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bw 7 3 8 1 universal high brightness led driver rev .1.4 jan. 201 3 ! fea t ures z u n i v e r s a l r e c t i f i e d 9 0 v a c t o 2 6 4 v a c i n p u t vo l t a g e r a n g e z b u i l t - i n a c t i v e p o w e r f a c t o r c o r r e c t i o n te c h n i q u e z l o w t h d , m e e t w i t h i e c - 6 1 0 0 0 - 3 - 2 c l a s s - c z h i g h e f f i c i e n c y a p p l i c a t i o n z b u i l t - i n o u t p u t s h o r t c i r c u i t p r o t e c t i o n w i t h auto-recovery z b u i l t - i n o u t p u t o v e r v o l t a g e p r o t e c t i o n w i t h auto-recovery z built-in gate clamp z c y c l e - b y - c y c l e c u r r e n t l i m i t z f a i l - s a f e , o u t p u t i s n o t s u b j e c t e d t o l i n e voltage if the mosfet fails. z e x c e l l e n t l y a c c u r a t e c o n s t a n t c u r r e n t z v e r y t i g h t l i n e a n d l o a d r e g u l a t i o n z c o n s t a n t o f f - t i m e z b u c k o r b u c k - b o o s t c o n f i g u r a t i o n applica t ions z a c / d c l e d d r i v e r a p p l i c a t i o n z d c / d c l e d d r i v e r a p p l i c a t i o n z s i g n a g e a n d d e c o r a t i v e l e d l i g h t i n g z r e s i d e n t i a l l i g h t i n g description the bw 738 1 is a cont rolle r for off-line le d co nverte r. the bw 738 1 operate with con s tant o ff-time, peak curre n t mod e control wi th active powe r facto r corre c tion fu nction. the controlle r se nses re al-tim e swit ch cur r e n t t o cy cle - by - c y c le cu rre nt limit . cycle-by-cycl e current limit a t t h e c s p i n e n s u r e a safe ope ratio n durin g sho r t-ci rcuit at the output. it can be co nfi g ured in eith er buck- b oos t (figure 1 ) or buck (fig ure2) application circui t. t h e d r i v e r output voltag e is limite d t o 19v to pro t ect extern al power mos fet. the controlle r al so monitors integrate d a c tual le d curre n t to perfo rm the excelle nt line and loa d regulatio n. th e cont rolle r make s the inducto r cu rre n t to follow th e shape of input voltage to perfo rm h i gh po we r fa ctor a nd lo w thd s o lution. the bw 738 1 provides complete protection feature s su ch as sh ort-circuit an d open -ci r cuit prote c tion. order informa t ion pin configura tions (t op view) bw 7381 - s8 r bruckewell circuit t yp e s8: sop-8 sh i p p i n g : r: tape & reel http://
bw 7 3 8 1 universal high brightness led driver pin descriptions pin name pin description cs switch current sense pin. gnd ic ground and reference. flt actual output current sensing pin. comp output pin of error amplifier. rt constant off-time setting. vin ac-line voltage sensing pin. vdd power supply pin for all internal circuit. out power mosfet driver output. typical application circuits buck-boost topology figure 1 rev .1.4 jan. 201 3 !
bw 7 3 8 1 universal high brightness led driver buck t opology ac+ ac r gn d 2 cs_flt 3 vin 6 rt 5 comp 4 vdd 7 out 8 cs 1 BW7381 ic_gnd ic_gnd ic_gnd led+ r ic_gnd ic_gnd ic_gnd ic_gnd ic_gnd gnd c1 l2 r1 v r line gnd v r li ne led r10 r11 r12 zd 1 d2 r9 e1 l1 r2 r5 r3 c4 c6 r6 r7 q1 c5 c3 c2 d1 figure 2 rev .1.4 jan. 201 3 !
