features 3 modes cycling function: bright dimming blinking reset to bright mode if power off time more than 5s adjustable output current: up to 750ma 8.5hz blinking mode l o w s w o n r e s i s t a n c e : 1 0 0 m ? over temperature protection over voltage protection sot23-6 package pb-free package low start-up voltage: 0.9v(typ.) white led torch (flashlight) the PAM2805 is a step-up dc-dc wled driver w i t h 3 m o d e s c y c l i n g f u n c t i o n ( 1 0 0 % brightness,25% brightness and 8.5hz blinking). t he un i qu e 3 mo de s c y cl i n g fu n ct i on ca n eliminate the needs of extra functional mcu or ic. the PAM2805 can deliver up to 750ma output current by setting an external resistor. the PAM2805 switches at a 1.0mhz constant frequency, allowing for the use of small value external inductor and ceramic capacitors. a low 95m v feedback voltage reduces the power loss in the rs for better efficiency. with its internal 2a, 100 device can provide high efficiency even at heavy load. the PAM2805 is available in sot23-6 package. applications general descriptio n m nmos switch, the n n n n n n n n n n n typical application block diagram 1 www.poweranalog.com 11/2011 rev1.0 PAM2805 3-modes/3w wled driver with 1 or 2 cell battery , power analog microelectronics inc 95mv reference + a1 - rc cc - a2 + comparator vout vin sw pwm logic + - pgnd 1.0mhz oscillator dimming and blinking logic fb ramp generator blk power off <5s power off <5s power off <5s iled=95mv/rs 2.2 h v in v out vin sw PAM2805 vout fb blk gnd l 20uf 10uf 1uf rs
pin configuration& marking information 2 p i n n u m b e r n a m e f u n c t i o n 1 v i n i n p u t v o l t a g e 2 g n d p o w e r g r o u n d 3 b l k c o n n e c t a 1 u f c a p f o r b l i n k i n g 4 f b f e e d b a c k 5 v o u t o u t p u t v o l t a g e 6 s w c o n n e c t e d t o a n i n t e r n a l n m o s s w i t c h 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 . . . supply voltage ...............................................6v output voltage...............................................6v storage temperature range......... ?65 c to 150 c lead temperature (soldering, 5 sec) ...........300 c ? ? ? recommended operating conditions junction temperature 40 to 125 ...............- c c operating temperature range .......-40 c to 85 c ? ? ? ? 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 - 6 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 - 6 j a 2 5 0 / 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 @ t a = 2 5 s o t 2 3 - 6 p d 4 0 0 m w x: internal code y: year w: weekly , power analog microelectronics inc www.poweranalog.com 11/2011 rev1.0 top view sot23-6 1 2 3 4 5 6 vin gnd fb vout sw blk PAM2805 3-modes/3w wled driver with 1 or 2 cell battery
3 electrical characteristic t =25 , l=2.2uh, c =10uf, c =10uf, unless otherwise noted. a o u t c =1uf, v =3.4v, blk f note1: v --- led forward voltage f p a r a m e t e r s y m b o l c o n d i t i o n s m i n t y p m a x u n i t i n p u t v o l t a g e r a n g e v i n 0 . 9 v f - 0 . 2 ( n o t e 1 ) v f e e d b a c k v o l t a g e v f b 9 0 9 5 1 0 0 m v s t a r t - u p v o l t a g e v s t a r t v i n : 0 v 3 v i l e d = 2 0 0 m a 0 . 9 v h o l d v o l t a g e v h o l d v i n : 3 v 0 v i l e d : 7 5 0 m a 1 0 0 m a 0 . 7 v o s c i l l a t o r f r e q u e n c y f o s c 0 . 8 5 1 . 0 1 . 1 5 m h z o v e r t e m p e r a t u r e s h u t d o w n o t s 1 5 0 o v e r t e m p e r a t u r e h y s t e r e s i s o t h 3 0 m a x i m u m o u t p u t c u r r e n t r a n g e i o ( m a x ) v i n = 2 . 4 v 7 5 0 m a q u i e s c e n t c u r r e n t i q i l e d = 0 m a , v o = 3 . 4 v , d e v i c e s w i t c h i n g a t 1 m h z 1 3 m a s w i t c h o n r e s i s t a n c e r d s o n v o = 3 . 4 v 0 . 1 c u r r e n t l i m i t i l i m v o = 3 . 4 v 2 a o v e r v o l t a g e p r o t e c t i o n ( v o u t ) v o v p 4 . 5 v b l i n k i n g f r e q u e n c y f b l k c b l k = 1 u f 7 8 . 5 1 0 h z , power analog microelectronics inc www.poweranalog.com 11/2011 rev1.0 PAM2805 3-modes/3w wled driver with 1 or 2 cell battery
