e l ek tr on isch e b a u e lemen te 01 -jun-2002 rev. a page 1 of 4 http://www.secosgmbh.com/ any changing of specification will not be informed individual r o h s c o m p l i a n t p r o d u c t typical circuit s 5u1284 4a ultra low dropout positive adjustable or fixed-mode regulator d e s c r i p t i o n the s5 u1284 is 4a regulator with extremely low dropout voltage. this product is specifically designed to provide well regulated supply for applications requiring 2.8v or lower voltages from 3.3v atx power supplies where high efficiency of the switch can be achieved without the cost and compliexity associated with switching regulator. one such application is the new graphic chipsets that requires anywhere from 2.4v to 2.7v supply. * adjustable or fixed output voltage 1.5v,1.8v,2.5v,3.3v,5.0v f e a t u r e s * 0. 7 v max. dropout voltage at 4a load current * output current limiting * good noise rejection * fast transient response * built-in thermal shutdown pin descriptions block diagram n a m e i / o d e s c r i p t i o n a d j ( g n d ) a r e s i s t o r d i v i d e r f r o m t h i s p i n t o t h e v o u t p i n a n d g r o u n d s e t s t h e o u t p u t v o l t a g e . ( g n d o n l y f o r f i x e d m o d e ) v s e n s e i t h e p i n i s t h e p o s i t i v e s i d e o f t h e r e f e r e n c e t h a t a l l o w s r e m o t e l o a d s e n s i n g t o a c h i e v e e x c e l l e n t l o a d r e g u l a t i o n . a m i n i m u m o f 1 0 u f c a p a c i t o r m u s t b e c o n n e c t e d f r o m t h i s p i n t o g r o u n d t o i n s u r e s t a b i l i t y . v i n i t h e i n p u t p i n o f r e g u l a t o r . t y p i c a l l y a l a r g e s t o r a g e c a p a c i t o r i s c o n n e c t e d f r o m t h i s p i n t o g r o u n d t o i n s u r e t h a t t h e i n p u t v o l t a g e d o e s n o t s a g b e l o w t h e m i n i m u m d r o p o u t v o l t a g e d u r i n g t h e l o a d t r a n s i e n t r e s p o n s e . t h i s p i n m u s t a l w a y s b e h i g h e r t h a n v o u t i n o r d e r f o r t h e d e v i c e t o r e g u l a t e . v c t r l i t h i s p i n i s t h e s u p p l y p i n f o r t h e i n t e r n a l c o n t r o l c i r c u i t a s w e l l a s t h e b a s e d r i v e f o r t h e p a s s t r a n s i s t o r . t h i s p i n m u s t a l w a y s b y h i g h e r t h a n t h e v o u t p i n i n o r d e r t h e d e v i c e t o r e g u l a t e . a m i n i m u m o f 1 0 0 u f c a p a c i t o r m u s t b e c o n n e c t e d f r o m t h i s p i n t o g r o u n d t o i n s u r e s t a b i l i t y . v o u t o t h e o u t p u t o f t h e r e g u l a t o r . a m i n i m u m o f 1 0 0 u f c a p a c i t o r m u s t b e c o n n e c t e d f r o m t h i s p i n t o g r o u n d t o i n s u r e s t a b i l i t y . S5U1284-25 m i l l i m e t e r r ef . m i n . m a x . r ef . m i n . m a x . a 4 . 4 0 4 . 8 0 c 2 1 . 2 5 1 . 4 5 b 0 . 6 6 0 . 9 1 l 2 1 . 2 7 r e f . l 4 0 . 0 0 0 . 3 0 b d 8 . 6 9 . 0 c 0 . 3 6 0 . 5 e 1 . 7 0 r e f . l 1 2 . 2 9 2 . 7 9 l 1 4 . 6 1 5 . 8 e 9 . 8 0 1 0 . 4 0 ? 8 ? m i l l i m e t e r
