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c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 1 a n p e c r e s e r v e s t h e r i g h t t o m a k e c h a n g e s t o i m p r o v e r e l i a b i l i t y o r m a n u f a c t u r a b i l i t y w i t h o u t n o t i c e , a n d a d v i s e c u s t o m e r s t o o b t a i n t h e l a t e s t v e r s i o n o f r e l e v a n t i n f o r m a t i o n t o v e r i f y b e f o r e p l a c i n g o r d e r s . 5 v t o 1 2 v s i n g l e b u c k v o l t a g e m o d e p w m c o n t r o l l e r a p w 8 7 2 6 f e a t u r e s g e n e r a l d e s c r i p t i o n w i d e 5 v t o 1 2 v s u p p l y v o l t a g e p o w e r - o n - r e s e t m o n i t o r i n g o n v c c excellent output voltage regulations - 0.6v internal reference - 0.6% over-temperature range integrated soft-start v o l t a g e m o d e p w m o p e r a t i o n w i t h e x t e r n a l c o m p e n s a t i o n u p t o 9 0 % d u t y r a t i o f o r f a s t t r a n s i e n t r e s p o n s e constant switching frequency - 300khz 10% i n t e g r a t e d b o o t s t r a p f o r w a r d p - c h m o s f e t 5 0 % u n d e r - v o l t a g e p r o t e c t i o n 1 2 5 % o v e r - v o l t a g e p r o t e c t i o n adjustable over-current protection threshold - using the r ds(on) of low-side mosfet s h u t d o w n c o n t r o l b y c o m p power good monitoring (tdfn-10 3mmx3mm package only) remote feedback sense for excellent output voltage (tdfn-10 3mmx3mm package only) tdfn3x3-10 package lead free and green devices available (rohs compliant) a p p l i c a t i o n s g r a p h i c c a r d s d s l , s w i t c h h u b w i r e l e s s l a n n o t e b o o k c o m p u t e r m o t h e r b o a r d l c d m o n i t o r / t v t h e a p w 8 7 2 6 i s a v o l t a g e m o d e , f i x e d 3 0 0 k h z s w i t c h i n g f r e q u e n c y , s y n c h r o n o u s b u c k c o n v e r t e r . t h e a p w 8 7 2 6 a l l o w s w i d e i n p u t v o l t a g e t h a t i s e i t h e r a s i n g l e 5 ~ 1 2 v o r t w o s u p p l y v o l t a g e ( s ) f o r v a r i o u s a p p l i c a t i o n s . a p o w e r - o n - r e s e t ( p o r ) c i r c u i t m o n i t o r s t h e v c c s u p p l y v o l t a g e t o p r e v e n t w r o n g l o g i c c o n t r o l s . a b u i l t - i n s o f t - s t a r t c i r c u i t p r e v e n t s t h e o u t p u t v o l t a g e s f r o m o v e r s h o o t a s w e l l a s l i m i t s t h e i n p u t c u r r e n t . a n i n t e r n a l 0 . 6 v t e m p e r a t u r e - c o m - p e n s a t e d r e f e r e n c e v o l t a g e w i t h h i g h a c c u r a c y i s d e - s i g n e d t o m e e t t h e r e q u i r e m e n t o f l o w o u t p u t v o l t a g e a p p l i c a t i o n s . t h e a p w 8 7 2 6 p r o v i d e s e x c e l l e n t o u t p u t v o l t - a g e r e g u l a t i o n s a g a i n s t l o a d c u r r e n t v a r i a t i o n . a p w 8 7 2 6 i s b u i l t i n r e m o t e s e n s e f u n c t i o n f o r a p p l i c a t i o n s t h a t r e - q u i r e r e m o t e s e n s e . ( t d f n - 1 0 3 m m x 3 m m p a c k a g e o n l y ) the controller?s over-current protection monitors the out- put current by using the voltage drop across the rds (on) of low-side mosfet, eliminating the need for a cur- rent sensing resistor that features high efficiency and low cost. in addition, the APW8726 also integrates excel- lent protection functions. the over-voltage protection (ovp) , under-voltage protection (uvp). ovp circuit which moni- tors the fb voltage to prevent the pwm output from over voltage, and uvp circuit which monitors the fb voltage to prevent the pwm output from under voltage or short circuit. the APW8726 is available in tdfn3x3-10 packages free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 2 a p w 8 7 2 6 s i m p l i f i e d a p p l i c a t i o n c i r c u i t phase fb gnd vcc lgate / ocset comp apw 8726 ( tdfn 3 x 3 - 10 ) v in v out ugate vcc supply ( 5 ~ 12 v ) boot on off fbrtn l o a d pok v + _ near v - _ near v + _ remote v - _ remote o r d e r i n g a n d m a r k i n g i n f o r m a t i o n n o t e : a n p e c l e a d - f r e e p r o d u c t s c o n t a i n m o l d i n g c o m p o u n d s / d i e a t t a c h m a t e r i a l s a n d 1 0 0 % m a t t e t i n p l a t e t e r m i n a t i o n f i n i s h ; w h i c h a r e f u l l y c o m p l i a n t w i t h r o h s . a n p e c l e a d - f r e e p r o d u c t s m e e t o r e x c e e d t h e l e a d - f r e e r e q u i r e m e n t s o f i p c / j e d e c j - s t d - 0 2 0 d f o r m s l c l a s s i f i c a t i o n a t l e a d - f r e e p e a k r e f l o w t e m p e r a t u r e . a n p e c d e f i n e s ? g r e e n ? t o m e a n l e a d - f r e e ( r o h s c o m p l i a n t ) a n d h a l o g e n f r e e ( b r o r c l d o e s n o t e x c e e d 9 0 0 p p m b y w e i g h t i n h o m o g e n e o u s m a t e r i a l a n d t o t a l o f b r a n d c l d o e s n o t e x c e e d 1 5 0 0 p p m b y w e i g h t ) . p i n c o n f i g u r a t i o n apw 872 6 handling code tem perature range package code package code qb : tdfn 3 x 3 - 10 operating ambient temperature range i : - 40 to 85 