1 www.semtech.com sc4205 very low dropout 1 amp regulator with enable power management notes: (1) maximum vo setpoint for 1.8v parts = 5.4v. (2) this device is designed to operate with ceramic input and output capacitors. revision: june 28, 2004 the sc4205 is a high performance positive voltage regulator designed for use in applications requiring very low dropout voltage at up to 1 amp. since it has superior dropout characteristics compared to regular ldos, it can be used to supply 2.5v on motherboards or 2.8v on peripheral cards from the 3.3v supply thus allowing the elimination of costly heatsinks. additionally, the sc4205 has an enable pin to further reduce power dissipation while shut down. the sc4205 provides ex- cellent regulation over variations in line, load and tem- perature. the sc4205 is available in the soic-8edp package with internally preset outputs that are also adjustable using external resistors. ? 350mv dropout @ 1a ? adjustable output from 1.2v to 4.8v ? 2.5v and 1.8v options (adjustable externally using resistors) ? over current and over temperature protection ? enable pin ? 10a quiescent current in shutdown ? low reverse leakage (output to input) ? surface mount and through-hole packages ? full industrial temperature range ? available in soic-8edp package ? battery powered systems ? motherboards ? peripheral cards ? network cards ? set top boxes ? medical equipment ? notebook computers description features applications vin c1 c2 u1 sc4205 4 3 2 8 1 5 6 7 nc vin en gnd nc nc vo adj vo enable vin c1 c2 u1 sc4205 4 3 2 8 1 5 6 7 nc vin en gnd nc nc vo adj vo enable volts r2 r2) (r1 1.2 vo + = typical application circuits enable c1 r1 r2 vo u1 sc4205 4 3 2 8 1 5 6 7 nc vin en gnd nc nc vo adj c2 vin
2 ? 2004 semtech corp. www.semtech.com sc4205 power management r e t e m a r a p l o b m y sx a ms t i n u e g a t l o v t u p n i v n i 7v n o i t a p i s s i d r e w o p p d d e t i m i l y l l a n r e t n iw p d e 8 - c i o s t n e i b m a o t n o i t c n u j e c n a t s i s e r l a m r e h t ) 1 ( a j 6 3w / c p d e 8 - c i o s e s a c o t n o i t c n u j e c n a t s i s e r l a m r e h t ) 1 ( c j 5 . 5w / c 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 o t a 5 8 + o t 0 4 -c e g n a r e r u t a r e p m e t n o i t c n u j g n i t a r e p o t j 0 5 1 + 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 s t g t s 0 5 1 + o t 5 6 -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 l t d a e l 0 0 3c ) l e d o m y d o b n a m u h ( g n i t a r d s e v d s e 4v k note: (1) 1 square inch of fr-4, double sided, 1 oz. minimum copper weight. r e t e m a r a pl o b m y ss n o i t i d n o c t s e tn i mp y tx a ms t i n u n i v e g n a r e g a t l o v g n i t a r e p ov n i 2 . 25 . 5 v t n e r r u c t n e c s e i u qi q v n i v 3 . 3 =5 7 . 0 5 7 . 1 a m v n i v , v 5 . 5 = n e v 0 =0 1 5 3 a o v e g a t l o v t u p t u o ) 1 ( v o i o a m 0 1 = % 1 -v o % 1 +v ) e g a t l o v d e x i f l a n r e t n i ( % 2 -% 2 + n o i t a l u g e r e n i l ) 1 ( g e r ) e n i l ( i t u o a m 0 1 =5 3 0 . 0 3 . 0 % n o i t a l u g e r d a o l ) 1 ( g e r ) d a o l ( i t u o a 1 o t a m 0 1 =2 . 0 4 . 0 % e g a t l o v t u o p o r d ) 2 ( ) 1 ( v d i o a m 0 1 =5 . 