typical performance characteristics t =25 , l=2.2uh , c =10uf, c =10uf, unless otherwise noted. a u t c =1uf, blk 4 1. led power efficiency vs input voltage 2. led current vs input voltage 3. dc input current vs input voltage 4. feedback voltage vs input voltage , power analog microelectronics inc www.poweranalog.com 11/2011 rev1.0 PAM2805 3-modes/3w wled driver with 1 or 2 cell battery 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 1 0 0 0 . 7 1 . 0 1 . 3 1 . 6 1 . 9 2 . 2 2 . 5 2 . 8 3 . 1 i n p u t v o l t a g e ( v ) i l e d = 3 5 0 m a i l e d = 7 5 0 m a 0 1 0 0 2 0 0 3 0 0 4 0 0 5 0 0 6 0 0 7 0 0 8 0 0 0 . 7 1 . 0 1 . 3 1 . 6 1 . 9 2 . 2 2 . 5 2 . 8 3 . 1 i n p u t v o l t a g e ( v ) i l e d = 7 5 0 m a ( 1 0 0 % b r i g h t n e s s ) i l e d = 3 5 0 m a ( 1 0 0 % b r i g h t n e s s ) i l e d = 7 5 0 m a ( 2 5 % b r i g h t n e s s ) i l e d = 3 5 0 m a ( 2 5 % b r i g h t n e s s ) 0 5 0 0 1 0 0 0 1 5 0 0 2 0 0 0 2 5 0 0 0 . 7 1 . 0 1 . 3 1 . 6 1 . 9 2 . 2 2 . 5 2 . 8 3 . 1 3 . 4 i n p u t v o l t a g e ( v ) i l e d = 7 5 0 m a ( 1 0 0 % b r i g h t n e s s ) i l e d = 3 5 0 m a ( 1 0 0 % b r i g h t n e s s ) 0 1 0 2 0 3 0 4 0 5 0 6 0 7 0 8 0 9 0 1 0 0 0 . 7 1 . 0 1 . 3 1 . 6 1 . 9 2 . 2 2 . 5 2 . 8 3 . 1 3 . 4 i n p u t v o l t a g e ( v ) i l e d = 3 5 0 m a ( 1 0 0 % b r i g h t n e s s ) i l e d = 7 5 0 m a ( 1 0 0 % b r i g h t n e s s ) i l e d = 3 5 0 m a ( 2 5 % b r i g h t n e s s ) i l e d = 7 5 0 m a ( 2 5 % b r i g h t n e s s )
5 7. overvoltage protection 5. 3 modes change 6. start-up waveform , power analog microelectronics inc www.poweranalog.com 11/2011 rev1.0 typical performance characteristics t =25 , l=2.2uh , c =10uf, c =10uf, unless otherwise noted. a u t c =1uf, blk PAM2805 3-modes/3w wled driver with 1 or 2 cell battery 8. switching waveform vin iled sw vin vout il vout il vout il sw
inductor selection capacitor selection diode selection led current setting 3 modes cycling low voltage startup and soft start the PAM2805 can use small value inductors due to its switching frequency of 1 mhz. the value of inductor will focus in the range of 2.2uh to 4.7uh for most PAM2805 applications. in typical high c u r r e n t w h i t e l e d a p p l i c a t i o n s , i t i s recommended to use a 4.7uh inductor. the inductor should have low dcr (dc resistance) to minimize the i r power loss, and it requires a current rating of 2a to handle the peak inductor current without saturating. an input capacitor is required to reduce the input ripple and noise for proper operation of the PAM2805. for good input decoupling, low esr (equivalent series resistance) capacitors should be used at the input. at least 2.2uf input capacitor is recommended for most applications. a minimum output capacitor value of 6.8uf is r e c o m m e n d e d u n d e r n o r m a l o p e r a t i n g conditions, while a 10uf-22uf capacitor may be required for higher power led current. a r e a s on a b l e v a l u e o f t h e o u tp u t c a p ac i t o r depends on the led current. the esr of the output capacitor is the im portant parameter to determine the output voltage ripple of the converter, so low esr capacitors should be used at the output to reduce the output voltage ripple. the small size