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1 www.semtech.com sc1404 mobile multi-output pwm controller with virtual current sense tm power management description features applications typical application circuit the sc1404 is a multiple-output power supply controller designed for battery operated systems. the sc1404 provides synchronous rectified buck converter control for two power supplies. an effi- ciency of 95% can be achieved. the sc1404 uses semtech?s proprietary virtual current sense tm technology along with external error amplifier compensation to achieve enhanced stability and dc accuracy over a wide range of output filter components while maintaining fixed frequency operation. the sc1404 also pro- vides two linear regulators for system housekeeping. the 5v lin- ear regulator takes its input from the battery; for efficiency, the output is switched to the 5v output when available. the 12v lin- ear regulator output is generated from a coupled inductor off the 5v switching regulator. control functions include: power up sequencing, soft start, power- good signaling, and frequency synchronization. line and load regulation is to +/-1% of the output voltage. the internal oscilla- tor can be adjusted to 200 khz or 300 khz or synchronized to an external clock. the mosfet drivers provide >1a peak drive current for fast mosfet switching. the sc1404 includes a psave# input to select pulse skipping mode for high efficiency at light load, or fixed frequency mode for low noise operation. 6 to 30v input range (operation possible below 6v) 3.3v and 5v dual synchronous outputs fixed-frequency or psave for maximum efficiency over wide load current range 5v/50ma linear regulator 12v/200ma linear regulator virtual current sense tm for enhanced stability accurate low-loss current limiting out-of-phase switching reduces input capacitance external compensation supports wide range of output filter components for reduced cost programmable power-up sequence power good output output overvoltage & overcurrent protection with output undervoltage shutdown 4a typical shutdown current 6mw typical quiescent power notebook and subnotebook computers automotive electronics desktop dc-dc converters revision: may 19, 2004
2 ? 2004 semtech corp. www.semtech.com sc1404 preliminary power management electrical characteristics absolute maximum ratings r e t e m a r a ps n o i t i d n o cn i mp y tx a ms t i n u s r e l l o r t n o c s p m s n i a m e g n a r e g a t l o v t u p n i 60 . 0 3v e g a t l o v t u p t u o v 3t i m i l t n e r r u c o t a 0 = d a o l v 3 , v 0 3 o t 0 . 6 = + v3 2 . 33 . 37 3 . 3v e g a t l o v t u p t u o v 5t i m i l t n e r r u c o t a 0 = d a o l v 5 , v 0 3 o t 0 . 6 = + v9 . 40 . 51 . 5v n o i t a l u g e r d a o ll v = # e v a s p , t i m i l t n e r r u c o t a 0 , s p m s r e h t i e4 . 0 -% n o i t a l u g e r e n i ll v = # e v a s p , v 0 3 < + v < 0 . 6 , s p m s r e h t i e5 0 . 0v / % unless otherwise noted: v+ = 15v, both pwms on, sync = 0v, vl load = 0ma, ref load = 0ma, psave# = 0v, t a =-40 to 85c. typical values are at t a = +25c. circuit = typical application circuit r e t e m a r a pn o i t p i r c s e dm u m i x a ms t i n u d n g o t 5 e s a h p , 3 e s a h p , + v , d d v s e g a t l o v e s a h p d n a y l p p u s0 3 + o t 3 . 0 -v d n g o t 5 e s a h p , 3 e s a h ps e g a t l o v e s a h p) c e s n 0 0 1 - t n e i s n a r t ( 0 . 2 -v d n g o t 5 h d , 3 h d , 5 t s b , 3 t s bs e g a t l o v t s o o b6 3 + o t 3 . 0 -v d n g o t d n g p d n u o r g l a n g i s o t d n u o r g r e w o p3 . 0 v d n g o t l vy l p p u s c i g o l6 + o t 3 . 0 -v ; 5 e s a h p o t 5 t s b ; 3 e s a h p o t 3 t s b y l p p u s e v i r d e t a g e d i s - h g i h6 + o t 3 . 0 -v 5 e s a h p o t 5 h d ; 3 e s a h p o t 3 h d s t u p t u o e v i r d e t a g e d i s - h g i h) 3 . 0 + x t s b + ( o t 3 . 0 -v d n g o t 5 l d , 3 l d d n g o t 3 h s c , 3 l s c , 5 h s c , 5 l s c s t u p t u o e v i r d e t a g e d i s - w o l s t u p n i e s n e s t n e r r u c d n a ) 3 . 0 + l v ( + o t 3 . 0 -v , # t e s e r , 5 n o , # e v a s p , q e s , c n y s , f e r d n g o t 5 p m o c , 3 p m o c , 5 b f , 3 b f , l v s t u p t u o / s t u p n i c i g o l) 3 . 0 + l v ( + o t 3 . 0 -v d n g o t # n d h s , 3 n o ) v 3 . 0 + + v ( + o t 3 . 0 -v d n g o t t r o h s f e r , l v s u o u n i t n o c t n e r r u c f e r 5 +a m t n e r r u c l v 0 5 +a m d n g o t t u o 2 1 ) 3 . 0 + d d v + ( o t 3 . 0 -v d n g o t t r o h s t u o 2 1 s u o u n i t n o c t n e r r u c t u o 2 1t n e r r u c t u p t u o v 2 10 0 2 +a m t j e g n a r e r u t a r e p m e t n o i t c n u j0 5 1 +c e c n a t s i s e r l a m r e h t e g a k c a pt n e i b m a o t n o i t c n u j6 7t t a w / c t s e g n a r e r u t a r e p m e t e g a r o t s0 0 2 + o t 5 6 -c t l e r u t a r e p m e t d a e l. x a m d n o c e s 0 1 , c 0 0 3 +c exceeding the specifications below may result in permanent damage to the device, or device malfunction. operation outside of th e parameters specified in the electrical characteristics section is not implied.
