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1 www.semtech.com SC4607 very low input, mhz operation, high efficiency synchronous buck power management revision: june 1, 2005 description features applications typical application circuit ? asynchronous start up ? bicmos voltage mode pwm controller ? operation of frequency to 1mhz ? 2.25v to 5.5v input voltage range ? output voltages as low as 0.5v ? +/-1% reference accuracy ? sleep mode (icc = 10a typ) ? adjustable lossless short circuit current limiting ? combination pulse by pulse & hiccup mode current limit ? high efficiency synchronous switching ? up to 97% duty cycle ? 1a peak current driver ? 10-pin msop package ? distributed power architecture ? servers/workstations ? local microprocessor core power supplies ? dsp and i/o power supplies ? battery-powered applications ? telecommunications equipment ? data processing applications the SC4607 is a voltage mode step down (buck) regula- tor controller that provides accurate high efficiency power conversion from an input supply range of 2.25v to 5.5v. the SC4607 is capable of producing an output voltage as low as 0.5v and has a maximum duty cycle of 97%. a high level of integration reduces external component count, and makes it suitable for low voltage applications where cost, size, and efficiency are critical. the SC4607 drives external, n-channel mosfets with a peak gate current of 1a. the SC4607 prevents shoot through currents by offering nonoverlap protection for the gate drive signals of the external mosfets. the SC4607 features lossless current sensing of the voltage drop across the drain to source resistance of the high side mosfet during its conduction period. the quiescent supply current in sleep mode is typically lower than 10a. a 1.2ms soft start is internally provided to prevent output voltage overshoot during start-up. the SC4607 is an ideal choice for converting 2.5v, 3.3v, 5v or other low input supply voltages. it?s available in 10 pin msop package *external components can be modified to provide a vout as low as 0.5v r3 c3 4.7u c2 2.2n c6 330u r1 14.3k c1 180p c14 0.1u vin = 2.25v - 5.5v r6 0 r5 0 d2 l1 1.8u c5 22u c4 22u vout = 1.5v (as low as 0.5v * ) / 12a c71 1u m1 c10 220u m2 c12 22u c9 4.7n r8 200 r7 10k r9 4.99k c20 560pf vcc 2 iset 3 comp 4 fs/sync 5 bst 1 drvh 10 drvl 8 vsense 6 gnd 7 phase 9 u1 SC4607 c11 22u r13 1
2 ? 2005 semtech corp. www.semtech.com SC4607 power management absolute maximum ratings electrical characteristics r e t e m a r a ps n o i t i d n o c t s e tn i mp y tx a mt i n u l l a r e v o e g a t l o v y l p p u s 5 . 5v p e e l s , t n e r r u c y l p p u sv 0 = c n y s / s f0 15 1a g n i t a r e p o , t n e r r u c y l p p u sv c c =v 5 . 525 . 3a m d l o h s e r h t n o - n r u t c c vt a c 5 2 =5 0 . 22 . 2v t a c 5 8 o t c 0 4 - =5 2 . 2 s i s e r e t s y h f f o - n r u t c c v 0 0 1v m r e i f i l p m a r o r r e e g a t l o v t u p n i e s n e s v ) e c n e r e f e r l a n r e t n i ( t a c 5 2 =5 9 4 . 05 . 05 0 5 . 0 v v c c t , v 5 . 5 - v 5 2 . 2 = a c 5 2 =5 2 9 4 . 05 . 05 7 0 5 . 0 t a c 5 8 o t c 0 4 - =5 1 9 4 . 05 8 0 5 . 0 t n e r r u c s a i b e s n e s v 0 0 2a n n i a g p o o l n e p o ) 1 ( v p m o c v 5 . 2 o t 5 . 0 =0 80 9b d h t d i w d n a b n i a g y t i n u ) 1 ( 8z h m e t a r w e l s ) 1 ( 4 . 2s / v r e t e m a r a pl o b m y sm u m i x a ms t i n u v ( e g a t l o v y l p p u s c c )7v s t n e r r u c ) l v r d , h v r d ( s r e v i r d t u p t u o s u o u n i t n o c k a e p 5 2 . 0 - / +a 0 0 . 1 - / +a ) t e s i , c n y s / s f , p m o c , e s n e s v ( s t u p n i 7 o t 3 . 0 -v t s b 3 1v e s a h p 5 . 7 o t 3 . 0 -v s n 0 5 < e s l u p t e s l u p e s a h p 5 . 7 o t 2 -v e g n a r e r u t a r e p m e t t n e i b m a g n i t a r e p ot a 5 8 + o t 0 4 -c e g n a r e r u t a r e p m e t e g a r o t st g t s 0 5 1 + o t 5 6 -c e r u t a r e p m e t n o i t c n u jt j 0 5 1 + o t 5 5 -c . c e s 0 1 ) g n i r e d l o s ( e r u t a r e p m e t d a e lt d a e l 0 0 3 +c ) l e d o m y d o b n a m u h ( g n i t a r d s ed s e4v k all voltages with respect to gnd. currents are positive into, negative out of the specified terminal. unless otherwise specified, vcc = 3.3v, ct = 270pf, t a = -40 c to 85 c , t a =t j 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 ? 2005 semtech corp. www.semtech.com SC4607 power management electrical characteristics (cont.) r e t e m a r a ps n o i t i d n o c t s e tn i mp y tx a mt i n u ) . t n o c ( r e i f i l p m a r o r r e h g i h t u o vi p m o c a m 5 . 5 - =v c c 5 . 0 -v c c 3 . 0 -v w o l t u o vi p m o c a m 5 . 5 =3 . 05 4 . 0 r o t a l l i c s o y c a r u c c a l a i t i n it a c 5 2 =5 2 55 7 55 2 6z h k y t i l i b a t s e g a t l o vt a v , c 5 2 = c c v 5 . 