bw 7 3 8 1 universal high brightness led driver absolute maximum ra tings (note 1 ) parameter sy mbol range unit powe r su pply pin v dd - 0 . 3 t o 3 0 v cs v o l t a g e t o g n d v cs - 0 . 3 t o 5 v fl t volt ag e to gnd v fl t - 0 . 3 t o 5 v com p vol t age to gnd v co m p - 0 . 3 t o 5 v vin volt age to gnd v in - 0 . 3 t o 5 v rt v o l t a g e t o g n d v rt - 0 . 3 t o 5 v out volt a ge to gnd v out - 0 . 3 t o 3 0 v operating jun c tion tempe r a t ure ra ng t j - 4 0 t o + 1 5 0 c operating am bient tempe r a t ure ra ng t op a - 4 0 t o + 8 5 c st o r a g e t e m p e r a t u r e r a n g t st g - 6 5 t o + 1 5 0 c lead temp erature (sol de ri ng 5 se c) t lead 260 c powe r dissi p ation @t a =2 5 c p d 0 . 4 w therm a l re si st ance jun c tio n to ambient (note 2) ja 160 c/w esd rating, human bo dy mode (note 3 ) v esd 2 k v recommended opera t ing conditions (note 4) parameter sy mbol operation conditions unit supply v o lt ag e v dd 2 0 v jun c tion t em peratu r e ran ge t j -20 to +125 c ambient t em peratu r e ran ge t a -20 to +85 c note 1: stresse s listed as the a bove absolute maximum r a ting s ma y cause pe rmanent damage to the device. t hese are for stre ss ratings. function al operation of th e d e v i c e a t t h es e o r a ny o t h e r conditions beyon d those indicat ed in the ope ratio nal sections o f the specificat ions is not implied. exp o sure t o a b s o l u t e m a x i m u m r a t i n g conditions for extende d period s ma y remain p ossibility to aff e ct device reliability . note 2 : the r mal resistance is specified w i th the component mou nted on a lo w eff e ctive thermal conductivity test b oard in free air a t t a =25 c. note 3 : d e v i c e s a r e e s d s e n s i t i v e . h a n d i n g p r e c a u t i o n r e c o m m e n d e d . note 4 : t he device is not guarant eed to func tion o u tside its operating conditions. rev .1.4 jan. 201 3 !
bw 7 3 8 1 universal high brightness led driver block diagram figure 3 rev .1.4 jan. 201 3 !
bw 7 3 8 1 universal high brightness led driver electrical characteristics t a = 25 c, unless other w i se specified. parameter sy mbol conditio n min t y p max u nit vdd section st a r t - u p t h r e s h o l d v dd(st ) 1 7 1 8 1 9 v und er voltag e locko ut thresh old v dd(uvl o) 7 .5 8 . 5 9. 5 v over v o lt a ge protectio n v ovp 2 7 2 8 2 9 v st a r t - u p c u r r e n t i inst v dd(st ) - 1 v 4 2 6 0 7 8 ua operating cu rre nt i ddq 5 6 0 8 0 0 1 0 4 0 u a current li mit section maximum cu rre nt sense v olt age v cspk 0 . 6 7 0 . 7 0 .74 v prop agatio n delay t dl y 7 0 n s outp ut c u rre nt inte gr a tio n referen c e v o lt age v iref 0 . 2 v erro r amp lifier section tr a n s c o n d u c t a n c e g m 8 4 1 2 0 1 5 6 u s maximum sink current i sink 5 3 u a maximum source current i sour ce 5 8 u a line sensing section source curre n t i se(vin ) 3 7 5 ua co nst a nt off time section reg ulated v o lt age v rt 0 . 9 5 1 1 . 0 5 v of f-time setting range t off r rt = 1 3 6 k~ 1 7 k 5 . 7 3 4 0 . 4 u s cons t a nt of f-time t off(lv) rt = 5 0 k, 8 5 v a c ~ 1 5 0 v a c 1 3 . 5 1 5 1 6 . 5 u s t off(hv) r t = 5 0 k , 1 8 0 v a c ~ 3 0 0 v a c 1 8 . 9 2 1 2 3 . 1 us driver section risi ng t i me t rise v dd =12v , c_l oad =1nf 48 ns falling t i m e t fa i l v dd =12v , c_l oad =1nf 31 ns clamp ed v olt age v ga t e 1 9 v rev .1.4 jan. 201 3 !