20 1 v m 0 2 i o a m 0 0 5 =0 90 0 3 v m 0 0 4 i o a 1 =0 8 10 0 4 v m 0 0 5 absolute maximum ratings electrical characteristics unless specified: v en = v in . adjustable option (v adj > v th(adj) ): v in = 2.2v to 5.5v and i o = 10a to 1a. fixed options (v adj = gnd): v in = (v o + 0.5v) to 5.5v and i o = 0a to 1a. values in bold apply over t j = -40c to 125c 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 sc4205 power management notes: (1) low duty cycle pulse testing with kelvin connections required. (2) defined as the input to output differential at which the output voltage drops to 1% below the value measured at a differential of 0.7v. (3) required to maintain regulation. voltage set resistors r1 and r2 are usually utilized to meet this requirement. adjustable versions only. (4) guaranteed by design. (5) when v adj exceeds this threshold, the ?sense select? switch disconnects the internal feedback chain from the error amplifier and connects v adj instead. r e t e m a r a pl o b m y ss n o i t i d n o c t s e tn i mp y tx a ms t i n u ) . t n o c ( o v t n e r r u c d a o l m u m i n i m ) 3 ( i o 1 0 1 a t i m i l t n e r r u ci l c 6 . 1 3 3 . 1 5 . 3 a j d a e g a t l o v e c n e r e f e r ) 1 ( v f e r v n i v , v 2 . 2 = j d a v = t u o i , o a m 0 1 =8 8 1 . 10 0 2 . 12 1 2 . 1v 6 7 1 . 14 2 2 . 1 t n e r r u c n i p t s u j d a ) 4 ( i j d a v j d a v = f e r 0 3 0 0 2 a n d l o h s e r h t n i p t s u j d a ) 5 ( v ) j d a ( h t 5 0 . 0 0 2 . 0 0 4 . 0 v n e t n e r r u c n i p e l b a n ei n e v n e v , v 0 = n i v 3 . 3 =5 . 1 0 1 a d l o h s e r h t n i p e l b a n ev h i v n i v 3 . 3 = 6 . 1 v v l i v n i v 3 . 3 = 4 . 0 n o i t c e t o r p e r u t a r e p m e t r e v o l e v e l p i r t h g i ht i h 0 7 1c s i s e r e t s y ht t s y h 0 2c electrical characteristics (cont.) unless specified: v en = v in . adjustable option (v adj > v th(adj) ): v in = 2.2v to 5.5v and i o = 10a to 1a. fixed options (v adj = gnd): v in = (v o + 0.5v) to 5.5v and i o = 0a to 1a. values in bold apply over t j = -40c to 125c
4 ? 2004 semtech corp. www.semtech.com sc4205 power management r e b m u n t r a pe g a k c a pt ( e g n a r . p m e t a ) r t x . x - s i 5 0 2 4 c s ) 2 ( ) 1 ( p d e 8 - c i o s5 8 + o t 0 4 - o c t r t x . x - s i 5 0 2 4 c s ) 3 ( ) 2 ( ) 1 ( b v e 5 0 2 4 c sd r a o b n o i t a u l a v e pin descriptions pin configuration ordering information notes: (1) where -x.x denotes voltage options. available voltages are: 2.5v and 1.8v. output voltage can be adjusted using external resistors, see pin descriptions on page 5. (2) only available in tape and reel packaging. a reel contains 2500 devices. (3) lead free product top view soic-8edp vin nc nc nc en vo adj gnd 1 2 3 4 en nc 5 6 7 8 nc adj vo vin nc gnd gnd exposed die pad bottom view soic-8edp e m a n n i pn o i t p i c s e d n i p j d a l a n r e t x e f i . s r o t s i s e r k c a b d e e f l a n r e t n i e h t y b t e s t a h t o t e g a t l o v t u p t u o e h t s t e s , d e d n u o r g n e h w , n i p s i h t : ) 1 e g a p n o s t i u c r i c n o i t a c i l p p a e e s ( e b l l i w e g a t l o v t u p t u o e h t , d e s u e r a s r o t s i s e r k c a b d e e f n e f o n o i t c a r f a o t t n e r r u c t n e c s e i u q e h t g n i c u d e r , f f o r o t a l u g e r e h t s n r u t v 4 . 0 w o l e b n i p s i h t g n i l l u p . t u p n i e l b a n e . d e s u g n i e b t o n f i n i v o t t c e n n o c . n e p o t f e l s i n i p s i h t f i d e l b a n e e b l l i w e c i v e d e h t . e u l a v g n i t a r e p o s t i d n g . n i p c i e h t t a r e h t e g o t d e t c e n n o c e b t s u m d a p e i d d e s o p x e e h t d n a n i p d n g e h t : e t o n . d n u o r g e c n e r e f e r . g n i k n i s t a e h r o f e c i v e d e h t n o d a p e i d d e s o p x e e h t e s u n i v m u m i n i m . v 5 . 5 d n a ) v 5 . 0 + o v ( n e e w t e b e b t s u m n i p s i h t o t t u p n i e h t , d a o l l l u f t a n o i t a l u g e r r o f . e g a t l o v t u p n i . v 2 . 2 = n i v o v. e c i v e d e h t f o t u p t u o r e w o p e h t s i n i p e h t volts r2 r2) (r1 1.200 vo + =