5 o t v 5 2 . 2 =5 . 0v / % t n e i c i f f e o c e r u t a r e p m e tt a c 5 8 o t c 0 4 - =2 0 . 0c / % y c n e u q e r f n o i t a r e p o m u m i n i m ) 1 ( 0 5z h k y c n e u q e r f n o i t a r e p o m u m i x a m ) 1 ( m 1z h y e l l a v o t k a e p p m a r 1v e g a t l o v k a e p p m a r 3 . 1v e g a t l o v y e l l a v p m a r 3 . 0v t i m i l t n e r r u c , t r a t s t f o s , p e e l s d l o h s e r h t p e e l ss f t a d e r u s a e m5 7v m t n e r r u c s a i b t u p n i p e e l sv c n y s v 0 =1 -a e m i t t r a t s t f o s ) 1 ( f w s z h k 5 7 5 =2 . 1s m t n e r r u c s a i b t e s it j c 5 2 =5 4 -0 5 -5 5 -a t e s i f o t n e i c i f f e o c e r u t a r e p m e t 8 2 . 0c / % e m i t k n a l b t i m i l t n e r r u c ) 1 ( 0 3 1s n e v i r d e t a g e l c y c y t u d 7 9% ) h v r d ( e c n a t s i s e r p u - l l u p ) 2 ( v t s b v - e s a h p i , v 3 . 3 = e c r u o s a m 0 0 1 - =7 . 2 ? ) h v r d ( e c n a t s i s e r n w o d - l l u p ) 2 ( v t s b v - e s a h p i , v 3 . 3 = k n i s a m 0 0 1 =4 . 2 ? ) l v r d ( e c n a t s i s e r p u - l l u p ) 1 ( v c c i , v 3 . 3 = e c r u o s a m 0 0 1 - =2 . 2 ? ) l v r d ( e c n a t s i s e r n w o d - l l u p ) 2 ( v c c i , v 3 . 3 = k n i s a m 0 0 1 =5 . 1 ? e m i t e s i r t u p t u ov c c c , v 3 . 3 = t u o f n 7 . 4 =5 3s n e m i t l l a f t u p t u ov c c c , v 3 . 3 = t u o f n 7 . 4 =7 2s n p a l r e v o - n o n m u m i n i m ) 1 ( 0 4s n notes: (1). guaranteed by design. (2). guaranteed by characterization. unless otherwise specified, vcc = 3.3v, ct = 270pf, t a = -40 c to 85 c , t a =t j
4 ? 2005 semtech corp. www.semtech.com SC4607 power management ordering information pin descriptions r e b m u n t r a pe c i v e d r t s m i 7 0 6 4 c s 0 1 - p o s m t r t s m i 7 0 6 4 c s ) 2 ( (10 pin msop) notes: (1) only available in tape and reel packaging. a reel contains 2500 devices. (2) lead free product. this product is fully weee and rohs compliant. pin configuration top view # n i pe m a n n i pn o i t c n u f n i p 1t s b o t s t c e n n o c t s b . t e f s o m e d i s h g i h l e n n a h c - n n a e v i r d o t r e t r e v n o c e h t s e l b a n e n i p s i h t a o t e g a t l o v n i p t s b e h t s t s o o b t i u c r i c p m u p e g r a h c e h t . t i u c r i c p m u p e g r a h c l a n r e t x e e h t . t e f s o m e d i s h g i h e h t f o e t a g e h t g n i v i r d r o f l e v e l e g a t l o v e c r u o s - o t - e t a g t n e i c i f f u s 2c c v a h t i w d n g o t n i p s i h t s s a p y b , y t i n u m m i e s i o n d e v o r p m i r o f . c i e h t r o f l i a r y l p p u s e v i t i s o p . r o t i c a p a c c i m a r e c r s e / l s e w o l f 7 . 4 o t 1 . 0 3t e s i e h t s e s u 7 0 6 4 c s e h t . t e f s o m e d i s h g i h e h t n i t n e r r u c t i m i l o t d e s u s i n i p t e s i e h t t i m i l t n e r r u c e h t . t i m i l t n e r r u c e h t t e s o t r e d r o n i s n i p t e s i d n a n i v e h t s s o r c a e g a t l o v t i u c r i c n o i t a c i l p p a l a c i p y t e h t n i 3 r ( r o t s i s e r l a n r e t x e n a f o e u l a v e h t y b t e s s i d l o h s e r h t e s n e s e h t s s o r c a p o r d e g a t l o v e h t g n i r a p m o c y b d e m r o f r e p s i g n i t i m i l t n e r r u c . ) m a r g a i d e d i s h g i h e h t f o e c n a t s i s e r e c r u o s o t n i a r d e h t s s o r c a p o r d e g a t l o v e h t h t i w r o t s i s e r o t n i a r d e h t s s o r c a p o r d e g a t l o v e h t . d o i r e p n o i t c u d n o c s ' t e f s o m e h t g n i r u d t e f s o m . s n i p e s a h p d n a n i v e h t m o r f d e n i a t b o s i t e f s o m e d i s h g i h e h t f o e c n a t s i s e r e c r u o s 4p m o c d n a y l l a n r e t n i d e t r e v n i s i t u p t u o s i h t t a e g a t l o v e h t . r e i f i l p m a e g a t l o v e h t f o t u p t u o e h t s i s i h t e h t m o r f k r o w t e n g a l - d a e l a . r o t a r a p m o c m w p e h t f o t u p n i g n i t r e v n i - n o n e h t o t d e t c e n n o c s c i t s i r e t c a r a h c r e t l i f c l e l o p o w t e h t r o f s e t a s n e p m o c n i p e s n e s v e h t o t n i p p m o c e h t e z i m i t p o o t r e d r o n i d e r i u q e r s i k r o w t e n g a l - d a e l e h t . l o r t n o c e d o m e g a t l o v o t t n e r e h n i . p o o l l o r t n o c e d o m e g a t l o v e h t f o e c n a m r o f r e p c i m a n y d 5c n y s / s f r o t i c a p a c g n i m i t l a n r e t x e n a h g u o r h t y c n e u q e r f r o t a l l i c s o m w p e h t s t e s n i p c n y s / s f e h t d e k o v n i s i n o i t a r e p o e d o m p e e l s . n i p d n g e h t o t n i p c n y s / s f e h t m o r f d e t c e n n o c s i t a h t g n i r u d t n e r r u c y l p p u s l a c i p y t