o c handling code tr : tape & reel assembly material g : halogen and lead free device apw 8726 xxxxx apw 872 6 qb : assembly material xxxxx - date code 5 6 vcc 7 fbrtn 8 fb 9 comp 10 pok boot 1 ugate 2 phase 3 gnd 4 lgate / ocset tdfn 3 x 3 - 10 ( top view ) 11 gnd free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 3 a p w 8 7 2 6 a b s o l u t e m a x i m u m r a t i n g s ( n o t e 1 ) symbol parameter rating unit v vcc vcc supply voltage (vcc to gnd) - 0.3 ~ 16 v boot supply voltage (boot to phase) - 0.3 ~ 16 v v boot boot supply voltage (boot to gnd) - 0.3 ~ 32 v > 20ns - 0.3 ~ v boot +0.3 v v ugate ugate voltage (ugate to phase) < 20ns - 5 ~ v boot +5 v > 20ns - 0.3 ~ v vcc +0.3 v v lgate lgate voltage (lgate to gnd) < 20ns - 5 ~ v vcc +5 v > 20ns - 0.3 ~ 16 v v phase phase voltage (phase to gnd) < 20ns - 5 ~ 25 v fb ,comp and fbrtn to gnd - 0.3 ~ 7 v pok to gnd - 0.3~v cc +0.3 v t j maximum j unction temperature 150 c t stg storage temperature - 65 ~ 150 c t sdr maximum lead soldering temperature, 10 seconds 260 c note1: stresses beyond those listed under "absolute maximum ratings" may cause permanent damage to the device. these are stress ratings only and functional operation of the device at these or any other conditions beyond those indicated under "recom- mended operating conditions" is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. t h e r m a l c h a r a c t e r i s t i c s symbol parameter typical value unit q ja thermal resistance - junction to ambient (note 2) tdfn3x3 - 10 55 c/w note 2: q ja is measured with the component mounted on a high effective thermal conductivity test board in free air. symbol parameter range unit v vcc vcc supply voltage (vcc to gnd) 4.5 ~ 13.2 v v out converter output voltage for APW8726 0.6 ~ 5 v v in converter input voltage 3~13.2 v i out converter output c urrent 0 ~ 25 a t a ambient temperature - 40 ~ 85 c t j junc tion temperature - 4 0 ~ 1 25 c r e c o m m e n d e d o p e r a t i n g c o n d i t i o n s ( n o t e 3 ) n o t e 3 : r e f e r t o t h e a p p l i c a t i o n c i r c u i t f o r f u r t h e r i n f o r m a t i o n . free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 4 a p w 8 7 2 6 e l e c t r i c a l c h a r a c t e r i s t i c s apw 8726 symbol parameter test condition s min. typ. max. unit input supply voltage and current vcc supply current (shutdown mode) ugate and lgate open; comp=gnd - - 550 m a i vcc vcc supply current ugate and lgate open - 2.5 10 ma power - on - rese t(por) rising vcc por threshold 3.8 4.1 4.4 v vcc por hysteresis 0.3 0.5 0.6 v oscillator f osc oscillator frequency 270 300 330 khz d v osc oscillator sawtooth amplitude (note 4) (1.2v~2.7v typical) - 1.5 - v d max maximum duty cycle - - 90 % ref erence v ref reference voltage t a = - 40 ~ 85 c 0.596 0.6 0.604 v error amplifier open - loop gain (note 4) r l = 10k w , c l = 10pf - 90 - db open - loop bandwidth (note 4) r l = 10k w , c l = 10pf - 20 - mhz fb input leakage current v fb = 0.6v - - 0.1 m a gate drivers high - side gate driver source current v boot = 12v, v ugate - phase = 6v - 1.0 - high - side gate driver sink current v boot = 12v, v ugate - phase = 6v - 1.1 - low - side gate driver source current v vcc = 12v, v lgate - gnd = 6v - 1.8 - low - side gate driver sink current v vcc = 12v, v lgate - gnd = 6v - 2.0 - a t d dead - time ( note 4) - 30 - ns p rotections v fb_uv fb under - voltage protection trip point percentage of v ref 45 50 55 % under - voltage debounce interval - 2 - m s under - voltage protection enable delay - 4 - ms v fb_ov fb over - voltage protection rising threshold v fb rising 120 125 130 % fb over - voltage protection falling threshold v fb falling 100 105 110 % over - voltage debounce interval - 2 - m s v ocp_max built - in maximum ocp voltage - 1200 - mv i ocset ocset current source 23 25 27 m a soft - start v disable shutdown threshold of v comp - - 0.4 v t ss internal soft - start interval - 4 - ms refer to the typical application circuit. these specifications apply over v vcc = 12v, t a = -40c to 85c, unless otherwise noted. typical values are at t a = 25c. free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 5 a p w 8 7 2 6 e l e c t r i c a l c h a r a c t e r i s t i c s ( c o n t . ) apw 8726 symbol parameter test condition s min. typ. max. unit remote sense i fbrtn remote sense source current - 12 - m a power good (only for tdfn3 ?? 3 - 10 package) i pok pok leakage current v pok =5v - 0.1 1 m a vfb is from low to ta rget value (pok goes high) 85 90 95 % vfb falling, pok goes low 45 50 55 % pok threshold vfb rising , pok goes low 120 125 130 % pok delay time - 3 - ms refer to the typical application circuit. these specifications apply over v vcc = 12v, t a = -40c to 85c, unless otherwise noted. typical values are at t a = 25c. note 4: guaranteed by design, not production tested. free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 6 a p w 8 7 2 6 p i n d e s c r i p t i o n pin no. tdfn3x3 - 10 name function 1 boot this pin provides the bootstrap voltage to the high - side gate driver for driving the n - channel mosfet. an external capacitor from phase to boot, an internal switch generates the bootstrap voltage for the high - s ide gate d r iver (ugate). 