3 ? 2004 semtech corp. www.semtech.com sc1404 power management electrical characteristics cont. r e t e m a r a ps n o i t i d n o cn i mp y tx a ms t i n u s d l o h s e r h t t i m i l - t n e r r u c ) 2 e t o n ( h s c x l s c - x ) t n e r r u c e v i t i s o p ( h s c x l s c - x ) t n e r r u c e v i t a g e n ( 0 45 5 0 5 - 0 7v m d l o h s e r h t g n i s s o r c o r e zh s c x l s c - x d e t s e t t o n , v 0 = # e v a s p5v m e m i t p m a r t r a t s - t f o s , t i m i l t n e r r u c l l u f % 5 9 o t e l b a n e m o r f f o t t c e p s e r h t i w c s o 2 1 5s k l c y c n e u q e r f r o t a l l i c s ol v = c n y s v 0 = c n y s 0 2 2 0 7 1 0 0 3 0 0 2 0 8 3 0 3 2 z h k r o t c a f y t u d m u m i x a ml v = c n y s v 0 = c n y s 2 9 4 9 4 9 6 9 % e s l u p h g i h t u p n i c n y sd e t s e t t o n0 0 3s n e s l u p w o l t u p n i c n y s h t d i w d e t s e t t o n0 0 3 e m i t l l a f / e s i r c n y sd e t s e t t o n0 0 2 y c n e u q e r f t u p n i c n y s e g n a r - 0 4 2 0 5 3 z h k t u p n i e s n e s - t n e r r u c t n e r r u c e g a k a e l v 0 . 5 = 5 h s c , v 3 . 3 = 3 h s c30 1a p m a r o r r e n i a g p o o l c d 5 p m o c / 3 p m o c o t e d o n k c a b d e e f l a n r e t n i m o r f8 1v / v t c u d o r p h t d i w d n a b n i a g 8z h m e c n a t s i s e r t u p t u o5 p m o c , 3 p m o c5 2s m h o k e c n e r e f e r d n a r o t a l u g e r l a n r e t n i e g a t l o v t u p t u o l v, v 0 3 < + v < v 6 ; + v = # n d h s i < a m 0 d a o l v 0 = 5 n o = 3 n o , a m 0 3 < 6 . 45 2 . 5v t u o k c o l e g a t l o v r e d n u l v d l o h s e r h t t l u a f v 7 . 0 = s i s e r e t s y h , e g d e g n i l l a f5 . 37 . 31 . 4 t u o k c o l r e v o h c t i w s l ve g d e g n i s i r - p u t r a t s t a r e v o h c t i w s5 . 4 e g a t l o v t u p t u o f e rd a o l l a n r e t x e o n5 4 . 25 . 25 5 . 2 n o i t a l u g e r d a o l f e ri < a 0 d a o l a 0 5 <5 . 2 1v m i < a m 0 d a o l a m 5 <0 5 unless otherwise noted: v+ = 15v, both pwms on, sync = 0v, vl load = 0ma, ref load = 0ma, psave# = 0v, t a =-40 to 85c. typical values are at t a = +25c. circuit = typical application circuit
4 ? 2004 semtech corp. www.semtech.com sc1404 preliminary power management r e t e m a r a ps n o i t i d n o cn i mp y tx a ms t i n u t n e r r u c k n i s f e re g a t l o v f e r n i e s i r v m 0 10 1a e g a t l o v t u o k c o l t l u a f f e re g d e g n i l l a f8 . 12 . 2v y l p p u s g n i t a r e p o + v t n e r r u c , n o s p m s v 5 , 5 t u o v o t r e v o d e h c t i w s l v i 5 d a o l i = 3 d a o l v 0 = # e v a s p , a 0 = 0 10 5a t n e r r u c y l p p u s y b d n a t s + v ; v 0 = # e v a s p , f f o s p m s h t o b , v 0 3 o t v 6 = + v # n d h s o t n i t n e r r u c s e d u l c n i 0 0 3 y l p p u s n w o d t u h s + v t n e r r u c v 0 = # n d h s , v 0 3 o t v 6 = + v1 -35 1 r e w o p t n e c s e i u q n o i t p m u s n o c s p m s n o d a o l o n , d e l b a n e s p m s6w m n o i t c e t e d t l u a f d l o h s e r h t p i r t e g a t l o v r e v o e g a t l o v t u p t u o d e d a o l n u o t t c e p s e r h t i w70 15 1% t l u a f e g a t l o v r e v o y a l e d n o i t a g a p o r p v p i r t e g a t l o v r e v o e v o b a % 2 n e v i r d t u p t u o h t 5 . 1s e g a t l o v r e d n u t u p t u o d l o h s e r h t e g a t l o v t u p t u o d e d a o l n u o t t c e p s e r h t i w5 65 75 8% e g a t l o v r e d n u t u p t u o e m i t t u o k c o l f o t t c e p s e r h t i w , d e l b a n e s p m s h c a e m o r f c s o 0 0 0 54 4 1 60 0 0 7s k l c n w o d t u h s l a m r e h t d l o h s e r h t c 0 1 = s i s e r e t s y h l a c i p y t0 5 1 +c # t e s e r d l o h s e r h t p i r t # t e s e r ; e g d e g n i l l a f , e g a t l o v t u p t u o d e d a o l n u o t t c e p s e r h t i w % 1 = s i s e r e t s y h l a c i p y t 2 1 -9 -5 -% y a l e d n o i t a g a p o r p # t e s e r p i r t # t e s e r w o l e b % 2 n e v i r d t u p t u o , e g d e g n i l l a f d l o h s e r h t 5 . 1s e m i t y a l e d # t e s e rf o t t c e p s e r h t i w c s o 0 0 0 , 7 20 0 0 , 2 30 0 0 , 7 3 s k l c s t u p t u o d n a s t u p n i e g a t l o v w o l t u p n i c i g o lc n y s , # n d h s , 5 n o , # e v a s p , 3 n o ) f e r = q e s ( 6 . 0v e g a t l o v h g i h t u p n i c i g o lc n y s , # n d h s , 5 n o , # e v a s p , 3 n o ) f e r = q e s ( 4 . 2v electrical characteristics cont. unless otherwise noted: v+ = 15v, both pwms on, sync = 0v, vl load = 0ma, ref load = 0ma, psave# = 0v, t a =-40 to 85c. typical values are at t a = +25c. circuit = typical application circuit
5 ? 2004 semtech corp. www.semtech.com sc1404 power management electrical characteristics cont. notes: (1) this device is esd sensitive. use of standard esd handling procedures required. (2) applicable from 0 to +85c. unless otherwise noted: v+ = 15v, both pwms on, sync = 0v, vl load = 0ma, ref load = 0ma, psave# = 0v, t a =-40 to 85c. typical values are at t a = +25c. circuit = typical application circuit r e t e m a r a ps n o i t i d n o cn i mp y tx a ms t i n u t n e r r u c e g a k a e l t u p n i c n y s , 5 n o , # e v a s pf e r = q e s1 -1 +a 3 n o t n e r r u c e g a k a e l t u p n iv 5 1 = 3 n o2 -2 +a # n d h s t n e r r u c e g a k a e l t u p n iv 5 1 = # n d h s1 -3 0 1 +a e g a t l o v w o l t u p t u o c i g o la m 4 = k n i s i , # t e s e r4 . 0v t n e r r u c h g i h t u p t u o c i g o lv 5 . 3 = # t e s e r1a m e c n a t s i s e r n w o d - l l u p 5 n of e r = q e s , v 0 = 3 n o , 5 n o0 0 1s m h o t n e r r u c e c r u o s / k n i s r e v i r d e t a g v 5 . 2 o t d e c r o f , 5 h d , 5 l d , 3 h d , 3 l d1a e c n a t s i s e r - n o r e v i r d e t a g , 3 e s a h p o t 3 h d , 3 h d o t 3 t s b , 5 e s a h p o t 5 h d , 5 h d o t 5 t s b , d n g p o t 3 l d , 3 l d o t l v d n g p o t 5 l d , 5 l d o t l v 5 . 