e h t . v m 5 7 w o l e b e g a t l o v a o t n i p c n y s / s f e h t g n i p m a l c y b a g n i t r e s n i y b e d o m s u o n o r h c n y s n i d e t a r e p o e b n a c 7 0 6 4 c s e h t . a 0 1 s i e d o m p e e l s e h t f o l a n i m r e t r e h t o e h t . n i p d n g d n a r o t i c a p a c g n i m i t e h t n e e w t e b s e i r e s n i r o t s i s e r . n i p c n y s / s f e h t o t d e t c e n n o c n i a m e r l l i w r o t i c a p a c g n i m i t 6e s n e s v e g a t l o v t u p t u o e h t s a s e v r e s d n a r e i f i l p m a e g a t l o v e h t f o t u p n i g n i t r e v n i e h t s i n i p s i h t e u l a v e c n e r e f e r l a n r e t n i n a o t d e r a p m o c s i e s n e s v . r e t r e v n o c k c u b e h t r o f t n i o p k c a b d e e f . d e r i s e d s i v 5 . 0 f o t u p t u o n a n e h w e g a t l o v t u p t u o e h t o t d e r i w d r a h s i e s n e s v . v 5 . 0 f o l a c i p y t e h t n i 9 r d n a 7 r ( y r a s s e c e n s i k r o w t e n r e d i v i d r o t s i s e r a , s e g a t l o v t u p t u o r e h g i h r o f . ) m a r g a i d t i u c r i c n o i t a c i l p p a 7d n g l l a . n i p s i h t o t t c e p s e r h t i w d e r u s a e m e r a s e g a t l o v l l a . c i e h t r o f d n u o r g r e w o p d n a l a n g i s s a t c e r i d d n a t r o h s s a s d a e l e v a h d l u o h s d n g o t d e t c e n n o c s r o t i c a p a c g n i m i t d n a s s a p y b . e l b i s s o p
5 ? 2005 semtech corp. www.semtech.com SC4607 power management # n i pe m a n n i pn o i t c n u f n i p 8l v r d e h t . 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 e h t f o e t a g e h t s e v i r d l v r d . n i p e v i r d e t a g e v i r d y r a t n e m e l p m o c s e d i v o r p y r t i u c r i c m w p e h t . t n e r r u c k a e p a 1 r o f d e t a r s i r e v i r d t u p t u o d e t n e v e r p s i s t e f s o m l a n r e t x e e h t f o n o i t c u d n o c s s o r c e h t . s e g a t s t u p t u o e h t o t s l a n g i s n i r i a p t e f s o m e h t f o s n i p r e v i r d l v r d d n a h v r d e h t n o e g a t l o v e h t g n i r o t i n o m y b s c i t s i r e t c a r a h c f f o - n r u t t e f r o f d e z i m i t p o y a l e d e m i t a h t i w n o i t c n u j n o c 9e s a h p e h t s e s u 7 0 6 4 c s e h t . t e f s o m e d i s h g i h e h t n i t n e r r u c t i m i l o t d e s u s i n i p e s a h p e h t t i m i l t n e r r u c e h t . t i m i l t n e r r u c e h t t e s o t r e d r o n i s n i p t e s i d n a n i v e h t s s o r c a e g a t l o v t i u c r i c n o i t a c i l p p a l a c i p y t e h t n i 3 r ( r o t s i s e r l a n r e t x e n a f o e u l a v e h t y b t e s s i d l o h s e r h t e s n e s e h t s s o r c a p o r d e g a t l o v e h t g n i r a p m o c y b d e m r o f r e p s i g n i t i m i l t n e r r u c . ) m a r g a i d e d i s h g i h e h t f o e c n a t s i s e r e c r u o s o t n i a r d e h t s s o r c a p o r d e g a t l o v e h t h t i w r o t s i s e r o t n i a r d e h t s s o r c a p o r d e g a t l o v e h t . d o i r e p n o i t c u d n o c s ? t e f s o m e h t g n i r u d t e f s o m . s n i p e s a h p d n a n i v e h t m o r f d e n i a t b o s i t e f s o m e d i s h g i h e h t f o e c n a t s i s e r e c r u o s 0 1h v r d t u p t u o e h t . t e f s o m ) h c t i w s n i a m ( e d i s h g i h e h t f o e t a g e h t s e v i r d h v r d . n i p e v i r d e t a g e v i r d y r a t n e m e l p m o c s e d i v o r p y r t i u c r i c m w p e h t . t n e r r u c k a e p a 1 r o f d e t a r s i r e v i r d d e t n e v e r p s i s t e f s o m l a n r e t x e e h t f o n o i t c u d n o c s s o r c e h t . s e g a t s t u p t u o e h t o t s l a n g i s n i r i a p t e f s o m e h t f o s n i p r e v i r d l v r d d n a h v r d e h t n o e g a t l o v e h t g n i r o t i n o m y b s c i t s i r e t c a r a h c f f o - n r u t t e f r o f d e z i m i t p o y a l e d e m i t a h t i w n o i t c n u j n o c pin descriptions (cont.)
6 ? 2005 semtech corp. www.semtech.com SC4607 power management block diagram marking information nnnn = part number (example: 1456) yyww = datecode (example: 0012) xxxx = semtech lot # (example: e901 xxxx 01-1) 4607 4607
7 ? 2005 semtech corp. www.semtech.com SC4607 power management typical characteristics oscillator internal accuracy vs input voltage 574 576 578 580 582 584 586 588 2.5 3 3.5 4 4.5 5 5.5 vcc (v) internal accuracy (khz) ta = 25c oscillator internal accuracy vs temperature 577 578 579 580 581 582 583 584 -40-200 20406080 temperature (c) internal accuracy (khz) vcc = 3.3v se nse voltage vs input voltage 499.4 499.5 499.6 499.7 499.8 499.9 500.0 2.5 3 3.5 4 4.5 5 5.5 vcc (v) sense voltage (mv) t a = 25c se nse voltage vs te mpe rature 498.0 498.5 499.0 499.5 500.0 500.5 -40-20 0 20406080 temperature (c) sense voltage (mv) vcc = 3.3v current limit bias current vs input voltage 50 51 52 53 54 55 2.5 3 3.5 4 4.5 5 5.5 vcc (v) current limit bias current (ua) t a = 25c current limit bias current vs te mpe rature 40 45 50 55 60 65 -40-200 20406080 temperature (c) current limit bias current (ua) vcc = 3.3v