d c s u p p l y v o l t a g e p o w e r d i s s i p a t i o n s t o r a g e t e m p e r a t u r e r a n g e o p e r a t i n g j u c t i o n t e m p e r a t u r e r a n g e p a r a m e t e r s y m b o l r a t i n g s u n i t v v i n 1 6 2 . 4 ~ 4 . 4 0 ~ + 1 5 0 - 6 5 ~ + 1 5 0 a b s o l u t e m a x i m u m r a t i n g s p d t s t t o p c o c o c o n t r o l i n p u t v o l t a g e v c t r l v 1 8 w e l e k t r o n i s c h e b a u e l e m e n t e h t t p : / / w w w . s e c o s g m b h . c o m / a n y c h a n g i n g o f s p e c i f i c a t i o n w i l l n o t b e i n f o r m e d i n d i v i d u a l 01-jun-2002 rev. a page 2 of 4 t a g e d o e s n o t s a g b e l o w t h e m i n i m u m d r o p o u t v o l t a g e d u ri n g t h e l o a d v h i g h e r t h a n v o u t i n o r d e r f o r t h e d e v i c e t o d e s c r i p ti o n g n d t y p i c a l l y a l a rg e s t o r a g e c a p a c i t o r i s c o n n e c t e d f r o m t h i s p i n t o g r o u n d t o i n s u r e t h a t t h e i n p u t 1 . 3 v o r o p e n = o u t p u t e n a b l e . n c S5U1284 4a ultra low dropout positive adjustable or fixed-mode regulator e l e c t r i c a l c h a r a c t e r i s t i c s u n l e s s o t h e r w i s e s p e c i f i e d , t h e s e s p e c i f i c a t i o n s a p p l y o v e r , c i n = 1 u f , c o u t = 1 0 u f , t j = 0 ~ 1 5 0 : . t y p i c a l v a l u e r e f e r t o t j = 2 5 : . v o u t = vs e n s e pa r a m e te r c o n d i ti o n s m i n t y p m a x u n i t r e f e r e n c e v o l t a g e s 5 u 1 2 8 4 - a d j i o = 1 0 m a, t j = 2 5 , : ( v i n -v o u t )= 0 . 7 v , vc t r l = v i n + 1 v 1 . 2 2 5 1 . 2 5 0 1 . 2 7 5 v s 5 u 1 2 8 4 -1 5 i o = 1 0 m a, t j = 2 5 , : 2 . 2 v vi n 1 2 v , vc t rl = vi n + 1 v 1 . 4 7 0 1 . 5 0 0 1 . 5 3 0 v s 5 u 1 2 8 4 -1 8 i o = 1 0 m a, t j = 2 5 , : 2 . 5 v vi n 1 2 v , vc t rl = vi n + 1 v 1 . 7 6 4 1 . 8 0 0 1 . 8 3 6 v s 5 u 1 2 8 4 -2 5 i o = 1 0 m a, t j = 2 5 , : 3 . 2 v vi n 1 2 v , vc t rl = vi n + 1 v 2 . 4 5 0 2 . 5 0 0 2 . 5 5 0 v s 5 u 1 2 8 4 -3 3 i o = 1 0 m a, t j = 2 5 , : 4 . 0 v vi n 1 2 v , vc t rl = vi n + 1 v 3 . 2 3 5 3 . 3 0 0 3 . 3 6 5 v o u t p u t v o l t a g e s 5 u 1 2 8 4 -5 0 i o = 1 0 m a, t j = 2 5 , : 5 . 7 v vi n 1 2 v , vc t rl = vi n + 1 v 4 . 9 0 0 5 . 0 0 5 . 1 0 0 v l i n e r e g u l a t o r s 5 u 1 2 8 4 - xx i o = 1 0 m a, t j = 2 5 , : v o u t + 0 . 7 < v i n < 1 2 , vc t rl = vi n + 1 v - - 0 . 2 % s 5 u 1 2 8 4 -ad j (v i n -v o u t )= 2 v , 0 m a< i o < 4 a , t j = 2 5 : , vc t rl = vi n + 1 v - - 1 % s 5 u 1 2 8 4 -1 5 v i n = 3 . 0 v , 0 m a< i o < 4 a , t j = 2 5 : , vc t rl = 4 v - 1 2 1 5 m v 5 s u 1 2 8 4 -1 8 v i n = 3 . 3 v , 0 m a< i o < 4 a , t j = 2 5 : , vc t rl = 4 . 3 v - 1 5 1 8 m v s 5 u 1 2 8 4 -2 5 v i n = 4 . 0 v , 0 m a< i o < 4 a , t j = 2 5 : , vc t rl = 5 v - 2 0 2 5 m v s 5 u 1 2 8 4 -3 3 v i n = 5 . 0 v , 0 m a< i o < 4 a , t j = 2 5 : , vc t rl = 6 v - 2 6 3 3 m v l o a d r e g u l a t i o n s 5 u 1 2 8 4 -5 0 v i n = 8 . 0 v , 0 m a< i o < 4 a , t j = 2 5 : , vc t rl = 9 v - 4 0 5 0 m v s 5 u 1 2 8 4 -ad j v a d j = 0 v , f o r a l l c o n d i t i o n s b e l o w . ( v o u t = 1 % v o u t ) v i n = 2 . 