17 s m h o d l o h s e r h t p a l r e v o - n o nd n g o t , 5 e s a h p , 3 e s a h p0 . 1v ) p a l r e v o - n o n ( h g u o r h t - t o o h s y a l e d e g d e g n i s i r x l d o t e g d e g n i l l a f x h d e g d e g n i s i r x h d o t e g d e g n i l l a f x l d , x l d d n a x h d n o d l o h s e r h t v 1 ( ) x h d r o x l d n o e c n a t i c a p a c l a n r e t x e o n 0 1 5 3 7 1 5 7 5 2 5 1 1 c e s n r o t a l u g e r r a e n i l v 2 1 d l o h s e r h t t n u h s d d v% 5 = s i s e r e t s y h , e g d e g n i s i r7 11 2v t n e r r u c t n u h s d d vv 0 2 = d d v50 10 3a m t n e r r u c e g a k a e l d d ve d o m y b d n a t s , v 5 = d d v0 3a e g a t l o v t u p t u o t u o 2 1a m 0 0 2 < d a o l < a m 05 5 . 1 11 . 2 15 7 . 2 1v t i m i l t n e r r u c t u o 2 1 v 3 1 = d d v , v 1 1 o t d e c r o f t u o 2 10 0 2a m d l o h s e r h t n o i t a l u g e r t u o 2 1e g d e g n i l l a f9 . 1 1v t n e r r u c d d v t n e c s e i u q d a o l t u o 2 1 o n , e d o m n u r , v 8 1 = d d v0 80 0 1a
6 ? 2004 semtech corp. www.semtech.com sc1404 preliminary power management pin descriptions note: all logic level inputs and outputs are open collector ttl compatible. # n i pe m a n n i pn o i t c n u f n i p 13 h s c. s p m s v 3 r o f t u p n i e s n e s t i m i l t n e r r u c . r o t s i s e r e s n e s t n e r r u c a f o e d i s r o t c u d n i e h t o t t c e n n o c 23 l s c. s p m s v 3 r o f t u p n i e s n e s e g a t l o v t u p t u o . r o t s i s e r e s n e s t n e r r u c a f o e d i s t u p t u o e h t o t t c e n n o c 33 p m o c. r e i f i l p m a r o r r e s p m s v 3 . 3 e h t f o t u p t u o d n a n i p n o i t a s n e p m o c 4t u o 2 1. t u p t u o r o t a l u g e r r a e n i l l a n r e t n i v 2 1 5d d v e g a t l o v r e v o v 9 1 a o t y l l a n r e t n i s t c e n n o c o s l a . r o t a l u g e r r a e n i l t u o 2 1 e h t r o f t u p n i e g a t l o v y l p p u s . p m a l c r o t a l u g e r t n u h s 6c n y s 0 0 2 r o f d n g o t e i t ; n o i t a r e p o z h k 0 0 3 r o f l v o t e i t . t c e l e s y c n e u q e r f d n a n o i t a z i n o r h c n y s r o t a l l i c s o . z h k 0 5 3 d n a z h k 0 4 2 n e e w t e b r o t a l l i c s o l a n r e t x e n a o t e z i n o r h c n y s o t y l l a n r e t x e e v i r d . z h k 75 n o n w o d t u h s v 5 w o l l a o t 5 n o h t i w s e i r e s n i r o t s i s e r m h o k 0 1 - k 1 a t c e n n o c . t u p n i l o r t n o c f f o / n o v 5 . v u / p v o n o 8d n g. t n i o p e c n e r e f e r k c a b d e e f d n a d n u o r g g o l a n a e s i o n w o l 9f e r . m u m i n i m f 1 h t i w d n g o t s s a p y b . t u p t u o e g a t l o v e c n e r e f e r v 5 . 2 0 1# e v a s p . e s u l a m r o n r o f d n g o t t c e n n o c . h g i h n e h w e d o m e v a s p s e l b a s i d t a h t t u p n i c i g o l 1 1# t e s e r d e x i f a r e t f a h g i h s e o g # t e s e r . l v o t d n g m o r f s g n i w s # t e s e r . t u p t u o t e s e r d e m i t w o l - e v i t c a . p u r e w o p l u f s s e c c u s a g n i w o l l o f y a l e d e l c y c k c o l c 0 0 0 , 2 3 2 15 p m o co t u p t u o d n a n i p n o i t a s n e p m o c. r e i f i l p m a r o r r e s p m s v 5 e h t f 3 15 l s c. s p m s v 5 r o f t u p n i e s n e s e g a t l o v t u p t u o . r o t s i s e r e s n e s t n e r r u c a f o e d i s t u p t u o e h t o t t c e n n o c 4 15 h s c. s p m s v 5 r o f t u p n i e s n e s t i m i l t n e r r u c . r o t s i s e r e s n e s t n e r r u c a f o e d i s r o t c u d n i e h t o t t c e n n o c 5 1q e s . # t e s e r y b d e s u ) s ( e g a t l o v r o t i n o m s t c e l e s d n a e c n e u q e s p u - r e w o p s p m s s t c e l e s t a h t t u p n i 6 15 h d. h c t i w s l e n n a h c - n e d i s - h g i h , v 5 e h t r o f t u p t u o e v i r d e t a g 7 15 e s a h p. n o i t c e n n o c ) r o t c u d n i ( e d o n g n i h c t i w s v 5 8 15 t s b. e v i r d e t a g e d i s - h g i h v 5 r o f n o i t c e n n o c r o t i c a p a c t s o o b 9 15 l dt e f s o m r e i f i t c e r s u o n o r h c n y s e d i s - w o l v 5 e h t r o f t u p t u o e v i r d e t a g 0 2d n g p. d n u o r g r e w o p 1 2l v t u p t u o s p m s v 5 e h t o t d e h c t i w s s i l v , y c n e i c i f f e d e v o r p m i r o f . t u p t u o r o t a l u g e r r a e n i l l a n r e t n i v 5 . d e l b a n e s i s p m s v 5 n e h w 2 2+ v. t u p n i e g a t l o v y r e t t a b 3 2# n d h s. w o l e v i t c a , t u p n i l o r t n o c n w o d t u h s 4 23 l d . t e f s o m r e i f i t c e r s u o n o r h c n y s e d i s - w o l v 3 e h t r o f t u p t u o e v i r d e t a g 5 23 t s b. e v i r d e t a g e d i s - h g i h v 3 r o f n o i t c e n n o c r o t i c a p a c t s o o b 6 23 e s a h p. n o i t c e n n o c ) r o t c u d n i ( e d o n g n i h c t i w s v 3 7 23 h d. h c t i w s l e n n a h c - n e d i s - h g i h v 3 e h t r o f t u p t u o e v i r d e t a g 8 23 n o. t u p n i l o r t n o c f f o / n o v 3
7 ? 2004 semtech corp. www.semtech.com sc1404 power management block diagram
8 ? 2004 semtech corp. www.semtech.com sc1404 preliminary power management pin configuration ordering information e c i v e de g a k c a pt ( . p m e t b m a ) r t s t i 4 0 4 1 c s8 2 - p o s s t ) 1 ( c 5 8 + - 0 4 - r t s s i 4 0 4 1 c s8 2 - p o s s ) 1 ( block diagram tssop-28/ssop-28 top view 3 h s c3 n o 3 l s c3 h d 3 p m o c3 e s a h p t u o 2 13 t s b d d v3 l d c n y s# n d h s 5 n o+ v d n gl v f e rd n g p # e v a s p5 l d # t e s e r5 t s b 5 p m o c5 e s a h p 5 l s c5 h d 5 h s cq e s sc1404 1 2 3 4 5 6 7 8 9 11 12 13 14 10 15 16 17 18 19 20 21 22 23 24 25 26 27 28 note: (1) only available in tape and reel packaging. a reel contains 2500 devices for tssop and 1000 devices for ssop.