8 ? 2005 semtech corp. www.semtech.com SC4607 power management application information enable: the SC4607 is enabled by applying a voltage greater than 2.25 volts to the vcc pin. the SC4607 is disabled when vcc falls below 1.95 volts or when sleep mode opera- tion is invoked by clamping the fs/sync pin to a voltage below 75mv. 10 a is the typical current drawn through the vcc pin during sleep mode. during the sleep mode, the high side and low side mosfets are turned off and the internal soft start voltage is held low. oscillator: the fs/sync pin is used to set the pwm oscillator fre- quency through an external timing capacitor that is con- nected from the fs/sync pin to the gnd pin. the re- sulting ramp waveform on the fs/sync pin is a triangle at the pwm frequency with a peak voltage of 1.3v and a valley voltage of 0.3v. the pwm duty ratio is limited by the ramp to a maximum of 97%, which allows the boot- strap capacitor to be charged during each cycle. the ca- pacitor tolerance adds to the accuracy of the oscillator frequency. the approximate operating frequency and soft start time are both determined by the value of the exter- nal timing capacitor as shown in table 1. g n i m i t l a n r e t x e e u l a v r o t i c a p a c ) f p ( y c n e u q e r f ) z h k ( ) s ( e m i t t r a t s t f o s 0 2 10 0 0 18 2 6 0 7 20 8 50 2 2 1 0 6 50 5 38 3 8 1 table 1: operating frequency and soft start time values based on the value of the external timing capacitor placed across the fs/sync and gnd pins synchronous mode operation is invoked by using a sig- nal from an external clock. a low value resistor (100 ? typical) must be inserted in series with the timing capaci- tor between the timing capacitor and the gnd pin. the other terminal of the timing capacitor will remain con- nected to the fs/sync pin. the external clock signal is then connected to the junction of the external timing capacitor and the added resistor as shown in figure 1. rsync 100 ohm ctiming external clock signal SC4607 fs/sync figure 1 uvlo: when the fs/sync pin is not pulled and held below 75mv, the voltage on the vcc pin determines the operation of the SC4607. as vcc increases during start up, the uvlo block senses vcc and keeps the high side and low side mosfets off and the internal soft start voltage low until vcc reaches 2.25v. if no faults are present, the SC4607 will initiate a soft start when vcc exceeds 2.25v. a hys- teresis (100mv) in the uvlo comparator provides noise immunity during its start up. soft start: the soft start function is required for step down control- lers to prevent excess inrush current through the dc bus during start up. generally this can be done by sourcing a controlled current into a timing capacitor and then using the voltage across this capacitor to slowly ramp up the error amp reference. the closed loop creates narrow width driver pulses while the output voltage is low and allows these pulses to increase to their steady state duty cycle as the output voltage reaches its regulated value. with this, the inrush current from the input side is con- trolled. the duration of the soft start in the SC4607 is controlled by an internal timing circuit which is used dur- ing start up and over current to set the hiccup time. the soft start time can be obtained from table 1. the SC4607 implements its soft start by ramping up the error amplifier reference voltage providing a controlled
9 ? 2005 semtech corp. www.semtech.com SC4607 power management application information (cont.) slew rate of the output voltage, then preventing over- shoot and limiting inrush current during its start up. dur- ing start up of a converter with a big capacitive load, the load current demands large supply current. to avoid this an external soft start scheme can be implemented as shown in figure 2. cs can be adjusted for different appli- cations. output of a converter q mmbt2222a-7 rp 47.5k rs 2.05k cs 330n pin comp vo figure 2 over current protection: the SC4607 detects over current conditions by sensing the voltage across the drain-to-source of the high side mosfet. the SC4607 determines the high side mosfet current level by sensing the drain-to-source conduction voltage across the high side mosfet via the v in (see the typical application circuit on page 1) and phase pin dur- ing the high side mosfet?s conduction period. this volt- age value is then compared internally to a user pro- grammed current