2 ugate high - side g ate dr iver output. this pin is the gate driver for high - side mosfet. 4 gnd signal and power ground. connecting this pin to system ground. 5 lgate/o cset low - side gate driver output and over - current setting inpu t. this pin is the gate driver for low - side mosfet. it also used to set the maximum inductor current. refer to the section in ? function description ? for detail. 6 vcc power s upply i nput. connect a nominal 5v to 12v power supply voltage to this pin. a powe r - on reset function monitors the input voltage at this pin. it is recommended that a decoupling capacitor (1 to 10 f) be connected to gnd for noise decoupling. 8 fb feedback i nput of converter . the converter senses feedback voltage via fb and regulate s th e fb voltage at 0.6v/ 0.8v. connecting fb with a resistor - divider from the output set s the output voltage of the converter . 9 comp this is a multiplexed pin. during soft - start and normal converter operation, this pin represents the output of the error ampl ifier. it is used to compensate the regulation control loop in combination with the fb pin . pulling comp low (v disable = 0. 4 v max.) will shut down the controller . when the pull - down device is released, the comp pin will start to rise. when the comp pin ris es above the v disable trip point, the APW8726 will begin a new i nitialization and soft - start cycle. 10 phase this pin is the return path for the high - side gate driver. connect ing this pin to the high - side mosfet source and connect a capacitor to boot for the bootstrap voltage. this pin is also used to monitor the voltage drop across the low - side mosfet for o ver - current protection. 3 pok pok is an open drain output used to indicate the status of the output voltage. connect the pok pin to 5 to 12v through a pull - high resistor. 7 fbrtn fb return ground. this pin is the negative node of the remote voltage sensing. 11 (exposed pad) gnd thermal pad. connect this pad to the system ground plan for good thermal conductivity. free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 7 a p w 8 7 2 6 t y p i c a l o p e r a t i n g c h a r a c t e r i s t i c s 0 . 59 0 . 595 0 . 6 0 . 605 0 . 61 - 20 0 20 40 60 80 100 r e f e r e n c e v o l t a g e ( v ) junction temperature ( ) o c reference voltage vs . junction temperature v cc = 12 v 120 s w i t c h i n g f r e q u e n c y ( k h z ) 250 260 270 280 290 300 310 320 330 340 350 switching frequency vs . junction temperature - 20 0 20 40 60 80 100 120 junction temperature ( o c ) 4 5 6 7 8 9 10 11 12 13 input voltage ( v ) o u t p u t v o l t a g e v a r i a t i o n ( % ) line regulation - 0 . 3 - 0 . 2 - 0 . 1 0 0 . 1 0 . 2 0 . 3 0 2 4 6 8 10 - 0 . 1 0 0 . 1 0 . 2 - 0 . 2 load regulation output current ( a ) o u t p u t v o l t a g e v a r i a t i o n ( % ) 0 . 3 - 0 . 3 - 20 0 20 40 60 80 100 120 18 22 24 26 28 30 32 o c s e t c u r r e n t s o u r c e ( m a ) i ocset vs . junction temperature 20 junction temperature ( o c ) 60 65 70 75 80 85 90 0 . 1 1 10 . 0 20 . 0 efficiency vs . load current f sw = 300 khz , v out = 1 . 2 v e f f i c i e n c y ( % ) vin = 12 v h - side : apw 3109 x 1 l - side : apw 3116 x 1 output current ( a ) free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 8 a p w 8 7 2 6 o p e r a t i n g w a v e f o r m s r e f e r t o t h e t y p i c a l a p p l i c a t i o n c i r c u i t . t h e t e s t c o n d i t i o n i s v i n = 1 2 v , t a = 2 5 o c u n l e s s o t h e r w i s e s p e c i f i e d . ch 1 : v in , 5 v / div ch 2 : v out , 500 mv / div time : 1 ms / div power on 1 3 2 ch 3 : v ugate , 10 v / div v in v out v ugate ch 2 : v out , 500 mv / div ch 3 : vu gate , 10 v / div time : 50 ms / div ch 1 : v in , 5 v / div power off 1 3 2 v in v out v ugate enable ch 1 : v comp , 1 v / div ch 2 : v out , 500 mv / div time : 1 ms / div ch 3 : v phase , 10 v / div v comp v out v phase 1 3 2 shutdown ch 1 : v comp , 1 v / div ch 2 : v out , 500 mv / div time : 10 ms / div ch 3 : v phase , 10 v / div v comp v out v phase 1 3 2 r load = 12 [ free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 9 a p w 8 7 2 6 o p e r a t i n g w a v e f o r m s r e f e r t o t h e t y p i c a l a p p l i c a t i o n c i r c u i t . t h e t e s t c o n d i t i o n i s v i n = 1 2 v , t a = 2 5 o c u n l e s s o t h e r w i s e s p e c i f i e d . over - current protection 1 ch 1 : v out , 500 mv / div ch 2 : i l , 10 a / div time : 20 ms / div 2 v out i l 2 ch 1 : v out , 500 mv / div ch 1 : p ok , 5 v / div time : 1 ms / div power ok 1 v out p ok 2 1 3 ch 1 : v out , 50 mv / div , ac ch 2 : i out , 5 a / div time : 200 us / div load transient 2 v out i out under - voltage protection ch 1 : v fb , 200 mv / div ch 2 : v phase , 10 v / div ch 3 : i l , 10 a / div time : 10 us / div 1 3 2 r ocset = open , r ds ( low side ) = 12 . 