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features applications general description n n n n n n n n n n n efficiency up to 93% 180 a(typ.) quiescent current output current: up to 1a internal synchronous rectifier 1.5mhz switching frequency soft start under-voltage lockout short led protection open led protection thermal shutdown 5-pin small sot23-5 packages 3aa or 4aa batteries powered flashlight 1 cell li-ion battery powered flashlight the pam2804 is a step-down constant current led driver. when the input voltage down to lower than led forward voltage, then pam2804 run into ldo mode. the pam2804 supports a range of input voltages from 2.5v to 6.0v, allowing the use of a single li+/li-polymer cell, 3aa or 4aa cell, usb, and other standard power sources. the fb voltage is only 0.1v to achieve high efficiency. pam2804 employ internal power switch and synchronous rectifier to minimize external part count and realize high efficiency. during shutdown, the input is disconnected from the output and the shutdown current is less than 1 a. other key features include under-voltage lockout to prevent deep batte ry discharge of the li+ battery. . n n n pb-free package typical application 1 www.poweranalog.com pam2804 1a step-down constant current, high efficiency led driver 10/2010 rev1.0 , power analog microelectronics inc vin sw gnd en l 4.7 h co 10f v c in in 10f rs fb w led 1~5w iled =0.1/rs 3aa or 4aa batteries 1 cell li-ion battery
block diagram 2 pin configuration & marking information top view sot23 5 - ee: product code of pam2804 x: internal code y: year w: week , power analog microelectronics inc www.poweranalog.com pam2804 1a step-down constant current, high efficiency led driver n a m e f u n c t i o n v i n c h i p m a i n p o w e r s u p p l y p i n g n d g r o u n d e n e n a b l e c o n t r o l i n p u t . f o r c e t h i s p i n v o l t a g e a b o v e 1 . 5 v , e n a b l e s t h e c h i p , a n d b e l o w 0 . 3 v s h u t s d o w n t h e d e v i c e . f b f e e d b a c k v o l t a g e t o i n t e r n a l e r r o r a m p l i f i e r , t h e t h r e s h o l d v o l t a g e i s 0 . 1 v . s w t h e d r a i n s o f t h e i n t e r n a l m a i n a n d s y n c h r o n o u s p o w e r m o s f e t . 1 2 3 5 4 en gnd sw fb vin pin description en fb + - iamp + - ircmp sw gnd synchronous rectifier nch ( ) main switch pch ( ) vin comp vin shutdown osc rs latch 0.6vref freq shift - + ea s q r q switching logic and blanking circuit slope comp 1.5m osc anti shoot thru - - 10/2010 rev1.0
3 absolute maximum ratings these are stress ratings only and functional operation is not implied exposure to absolute maximum ratings for prolonged time periods may affect device reliability all voltages are with respect to ground . . . input voltage..................................-0.3v to 6.5v en, fb pin voltage...........................- sw pi n voltage.....................- 0.3v to v 0.3v to v +0.3v junction temperature................................150c storage temperature range........-65c to 150c soldering temperature......................300c 5sec ( ) in in , recommended operating conditions supply voltage................................2.5v to 6.0v c c c c operation temperature range.........-40 to 85 junction temperature range........-40 to 125 thermal information p a r a m e t e r p a c k a g e s y m b o l m a x i m u m u n i t t h e r m 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 ) s o t 2 3 - 5 n o t e j c 1 3 0 t h e r m a l r e s i s t a n c e ( j u n c t i o n t o a m b i e n t ) s o t 2 3 - 5 j a 2 5 0 c / w i n t e r n a l p o w e r d i s s i p a t i o n s o t 2 3 - 5 p d 4 0 0 m w , power analog microelectronics inc www.poweranalog.com pam2804 1a step-down constant current, high efficiency led driver note: the maximun output current for sot23-5 package is limited by internal power dissipation capacity as described in application information herein after. 10/2010 rev1.0