limit threshold. note that user should place kelvin sensing connections directly from the high side mosfet source to the phase pin. the current limit threshold is programmed by the user based on the rds(on) of the high side mosfet and the value of the external set resistor rset (where rset is represented by r3 in the applications schematics of this document). the SC4607 uses an internal current source to pull a 50a current from the input voltage to the iset pin through external resistor rset. the current limit threshold resistor (rset) value is calcu- lated using the following equation: a 50 r i r ) on ( ds max set ? = the r ds(on) sensing used in the SC4607 has an addi- tional feature that enhances the performance of the over current protection. because the r ds(on) has a positive temperature coefficient, the 50 a current source has a positive coefficient of about 0.28%/c providing first or- der correction for current sensing vs temperature. this compensation depends on the high amount of thermal transferring that typically exists between the high side n- mosfet and the SC4607 due to the compact layout of the power supply. when the converter detects an over current condition (i > i max ) as shown in figure 3, the first action the SC4607 takes is to enter the cycle by cycle protection mode (point b to point c), which responds to minor over current cases. then the output voltage is monitored. if the over current and low output voltage (set at 70% of nominal output voltage) occur at the same time, the hiccup mode op- eration (point c to point d) of the SC4607 is invoked and the internal soft start capacitor is discharged. this is like a typical soft start cycle: nom o v ? ? 6 . 0 nom o v ? o v o i i max d c b a nom o v ? ? 6 . 0 nom o v ? o v o i i max d c b a figure 3. over current protection characteristic of SC4607 power mosfet drivers: the SC4607 has two drivers which are optimized for driv- ing external power n-channel mosfets.. the driver block consists two 1 amp drivers. drvh drives the high side n-mosfet (main switch), and drvl drives the low side n-mosfet (synchronous rectifier transistor). the output drivers also have gate drive non-overlap mechanism that provides a dead time between drvh and drvl transitions to avoid potential shoot through problems in the external mosfets. by using the proper design and the appropriate mosfets, the SC4607 is capable of driving a converter with up to 12a of output 0.7
10 ? 2005 semtech corp. www.semtech.com SC4607 power management current. as shown in figure 4, t d1, the delay from the top mosfet off to the bottom mosfet on is adaptive by detecting the voltage of the phase node. t d2 , the delay from the bottom mosfet off to the top mosfet on is fixed, is 40ns for the SC4607. this control scheme guar- antees avoidance of cross conduction or shoot through between the upper and lower mosfets and also mini- mizes the conduction loss in the body diode of the bot- tom mosfet for high efficiency applications. bottom mosfet gate drive top mosfet gate drive phase node ground t d1 t d2 bottom mosfet gate drive top mosfet gate drive phase node ground t d1 t d2 figure 4. timing waveforms for gate drives and phase node inductor selection: the factors for selecting the inductor include its cost, efficiency, size and emi. for a typical SC4607 applica- tion, the inductor selection is mainly based on its value, saturation current and dc resistance. increasing the in- ductor value will decrease the ripple level of the output voltage while the output transient response will be de- graded. low value inductors offer small size and fast tran- sient responses while they cause large ripple currents, poor efficiencies and more output capacitance to smooth out the large ripple currents. the inductor should be able to handle the peak current without saturating and its copper resistance in the winding should be as low as possible to minimize its resistive power loss. a good trade- off among its size, loss and cost is to set the inductor ripple current to be within 15% to 30% of the maximum output current. the inductor value can be determined according to its operating point and the switching frequency as follows: omax s in out in out i i f v ) v v ( v l ? ? ? ? ? ? = where: f s = switching frequency and ? i = ratio of the peak to peak inductor current to the maximum output load current. the peak to peak inductor current is: omax p p i i i ? ? = ? after the required inductor value is selected, the proper selection of the core material is based on the peak in- ductor current and efficiency requirements. the core must be able to handle the peak inductor current i peak without saturation and produce low core loss during the high frequency operation is: 2 i i i p p omax peak ? + = the power loss for the inductor includes its core loss and copper loss. if possible, the winding resistance should be minimized to reduce inductor?s copper loss. the core loss can be found in the manufacturer?s datasheet. the inductor? copper loss can be estimated as follows: winding lrms 2 copper r i p ? = where: i lrms is the rms current in the inductor. this current can be calculated as follow is: 2 omax lrms i 3 1 1 i i ? ? + ? = output capacitor selection: basically there are two major factors to consider in se- lecting the type and quantity of the output capacitors. the first one is the required esr (equivalent series re- sistance) which should be low enough to reduce the volt- age deviation from its nominal one during its load changes. the second one is the required capacitance, which should be high enough to hold up the output voltage. before the SC4607 regulates the inductor current to a new value during a load transient, the output capacitor delivers all the additional current needed by the load. the esr and esl of the output capacitor, the loop parasitic inductance between the output capacitor and the load combined with inductor ripple current are all major contributors to the output voltage ripple. surface mount speciality poly- mer aluminum electrolytic chip capacitors in ue series from panasonic provide low esr and reduce the total capacitance required for a fast transient response. poscap from sanyo is a solid electrolytic chip capacitor that has a low esr and good performance for high fre- quency with a low profile and high capacitance. above mentioned capacitors are recommended to use in application information (cont.)
11 ? 2005 semtech corp. www.semtech.com SC4607 power management application information (cont.) SC4607 application: input capacitor selection: the input capacitor selection is based on its ripple cur- rent level, required capacitance and voltage rating. this capacitor must be able to provide the ripple current by the switching actions. for the continuous conduction mode, the rms value of the input capacitor can be cal- culated from: 2 in out in out omax ) rms ( cin v ) v v ( v i i ? ? ? = this current gives the capacitor?s power loss as follows: ) esr ( cin ) rms ( cin 2 cin r i p ? = this capacitor?s rms loss can be a significant part of the total loss in the converter and reduce the overall con- verter efficiency. the input ripple voltage mainly depends on the input capacitor?s esr and its capacitance for a given load, input voltage and output voltage. assuming that the input current of the converter is constant, the required input capacitance for a given voltage ripple can be calculated by: ) r i v ( fs ) d 1 ( d i c ) esr ( cin omax i omax in ? ? ? ? ? ? ? = where: d = v out /v in , duty ratio and ? v i = the given input voltage ripple. because the input capacitor is exposed to the large surge current, attention is needed for the input capacitor. if tantalum capacitors are used at the input side of the converter, one needs to ensure that the rms and surge ratings are not exceeded. for generic tantalum capaci- tors, it is wise to derate their voltage ratings at a ratio of 2 to protect these input capacitors. boost capacitor selection: the boost capacitor selection is based on its discharge ripple voltage, worst case conduction time and boost current. the worst case conduction time t w can be esti- mated as follows: max s d f 1 tw ? = where: f s = the switching frequency and dmax = maximum duty ratio, 0.97 for the SC4607. the required minimum capacitance for boost capacitor will be: w d b boost t v i c ? = where: i b = the boost current and v d = discharge ripple voltage. with f s = 300kh, v d =0.3v and i b =50ma, the required capacitance for the boost capacitor is: nf 540 97 . 0 k 300 1 3 . 0 05 . 0 d f 1 v i c max s d b boost = ? ? = ? ? = power mosfet selection: the SC4607 can drive an n-mosfet at the high side and an n-mosfet synchronous rectifier at the low side. the use of the high side n-mosfet will significantly re- duce its conduction loss for high current. for the top mosfet, its total power loss includes its conduction loss, switching loss, gate charge loss, output capacitance loss and the loss related to the reverse recovery of the bot- tom diode, shown as follows: s in rr oss s gate gt 2 gs gd g gate s in peak _ top on _ top rms _ top 2 total _ top f v ) q q ( f v q ) q q ( r v f v i r i p ? ? + + ? ? + + ? ? ? + ? = where: r g = gate drive resistor, q gd = the gate to drain charge of the top mosfet, q gs2 = the gate to source charge of the top mosfet, q gt = the total gate charge of the top mosfet, q oss = the output charge of the top mosfet and q rr = the reverse recovery charge of the bottom diode. for the top mosfet, it experiences high current and high voltage overlap during each on/off transition. but for the
