energy. OB2279 self adjusts the switching m o de according to the loading conditi on. at fro m no load to light/m ediu m load conditi on, the fb input dro p s below burst m ode thresh old level. d e vice enters burst mode control. the gate drive output switches only when v dd voltage drops below a preset level and fb input is active to output an on state. otherwise th e gate drive re m a ins at off state to minim ize the switching loss thus reduce the standb y p o wer consum ption to the greatest extend. the nature of high f requency switching also reduces the audio noise at any loading conditi ons. z oscillator operation a resistor connected between ri and g nd sets the constant current source to charge/discharge the internal cap and t hus t h e p wm oscillator frequenc y is determ ined. the relationship between ri and switching frequenc y fol lo w s the belo w equation within the specified ri in kohm range at nom ina l loading operational condit i on. ) ( ) ( 6500 khz kohm ri f osc z current s e nsing and leading edge blanking (leb) cy cle-by -c ycle current lim iting is offered in OB2279 curr ent m ode pwm control. the switch current is det ected by a se nse resi stor i n to the sense pin. an i n ternal leading e dge blanki ng circuit chops off the sense voltage spike at initial mosfet on state due to snubber dio d e reverse recovery so that the external rc filtering on sense input is no longer needed. the current lim i t com p ar ator is disabled and cannot t u rn off the e x ternal mosfet duri ng the blanking period. th e pwm duty c y cle is determ ined b y the current sense input voltage and the fb input voltage. z internal synchroni z ed sl ope compen sation built-in slope com p ensati on circuit adds voltage ram p onto the current sense input voltag e for pwm generation. this greatly im proves the close loop stability at ccm and pr events the sub-harm onic oscillation and thus reduces the output ripple voltage. z over te mp erature p r otection with latch shutdown(only to t and l version) a ntc resi stor in series with a regular resistor should connect between rt and gnd for te m p erature sensing and protection. ntc resi stor value becom e s lower when the am bient te m p eratur e rises. with the fixed internal current i rt flowing throug h the resistors, the voltage at rt pin beco m es low e r at high tem p erature. the internal otp circuit is trigge red and shutdown the mosfet when the sensed input volta ge is lower than v th _otp. otp is a latched shutd o wn. on-bright confidential to bona fide (?)
?on-bright electronics confidential - 10 - ob_doc_ds_79a0 OB2279 current mode pwm c ontroller f r e q shuffling w i th latc h shu tdow n z rt pin used as latch shutdown input control rt pin coul d also be used as a control inp u t to im plem ent sy stem latch shutdown fu ncti on. an exa m ple is to i m ple m ent sy ste m ov p protection wi th a latch sh u tdown f uncti on t h rou gh a photo couple r and affiliated circuits. when ovp detection signal connected to rt is lower than v th _otp for version t/l device, (or v th _ot_latch for version v), ob2 279 co ntrols sy stem into latch shutdown. the recovery of t h e ac/dc sy stem could only start by resetting internal latch when vdd voltage drops below vdd_de- latch value. this cou ld be ach ieved b y unplu ggin g /r e-pluggin g of ac source in ac start- up confi guration. z gate drive OB2279 gate is connected to the gate of an external mosfet for power swit ch control. t o o weak the g a te drive str e ngth results in higher conduction and switch loss of mosfet while too strong gate dr ive outp u t co m p ro mises the emi. good tradeoff is achiev e d through the built-in totem pole gate drive d esign with r ight outpu t strength and dead tim e control. the lo w idle loss and good emi sy stem d esign is easi er to achieve with this dedicated control schem e. an internal 16.5v clam p is added for mosfet gate protection at higher than expected vdd input. z protection controls good s y stem reliabilit y is achieved with OB2279?s rich protection features including c y cle-by -c y c le current lim iting (ocp), over load prot ection (olp) with auto-recovery (v and t version) or latch shutdown(l version), ove r tem p erature protection (otp) with auto-recovery (v version) or latch shutdown(t and l version), on-chip vdd over voltage prote c tion (ovp) with latch shutdown and under vo ltage lockout (uv lo). vdd o v p protection is a latched shutdown in OB2279. the ocp thr eshold value is self adjusted lower at higher curren t into vin p in. this oc p threshold slope adjust ment helps to com p ens a te th e increa sed output power lim it at high er ac voltage caused by inherent over-current sensing and contr o l delay. a constant out put p o wer lim it is achieved with reco mmende d ocp co m p ensation sche m e. at output o v erload cond ition, fb vo ltage is set higher. when fb input exceeds power li m it threshold val u e for m o re than 80m s, control circuit reacts to turnoff the power mosfet. this is so called olp shutdown . it is either auto-recovery or latched shutdown dependi ng on version of OB2279. sim ilarly , c ontrol circui t shutdowns the power mosfet when an over tem p erature condition is detected. this shutdown is either auto-recovery or latched depending o n versi on of ob227 9 been used. vdd is su pplied with transformer auxiliar y winding ou tp ut. it is clamped when vdd is higher than 35v. mosfet is sh ut down whe n vdd drops below uvlo(enter) lim it and device enters power on start-up sequence therea fter. on-bright confidential to bona fide (?)
?on-bright electronics confidential - 11 - ob_doc_ds_79a0 OB2279 current mode pwm c ontroller f r e q shuffling w i th latc h shu tdow n package mechanical data 8-pin plastic dip on-bright confidential to bona fide (?)
?on-bright electronics confidential - 12 - ob_doc_ds_79a0 OB2279 current mode pwm c ontroller f r e q shuffling w i th latc h shu tdow n 8-pin plastic sop on-bright confidential to bona fide (?)
?on-bright electronics confidential - 13 - ob_doc_ds_79a0 OB2279 current mode pwm c ontroller f r e q shuffling w i th latc h shu tdow n important notice right t o mak e ch a nge s on-bright electronics corp. reserv es the right to m a ke corrections, m odific a tions, enhancements, i m provem e nt s and other changes to its products and ser vices at any tim e an d to disconti nue any product or service without not ice. customers should obtain the l a test relevant inform ation before placing orders and sh ould verify that such inform atio n is current and com p lete. warra nt y informa t ion on-bright electronics corp. warrants p e rform ance of its ha rdware products to the speci fications applicable at the tim e of sale in accordance with its s tandard warranty . testing a nd othe r quality control te chniques are used to the extent it dee m s nece ssary to support this warra nty . except where m a ndate d by government requirements , testing of all param e t e rs of each product is not necessarily performed. on-bright electronics corp. assumes no liability for a pplication assistance or custom e r product de sign. customers are responsible for their pro ducts and ap pli cations using on-bright ?s com ponents, data sheet and application n o tes. to m inimize the risk s associated with custo m er produc ts and application s , custo m ers should provide adeq uate design and o p erating safeguards. life support on-bright el ectronics corp.? s products are not designe d to be used as co m ponents in de vices intended to support or sustain hum an life. on-bright electronics corp. will not be held li able for any dam a ges or claim s resulting fro m the use of its products in medical applications. military on-bright electronics corp.?s pr oducts are not designed fo r use in m ilitary applications. on-bright electronics corp. will not be held li able for a ny dam a ges or claim s r esulting from the use of its products in military applications. on-bright confidential to bona fide (?)

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