9 ? 2004 semtech corp. www.semtech.com sc1404 power management detailed description the sc1404 is a versatile multiple-output power supply controller for battery operated systems. the sc1404 provides synchronous rectified buck control in fixed frequency forced-continuous (pwm) mode and hysteretic psave mode, for two switching power supplies over a wide load range. out of phase switching reduces input noise and rms current, which reduces the input filter inductors and capacitors. the two switchers have on-chip preset output voltages of 5.0v and 3.3v. the control circuitry for each pwm controller includes digital softstart, voltage error amplifier with built-in slope compensation, pulse width modulator, power save, overcurrent, overvoltage and undervoltage fault protection. two linear regulators and a precision reference voltage are also provided. the 5v/30ma linear regulator (vl) uses battery power to feed the gate drivers. for improved efficiency, vl automatically switches over the +5v converter output if available. the 12v linear regulator supplies up to 200ma. semtech?s proprietary virtual current sense tm provides greater advantages in the aspect of stability and signal-to-noise ratio than the conventional current sense method. pwm control there are two separate pwm control blocks for each switcher. they are switched out-of-phase with each other. this interleaved topology reduces input filter requirements by reducing current drawn from the filter capacitors. to avoid both switchers switching at the same instance, there is a built-in delay between the turn-on of the 3.3v switcher and 5v switcher, the amount of which depends on the input voltage (see out-of-phase switching). the pwm provides two modes of control over the entire load range. the sc1404 operates in forced continuous conduction mode as a fixed frequency peak current mode controller with falling edge modulation. current sense is done differently than in conventional peak current mode control. semtech?s proprietary virtual current sense tm emulates the necessary inductor current information for proper functioning of the ic. in order to accommodate a wide range of output filters, a comp pin is also available for compensating the error amplifier externally. a nominal error amplifier gain of 18 improves the system loop gain and the output transient behavior. when operating in continuous conduction mode, the high-side mosfet is turned on at the start of each switching cycle. it is turned off when the desired duty cycle is reached. active shoot-through protection will delay the lower mosfet turn-on until the phase node drops below 1v. the low-side mosfet remains on until the beginning of the next switching cycle. again, active shoot-through protection ensures that the low-side mosfet gate voltage drops low before the high-side mosfet turns on. under light load conditions when the psave# pin is low, the sc1404 operates hysteretically in the discontinuous conduction mode to reduce its switching frequency and switching bias current. the switching of the output mosfet does not depend on a given oscillator frequency, but on the hysteretic voltage set around the nominal output voltage. when entering psave# mode (from heavy to light load), if the minimum (valley) inductor current measured at cshx-cslx is below the zero cross threshold (typically 5 mv) for four switching cycles, the virtual current sense circuitry will shut off and the mode changes to hysteretic mode. as the load current increases, if the minimum (valley) inductor current is above the threshold for four switching cycles, the converter stops psave mode and enters pwm operation. the change in frequency between hysteretic psave and pwm mode provides hysteresis to inhibit chattering between the two modes of operation. gate drive / control the gate drivers on the sc1404 are designed to switch large mosfets. the high-side gate driver must drive the gate of high-side mosfet above the v+ input. the supply for the gate drivers is generated by charging a boostrap capacitor from the vl supply when the low-side driver is on. in continuous conduction mode, the low-side driver output that controls the synchronous rectifier in the power stage is on when the high-side driver is off. under light load conditions when psave# pin is low, the inductor ripple current will approach the point where it reverses polarity. this is detected by the low-side driver control and the synchronous rectifier is turned off before the current reverses, preventing energy drain from the output. the low-side driver operation is also affected by various fault conditions as described in the fault protection section. internal bias supply the vl linear regulator is a 5v output that powers the gate drivers, 2.5v reference and internal controls of the sc1404. the regulator is capable of supplying up to 30ma (including mosfet gate charge current). the vl pin should be bypassed to gnd with 4.7uf to supply the large gate drive current pulses. the regulator receives input power from the v+ battery input. effi- ciency is improved by providing a bootstrap for the vl output. when the 5v smps output voltage reaches 5v, internal circuitry turns on a pmos device between csl5 and vl. the internal vl regulator is then disabled, and vl bias is provided by the high efficiency 5v switcher. the ref output is accurate to +/- 2% over temperature. it is capable of delivering 5ma max and should be bypassed with 1uf minimum capacitor. loading the ref pin will reduce the ref voltage slightly as seen in the following table.
10 ? 2004 semtech corp. www.semtech.com sc1404 preliminary power management g n i d a o l e c n a t s i s e r ) m h o ( 1 1 5k 7 6 . 2k 9 . 9 4k 5 5 2g e m 1 f e r v n o i t a i v e d v m 3 . 8v m 1 . 3v m 5 . 0v m 3 . 0v m 0 current sense (csh, csl) output current of each supply is sensed at the csh and csl pins. overcurrent is reached when the current sense voltage exceeds 55mv typical. on a cycle-by-cycle basis, a positive overcurrent turns off the high-side driver and a negative overcurrent turns off the low-side driver. oscillator when the sync pin is high the oscillator runs at 300khz; when sync is low the frequency is 200khz. the oscillator will synchronize to the falling edge of a clock on the sync pin with a frequency between 240khz and 350khz. in general, 200khz operation provides highest efficiency, while 300khz allows for smaller output ripple and/or smaller filter components. fault protection in addition to cycle-by-cycle current limit, the sc1404 provides overtemperature, output overvoltage, and undervoltage protection. overtemperature protection will shut the device down if die temperature exceeds 150 c, with 10 c hysteresis. if either smps output is more than 10% above its nominal value, both smps are latched off and the low side mosfets are latched on. to prevent the output from ringing below ground in a fault condition, a 1a schottky diode should be placed across each output. two different levels of undervoltage (uv) are detected. if the output falls 9% below its nominal value, the reset# output is pulled low. if the output falls 25% below its nominal value, both smps are latched off. both of the latched faults (ovp and uv) persist until shdn or on3 is toggled, or the v+ input is brought below 1v. shutdown and operating modes holding the shdn pin low disables the sc1404, reducing the v+ input current to less than 10ua. when shdn is high, the part enters standby mode where the vl regulator and vref are enabled. turning on either smps will put the sc1404 in run mode. n d h s3 n o5 n oe d o mn o i t p i r c s e d w o lxx - t u h s n w o d s a i b m u m i n i m t n e r r u c h g i hw o lw o ly b d n a t sl v d n a f e r v r o t a l u g e r e l b a n e h g i hh g i hh g i hn u r e d o m s p m s h t o b g n i n n u r power up controls and soft start the user controls the sc1404 reset# through the seq, on3 and on5 pins, as shown in the startup sequence chart. at startup, reset# is held low for 32k switching cycles, and then reset# is determined by the output voltages and the seq pin. to prevent surge currents at startup, each smps has a counter and dac to incrementally raise the current limit (csh-csl voltage). the current limit follows discrete steps of typically 25%, 40%, 60%, 80%, and 100%, each step lasting 128 clock cycles. to charge up the output capacitors, inductor current at startup must exceed load current. when the output voltage reaches it?s nominal value the smps will reduce duty cycle, but the excess li 2 energy of the inductor must flow into the load and output capacitors. if the output capacitor is relatively small, the peak output voltage can approach the overvoltage trip point. to prevent nuisance ovp at startup, the inductance and capacitance must meet the following criteria: 59 . 1 2 2 _ _ ? oc max nom o min max il v c l il max_oc is the maximum inductor current set by the current-limit components, and v o_nom is the nominal output voltage. 12out supply the 12out linear regulator is capable of supplying 200ma. the input voltage to the 12out regulator is generated by a secondary winding on the 5v smps inductor. a heavy load on the 12out regulator when the 5v smps operates in psave mode will cause vdd to sag, causing 12out to drop. if 12out output drops 0.8% from its nominal value, the 5v smps is forced out of psave mode and into pwm mode for several cycles. this recharges the bulk input capacitor on vdd. the 12out linear regulator has internal protection to prevent damage under short circuit conditions. overvoltage protection is provided on the vdd input. if vdd rises above 19v, a 10ma shunt load is applied to vdd to reduce the voltage. the overvoltage threshold has 0.5v hysteresis.