bw 7 3 8 1 universal high brightness led driver applica t ion informa t ion 1. function description the bw 7381 is a high performan ce co ntrolle r whi c h monito rs a c tual outp u t current. these re sult s bw 7381 en a b le tight line and load reg u lation. the bw 7381 uses con s tant off-time pea k cu rre nt mod e control to control the switchi ng cu rrent in the mosfet. at initial, vdd ca pa cito r charged t hrou gh start-up re si stor until it achi eves 18v. th en bw 738 1 turns-o n the mosfet and make its shape of p ea k curre n t flow input sine wave. this pe rform s high power facto r and lo w total harmo nic di stortion. the output curre n t flow through a curre n t sensin g resi sto r and feedba ck to flt pin. th e controller alway s adju s ts the amplit ude of curre n t comma nd base on the potential of flt pin. on ce the pea k curre n t rea c hes the current comma n d , controll er turns off the mosfet. th e re sisto r co n necte d at rt pin determin e s the off-time. at the switching on-time, controlle r se nse s and limits the maximum switch curre nt by cs pin. thi s en su re s t he current i n mosfet be l imited in safe operatin g area. the bw 738 1 built-in output sho r t-ci rcuit and over-volta ge prote c tion. while the m o sfet turn s off at the off-time, the vdd cap acito r can get charg e by output voltage, and co ntro lle r can set output over voltage prot ection threshold by spe c ified ze ne r diode. if the led st ring i s o p e n , t h e o u t p u t v o l t a g e will be b o o s t over the d e si gned l e vel un til the vdd arriv e to 28v . the bw 7381 goes into over-volta ge prote c tion a n d latche s the mosfet. the co ntrolle r start s up the system agai n while the vdd falls to 8.5v (uvl o). the r ef ore, the conve r ter auto-re covery output while t h e o u t p u t o p e n c i r c u i t con d ition re moved. in case of outpu t sho r t-ci rcuit con dition. the vdd cap a c itor cannot get charg e from outp u t voltage. so, the conv erter re peat s start-up and uvlo. ho we ver, the bw 7381 provide s full prote c tio n s such a s ocp, ovp, gate-voltag e clamp a nd cy cle-by-cycle current limit. 2. pin det a il 2-1. cs mosfet cu rrent se nsin g, use fo r cy cle by cycl e swit ch pe ak current co ntrol . 4 ) (lim 7 . 0 r v i it l 2-2. gnd gnd is the re feren c e no de of internal ci rcuit. 2-3. fl t actual outp u t current sen s in g, the signal feedba ck to error amplifie r and comp a r e with the internal reference voltage (0.2v). 2 2 . 0 r v i o 2-4. comp this i s the o u t put of the g m amplifie r . co n n e c t with a suit abl e rc n etwo r k to ground. rev .1.4 jan. 201 3 u
bw 7 3 8 1 universal high brightness led driver 2-5. rt cons t a nt of f-time s e tup. for lo w-lin e, 85v a c to 150 v a c ! : s k r toff t p 15 50 u : for hig h -lin e, 180 to 300v a c ! : s k r toff t p 21 50 u : 2-6. vin sense si gna l input from the rectified line volt age. 2-7. vdd powe r sup ply for the controlle r durin g norm a l operation. the controller will st art up when vdd rea c he s 1 8v (typical ) and will sh ut-d own whe n v dd volt age is belo w 8.5v (typical). a decou plin g ca p a citor sh ould be con necte d between the v dd and g nd pi n as cl ose as p ossible. 2-8. out gate drive for external mosfet s w itch. 3. design flow the typical appli c ation ci rcuit fo r de si gn flow belo w plea se refers to figure 1. 3-1. input signal sampling the bw 73 81 sen s e inp ut signal from re ctifie d line volt age. vin pin in se ries with a re sisto r of 1.6m, r7 to system grou nd. it is need to p a y attention to enoug h volt ag e rating for re sisto r . : m r 6 . 1 7 3-2. low pass filter for s w itch and output current sensing tw o r-c lo w p a ss filter are must for mosfet swit ch cu rre n t sen s ing an d actu al outp ut cu rre nt sen s in g. the followin g is re comm end val ues : : k r 7 . 4 3 f c p 1 4 : 100 5 r pf c 100 5 3-3. loop com pensation place a ca p a citor of 2.2uf for compen sation is re comm en d. f c p 2 . 2 6 3-4. output current sensing resistor the output cu rre nt can be set up by a current sen s in g re si s t or , r 2 . the resi st an ce i s calcul ated followin g the equatio n belo w . o i v r 2.0 2 rev.1.4 jan. 2013 !