electrical characteristic t =25 , v =4.2v, real wled load, c =10f, c =10f, l=4.7h, unless otherwise noted. a in in o c 4 , power analog microelectronics inc www.poweranalog.com pam2804 1a step-down constant current, high efficiency led driver p a r a m e t e r s y m b o l t e s t c o n d i t i o n s m i n t y p m a x u n i t s i n p u t v o l t a g e r a n g e v i n 2 . 5 6 . 0 v r e g u l a t e d f e e d b a c k v o l t a g e v f b 0 . 0 9 5 0 . 1 0 . 1 0 5 v p e a k i n d u c t o r c u r r e n t i p k v i n = 5 v 1 . 5 a q u i e s c e n t c u r r e n t i q n o l o a d 1 8 0 a s h u t d o w n c u r r e n t i s d v e n = 0 v 1 a o s c i l l a t o r f r e q u e n c y f o s c v o = 1 0 0 % 1 . 2 1 . 5 1 . 8 m h z p m o s f e t 0 . 3 0 . 4 5 d r a i n - s o u r c e o n - s t a t e r e s i s t a n c e r d s ( o n ) i d s = 1 0 0 m a n m o s f e t 0 . 3 5 0 . 5 s w l e a k a g e c u r r e n t i l s w 0 . 0 1 1 a h i g h e f f i c i e n c y 9 3 % e n t h r e s h o l d h i g h v e h 1 . 5 v e n t h r e s h o l d l o w v e l 0 . 3 v e n l e a k a g e c u r r e n t i e n 0 . 0 1 a o v e r t e m p e r a t u r e p r o t e c t i o n o t p 1 5 0 c o t p h y s t e r e s i s o t h 3 0 c 10/2010 rev1.0
0 5 0 1 0 0 1 5 0 2 0 0 2 5 0 3 0 0 3 5 0 2 . 5 3 3 . 5 4 4 . 5 5 5 . 5 6 v i n ( v ) 0 2 0 0 4 0 0 6 0 0 8 0 0 1 0 0 0 1 2 0 0 2 . 5 3 3 . 5 4 4 . 5 5 5 . 5 6 v i n ( v ) 0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 0 . 6 2 0 7 0 1 2 0 t e m p e r a t u r e ( ) v i n = 4 . 2 v v i n = 3 . 6 v v i n = 2 . 7 v 5 , power analog microelectronics inc www.poweranalog.com pam2804 1a step-down constant current, high efficiency led driver typical performance characteristics c t =25 , c =10 f, c =10 f, l=4.7 h, unless otherwise noted. a in o 10/2010 rev1.0 eifficiency vs input voltage output current vs input voltage output current vs input voltage output current vs input voltage 8 2 % 8 4 % 8 6 % 8 8 % 9 0 % 9 2 % 9 4 % 9 6 % 3 3 . 5 4 4 . 5 5 5 . 5 6 i n p u t v o l t a g e ( v ) 3 3 0 m a 7 5 0 m a 1 a rcs=0.3ohm 0 0 . 1 0 . 2 0 . 3 0 . 4 0 . 5 0 . 6 0 . 7 0 . 8 3 3 . 5 4 4 . 5 5 5 . 5 6 i n p u t v o l t a g e ( v ) r vs input voltage dson rdson vs temperature 0 . 1 0 . 1 5 0 . 2 0 . 2 5 0 . 3 0 . 3 5 0 . 4 2 3 4 5 6 i n p u t v o l t a g e rcs=0.135ohm rcs=0.1ohm vin =3.6v
pam2804 1a step-down constant current, high efficiency led driver 6 , power analog microelectronics inc www.poweranalog.com typical performance characteristics t =25 c, c =10 f, c =10 f, l=4.7 h, unless otherwise noted. a in o o 10/2010 rev1.0 quiescent current vs input voltage start up with enable 0 2 0 4 0 6 0 8 0 1 0 0 1 2 0 1 4 0 1 6 0 1 8 0 2 0 0 3 3 . 5 4 4 . 5 5 5 . 5 6 i n p u t v o l t a g e ( v ) s w i t c h o n s w i t c h o f f
7 , power analog microelectronics inc www.poweranalog.com pam2804 1a step-down constant current, high efficiency led driver 10/2010 rev1.0 application information the basic pam2804 application circuit is shown in page 1. external component selection is determined by the load requirement, selecting l first and then cin and cout. for most applications, the value of the inductor will fall in the range of 1h to 4.7h. its value is chosen based on the desired ripple current. large value inductors lower ripple current and small value inductors result in higher ripple currents. higher v or vout also increases the ripple current as shown in equation 1. a reasonabl e starting point for setting ripple current is i = 400ma (40% of 1a). (1) the dc current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation. thus, a 1.4a rated inductor should be enough for most applications (1a + 400ma). for better efficiency, choose a low dc-resis tance inductor. higher values, lower cost ceramic capacitors are now becoming available in smaller case sizes. their high ripple current, high voltage rating and low esr make them ideal for switching regulator applications. using ceramic capacitors can achieve very low output ripple and small circuit size. when choosing the input and output ceramic capacitors, choose the x5r or x7r dielectric formulations. these dielectrics have the best temperature and voltage charac teristics of all the ceramics for a given value and size. inductor selection using ceramic input and output capacitors in l thermal consideration thermal protection limits power dissipation in the pam2804. when the junction temperature exceeds 150c, the otp (over temperature protection) starts the thermal shutdown and turns the pass transistor off. the pass transistor r e s u m e s o p e r a t i o n a f t e r t h e j u n c t i o n temperature drops below 120c. f o r c o n t i n u o u s o p e r a t i o n , t h e j u n c t i o n temperature should be maintained below 125c. the power dissipation is defined as: i is the step-down converter quiescent current. the term tsw is used to estimate the f ull load step-down converter switching losses. q ( ) ( ) ? ? d ? ? ? ? o u t o u t l i n 1 v i = v 1 - f l v ( ) ( ) o d s o n h i n o d s o n l 2 d o s w s o q i n i n v r + v - v r p = i + t f i + i v v