11 ? 2004 semtech corp. www.semtech.com sc1404 power management reference circuit design the schematic for the reference circuit is shown on page 20. the reference circuit is configured as follows: switching regulator 1 vout1 = 3.3v @ 6a switching regulator 2 vout2 = 5.0v @ 6a vl regulator vout3 = 5.0v @ 30ma 12v regulator vout4 = 12.0v @ 200ma input voltage vin = 7 to 21v designing the output filter before calculating the filter inductance and capacitance, an acceptable inductor ripple current is determined. ripple current is usually set at 10% to 20% of the maximum load. however, increasing the ripple current allows for a smaller inductor and will also quicken the output transient response. in this example, we set the ripple current to be 25% of maximum load. a a i o 5 . 1 6 % 25 = = ? the inductance is found from ripple current, frequency, input voltage, and output voltage. minimum required inductance is found at maximum vin, where ripple current is the greatest. uh io f vin vo vo min l 18 . 6 ) / 1 ( = ? ? = for the reference design, the coiltronics dr127-6r8 is used. this is acceptable for the 3v output, which uses a simple inductor. the 5v inductor must have a 12v winding with a turns ratio of 2.2:1. for the 5v inductor, the tti-8215 from transpower technologies is used, which has 5v inductance of 6.4uh. to specify the output capacitance, the allowable output ripple voltage must be determined. output ripple is often specified at 1% of the output voltage. for the 3.3v output, we selected a maximum ripple voltage of 33mvp-p. the maximum allowable esr would then be: ? = = ? ? = m a mv i v esr o o max 22 5 . 1 / 33 / panasonic sp polymer aluminum capacitors are a good choice. for this design, use one 180uf, 4v device, with esr of 15m ? . the output capacitor must support the inductor rms ripple current. to check the actual ripple versus the capacitor?s rms rating: a a i i o actual rms 43 . 0 12 5 . 1 12 _ = = ? = this is much less than the capacitor?s ripple rating of 3.3a. choosing the main switching mosfet the irf7143 is used in the reference design. before choosing the main (high-side) mosfet, we need to check three parameters: volt- age, power, and current rating. the maximum drain to source voltage of the mosfet is mainly determined by the switcher topology. with a buck topology, v 21 v v max _ in max _ ds = = the irf7413 is a 30v device, which allows for 70% derating at 21v operation. the mosfet power dissipation has three components: conduction losses, switching losses, and gate drive losses. the conduction loss is determined using the rms mosfet current; the equation is q e s3 n o5 n ot e s e rn o i t p i r c s e d f e rw o lw o l. s p m s v 3 . 3 s w o l l o f . f f o s s p m s h t o b . e d o m l o r t n o c t r a t s t n a d n e p e d n i f e rw o lh g i h. w o l. f f o s p m s v 3 . 3 , n o s p m s v 5 f e rh g i hw o l. s p m s v 3 . 3 s w o l l o f. f f o s p m s v 5 , n o s p m s v 3 . 3 f e rh g i hh g i h. s p m s v 3 . 3 s w o l l o f. n o s s p m s h t o b d n gw o lx . w o l. f f o s s p m s h t o b d n gh g i hw o l / h g i he r a s t u p t u o h t o b r e t f a h g i h . n o i t a l u g e r n i , h g i h = 5 n o f i . h g i h s e o g 3 n o n e h w s t r a t s v 5 . f f o s i v 3 , w o l = 5 n o f i . n o s i v 3 l vw o lx . w o l. f f o s s p m s h t o b l vh g i hw o l / h g i he r a s t u p t u o h t o b r e t f a h g i h . n o i t a l u g e r n i , h g i h = 5 n o f i . h g i h s e o g 3 n o n e h w s t r a t s v 3 . f f o s i v 5 , w o l = 5 n o f i . n o s i v 5 startup sequence chart applications information
12 ? 2004 semtech corp. www.semtech.com sc1404 preliminary power management shown below. the mosfet current is a trapezoid waveform with values equal to: 2 ? i i i l load min ? = 2 ? i i i l load max + = l fs d) (1 vo ? i l ? ? ? = vin vo d = () 2 2 max max min min rms i i i i d i + ? + ? = as input voltage decreases, the duty cycle increases and the ripple current decrease, and overall the rms mosfet current will increase. the conduction losses are then given by the formula below, where rds(on) is 18m-ohm for the irf7413 at room temperature. note that rds(on) increases with temperature. 2 rms ds(on) conduction i r p ? = the mosfet switching loss is estimated according to: g out s 2 in rss switching i i f v c p ? ? ? = crss is the mosfet?s reverse transfer capacitance, 240pf for irf7413. ig is the gate driver current, which is 1a for sc1403. the mosfet gate drive loss is estimated from: s 2 g gate f vgfs c 2 1 p ? ? ? = cg is the effective gate capacitance, equal to the total gate charge divided by vgs, from the vendor datasheet, and is 7.9nf for the irf7413. vgfs is the final gate-source voltage, 5v in this case. the total mosfet loss is the sum of the three loss components. gate switching conduction total_diss p p p p + + = the mosfet dissipation under conditions of 15v input, 6a load, and ambient temperature of 25c, can be determined as: dnom = 0.22 ? il = 1.26a imin = 5.37a imax = 6.63a irms = 4.88a rds(on) (100c) = 18 mohm pconduction = 429mw pswitching = 97mw pgate = 30mw ptotal_diss = 429 + 97 + 30 = 556 mw the junction temperature rise resulting from the power dissipa- tion is calculated as: ja t j p ? t ? = p t is the total device dissipation, and ja is the package thermal resistance, which is 50c/w for the irf7413. the junction tem- perature rise is then: ? t j = 0.556w . 50c/w = 27.8 this is an acceptable temperature rise, so no special heat sinking is required. designing the loop a good loop design is a combination of the power train and com- pensation design. in the sc1404, the control-to-output/power train response is dominated by the load impedance, the inductor, out- put capacitance, and the esr of the output caps. the low fre- quency gain is dominated by the output load impedance and the effective current sense resistor. inherent to virtual current sense tm , there is one additional low frequency pole sitting between 100hz and 1khz and a zero between 15khz and 25khz. he output of error amplifier comp pin is available for external compensation. a traditional pole-zero-pole compensation is not necessary in the design using sc1404, a simple high frequency pole is usually sufficient. single-pole compensation method given parameters: vin = 19v, vout = 3.3v @ 2.2a, output impedance, ro = 3.3v/2.2a = 1.5 ? , panasonic sp cap, co = 180uf, resr = 15 ? m , output inductor, lo = 4.7uh switching frequency, fs = 300khz simulated control-to-output gain & phase response (up to 100khz) is plotted below. -50 -40 -30 -20 -10 0 10 20 30 40 50 1.00e+02 1.00e+03 1.00e+04 1.00e+05 f (hz) gain (db)
13 ? 2004 semtech corp. www.semtech.com sc1404 power management applications information applications information -200 -150 -100 -50 0 50 100 150 200 1.00e+02 1.00e+03 1.00e+04 1.00e+05 f (hz) phase (deg) measured control-to-output gain & phase response (up to 100khz) is plotted below. -50 -40 -30 -20 -10 0 10 20 30 40 50 1.00e+02 1.00e+03 1.00e+04 1.00e+05 f (hz) gain (db) -200 -150 -100 -50 0 50 100 150 200 1.00e+02 1.00e+03 1.00e+04 1.00e+05 f (hz) phase (deg) single-pole compensation is achieved using a 100pf capacitor from the comp pin to ground. the simulated feedback gain & phase response (up to 100khz) is plotted below. -15 -10 -5 0 5 10 15 20 25 1.00e+02 1.00e+03 1.00e+04 1.00e+05 f (hz) gain (db) -100 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 1.00e+02 1.00e+03 1.00e+04 1.00e+05 f (hz) phase (deg) measured feedback gain & phase responses (up to 100khz) is plotted below.