5 m w v fb v phase i l free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 1 0 a p w 8 7 2 6 b l o c k d i a g r a m power - on reset sample and hold to lgate v rocset soft start and fault logic gate control v rocset sense low side error amplifier v ref oscillator pwm comparator uvp comparator regulator v ref ( 0 . 6 v typical ) izcmp phase ugate boot comp gnd fb vcc soft - start inhibit i ocset ( 25 m a typical ) lgate ovp comparator 1 . 25 0 . 5 0 . 4 v disable vcc fbrtn free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 1 1 a p w 8 7 2 6 t y p i c a l a p p l i c a t i o n c i r c u i t note: power ok indicator (pok) (only for tdfn3x3-10 package). phase fb gnd vcc lgate / ocset comp apw 8726 c in 2 220 f x 2 c in 1 1 f l 1 0 . 5 h v in v out ugate c out 1000 f x 2 vcc supply ( 5 ~ 12 v ) boot r 1 1 k w r 2 1 k w 6 9 8 4 5 10 2 1 r 4 2 r 2 c 4 1 f c 2 100 nf r 2 2 k w c 1 100 pf q 1 apm 2510 q 2 apm 2556 on off c 3 0 . 1 f r ocset q 3 2 n 7002 c out mlcc 22 f x 4 fbrtn l o a d 7 pok 3 r 5 100 k w v + _ near v - _ near v + _ remote v - _ remote r 3 1 k w c 3 22 nf free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 1 2 a p w 8 7 2 6 f u n c t i o n d e s c r i p t i o n p o w e r - o n - r e s e t ( p o r ) t h e p o w e r - o n - r e s e t ( p o r ) f u n c t i o n o f a p w 8 7 2 6 c o n - t i n u a l l y m o n i t o r s t h e i n p u t s u p p l y v o l t a g e ( v c c ) a n d e n - s u r e s t h a t t h e i c h a s s u f f i c i e n t s u p p l y v o l t a g e a n d c a n w o r k w e l l . t h e p o r f u n c t i o n i n i t i a t e s a s o f t - s t a r t p r o c e s s w h i l e t h e v c c v o l t a g e j u s t e x c e e d s t h e p o r t h r e s h o l d ; t h e p o r f u n c t i o n a l s o i n h i b i t s t h e o p e r a t i o n s o f t h e i c w h i l e t h e v c c v o l t a g e f a l l s b e l o w t h e p o r t h r e s h o l d . s o f t - s t a r t the APW8726 builds in a soft-start function about 1.5ms (typ.) interval, which controls the output voltage rising as well as limiting the current surge at the start-up. during soft-start, an internal ramp voltage connected to the one of the positive inputs of the error amplifier replaces the reference voltage (0.6v typical) until the ramp voltage reaches the reference voltage. the soft-start circuit inter- val is shown as figure 1. f i g u r e 1 . s o f t - s t a r t i n t e r v a l o v e r - c u r r e n t p r o t e c t i o n o f t h e p w m c o n v e r t e r the over-current function protects the switching converter against over-current or short-circuit conditions. the con- troller senses the inductor current by detecting the drain- to-source voltage which is the product of the inductor?s current and the on-resistance of the low-side mosfet during it?s on-state. this method enhances the converter?s efficiency and reduces cost by eliminating a current sens- ing resistor required. a r e s i s t o r ( r o c s e t ) , c o n n e c t e d f r o m t h e l g a t e / o c s e t t o g n d , p r o g r a m s t h e o v e r - c u r r e n t t r i p l e v e l . b e f o r e t h e i c i n i t i a t e s a s o f t - s t a r t p r o c e s s , a n i n t e r n a l c u r r e n t s o u r c e , i o c s e t ( 2 5 m a t y p i c a l ) , f l o w i n g t h r o u g h t h e r o c s e t d e v e l o p s a v o l t a g e ( v r o c s e t ) a c r o s s t h e r o c s e t . t h e d e v i c e h o l d s v r o c s e t a n d s t o p s t h e c u r r e n t s o u r c e i o c s e t d u r i n g n o r m a l o p e r a t i o n . w h e n t h e v o l t a g e a c r o s s t h e l o w - s i d e m o s f e t e x c e e d s t h e v r o c set , the APW8726 turns off the high-side and low-side mosfet,and the device will enters hiccup mode until the over-current phenomenon is released. the APW8726 has an internal ocp voltage, v ocp_max , and the value is 1.2v (typical). when the r ocset x i ocset exceed 1.2v or the r ocset is floating or not connected, the v rocset will be the default value 1.2v. the over current threshold would be 1.2v across low-side mosfet. the threshold of the valley inductor current-limit is therefore given by: ) side low ( r r i 2 i ) on ( ds ocset ocset limit - = for the over-current is never occurred in the normal oper- ating load range, the variation of all parameters in the above equation should be considered: - the r ds(on) of low-side mosfet is varied by tempera- ture and gate to source voltage. users should deter- mine the maximum r ds(on) by using the manufacturer?s datasheet. - the minimum i ocset (23 m a) and minimum r ocset should be used in the above equation. - note that the i limit is the current flow through the low- side mosfet; i limit must be greater than valley inductor current which is output current minus the half of induc- tor ripple current. v out ( ocset duratiom , t 2 - t 1 , less than 0 . 9 ms ) t 1 t 2 t 3 v vcc time voltage ( v ) v pok pok delay time ocset count start 0 . 9 x v ref ocset count completed t 4 t 0 for avoid large inductor current occurring in short circuit before power on, the controller reduces internal current source, iocset, to half during soft start time. it means that when APW8726 is in soft start interval, the internal cur- rent source, iocset, is only 12.5 m a (typical). 