bw 7 3 8 1 universal high brightness led driver 3-5. ovp threshold v o lt age the bw 73 81 perform ou tput over volt age prote c tion th ough v d d pin. on ce vdd pin excee d in 28 v , bw 7381 turns of f and lat c h out the mosfet swi t che r . the o v p threshol d volt age can b e set by the zener di ode, zd 1 . v ovp zd 28 1 3-6. vdd, sup p l y curren t circuit at the begi nning in st a r t-up, the o utput volt age is n o t high eno ugh to charge vdd ca p a citor . th erefo r e vdd ca p a citor hav e to save enou gh ene rgy for ic o peratin g bia s duri ng st a r t - u p . t o d e t e r m i n e t h e ca p a ci t a n ce , w e n e e d to calculate the ic ope rating c u rrent, idd firs t. ma freq ciss idd 5 . 1 20 u u # in gene ral, a s sume the v dd ca p a citor need to kee p eno ugh e nergy for 50m s. t hen th e ca p a cit an c e can be calcula t ed. v v ms idd c 5 . 8 18 50 2 u t nf c 100 3 place the vdd ca p a cito r c 2 a n d b y p a s s ca p a cit o r c 3 a s c l o s e t o i c a s p o s s i b l e . morevoer , a curre nt sp ike filter re si stor r1 1 is sugg est (10 : ~22 : ) to pl ace b etwe en vdd an d c3. 3-7. s t art-up resistor at the initial st age, the vdd ca p a cit o r get cha r ge thro u gh st art - up resi sto r toward s th e st a r t-up th re shold volt ag e. the small e r st art-up resi sto r the large r po wer dissip ation. the large r st a r t-up re sist or the long er cha r ge time. 18 2 ) arg ( 3 2 1 u u t c c vac e ch t r 3-8. off-t i me setting the d u ty cycle in bu ck-b o o st conve r ter is a function of v i n and v o . o o pk v vac v duty 2 ) ( the of f-time can be set ma nually by adjusting the size of an external re si stor (r t ) . the bw 738 1 automaticall adju s t s the of f-time with the line volt age (v a c ). t o cal c ul at the ope rating of f-time and r t , the maximum switchi ng freq uen cy at pea k of line cycle must be determi ned first. freq duty toff pk h ) ( 1 4 . 1 h l toff toff : u k s toff r h 50 21 6 p whe r e : tof f h is the o f f-time at hig h -line (1 80v a c to 300v a c ), tof f l is the of f-time at low-lin e (90v a c to 135v a c ), 3-9. pow e r inductor assu me a t a rget ef ficien cy to estimate input power an d in put pea k cu rrent. k o o i v pin u 2 ) ( u vac pin i pk in rev .1.4 jan. 201 3 u
bw 7 3 8 1 universal high brightness led driver in buck-bo o s t converte r , the averag e of curre n t flow in mosfet is equal to the inpu t curre n t. if given a ratio of maximum inducto r curre n t ripple to maximum inducto r pe a k cu rrent, ! j l 0j l(pk) /! th en the induct or pea k cu rre nt can be estimated by the equatio n: ) ( ) ( ) ( ) ( 2 2 pk pk l l pk in pk l duty i i i i u ? ? 1 ? ' the maximu m inducto r current rippl e, j l is : ) ( ) ( pk l l pk l l i i i i ' u ' from the basic ind uctor eq uat ion, the indu ct an ce i s : toff i v l l o u ' follow the e q uation s abov e, the induct a nce and maximu m inducto r cu rre nt can b e computed. the mag netic desig n of the inducto r mu st ensure that there is a sufficient flux density marg in to avoid satu rati on with op era t ing curre n t being applie d. 3-10. sw itch cur r ent sensing resistor the bw 73 81 sen s e swit ch current from cs pin to provide cycle-by-c ycle current limit. while the cs pin goes exe c ss o f 700mv , the bw 738 1 force m o sfe t swit che r turn of f. desig n the pea k indu ctor current to 75 percent of switche r cu r r e n t l i m i t i s r e co m m e n d . ) ( 4 53 . 0 peak l i v r 4 ) (lim 7 . 0 r v i it l rev .1.4 jan. 201 3 !
bw 7 3 8 1 universal high brightness led driver pa c k a g e o u t l i n e d i m e n s i o n s

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