14 ? 2004 semtech corp. www.semtech.com sc1404 preliminary power management applications information . -15 -10 -5 0 5 10 15 20 25 1.00e+02 1.00e+03 1.00e+04 1.00e+05 f (hz) gain (db) -180 -160 -140 -120 -100 -80 -60 -40 -20 0 20 1.00e+02 1.00e+03 1.00e+04 1.00e+05 frequency (hz) phase (deg) simulated overall gain & phase responses (up to 100khz) is plot- ted below. -80 -60 -40 -20 0 20 40 60 80 1.00e+02 1.00e+03 1.00e+04 1.00e+05 f (hz) gain (db) -20 0 20 40 60 80 100 120 140 160 180 1.00e+02 1.00e+03 1.00e+04 1.00e+05 f (hz) phase (deg) measured overall gain & phase response of the single-pole com- pensation using sc1404 is plotted below. -20 0 20 40 60 80 100 120 140 160 180 1.00e+02 1.00e+03 1.00e+04 1.00e+05 f (hz) phase (deg) p a c t u p t u on o i t a s n e p m o c d e d n e m m o c e r e u l a v p a c f 0 8 1 = f p 0 0 2 f 0 0 0 1 >f p 0 3 3
15 ? 2004 semtech corp. www.semtech.com sc1404 power management applications information input capacitor selection and out-of-phase switching the sc1404 uses out-of-phase switching between the two converters to reduce input ripple current, allowing smaller cheaper input capacitors compared to in-phase switching. the figure below shows in-phase switching. i3in is the input current for the 3v converter, i5in is the input current for the 5v converter. the two converters start each switching cycle simultaneously, causing a significant amount of overlap and a high peak current. the total input current the third waveform, which shows how the two currents add together. the fourth waveform is current in and out of the input capacitors. i3in i5in iin average icap 0 0 d3 d5 the next figure shows out-of-phase switching. the 3v and 5v pulses are spaced apart, so there is no overlap. this gives two benefits; the peak current is reduced, and the effective switch frequency is raised. both of these make filtering easier. the third waveform is the total input current, and the fourth waveform shows the current flowing in and out of the input capacitors. the rms value of the capacitor current is significantly lower than the in- phase case, which allows for smaller capacitors. i3in i5in icap iin average 0 0 d3 d5 as the input voltage is reduced, the duty cycle of both converters increases. at input voltages less than 8.3v, it is impossible to prevent overlap regardless of the phase between the converters. overlap is seen in the following figure. i5in iin 0 average icap 0 period phase lead d3 d5 from an input filter standpoint it is desirable to minimize the overlap; but it is also desirable to keep the turn-on and turn-off transitions of the two converters separated in time, to minimize interaction between the two converters. the sc1404 keeps the turn-on and turn-off transitions separated in time by changing the phase between the converters depending on the input voltage. the following table shows the phase relationship between 3v and 5v turn-on, based on input voltage. t u p n it u p n i t u p n i t u p n it u p n i e g a t l o ve g a t l o v e g a t l o v e g a t l o ve g a t l o v v 5 o t v 3 m o r f d a e l e s a h pv 5 o t v 3 m o r f d a e l e s a h p v 5 o t v 3 m o r f d a e l e s a h p v 5 o t v 3 m o r f d a e l e s a h pv 5 o t v 3 m o r f d a e l e s a h p v 6 . 9 > n i vd o i r e p g n i h c t i w s f o % 1 4 v 5 d n a v 3 . 3 n e e w t e b p a l r e v o o n n i v > v 6 . 9 v 7 . 6 > d o i r e p g n i h c t i w s f o % 9 5 s u o e n a t l u m i s t n e v e r p o t p a l r e v o l l a m s g n i h c t i w s v 5 / v 3 n i v > 7 . 6d o i r e p g n i h c t i w s f o % 4 6 s u o e n a t l u m i s t n e v e r p o t p a l r e v o l l a m s g n i h c t i w s v 5 / v 3
16 ? 2004 semtech corp. www.semtech.com sc1404 preliminary power management typical characteristics input ripple current can be calculated from the following equations. cycle duty 3v 3.3v/v d3 in = = cycle duty 5v 5v/v d5 in = = current load dc 3v i3 = current load dc 5v i5 = d ovl = overlapping duty cycle of the 3v and 5v pulses (varies according to input voltage) in ovl v 9.6v for 0 d = 9.6v v 6.7v for 0.41) - (d5 d in ovl < = 6.7 v for 0.36) - (d5 d in ovl < = current input dc average i in = 5 5 3 3 d i d i i in ? + ? = in sw_rms v from drawn current rms i = i5 i3 d 2 i5 d5 i3 d3 i ovl 2 2 sw_rms 2 ? ? ? + ? + ? = 2 2 in_ave sw_rms rms_cap i i i + = the worst-case ripple current varies by application. for the case 6a load on both outputs, the worst-case ripple occurs at vin = 7.5v, and the rms capacitor current is 4.2a. the reference design uses 4 paralleled ceramic capacitors, (murata grm32nf51e106z, 10 uf 25v, size 1210). each capacitor is rated at 2.2a. choosing synchronous mosfet and schottky diode since this is a buck topology, the voltage and current ratings of the synchronous mosfet are the same as the main switching mosfet. it makes sense cost- and volume-wise to use the same mosfet for the main switch as for the synchronous mosfet. therefore, irf7413 is used again in the design for synchronous mosfet. to improve overall efficiency, an external schottky diode is used in parallel with the low side mosfet. the freewheeling current enters the schottky diode instead of the inefficient body diode of the synchronous mosfet. it is really important when laying out the board to place the synchronous mosfet and schottky diode close to each other to reduce the current ramp-up and ramp-down time due to parasitic inductance between the channel of the mosfet and the schottky diode. the current rating of the schottky diode can be determined by the following equation: 0.2a ts 100n load i if_avg = ? = where 100nsec is the estimated time between the mosfet turn- off and the schottky diode turn-on and ts = 3.33us.a schottky diode with a forward current of 0.5a is sufficient for this design. operation below 6v input the sc1404 will operate below 6v input voltage with careful design, but there are limitations. the first limitation is the maximum available duty cycle from the sc1404, which limits the obtainable output voltage. the design should minimize all circuit losses through the system in order to deliver maximum power to the output. a second limitation with operation below 6v is transient response. when load current increases rapidly, the output voltage drops slightly; the feedback loop normally increases duty cycle briefly to bring the output voltage back up. if duty cycle is already near the maximum limit, the duty cycle cannot increase enough to meet the demand, and the output voltage sags more than normal. this problem can not be solved by changing the feedback compensation, it is a function of the input voltage, duty cycle, and inductor and capacitor values. if an application requires 5v output from an input voltage below 6v, the following guidelines should be used: 1 - set the switching frequency to 200 khz (tie sync to ground). this increases the maximum duty cycle compared to 300 khz operation. 2 - minimize the resistance in the power train. select mosfets, inductor, and current sense resistor to provide the lowest resistance as is practical. 3 - minimize the pcb resistance for all traces carrying high current. this includes traces to the input capacitors, mosfets and diodes, inductor, current sense resistor, and output capacitor. 4 - minimize the resistance between the sc1404 circuit and the power source (battery, battery charger, ac adaptor). 5 - use low esr capacitors on the input to prevent the input voltage dropping during on-time. 6 - if large load transients are expected, high capacitance and low esr capacitors should be used on both the input and output.