2 i i i ) max ( out limit d - > where d i = output inductor ripple current - the overshoot and transient peak current also should be considered. free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 1 3 a p w 8 7 2 6 f u n c t i o n d e s c r i p t i o n ( c o n t . ) u n d e r - v o l t a g e p r o t e c t i o n o v e r - v o l t a g e p r o t e c t i o n ( o v p ) o f t h e p w m c o n v e r t e r t h e o v e r - v o l t a g e p r o t e c t i o n m o n i t o r s t h e f b v o l t a g e t o p r e v e n t t h e o u t p u t f r o m o v e r - v o l t a g e c o n d i t i o n . w h e n t h e o u t p u t v o l t a g e r i s e s a b o v e 1 2 5 % o f t h e n o m i n a l o u t p u t v o l t a g e , t h e a p w 8 7 2 6 t u r n s o f f t h e h i g h - s i d e m o s f e t a n d t u r n s o n t h e l o w - s i d e m o s f e t u n t i l t h e o u t p u t v o l t - a g e f a l l s b e l o w t h e f a l l i n g b e l o w 1 0 5 % , t h e o v p c o m - p a r a t o r i s d i s e n g a g e d a n d b o t h h i g h - s i d e a n d l o w - s i d e d r i v e r s t u r n o f f . s h u t d o w n a n d e n a b l e the APW8726 can be shut down or enabled by pulling low the voltage on comp. the comp is a dual-function pin. during normal operation, this pin represents the out- put of the error amplifier. it is used to compensate the regulation control loop in combination with the fb pin. pulling the comp low (v disable = 0.4v maximum) places the controller into shutdown mode which ugate and lgate are pulled to phase and gnd respectively. when the pull-down device is released, the comp volt- age will start to rise. when the comp voltage rises above the v disable threshold, the APW8726 will begin a new ini- tialization and soft-start process. a d a p t i v e s h o o t - t h r o u g h p r o t e c t i o n o f t h e p w m c o n - v e r t e r remote sense APW8726 has a fbrtn pin for applications that require remote sense. in some applications where high current, low voltage and accurate output voltage regulation are needed, fbrtn can sense the negative terminal of re- mote load capacitor directly, and improve output voltage drop which is due to the board interconnection loss. the gate drivers incorporate an adaptive shoot-through protection to prevent high-side and low-side mosfets from conducting simultaneously and shorting the input supply. this is accomplished by ensuring the falling gate has turned off one mosfet before the other is allowed to rise. during turn-off the low-side mosfet, the lgate voltage is monitored until it is below 1.5v threshold, at which time the ugate is released to rise after a constant delay. during turn-off of the high-side mosfet, the ugate-to- phase voltage is also monitored until it is below 1.5v threshold, at which time the lgate is released to rise after a constant delay. t h e u n d e r - v o l t a g e f u n c t i o n m o n i t o r s t h e v o l t a g e o n f b ( v f b ) b y u n d e r - v o l t a g e ( u v ) c o m p a r a t o r t o p r o t e c t t h e p w m c o n v e r t e r a g a i n s t s h o r t - c i r c u i t c o n d i t i o n s . w h e n t h e v f b f a l l s b e l o w t h e f a l l i n g u v p t h r e s h o l d ( 5 0 % v r e f ) , a f a u l t s i g n a l i s i n t e r n a l l y g e n e r a t e d a n d t h e d e v i c e t u r n s o f f h i g h - s i d e a n d l o w - s i d e m o s f e t s. the device will enters hic- cup mode until the under-voltage phenomenon is released. t h i s o v p s c h e m e o n l y c l a m p s t h e v o l t a g e o v e r s h o o t a n d d o e s n o t i n v e r t t h e o u t p u t v o l t a g e w h e n o t h e r w i s e a c t i - v a t e d w i t h a c o n t i n u o u s l y h i g h o u t p u t f r o m l o w - s i d e m o s f e t d r i v e r . i t ? | s a c o m m o n p r o b l e m f o r o v p s c h e m e s w i t h a l a t c h . o n c e a n o v e r - v o l t a g e f a u l t c o n d i t i o n i s s e t , i t c a n b e r e s e t b y r e l e a s i n g c o m p o r t o g g l i n g v c c p o w e r - o n - r e s e t s i g n a l . power ok indicator the APW8726 features an open-drain pok output pin to indicate one of the ic's working statuses including soft- start, under-voltage fault, over-current fault. in normal operation, when the output voltage rises 90% of its target value, the pok goes high. when the output voltage outruns 50% or 125% of the target voltage, pok signal will be pulled low immediately. free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 1 4 a p w 8 7 2 6 a p p l i c a t i o n i n f o r m a t i o n o u t p u t v o l t a g e s e l e c t i o n the output voltage can be programmed with a resistive divider. use 1% or better resistors for the resistive divider is recommended. the fb pin is the inverter input of the error amplifier, and the reference voltage is 0.6v. the output voltage is determined by: w h e r e r 1 i s t h e r e s i s t o r c o n n e c t e d f r o m v o u t t o f b a n d r 2 i s t h e r e s i s t o r c o n n e c t e d f r o m f b t o t h e g n d . ? ? ? ? ? + = 2 1 out r r 1 0.6 v o u t p u t c a p a c i t o r s e l e c t i o n t h e s e l e c t i o n