12 ? 2005 semtech corp. www.semtech.com SC4607 power management voltage according to ) r r 1 ( 5 . 0 v 9 7 out + ? = figure 4. compensation network provides 3 poles and 2 zeros. c2 r1 c1 c4 r vout l1 c9 r8 r7 r9 vcc iset comp fs/sync bst drvh drvl vsense gnd phase SC4607 figure 4. compensation network provides 3 poles and 2 zeros. c2 r1 c1 c4 r vout l1 c9 r8 r7 r9 vcc iset comp fs/sync bst drvh drvl vsense gnd phase SC4607 figure 5. compensation network provides 3 poles and 2 zeros. for voltage mode step down applications as shown in figure 5, the power stage transfer function is: 4 1 2 1 4 c i vd c l s r l s 1 c r 1 s 1 v ) s ( g + + ? + = where: r = load resistance and r c = c 4 ?s esr. the compensation network will have the characteristic as follows: 2 p 2 z 1 p 1 z i comp s 1 s 1 s 1 s 1 s ) s ( g + ? + ? + + ? = where ) c c ( r 1 2 1 7 i + ? = 2 1 1 z c r 1 ? = 9 8 7 2 z c ) r r ( 1 ? + = application information (cont.) bottom mosfet, its switching voltage is the body diode?s forward drop of the bottom mosfet during its on/off transition. so the switching loss for the bottom mosfet is negligible. its total power loss can be determined by: f avg d s gate gb on _ bot rms _ bot 2 total _ bot v _ i f v q r i p ? + ? ? + ? = where: q gb = the total gate charge of the bottom mosfet and v f = the forward voltage drop of the body diode of the bottom mosfet. for a low voltage and high output current application such as the 3.3v/1.5v@12a case, the conduction loss is of- ten dominant and selecting low r ds(on) mosfets will no- ticeably improve the efficiency of the converter even though they give higher switching losses. the gate charge loss portion of the top/bottom mosfet?s total power loss is derived from the SC4607. this gate charge loss is based on certain operating conditions (f s , v gate , and i o ). the thermal estimations have to be done for both mosfets to make sure that their junction temperatures do not exceed their thermal ratings according to their total power losses p total , ambient temperature t a and their thermal resistance r ja as follows: ja total a (max) j r p t t + < loop compensation design: for a dc/dc converter, it is usually required that the converter has a loop gain of a high cross-over frequency for fast load response, high dc and low frequency gain for low steady state error, and enough phase margin for its operating stability. often one can not have all these properties at the same time. the purpose of the loop compensation is to arrange the poles and zeros of the compensation network to meet the requirements for a specific application. the SC4607 has an internal error amplifier and requires the compensation network to connect among the comp pin and vsense pin, gnd, and the output as shown in figure 5. the compensation network includes c1, c2, r1, r7, r8 and c9. r9 is used to program the output
13 ? 2005 semtech corp. www.semtech.com SC4607 power management 2 1 1 2 1 1 p c c r c c ? ? + = 9 8 2 p c r 1 ? = after the compensation, the converter will have the fol- lowing loop gain: c l s r l s 1 c r 1 s 1 s 1 s 1 s 1 s 1 s v v 1 ) s ( g ) s ( g g ) s ( t 1 2 1 4 c 2 p 2 z 1 p 1 z i i m vd comp pwm + + ? + ? + ? + ? + + ? ? ? = ? ? = where: g pwm = pwm gain v m = 1.0v, ramp peak to valley voltage of SC4607 the design guidelines for the SC4607 applications are as following: 1. set the loop gain crossover corner frequency c for given switching corner frequency s = 2 f s, 2. place an integrator at the origin to increase dc and low frequency gains. 3. select z1 and z2 such that they are placed near o to damp the peaking and the loop gain has a -20db/dec rate to go across the 0db line for obtaining a wide bandwidth. 4. cancel the zero from c 4 ?s esr by a compensator pole p1 ( p1 = esr = 1/( r c c 4 )). 5. place a high frequency compensator pole p 2 ( p 2 = f s ) to get the maximum attenuation of the switch- ing ripple and high frequency noise with the adequate phase lag at c . the compensated loop gain will be as given in figure 6: -20db/dec 0db gvd t(s) z1 z2 o c p1 esr p2 loop gain t(s) power stage g vd (s) -40db/dec -20db/dec 0db gvd t(s) z1 z2 o c p1 esr p2 loop gain t(s) power stage g vd (s) -40db/dec figure 6. asymptotic diagrams of power stage and its loop gain. application information (cont.) layout guidelines: in order to achieve optimal electrical, thermal and noise performance for high frequency converters, special at- tention must be paid to the pcb layouts. the goal of lay- out optimization is to identify the high di/dt loops and minimize them. the following guideline should be used to ensure proper functions of the converters. 1. a ground plane is recommended to minimize noises and copper losses, and maximize heat dissipation. 