17 ? 2004 semtech corp. www.semtech.com sc1404 power management 5v start-up with slow vin ramp. proper startup of the 5v output can be hampered by slow dv/dt on the input. the sc1404 will power up and attempt to generate an output when the input voltage exceeds 4.5 volts. if the input has a slow dv/dt, the input voltage will not rise significantly during the start-up sequence, leading to two conditions. first, the vl supply can be hundreds of mv below 5v, since the input may not yet be above 5v. second, the duty cycle will be at maximum, leading to very small off-times. these two conditions tend to reduce the boost voltage; if continued indefinitely, the boost capacitor may be unable to recharge fully, and eventually the high-side driver loses its boost bias. to avoid this the following steps should be taken: 1. if possible the dv/dt of the input supply should exceed .02v/ usec. this dv/dt condition only applies when the input passes between 4 and 6 volts, the point at which the sc1404 begins a startup sequence. an alternative is to make sure the input voltage reaches 6 volts within 100 usec of sc1404 startup at approximately 4.2 volts. this is sufficiently fast to allow vl and duty cycle to achieve normal levels and prevents the boost voltage from falling. 2. if the input dv/dt cannot meet condition 1, the startup of the sc1404 should be delayed until the input voltage reaches 6v. this can be done using either the shdn# or on5 pin. if the dv/dt is moderate (slews from 4 to 6 volts in several msecs), an rc delay on either the shdn# or on5 pin should be enough to delay turn-on until the input reaches 6v. 3. for slow dv/dt on the input (10?s of msec), the sc1404 should be held off until the input reaches 6v. this can be done using a comparator or external logic to hold the shdn# or on5 pin low until the input reaches 6v. 12v load limitations the 12v regulator derives input power from a secondary winding on the 5v inductor. during the 5v off-time, the inductor transfers energy from the 5v winding to the secondary winding, thereby providing a crudely regulated 15v that feeds the 12v regulator. note that duty cycle increases at low input voltages, and therefore the on-time decreases. at low input voltages, the duty cycle increases to maintain the 5v output. the off-time consequently decreases, which has two detrimental effects. it allows less time to recharge the raw 15v capacitor, and it also raises the peak 15v current required to maintain the average 12v load. the 15v winding needs higher peak current, delivered in less time. but the stray (leakage) inductance of the inductor resists rapid changes in winding current, and ultimately limits how much current can be drawn from 15v before the voltage falls. the following guidelines for 12v loading apply to the typical circuit, page 22. e g n a r n i ve g n a r n i v e g n a r n i v e g n a r n i ve g n a r n i vs n o i t i d n o c d a o l v 2 1s n o i t i d n o c d a o l v 2 1 s n o i t i d n o c d a o l v 2 1 s n o i t i d n o c d a o l v 2 1s n o i t i d n o c d a o l v 2 1 >v 0 1d a o l v 2 1< d a o l v 5 * 2 / 1 x a m a m 0 0 2 = d a o l v 2 1 v 0 1 - v 7d a o l v 2 1< d a o l v 5 * 2 / 1 : d a o l v 2 1 e t a r e d y l r a e n i l v 0 1 t a a m 0 0 2 v 7 t a a m 0 0 1 v 7 - v 6d a o l v 2 1< d a o l v 5 * 2 / 1 : d a o l v 2 1 e t a r e d y l r a e n i l v 0 1 t a a m 0 0 1 v 7 t a a m 5 2
18 ? 2004 semtech corp. www.semtech.com sc1404 preliminary power management overvoltage test measuring the overvoltage trip point can be problematic. any buck converter with synchronous mosfets can act as a boost con- verter, sending energy from output to input. in some cases the energy sent to the input is enough to drive the input voltage be- yond normal levels, causing input overvoltage. to prevent this, enable the sc1404 psave# feature, which effectively disables the low side mosfet drive so that little energy, if any, is transferred back to the input. semtech recommends the following circuit for measuring the ov- ervoltage trip point. d1 prevents the output voltage from damag- ing lab supply 1. r1 limits the amount of energy that can be cycled from the output to the input. r2 absorbs the energy that might flow from output to input, and d2 protects lab supply from pos- sible damage. the on5 signal is monitored to indicate when overvoltage occurs. initial conditions: both lab supplies set to zero volts no load connected to 3v or 5v psave# enabled (psave# tied to gnd) on5 enabled on3 enabled dvms monitoring on5 and the output under test. oscilloscope probe connected to phase node of the output under test (not strictly required). set lab supply 2 to provide 10v at the sc1404 input. the phase node of the output being tested should show some switching ac- tivity. the on5 pin should be above 4v. slowly increase lab supply 1 until the output under test rises slightly above it?s normal dc level. as lab supply 1 increases, switching activity at the phase node will cease. the on5 pin should remain above 4v. increase lab supply 1 in very small increments, monitoring both on5 and the output under test. the overvoltage trip point is the highest voltage seen at the output before on5 pulls low (approxi- mately 0.3v). do not record the voltage seen at the output after on5 has pulled low; when on5 pulls low, the current flowing in d1 changes, corrupting the voltage seen at the output. 1k d1 e.g. 1n4004 r2 75 to dvm d1 e.g. 1n4004 vin supply r1 470 2 sc1404 evaluation board lab output test under 1 supply lab to dvm 1/2w on5 vl 1/2w 3.3v efficiency 50 60 70 80 90 100 0.01 0.1 1 10 load current (a) efficiency (%) 6v 10v 19v 5v efficiency 80 85 90 95 100 0.01 0.1 1 10 load current (a) efficiency (%) 6v 10v 19v typical characteristics
19 ? 2004 semtech corp. www.semtech.com sc1404 power management as with any high frequency switching regulator design, a good pcb layout is essential to optimize performance of the converter. be- fore starting pcb layout, a careful layout strategy is strongly recom- mended. see the pcb layout in the sc1404 evaluation kit manual for example. in most applications, fr4 board material with 4 or more layers and at least 2-ounce copper is recommended(for output current up to 6a). use at least one inner layer for ground connection. it is good practice to tie signal ground and power ground together at one single point so that the signal ground is not easily contaminated. also be sure that high current paths have low in- ductance and resistance by making trace widths as wide as pos- sible and lengths as short as possible. use low-impedance by- passing for lines that pull large amounts of current in short periods of time. the following step by step layout strategy is recommended. step #1. power train components placement. a. power train arrangement. place power train components first. the figure below shows the recommended power train arrangement. q1 is the main switching mosfet, q2 is the low side mosfet, d1 is the schottky diode and l1 is the output inductor. q2 d1 q1 l1 the phase node is generally the largest source of noise in the converter circuit since it switches