o f c o u t i s d e t e r m i n e d b y t h e r e q u i r e d e f f e c - t i v e s e r i e s r e s i s t a n c e ( e s r ) a n d v o l t a g e r a t i n g r a t h e r t h a n t h e a c t u a l c a p a c i t a n c e r e q u i r e m e n t . t h e r e f o r e , s e l e c t i n g h i g h p e r f o r m a n c e l o w e s r c a p a c i t o r s i s i n t e n d e d f o r s w i t c h i n g r e g u l a t o r a p p l i c a t i o n s . i n s o m e a p p l i c a t i o n s , m u l t i p l e c a p a c i t o r s h a v e t o b e p a r a l l e l e d t o a c h i e v e t h e d e s i r e d e s r v a l u e . i f t a n t a l u m c a p a c i t o r s a r e u s e d , m a k e s u r e t h e y a r e s u r g e t e s t e d b y t h e m a n u f a c t u r e s . i f i n d o u b t , c o n s u l t t h e c a p a c i t o r s m a n u f a c t u r e r . i n p u t c a p a c i t o r s e l e c t i o n the input capacitor is chosen based on the voltage rat- ing and the rms current rating. for reliable operation, select the capacitor voltage rating to be at least 1.3 times higher than the maximum input voltage. the maximum rms current rating requirement is approximately i out /2 where i out is the load current. during power up, the input capacitors have to handle large amount of surge current. if tantalum capacitors are used, make sure they are surge tested by the manufactures. if in doubt, consult the ca- pacitors manufacturer. for high frequency decoupling, a ceramic capacitor be- tween 0.1 m f to 1 m f can connect between vcc and ground pin. i n d u c t o r s e l e c t i o n t h e i n d u c t a n c e o f t h e i n d u c t o r i s d e t e r m i n e d b y t h e o u t - p u t v o l t a g e r e q u i r e m e n t . t h e l a r g e r t h e i n d u c t a n c e , t h e l o w e r t h e i n d u c t o r ? s c u r r e n t r i p p l e . t h i s w i l l t r a n s l a t e i n t o l o w e r o u t p u t r i p p l e v o l t a g e . t h e r i p p l e c u r r e n t a n d r i p p l e v o l t a g e c a n b e a p p r o x i m a t e d b y : w h e r e f s i s t h e s w i t c h i n g f r e q u e n c y o f t h e r e g u l a t o r . d v o u t = i r i p p l e x e s r in out sw out in ripple v v l f v v i - = a t r a d e o f f e x i s t s b e t w e e n t h e i n d u c t o r ? s r i p p l e c u r r e n t a n d t h e r e g u l a t o r l o a d t r a n s i e n t r e s p o n s e t i m e . a s m a l l e r i n - d u c t o r w i l l g i v e t h e r e g u l a t o r a f a s t e r l o a d t r a n s i e n t r e - s p o n s e a t t h e e x p e n s e o f h i g h e r r i p p l e c u r r e n t a n d v i c e v e r s a . t h e m a x i m u m r i p p l e c u r r e n t o c c u r s a t t h e m a x i - m u m i n p u t v o l t a g e . a g o o d s t a r t i n g p o i n t i s t o c h o o s e t h e r i p p l e c u r r e n t t o b e a p p r o x i m a t e l y 3 0 % o f t h e m a x i m u m o u t p u t c u r r e n t . o n c e t h e i n d u c t a n c e v a l u e h a s b e e n c h o s e n , s e l e c t i n g a n i n d u c t o r i s c a p a b l e o f c a r r y i n g t h e r e q u i r e d p e a k c u r - r e n t w i t h o u t g o i n g i n t o s a t u r a t i o n . i n s o m e t y p e s o f i n d u c t o r s , e s p e c i a l l y c o r e t h a t i s m a k e o f f e r r i t e , t h e r i p p l e c u r r e n t w i l l i n c r e a s e a b r u p t l y w h e n i t s a t u r a t e s . t h i s w i l l r e s u l t i n a l a r g e r o u t p u t r i p p l e v o l t a g e . pwm compensation the output lc filter of a step down converter introduces a double pole, which contributes with -40db/decade gain slope and 180 degrees phase shift in the control loop. a compensation network among comp, fb, and v out should be added. the compensation network is shown in figure 5. the output lc filter consists of the output induc- tor and output capacitors. the transfer function of the lc filter is given by: the f lc is the double poles of the lc filter, and f esr is the zero introduced by the esr of the output capacitor. v phase l v out c out esr figure 2. the output lc filter out esr c esr 2 1 f p = free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 1 5 a p w 8 7 2 6 a p p l i c a t i o n i n f o r m a t i o n ( c o n t . ) f lc f esr -40db/dec -20db/dec frequency(hz) g a i n ( d b ) figure 3. the lc filter gain and frequency the pwm modulator is shown in figure 4. the input is the output of the error amplifier and the output is the phase node. the transfer function of the pwm modulator is given by: osc in pwm v v gain d = figure 4. the pwm modulator output of error amplifier g v osc pwm comparator driver driver phase v in osc the compensation network is shown in figure 5. it provides a close loop transfer function with the highest zero crossover frequency and sufficient phase margin. the transfer function of error amplifier is given by: the poles and zeros of the transfer function are: v ref v out v comp r 1 r 3 c 3 r 2 c 2 c 1 fb figure 5. compensation network ( ) c3 r3 2 1 f c2 c1 c2 c1 r2 2 1 f c3 r3 r1 2 1 f c2 r2 2 1 f p2 p1 z2 z1 p = ? ? ? ? + p = + p = p = ( ) ? ? ? ? + ? ? ? ? + + ? ? ? ? ? + + ? ? ? ? + + = ? ? ? ? + ? ? ? ? + = = c3 r3 1 s c2 c1 r2 c2 c1 s s c3 r3 r1 1 s c2 r2 1 s c1 r3 r1 r3 r1 sc3 1 r3 r1// sc2 1 r2 // sc1 1 v v gain out comp amp the closed loop gain of the converter can be written as: gain lc x gain pwm x gain amp figure 6. shows the asymptotic plot of the closed loop converter gain, and the following guidelines will help to design the compensation network. using the below guidelines should give a compensation similar to the curve plotted. a stable closed loop has a -20db/ decade slope and a phase margin greater than 45 degree. 