0 5 v , i o = 1 . 5 a v i n = 2 . 0 5 v , i o = 3 . 0 a v i n = 2 . 0 5 v , i o = 4 . 0 a - 1 . 1 0 1 . 1 5 1 . 1 8 1 . 2 5 v d r o p o u t v o l t a g e (vc t rl -v o u t ) (f i x e d m o d e l ) v i n = v o u t + 0 . 8 v , i o = 4 . 0 a ( v o u t = 1 % v o u t ) - 1 . 1 0 1 . 2 5 v s 5 u 1 2 8 4 -ad j v a d j = 0 v , f o r a l l c o n d i t i o n s b e l o w . ( v o u t = 1 % v o u t ) vc t rl = 2 . 7 5 v , i o = 1 . 5 a vc t rl = 2 . 7 5 v , i o = 3 . 0 a vc t rl = 2 . 7 5 v , i o = 4 . 0 a - 0 . 2 6 0 . 5 0 0 . 7 0 0 . 3 8 0 . 6 0 0 . 8 5 v s 5 u 1 2 8 4 -1 5 vc t rl = 3 . 3 v , i o = 4 . 0 a ( v o u t = 1 % v o u t ) s 5 u 1 2 8 4 -1 8 s 5 u 1 2 8 4 -2 5 s 5 u 1 2 8 4 -3 3 d r o p o u t v o l t a g e (v i n -v o u t ) s 5 u 1 2 8 4 -5 0 vc t rl = v o u t + 1 . 5 v , i o = 4 . 0 a ( v o u t = 1 % v o u t ) - 0 . 7 0 0 . 8 5 v c u rr e n t l i m i t vc t rl = 2 . 7 5 v , vi n = 2 . 0 5 v , v o = 1 0 0 m v , v a d j = 0 v 4 . 2 - - a m i n i m u m l o a d c u r r e n t vc t rl = 5 v , v i n = 3 . 3 v , v a d j = 0 v - 5 1 0 m a t h e rm a l r e g u l a t i o n 3 0 m s p u l s e - 0 . 0 1 0 . 0 2 % / w r i p p l e r e j e c t i o n vc t rl = 5 v , v i n = 5 v , i o = 4 . 0 a, v a d j = 0 v , t j = 2 5 : , v ri p p l e = 1 v p p a t 1 2 0 h z 6 0 7 0 - d b s 5 u 1 2 8 4 -ad j v a d j = 0 v , f o r a l l c o n d i t i o n s b e l o w . vc t rl = 2 . 7 5 v , vi n = 2 . 0 5 v , i o = 1 . 5 a vc t rl = 2 . 7 5 v , vi n = 2 . 0 5 v , i o = 3 . 0 a vc t rl = 2 . 7 5 v , vi n = 2 . 0 5 v , i o = 4 . 0 a - 6 3 0 3 3 2 5 6 0 7 0 m a s 5 u 1 2 8 4 -1 5 vc t rl = 3 . 3 v , v i n = 2 . 3 v , i o = 4 . 0 a s 5 u 1 2 8 4 -1 8 s 5 u 1 2 8 4 -2 5 s 5 u 1 2 8 4 -3 3 c o n t r o l pi n c u rr e n t s 5 u 1 2 8 4 -5 0 vc t rl = v o u t + 1 . 5 v , vi n = v o u t + 0 . 8 v , i o = 4 . 0 a - 3 3 7 0 m a ad j u s t p i n c u rr e n t vc t rl = 2 . 7 5 v , vi n = 2 . 0 5 v , i o = 1 0 m a, v a d j = 0 - 5 0 1 5 0 u a q u i e s c e n t c u rr e n t vc t rl = 1 3 v , v i n = 1 2 v , i o = 1 0 m a (f i x e d m o d e l ) - - 1 2 m a t h e rm a l r e s i s t a n c e j u n c t i o n -t o -c a s e c o n t r o l c i rc u i t r y / p o w e r t r a n s i s t o r - 3 . 5 - / : w
01-jun-2002 rev. a page 3 of 4 h t p : / / w w w . s e c o s g m b h . c o m / a n y c h a n g i n g o f s p e c i f i c a t i o n w i l l n o t b e i n f o r m e d i n d i v i d u a l e l e k t r o n i s c h e b a u e l e m e n t e n o t e 1 : s 5 u 1 2 8 4 - a d j i n c o r p o r a t e s a n i n t e r n a l t h e r m a l s h u t d o w n t h a t p r o t e c t s t h e d e v i c e w h e r e t h e j u n c t i o n t e m p e r a t u r e e x c e e d s t h e a l l o w a b l e m a x i m u m j u n c t i o n t e m p e r a t u r e . f u n c t i o n a l d e s c r i p t i o n i n t r o d u c t i o n t h e s 5 u 1 2 8 4 r e g u l a t o r i s 5 - t e r m i n a l d e v i c e d e s i g n e d s p e c i f i c a l l y t o p r o v i d e e x t r e m e l y l o w d r o p o u t v o l t a g e c o m p a r a b l e t o t h e p n p t y p e without