2. start the pcb layout by placing the power compo- nents first. arrange the power circuit to achieve a clean power flow route. put all the connections on one side of the pcb with wide copper filled areas if possible. 3. the vcc bypass capacitor should be placed next to the vcc and gnd pins. 4. the trace connecting the feedback resistors to the output should be short, direct and far away from the noise sources such as switching node and switching components. 5. minimize the traces between drvh/drvl and the gates of the mosfets to reduce their impedance to drive the mosfets. 6. minimize the loop including input capacitors, top/bot- tom mosfets. this loop passes high di/dt current. make sure the trace width is wide enough to reduce copper losses in this loop. 7. iset and phase connections to the top mosfet for current sensing must use kelvin connections. 8. maximize the trace width of the loop connecting the inductor, bottom mosfet and the output capacitors. 9. connect the ground of the feedback divider and the compensation components directly to the gnd pin of the SC4607 by using a separate ground trace. then connect this pin to the ground of the output capacitor as close as possible
14 ? 2005 semtech corp. www.semtech.com SC4607 power management design example 2: 3.3v to 2.5v @ 20a application with SC4607 application information (cont.) design example 1: 3.3v to1.5v @12a application with SC4607 r3 1.05k c3 4.7u c2 1.5n r1 20k c1 270p c18 0.1u vin=3.3v c7 330u d2 l1 1.3u c5 22u c4 22u c17 1u m11 m12 m22 c10 150u m21 c9 2.7n r8 365 vo=2.5v/20a r7 16.5k r9 4.12k r6 0 r5 0 c16 560pf etqpaf1r3ea 4tpd330m 4 x c3216x5r0j226m 2 x 4tpe150m 4 x si7882 vcc 2 iset 3 comp 4 fs/sync 5 bst 1 drvh 10 drvl 8 vsense 6 gnd 7 phase 9 u1 SC4607 c13 22u c14 22u c11 150u r13 1 r3 c3 4.7u c2 2.2n c7 330u r1 14.3k c1 270p c14 100u vin=3.3v d2 l1 2.3u c5 22u c4 22u c71 1u m1 r6 0 r5 0 c13 100u m2 c11 22u c9 5.6n r8 169 vo=1.5v/12a r7 8.25k r9 4.12k c16 560pf c10 22u vcc 2 iset 3 comp 4 fs/sync 5 bst 1 drvh 10 drvl 8 vsense 6 gnd 7 phase 9 u1 SC4607 r13 1
15 ? 2005 semtech corp. www.semtech.com SC4607 power management m e t iy t qe c n e r e f e re u l a vr e r u t c a f u n a m / . o n t r a p 111 cf p 0 7 2 212 cf n 2 . 2 317 1 cf u 1 44 1 1 c , 0 1 c , 5 c , 4 c0 1 2 1 , f u 2 2m 6 2 2 j 0 r 5 x 5 2 2 3 c : n / p k d t 517 c0 7 8 2 , f u 0 3 3m 0 3 3 d p t 6 : n / p o y n a s 619 cf n 6 . 5 718 1 cf n 1 . 0 816 1 cf p 0 6 5 912 d1 t l 0 2 5 0 r b m1 t l 0 2 5 0 r b m : n / p i m e s n o 0 111 lh u 3 . 2 c i n o r t c e l e r e p o o c 3 r 2 - 1 c h : n / p 1 12 2 m , 1 m8 - o s , k c a p r e w o pp d 2 8 8 7 i s : n / p y a h s i v 2 111 rk 3 . 4 1 3 113 rk 4 . 1 4 12 6 r , 5 r0 5 117 rk 5 2 . 8 6 118 r9 6 1 7 119 rk 2 1 . 4 8 113 1 r1 9 113 c5 0 8 0 , f u 7 . 4 0 22 4 1 c , 3 1 c0 7 8 2 , f u 0 0 1m 0 0 1 b p t 6 : n / p o y n a s 1 211 u7 0 6 4 c sr t s m i 7 0 6 4 c s : n / p h c e t m e s . e g a k c a p 3 0 6 0 d m s n i e r a s r o t i c a p a c d n a s r o t s i s e r l l a , d e i f i c e p s s s e l n u % 0 2 - / + e r a s r o t i c a p a c l l a d n a % 1 - / + e r a s r o t s i s e r bill of materials - 3.3v to 1.5v @ 12a
16 ? 2005 semtech corp. www.semtech.com SC4607 power management pcb layout - 3.3v to 1.5v @ 12a top top bottom bottom bottom bottom top top
17 ? 2005 semtech corp. www.semtech.com SC4607 power management semtech corporation power management products division 200 flynn road, camarillo, ca 93012 phone: (805)498-2111 fax (805)498-3804 outline drawing - msop-10 contact information land pattern - msop-10 bbb c a-b d dimensions "e1" and "d" do not include mold flash, protrusions 3. or gate burrs. datums and to be determined at datum plane controlling dimensions are in millimeters (angles in degrees). -b- notes: 1. 2. -a- -h- side view a b c d h plane 0 .010 .004 - .016 .003 .024 (.037) - .000 .030 - - - - 0.25 0.10 8 0 - 8 0.60 (.95) .032 .009 0.40 0.08 .043 .006 .037 0.75 0.00 - 0.80 0.23 - 0.95 1.10 0.15 - - - e .193 bsc .020 bsc detail aaa c seating indicator ccc c 2x n/2 tips pin 1 2x e/2 10 see detail a1 a a2 bxn d 0.25 a plane gage .003 e1 12 n .114 .114 .118 .118 .007 - 10 01 c (l1) l a 0.08 3.00 3.00 4.90 bsc 0.50 bsc .122 .122 2.90 2.90 .011 0.17 3.10 3.10 0.27 - reference jedec std mo-187 , variation ba. 4. dim ccc a1 e bbb aaa 01 l1 n l d e1 e a2 b c a millimeters nom inches dimensions min nom max min max e this land pattern is for reference purposes only. consult your manufacturing group to ensure your company's manufacturing guidelines are met. notes: 1. p (c) x z g y .063 .224 .011 .020 .098 (.161) 5.70 1.60 0.30 0.50 2.50 (4.10) millimeters dimensions dim inches y z g p x c

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