at very high rate of speed. the phase node connections should be kept to a minimum size con- sistent with its connectivity and current carrying requirements. place the schottky diode as close to the phase node as possible to minimize the trace inductance between it and the low side mosfet, to reduce the efficiency loss due to the current ramp-up and down time. this is important when the converter needs to handle high di/dt requirements. layout guidelines b. current sense. minimize the length of current sense signal traces. keep them less than 15mm. kelvin connections should be used; try to keep the traces parallel to each other and route them close to each other as much as possible. even though sc1404 implements virtual current sense scheme, the current sense signal is sampled by the sc1404 to determine the psave threshold. see the follow- ing figure for a kelvin connection of the current sense signal. c. gate drive. sc1404 has built-in gate drivers capable of sinking/sourcing 1a peaks. upper gate drive signals are noisier than the lower ones. therefore, place them away from sensitive analog circuitries. make sure the lower gate traces are as close as possible to the ic pins and both upper and lower gate traces as wide as possible. step #2: pwm controller placement (pins) and signal ground is- land. connect all analog grounds to a separate solid copper island plane, which connects to the sc1404?s gnd pin. this includes ref, comp3, comp5, sync, on3, on5, psv# and reset#. step #3: ground plane arrangement. there are several ways to tie the different grounds together. since this is a buck topology converter, the output ground is relatively quieter than the input ground. therefore connect analog ground to power ground at the output side. often it is useful to use a separate ground symbol for the two grounds, and tie the two grounds together at a single point through a 0 ? resistor. the power ground for the input side and the power ground for the output side is the same ground and they can be tied together using internal planes. csh csl sc1404 rcs l1
20 ? 2004 semtech corp. www.semtech.com sc1404 preliminary power management evaluation board schematic 3_3v seq r22 0 ohm dh3 csh5 r23 0 ohm s1 dip_sw5_pth 1 2 3 4 5 10 9 8 7 6 on3 d6 mbrs1100t3 c13 100pf c14 100pf r12 2m 1 2 r14 2m 1 2 r15 2m 1 2 r17 2m 1 2 shdn# bst3 comp3 reset# comp5 comp3 comp5 t-on5 bst5r ref c25 1uf/16v d4 30bq015 a c j2 gnd 1 j3 gnd 1 d2 30bq015 a c j4 gnd 1 c18 no_pop j15 shdn# 1 j5 gnd 1 j1 2 r e 1 v+ r7 0.005 c9 4.7uf/35v c19 150uf/6.3v d1 bat54a bst5 l1 6.8uh 1 2 r6 0.005 vl t/l2 tti 8215 1 5 7 4 10 6 vin jp4 1 2 lx3 dh5 j27 v+ 1 psv# j1 b_jack_pair pos 1 neg 2 dl3 u1 sc1404its csh3 1 csl3 2 comp3 3 12out 4 vdd 5 sync 6 time/on5 7 gnd 8 ref 9 psave 10 reset 11 comp5 12 csl5 13 csh5 14 seq 15 dh5 16 phase5 17 bst5 18 dl5 19 pgnd 20 vl 21 v+ 22 shdn 23 dl3 24 bst3 25 phase3 26 dh3 27 run/on3 28 lx5 r4 0 1 2 r5 0 1 2 jp1 1 2 jp2 1 2 jp3 1 2 vdd j13 t- on5 1 j11 on3 1 csh3 vin dl5 sy nc c43 no_pop c40 0.1uf vl c35 0.1uf c36 0.1uf c34 0.1uf c33 0.1uf s c 1404 e v b s chem ati c c1 10uf/25v 1 2 r18 no_pop c12 0.1uf c10 0.1uf r21 no_pop r1 10 1 2 c3 0.22uf r20 no_pop r19 no_pop j16 3_3v 1 j17 csl3 1 j18 5v 1 j19 csh5 1 j20 csl5 1 j21 csh3 1 c11 4.7uf/16v c4 0.22uf d3 140t3 a c c26 0.1uf r16 1k 1 2 j6 b_jack_pair pos 1 neg 2 j7 b_jack_pair pos 1 neg 2 r13 2m 1 2 c20 no_pop c15 0.22uf c16 0.22uf d5 140t3 a c c29 no_pop c28 no_pop j22 lx3 1 j23 lx5 1 c38 1uf c39 1uf c22 4.7uf/16v c2 10uf/25v 1 2 d q1 irf7413 4 1 2 3 5 6 7 8 bst3r c42 4.7uf/25v j9 sync 1 j24 vin 1 vdd j14 v l 1 j10 p 1 c5 10uf/25v 1 2 c6 10uf/25v 1 2 j8 r e 1 d q2 irf7413 4 1 2 3 5 6 7 8 d q3 irf7413 4 1 2 3 5 6 7 8 3_3v 5 v vl vin ref v l +12v re s d q4 irf7413 4 1 2 3 5 6 7 8 c41 no_pop vin c37 0.01uf c17 180uf/4v j25 +12v 1 j26 gnd 1 5v c27 0.01uf
21 ? 2004 semtech corp. www.semtech.com sc1404 power management evaluation board bill of materials m e t iy t qn o i t a n g i s e dr e b m u n t r a pn o i t p i r c s e dr e r u t c a f u n a mm r o f r o t c a f 14 6 c , 5 c , 2 c , 1 c5 2 0 z 6 0 1 v 5 y 0 3 2 m r gv 5 2 , f u 0 1a t a r u m0 1 2 1 21 6 1 c , 5 1 c , 4 c , 3 c, v 0 5 , f u 2 2 . 0 v 5 y c i n o s a n a p5 0 8 39 cv 5 3 , f u 7 . 4e s a c _ b 4- 3 c , 4 3 c , 3 3 c , 6 2 c , 2 1 c , 0 1 c 0 4 c , 6 3 c , 5 r 7 x , v 0 5 , f u 1 . 0c i n o s a n a p3 0 6 0 52 2 c , 1 1 cn 0 5 2 m 5 7 4 yv 6 1 , f u 7 . 4p a c a v o n2 1 8 1 63 1 c , 4 1 ck 1 0 1 h 1 c v 1 j c ev 0 5 , f p 0 0 1c i n o s a n a p3 0 6 0 77 1 cr 1 8 1 g 0 e u - f e ev 4 , f u 0 8 1c i n o s a n a p3 4 3 7 _ e s a c _ d 89 1 cr 1 5 1 j 0 e u - f e ev 3 . 6 , f u 0 5 1c i n o s a n a p3 4 3 7 _ e s a c _ d 95 2 c5 0 1 c 1 b f 3 j c ev 6 1 , f u 1c i n o s a n a p6 0 2 1 0 17 2 c , 7 3 ck 4 0 1 c 1 b v 1 j c ev 0 5 , f u 1 0 . 0c i n o s a n a p3 0 6 0 1 18 3 c , 9 3 cf u 13 0 6 0 2 12 4 cv 5 2 , f u 7 . 4 3 111 da 4 5 t a b, a m 0 0 2 , v 0 3 e d o n a _ c l a u d x e t e z3 2 - t o s 4 12 4 d , 2 d5 1 0 q b 0 3. r . ic m s 5 12 5 d , 3 d3 t 0 4 1 s r b ma 1 , v 0 4 y k t t o h c s a l o r o t o mb m s 6 116 d3 t 0 0 1 1 s r b ma l o r o t o mb m s
22 ? 2004 semtech corp. www.semtech.com sc1404 preliminary power management m e t iy t qn o i t a n g i s e dr e b m u n t r a pn o i t p i r c s e dr e r u t c a f u n a mm r o f r o t c a f 7 14 4 p j , 3 p j , 2 p j , 1 p jg r e b n i p 2 r o t c e n n o c g r e b 8 13 7 j , 6 j , 1 jk c a j a n a n a b r i a p 9 14 27 2 j - 8 j , 5 j - 2 js t n i o p t s e t 0 211 l8 r 6 - 7 2 1 r dr o t c u d n i t m s h u 8 . 6 s c i n o r t l i o c 1 24 4 q , 3 q , 2 q , 1 q3 1 4 7 f r il e n n a h c - n v 0 3 t e f s o m l a n o i t a n r e t n i r e i f i t c e r 8 o s 2 211 ry n am h o 0 1y n a3 0 6 0 3 24 3 2 r , 2 2 r , 5 r , 4 ry n am h o 0y n a3 0 6 0 4 22 7 r , 6 r3 4 b f 5 0 0 r 2 1 5 2 l s wm h o m 5e l a d y a h s i v2 1 5 2 5 25 7 1 r , 5 1 r , 4 1 r , 3 1 r , 2 1 ry n am h o g e m 2y n a3 0 6 0 6 216 1 ry n am h o k 1y n a3 0 6 0 7 211 w sn o i t i s o p - 5 h c t i w s p i d y n a 8 2 1 2 l / t5 1 2 8 - i t tr e w o p s n a r t s e i g o l o n h c e t 9 211 us t i 4 0 4 1 c sh c e t m e s evaluation board bill of materials cont.
23 ? 2004 semtech corp. www.semtech.com sc1404 power management evaluation board gerber plots t t t t t op op op op op inner1 inner1 inner1 inner1 inner1 bottom bottom bottom bottom bottom inner2 inner2 inner2 inner2 inner2
24 ? 2004 semtech corp. www.semtech.com sc1404 preliminary power management outline drawing - tssop-28 land pattern - tssop-28
25 ? 2004 semtech corp. www.semtech.com sc1404 power management outline drawing - ssop-28 semtech corporation power management products division 200 flynn road, camarillo, ca 93012 phone: (805)498-2111 fax (805)498-3804 contact information .281 (7.15) z g y p (c) 5.50 .216 0.65 .026 0.43 .017 1.65 .065 8.80 .346 x inches dimensions z p y x dim c g millimeters this land pattern is for reference purposes only. consult your manufacturing group to ensure your company's manufacturing guidelines are met. notes: 1. land pattern - ssop-28

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