stability the s5 u1284-xx requires the use of an output capacitor as part of the frequency compensation in order to make the regulator stable. typical designs for the microprocessor application use standard electrolytic with typical esr in the range of 50 to 100 mohm and an output capacitance of 100uf to 1000uf. fortunately as the capacitance increases, the esr decreases resulting in a fixed rc time constant. the s5 u1284-xx takes advantage of the phenomena in making the overakk regulator loop stable. for most applications a min. of 100uf aluminum electrolytic capacitor insures both stability and good transient response. t h e s 5 u 1 2 8 4 - a d j k e e p s a c o n s t a n t 1 . 2 5 v b e t w e e n t h e v s e n s e p i n a n d t h e a d j p i n . b y p l a c i n g a r e s i s t o r r 1 a c r o s s t h e s e t w o p i n s a n d c o n n e c t i n g t h e v s e n s e a n d v o u t p i n t o g e t h e r , a c o n s t a n t c u r r e n t f l o w s t h r o u g h r 1 , a d d i n g t o t h e l a d j c u r r e n t a n d i n t o t h e r 2 r e s i s t o r p r o d u c i n g a v o l t a g e e q u a l t o t h e ( 1 . 2 5 / r 1 ) * r 2 + l a d j * r 2 . t h i s v o l t a g e i s t h e n a d d e d t o t h e 1 . 2 5 v t o s e t t h e o u t p u t v o l t a g e . t h i s i s s u m m a r i z e d i n t h e a b o v e e q u a t i o n . s i n c e t h e m i n . l o a d c u r r e n t r e q u i r e m e n t o f t h e s 5 u 1 2 8 4 - a d j i s 1 0 m a , r 1 i s t y p i c a l l y s e l e c t e d t o b e 1 2 1 o h m r e s i s t o r s o t h a t i t a u t o m a t i c a l l y s a t i s f i e s t h i s c o n d i t i o n . n o t i c e t h a t s i n c e l a d j i s t y p i c a l l y i n t h e r a n g e o f 5 5 u a i t o n l y a d d s a s m a l l e r r o r t o t h e o u t p u t v o l t a g e a n d s h o u l d o n l y b e c o n s i d e r e d w h e n a v e r y p r e c i s e o u t p u t v o l t a g e s e t t i n g i s r e q u i r e d . o u t p u t v o l t a g e s e t t i n g t h e s 5 u 1 2 8 4 c a n b e p r o g r a m m e d t o a n y v o l t a g e i n t h e r a n g e o f 1 . 2 5 v t o 1 5 . 5 v w i t h t h e a d d i t i o n o f r 1 a n d r 2 e x t e r n a l r e s i s t o r s a c c o r d i n g t o t h e f o l l o w i n g f o r m u l a : load regulator since the s5 u1284 has separate pins for the output (vout) and the sense (vsense), it is ideal for providing true remote sensing of output voltage at the load. this means that the voltage drops due to parasitic resistance such pcb traces between the regulator and the load are compensated for using remote sensing. figure following shows a typical application of the s5 u1284-adj with remote sensing. the disadvantage of the extra power dissipation due to the base current associated with pnp regulators. this is done by bringing out the control pin of the regulator that provides the base current to the power npn and connecting it to a voltage that is greater than the voltage present at the vin pin. this flexibility makes the s5 u1284 ideal for applications where dual inputs are available such as a computer motherboard with an atx