5 ? 2004 semtech corp. www.semtech.com sc4205 power management block diagram
6 ? 2004 semtech corp. www.semtech.com sc4205 power management introduction the sc4205 is intended for applications such as graphics cards where high current capability and very low dropout voltage are required. it provides a very simple, low cost solution that uses very little pcb real estate. additional features include an enable pin to allow for a very low power consumption standby mode, and a fully adjustable output. component selection input capacitor: a 4.7f ceramic capacitor is recommended. this allows for the device being some distance from any bulk capacitance on the rail. additionally, input droop due to load transients is reduced, improving load transient response. additional capacitance may be added if required by the application. output capacitor: a minimum bulk capacitance of 2.2f, along with a 0.1f ceramic decoupling capacitor is recommended. increasing the bulk capacitance will improve the overall transient response. the use of multiple lower value ceramic capacitors in parallel to achieve the desired bulk capacitance will not cause stability issues. although designed for use with ceramic output capacitors, the sc4205 is extremely tolerant of output capacitor esr values and thus will also work comfortably with tantalum output capacitors. for refer- ence, the phase-margin contour of figure 1 can be used to choose an appropriate output capacitor for a given stability requirement. noise immunity: in very electrically noisy environments, it is recommended that 0.1f ceramic capacitors be placed from in to gnd and out to gnd as close to the device pins as possible. external voltage selection resistors: the use of 1% resistors, and designing for a current flow 10a is recommended to ensure a well regulated output (thus r2 120k ? ). applications information thermal considerations the power dissipation in the sc4205 is approximately equal to the product of the output current and the input to output voltage differential: () o d i vout vin p ? ? the absolute worst-case dissipation is given by: () ) ( ) ( ) ( ) ( ) ( ) ( max q max max o min max max d i vin i vout vin p ? + ? ? = for a typical scenario, v in = 3.3v 5%, v out = 2.8v and i o = 1a, therefore: v in(max) = 3.465v, v out(min) = 2.744v and i q(max) = 1.75ma, thus p d(max) = 727mw. using this figure, and assuming t a(max) = 70c, we can calculate the maximum thermal impedance allowable to maintain t j 150c: () () w c p t t r max d max a max j max a j th / 110 727 . 70 150 ) ( ) ( ) ( ) )( ( = ? = ? = ? this should be achievable for the soic-8edp package using pcb copper area to aid in conducting the heat away, such as one square inch of copper connected to the pins of the device. internal ground/power planes and air flow will also assist in removing heat. for higher ambient tem- peratures it may be necessary to use additional copper area.
7 ? 2004 semtech corp. www.semtech.com sc4205 power management outline drawing - soic-8edp land pattern - soic-8edp
8 ? 2004 semtech corp. www.semtech.com sc4205 power management semtech corporation power management products division 200 flynn road, camarillo, ca 93012 phone: (805)498-2111 fax (805)498-3804 contact information
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