1. choose a value for r1, usually between 1k and 5k. 2. select the desired zero crossover frequency f o : (1/5 ~ 1/10) x f s >f o >f esr use the following equation to calculate r2: 3. place the first zero f z1 before the output lc filter double pole frequency f lc . f z1 = 0.75 x f lc calculate the c2 by the equation: r1 f f v v r2 lc o in osc d = 0.75 f r2 2 1 c2 lc p = free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 1 6 a p w 8 7 2 6 a p p l i c a t i o n i n f o r m a t i o n ( c o n t . ) 4. set the pole at the esr zero frequency f esr : f p1 = f esr calculate the c1 by the equation: 5. set the second pole f p2 at the half of the switching frequency and also set the second zero f z2 at the output lc filter double pole f lc . the compensation gain should not exceed the error amplifier open loop gain, check the compensation gain at f p2 with the capabilities of the error amplifier. f p2 = 0.5 x f s f z2 = f lc combine the two equations will get the following component calculations: 1 f c2 r2 2 c2 c1 esr - p = 1 c esr s c l s c esr s 1 gain out out 2 out lc + + + = the poles and zero of this transfer functions are: figure 6. converter gain and frequency s lc s out lc f r3 1 c3 1 f 2 f r1 r3 c l 2 1 f p = - = p = f lc frequency(hz) g a i n ( d b ) 20log (r 2 /r 1 ) 20log ( v in / g v osc ) f z1 f z2 f p1 f p2 f esr pwm & filter gain converter gain compensation gain m o s f e t s e l e c t i o n t h e s e l e c t i o n o f t h e n - c h a n n e l p o w e r m o s f e t s i s d e t e r - m i n e d b y t h e r d s ( o n ) , r e v e r s e t r a n s f e r c a p a c i t a n c e ( c r s s ) , a n d m a x i m u m o u t p u t c u r r e n t r e q u i r e m e n t . t h e l o s s e s i n t h e m o s f e t s h a v e t w o c o m p o n e n t s : c o n d u c t i o n l o s s a n d t r a n s i t i o n l o s s . f o r t h e u p p e r a n d l o w e r m o s f e t , t h e l o s s e s a r e a p p r o x i m a t e l y g i v e n b y t h e f o l l o w i n g e q u a t i o n s : p u p p e r = i o u t 2 ( 1 + t c ) ( r d s ( o n ) ) d + ( 0 . 5 ) ( i o u t ) ( v i n ) ( t s w ) f s w p l o w e r = i o u t 2 ( 1 + t c ) ( r d s ( o n ) ) ( 1 - d ) w h e r e i o u t i s t h e l o a d c u r r e n t t c i s t h e t e m p e r a t u r e d e p e n d e n c y o f r d s ( o n ) f s w i s t h e s w i t c h i n g f r e q u e n c y t s w i s t h e s w i t c h i n g i n t e r v a l d i s t h e d u t y c y c l e n o t e t h a t b o t h m o s f e t s h a v e c o n d u c t i o n l o s s e s w h i l e t h e u p p e r m o s f e t i n c l u d e s a n a d d i t i o n a l t r a n s i t i o n l o s s . t h e s w i t c h i n g i n t e r n a l , t s w , i s t h e f u n c t i o n o f t h e r e v e r s e t r a n s f e r c a p a c i t a n c e c r s s . f i g u r e 7 i l l u s t r a t e s t h e s w i t c h - i n g w a v e f o r m i n t e r n a l o f t h e m o s f e t . t h e ( 1 + t c ) t e r m f a c t o r s i n t h e t e m p e r a t u r e d e p e n d e n c y o f t h e r d s ( o n ) a n d c a n b e e x t r a c t e d f r o m t h e ? r d s ( o n ) v s t e m - p e r a t u r e ? c u r v e o f t h e p o w e r m o s f e t . f i g u r e 7 . s w i t c h i n g w a v e f o r m a c r o s s m o s f e t v o l t a g e a c r o s s d r a i n a n d s o u r c e o f m o s f e t time v ds t sw free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 1 7 a p w 8 7 2 6 a p p l i c a t i o n i n f o r m a t i o n ( c o n t . ) figure 8. layout guidelines - keep the switching nodes (ugate, lgate, and phase) away from sensitive small signal nodes since these nodes are fast moving signals. therefore, keep traces to these nodes as short as possible. - the traces from the gate drivers to the mosfets (ug and lg) should be short and wide. - place the source of the high-side mosfet and the drain of the low-side mosfet as close as possible. minimiz- ing the impedance with wide layout plane between the two pads reduces the voltage bounce of the node. - decoupling capacitor, compensation component, the resistor dividers, and boot capacitors should be close their pins. (for example, place the decoupling ceramic capacitor near the drain of the high-side mosfet as close as possible. the bulk capacitors are also placed near the drain). - the input capacitor should be near the drain of the up- per mosfet; the output capacitor should be near the loads. the input capacitor gnd should be close to the output capacitor gnd and the lower mosfet gnd. ances and the magnitude of voltage spike. and signal and power grounds are to be kept separate till combined using ground plane construction or single