8 , power analog microelectronics inc www.poweranalog.com pam2804 1a step-down constant current, high efficiency led driver 10/2010 rev1.0 application information for the condition where the step-down converter is in dropout at 100% duty cycle, the total device dis sipation reduces to: since r , quiescent current, and switching losses all vary with input voltage, the total losses should be investigated over the complete input voltage range. the maximum power dissipation de pend s on th e ther ma l r esi sta nc e of ic package, pcb layout, the rate of surrounding airflow and temperature difference between junction and ambient. the maximum power dissipation can be calc ulated by the following formula: where tj(max) is the maximum allowable junction temperature 125c.t is the ambient temperature and is the thermal resistance from the junction to the ambient. based on the standard jedec for a two layers thermal test board, the thermal resistance of sot23-5 package is 250c/w. the maximum power dissipation at t = 25c can be calculated by following formula: p =(125c-25c)/250c/w=0.4w the internal feedback(fb) voltage is 0.1v (typical). the output current is ca lculated as below: iled=0.1/rs the output current is given by the following table. as the input voltage approaches the led forward voltage, the pam2804 turns the p-chan nel transistor continuously on. in this mode the voltage drop on led is equal to the input voltage minus the voltage drop across the p - channel transistor, inductor and current resistor: v = v ?iled (r + r + r ) where r = p-channel switch on resistance, iled = led current, r = inductor dc resistance, r = indu ctor dc resistance. when the die temperature exceeds 150c, a reset occurs and the reset remains until the temperature decrease to 120c, at which time the circuit can be restarted. ds(on) a ja ja a d leddrop in dson l s dson l s setting the output current 100% duty cycle operation thermal shutdown 2 d o d s o n h q i n p = i r + i v j ( m a x ) a d j a t - t p = r s ( ) i l e d ( m a ) 0 . 2 8 6 3 5 0 0 . 1 4 3 7 0 0 0 . 1 1 0 0 0
9 , power analog microelectronics inc www.poweranalog.com pam2804 1a step-down constant current, high efficiency led driver 10/2010 rev1.0 application information pcb layout check list when laying out the printed circuit board, the following checklist should be used to ensure proper operation of the pam2804. these items are also illustrated graphically in figure 1. check the following in your layout: 1. the power traces, consisting of the gnd trace, the sw trace and the vin trace should be kept shor t, direct and wide. 2. does the v pin connect directly to the current sense resistor? the current sense resistor to gnd trace should be kept short, direct and wide. 3. does the (+) plate of cin connect to vin as closely as possible? this capacitor provides the ac current to the internal power mosfets. 4. keep the switching node, sw, away from the sensitive vfb node. 5. keep the (?) plates of c and c as close as possible. fb in out
ordering information pam 2804 x x x xxx fb voltage number of pins package type pin configuration 10 , power analog microelectronics inc www.poweranalog.com pam2804 1a step-down constant current, high efficiency led driver p i n c o n f i g u r a t i o n p a c k a g e t y p e n u m b e r o f p i n s f b v o l t a g e a t y p e 1 . e n 2 . g n d 3 . s w 4 . v i n 5 . f b a : s o t - 2 3 b : 5 0 1 0 : 0 . 1 v 10/2010 rev1.0 p a r t n u m b e r m a r k i n g p a c k a g e t y p e s t a n d a r d p a c k a g e p a m 2 8 0 4 a a b 0 1 0 r e f e r t o p 2 s o t - 2 3 - 5 3 , 0 0 0 u n i t s / t a p e & r e e l
outline dimensions 11 , power analog microelectronics inc www.poweranalog.com pam2804 1a step-down constant current, high efficiency led driver l ref. l1 (ref.) sot23-5 m i l l i m e t e r r e f . m i n m a x a 1 . 1 0 m a x a 1 0 0 . 1 0 a 2 0 . 7 0 1 c 0 . 1 2 r e f . d 2 . 7 0 3 . 1 0 e 2 . 6 0 3 . 0 0 e 1 1 . 4 0 1 . 8 0 l 0 . 4 5 r e f . l 1 0 . 6 0 r e f . 0 o 1 0 o b 0 . 3 0 0 . 5 0 e 0 . 9 5 r e f . e 1 1 . 9 0 r e f . d e1 b e 10/2010 rev1.0

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