preliminar y ML0308 ML0308 backlight led boost converter the ML0308 is a step-up dc-dc converter specifically designed to drive up to f our wh ite leds in series from a single lith ium - ion cell. the de vice provid e s regula t ed and inheren t ly m a tched current to th e leds with addition a l f unction s : autom a tic soft-start, output overvoltage protection, on/o f f and dimm i ng control. the ML0308 switches at 1.0 mhz, featuring the use of ti ny external components. p a ck age info rm a t io n features z inheren tly-m atched led curren t z drives up to four white leds from 3.6v supply z autom a tic s o f t -star t z output overvoltage protection z high ef ficiency applications z led backlighting with dimm ing control z high ef ficiency step-up converter ma rki ng di ag ra m fig u r e 1 : t y p i ca l app lica tio n cir c u it www.datasheet.net/ datasheet pdf - http://www..co.kr/
preliminar y ML0308 absolut e maximum ra tings r a t i n g p i n v a l u e u n i t input voltage vin 6.0 v output voltage sw 18 v e n 1 0 v f b v i n + 0 . 3 v operating temperature -30 to 80 c s t orage tem p erature -40 to 125 c electical charactistics all specifications apply under the co ndition v in = 3. 0v and t a = 25 B B B www.datasheet.net/ datasheet pdf - http://www..co.kr/
preliminar y ML0308 pin func tion des cription p i n d e s c r i p t i o n sw (pin 1) th is p i n is th e p o wer sid e of t h e ex tern al i ndu ctor an d m u st b e co nnecte d t o the exte rnal scho ttk y d i o d e . it p r ov id es the ou tpu t current to th e l o ad. si n ce th e boo st co nv erter ope rat e s i n a c u r r ent l o o p m ode, t h e out put vol t a ge can ra n g e up t o 1 6 v b u t s h al l n o t exceed this limit. gnd (pin 2 ) th is p i n is th e syste m g r oun d f o r th e ML0308 an d carr i es bo th t h e p o w e r an d th e an alog sig n a ls. hi g h qu ality g r o und m u st b e p r ov ided to avo i d sp ik es and / o r un co n t ro lled ope rat i o n. c a r e m u st be o b se rve d t o a voi d h i gh ? d e nsity curren t fl o w in a li mited pcb cop p e r t r ac k s o ar ob ust gr o u n d pl ane c o nnec t i on i s recom m e nde d. fb (pin 3) thi s pi n p r o v i d es t h e out put cur r ent ra nge a d j u st m e nt by m eans o f a sen s e resi st o r connected to t h e internal anal og control circ uitry. en (pin 4) thi s pi n i s t h e chi p -ena bl e pi n. g r o u n d t h i s pi n t o s h ut d o w n t h e chi p . a p p l y a cl ock with d i f f eren t d u t y ratio to co nt r o l b r i g ht nes s o f t h e le ds. vin (pin 5) th e ex tern al vo ltag e sup p l y i s conn ected t o th is p i n . a h i gh q u a lity reserv o i r cap acito r m u st be co nne ct ed acr oss pi n 5 a n d gr o u n d t o achi e ve t h e speci fi ed o u t p u t vol t a ge param e t e rs. a 4. 7u f/ 6. 3 v, l o w e s r capaci t o r m u st be co n n ect ed a s cl ose as pos si bl e acros s pi n 5 a n d gr o u n d pi n 2 . internal bloc k di agr am fi gu r e 2: i n t e rnal bl ock di ag r a m www.datasheet.net/ datasheet pdf - http://www..co.kr/
preliminar y ML0308 theor y of opera t ion the ML0308 uses a pfm, current mode control schem e to provide excellent line and load regulation. its operation can be best explaine d w ith reference to figure 2 and fi gure 1. the oscillator generates a clock of 1.0mhz with 75% duty ratio for the m a in control logic. w h en en pin goes high, the power mosfet s w itches at 1.0 mhz to drive the led curre nt up to the tar g et level. w h en t h e inductor curren t rea c h es the lim it, com p arator a3 will to g g le and the mosfet will s t op char ging the ind u ctor until the ind u ctor cu rren t f a lls be low the lim it. theref ore, sof t -start is ach i eved and po tential haz a r d s from explosive startup are avoided. when led curre nt reaches and rises over the regulation point, feedback voltage at fb pin will rais e over 200mv a nd com p arato r a2 to ggles. the chip will then stop switching th e mosfet until led c u rrent f a lls b e lo w the th r e shold. ther ef ore, led curren t is re g ulated and the threshold. hist or y of re vision r e v d e s c r i p t i o n da t e p r e 0 p r e l i m i n a r y r e l e a s e 1 2 / 0 3 / 2 0 0 4 p r e 1 p r e l i m i n a r y r e l e a s e 1 1 8 / 0 8 / 2 0 0 4 disclaimer : the i n f o rm at i on prese n t e d i n t h i s doc um ent d o es n o t f o rm p a rt o f a n y q u o t a t i on or co nt ra ct , i s bel i e ve d t o be acc urat e a n d reliable and m a y be c h ange d without notice. no liability will be accepte d by the pub lishe r for a n y conse que nce of its use. www.datasheet.net/ datasheet pdf - http://www..co.kr/
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