point grounding. figure 8. illustrates the layout, with bold lines indicating high current paths; these traces must be short and wide. components along the bold lines should be placed lose together. below is a checklist for your layout: layout consideration in any high switching frequency converter, a correct lay- out is important to ensure proper operation of the regulator. with power devices switching at 300khz,the resulting current transient will cause voltage spike across the interconnecting impedance and parasitic circuit elements. as an example, consider the turn-off transition of the pwm mosfet. before turn-off, the mosfet is car- rying the full load current. during turn-off, current stops flowing in the mosfet and is free-wheeling by the lower mosfet and parasitic diode. any parasitic inductance of the circuit generates a large voltage spike during the switching interval. in general, using short and wide printed circuit traces should minimize interconnecting imped - the drain of the mosfets (v in and phase nodes) should be a large plane for heat sinking. - the r ocset resistance should be placed near the ic as close as possible. vcc boot phase ugate lgate v in v out l o a d apw 8726 r ocset close to ic free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 1 8 a p w 8 7 2 6 p a c k a g e i n f o r m a t i o n t d f n 3 x 3 - 1 0 note : 1. followed from jedec mo-229 veed-5. aaa c nx a3 a1 b a k l e e 2 pin 1 corner d2 pin 1 e d s y m b o l min. max. 0.80 0.00 0.18 0.30 2.20 2.70 0.05 1.40 a a1 b d d2 e e2 e l millimeters a3 0.20 ref tdfn3x3-10 0.30 0.50 1.75 0.008 ref min. max. inches 0.031 0.000 0.007 0.012 0.087 0.106 0.055 0.012 0.020 0.70 0.069 0.028 0.002 0.50 bsc 0.016 bsc 0.20 0.008 k 2.90 3.10 0.114 0.122 2.90 3.10 0.114 0.122 0.08 0.003 aaa free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 1 9 a p w 8 7 2 6 application a h t1 c d d w e1 f 330.0 ? 2.00 50 min. 12.4+2.00 - 0.00 13.0+0.50 - 0.20 1.5 min. 20.2 min. 12.0 ? 0.30 1.75 ? 0.10 5.5 ? 0.05 p 0 p1 p 2 d 0 d1 t a 0 b 0 k 0 tdfn3x3 - 10 4.0 ? 0.10 8.0 ? 0.10 2.0 ? 0.05 1.5+0.10 - 0.00 1.5 min. 0.6+0.00 - 0.40 3.30 ? 0.20 3.30 ? 0.20 1.30 ? 0.20 (mm) c a r r i e r t a p e & r e e l d i m e n s i o n s a e 1 a b w f t p0 od0 b a0 p2 k0 b 0 section b-b section a-a od1 p1 h t1 a d d e v i c e s p e r u n i t package type unit quantity tdfn3x3 - 10 tape & reel 3000 free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 2 0 a p w 8 7 2 6 t a p i n g d i r e c t i o n i n f o r m a t i o n t d f n 3 x 3 - 1 0 user direction of feed c l a s s i f i c a t i o n p r o f i l e free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 2 1 a p w 8 7 2 6 c l a s s i f i c a t i o n r e f l o w p r o f i l e s profile feature sn - pb eutectic assembly pb - free assembly preheat & soak temperature min (t smin ) temperature max (t smax ) time (t smin to t smax ) ( t s ) 100 c 150 c 60 - 120 seconds 150 c 200 c 60 - 1 2 0 seconds average ramp - up rate (t smax to t p ) 3 c/second ma x. 3 c/second max. liquidous temperature ( t l ) time at l iquidous (t l ) 183 c 60 - 150 seconds 217 c 60 - 150 seconds peak package body temperature (t p ) * see classification temp in table 1 see classification temp in table 2 time (t p ) ** within 5 c of the spe cified c lassification t emperature ( t c ) 2 0 ** seconds 3 0 ** seconds average r amp - down rate (t p to t smax ) 6 c/second max. 6 c/second max. time 25 c to p eak t emperature 6 minutes max. 8 minutes max. * tolerance for peak profile temperature (t p ) is defined as a supplier minimum and a user maximum. ** tolerance for time at peak profile temperature (t p ) is defined as a supplier minimum and a user maximum. table 2. pb - free process ? classification temperatures (tc) package thickness volume mm 3 <350 volume mm 3 350 - 2000 volume mm 3 >2000 <1.6 mm 260 c 260 c 260 c 1.6 mm ? 2.5 mm 260 c 250 c 245 c 3 2.5 mm 250 c 245 c 245 c table 1. snpb eutectic process ? classification temperatures (tc) package thickness volume mm 3 <350 volume mm 3 3 350 <2.5 mm 235 c 22 0 c 3 2.5 mm 220 c 220 c test item method description solderability jesd - 22, b102 5 sec, 245 c holt jesd - 22, a108 1000 hrs, bias @ t j =125 c pct jesd - 22, a102 168 hrs, 100 % rh, 2atm , 121 c tct jesd - 22, a104 500 cycles, - 65 c~150 c hbm mil - std - 883 - 3015.7 vhbm ? 2kv mm jesd - 22, a1 15 vmm ? 200v latch - up jesd 78 10ms, 1 tr ? 100ma r e l i a b i l i t y t e s t p r o g r a m free datasheet http:///
c o p y r i g h t ? a n p e c e l e c t r o n i c s c o r p . r e v . a . 1 - s e p . , 2 0 1 2 w w w . a n p e c . c o m . t w 2 2 a p w 8 7 2 6 c u s t o m e r s e r v i c e a n p e c e l e c t r o n i c s c o r p . head office : no.6, dusing 1st road, sbip, hsin-chu, taiwan, r.o.c. tel : 886-3-5642000 fax : 886-3-5642050 t a i p e i b r a n c h : 2 f , n o . 1 1 , l a n e 2 1 8 , s e c 2 j h o n g s i n g r d . , s i n d i a n c i t y , t a i p e i c o u n t y 2 3 1 4 6 , t a i w a n t e l : 8 8 6 - 2 - 2 9 1 0 - 3 8 3 8 f a x : 8 8 6 - 2 - 2 9 1 7 - 3 8 3 8 free datasheet http:///

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