style power supply that provides 5v and 3.3v to the board. one such application is the new graphic chip sets that require anywhere from 2.4v to 2.7v supply. the s5 u1284 can easily be programmed with the addition of two external resistors to any voltages within the range of 1.25v to 15.5v. another major requirment of these graphic chips is the need to switch the load current from zero to several amps in tens of nanoseconds at the processor pins, which translates to an approximately 300 to 500ns of current step at the regulator. in addition, the output voltage tolerances are also extremely tight and they include the transient response as part of the specification. the s5 u1284 is specifically designed to meet the fast current transient needs as well as providing an accurate initial voltage, reducing the overall system cost with the need for fewer number of output capacitors. another feature of the device is its true remote sensing capability that allows accurate voltage setting at the load rather than at the device. s5 u 1284-adj s5 u 1284-adj s5 u1284 4a ultra low dropout positive adjustable or fixed-mode regulator
e l ek tr on isch e b a u e lemen te 01 -jun-2002 rev. a page 4 of 4 http://www.secosgmbh.com/ any changing of specification will not be informed individual t h e r m a l d e s i g n t h e s 5 u 1 2 8 4 - x x i n co r p o r a t e s a n i n t e r n a l t h e r m a l sh u t d o w n t h a t p r o t e ct s t h e d e vi ce w h e n t h e j u n c t i o n t e m p e r a t u r e e x ce e d s t h e m a x i m u m a l l o w a b l e j u n c t i o n t e m p e r a t u r e s. a l t h o u g h t h i s d e vi ce ca n o p e r a t e w i t h j u n c t i o n t e m p e r a t u r e s i n t h e r a n g e o f 1 5 0 : , i t i s r e co m m e n d e d t h a t t h e se l e ct e d h e a t si n k b e ch o se n su ch t h a t d u r i n g m a x i m u m co n t i n u o u s l o a d o p e r a t i o n , t h e j u n ct i o n t e m p e r a t u r e i s ke p t b e l o w t h i s n u m b e r . t h e e x a m p l e b e l o w sh o w s t h e st e p s i n se l e ct i n g t h e p r o p e r su r f a ce m o u n t p a ck a g e . a ssu m i n g , t h e f o l l o w i n g co n d i t i o n s : v o u t = 2 . 5 v , v i n = 3 . 3 v , v c t r l = 5 v , i o u t = 2 a d c a vg . c a l cu l a t e t h e m a x i m u m p o w e r d i s si p a t i o n u si n g t h e f o l l o w i n g e q u a t i o n : p d = i o u t * ( v i n - v o u t ) + ( i o u t / 6 0 ) * ( v ct r l - v o u t ) p d = 2 * ( 3 . 3 - 2 . 5 ) + ( 2 / 6 0 ) * ( 5 - 2 . 5 ) = 1 . 6 8 w u si n g t a b l e b e l o w se l e ct t h e p r o p e r p a cka g e a n d t h e a m o u n t o f co p p e r b o a r d n e e d e d . p a cka g e c o p p e r a r e a j a ( / w ) : m a x p d ( t a = 2 5 ) : m a x p d ( t a = 4 5 ) : t o - 2 6 3 - 5 l p a d s i z e 1 . 4 * 1 . 4 2 5 ~ 4 5 2 . 4 w ~ 4 . 4 w 2 . 0 w ~ 3 . 6 w c h a r a c t e r i s t i c s c u r v e note: above table is based on the max. junction temperature of 135 c. o S5U1284 4a ultra low dropout positive adjustable or fixed-mode regulator
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