of ceramic capacitors is an excellent choice for PAM2805 applications. the x5r and x7r types are preferred because they maintain capacitance over wide voltage and temperature ranges. it's indispensable to use a schottky diode rated at 2a with the PAM2805. using a schottky diode with a lower forward voltage drop is better t o improve the power led efficiency, and its voltage rating should be greater than the output voltage. ss22 is recommended schottky diode for rectifier. the led current is set by the single external rs resistor connected to the fb pin as shown in the typical application circuit on page 1. the typical fb reference is internally regulated to 95mv. the led current is 95mv/r1. it's recommended to use a 1% or better precision resistor for the better led current accuracy. the formula for rs selection is shown as follows: rs(ohm)=95mv/i (ma) at vin=3v. typically, for 1w(330ma) and 3w(750ma) led light applications, the rs are 0.288ohm and 0.127ohm respectively. t h e pa m 2 8 0 5 h a s t h r e e m o d e s : 1 0 0 % brightness, 25% brightness and blinking(typical 8.5hz). the mode change is triggered by power on/off actions and cycles in the following sequence: bright, dimming, blinking and back to bright mode. the PAM2805 will reset to the bright mode after being powe r off for more than 5 seconds. the PAM2805 has a build-in low voltage startup circuit for the best battery life solution. it can start up at 0.9v vin typically when the preset led current is 200ma. the soft-start function is made by clamping the output voltage of error amplifier with another voltage source which increases slowly from zero t o ne a r v in du r i n g th e s of t- s ta r t p e r i o d . therefore, the duty cycle of the pwm will be increased from zero to maximum in this period. the charging time of the inductor will be limited by the smaller duty so that the inrush current can be reduced to an acceptable value.` 2 led over voltage protection the output voltage of PAM2805 is monitored by over voltage protection circuit. once vout goes over v , typically 4.5v, the power nmos is turned off and sw pin stops switching. then, the vout is clamped to around v . ovp ovp application information 6 , power analog microelectronics inc www.poweranalog.com 11/2011 rev1.0 PAM2805 3-modes/3w wled driver with 1 or 2 cell battery
over current protection pcb layout guidelines the inductor current during charging period is detected by a current sensing circuit. when the value is larger than current limiting i , the power nmos is turned off so that the inductor will be forced to leave charging stage and enter discharging stage. therefore, the inductor peak current will not exceed i , whose minimum value is 2a. as for all switching power supplies, the layout and components placement of the PAM2805 is an important step in the design; especially at h i g h p e a k c u r r e n t s a n d h i g h s w i t c h i n g frequencies. the input capacitor and output capacitor should be placed respectively as close as possible to the input pin and output pin of the ic; the inductor and schottky diode should be placed as close as possible to the switch pin by using wide and short traces for the main current path; the current sense resistor should be placed as close as possible between the ground pin and feedback pin. lim lim application information 7 , power analog microelectronics inc www.poweranalog.com 11/2011 rev1.0 PAM2805 3-modes/3w wled driver with 1 or 2 cell battery
ordering information 8 number of pins: f(6) package type: a PAM2805 x x x x 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 5 a f e c x y w s o t 2 3 - 6 3 , 0 0 0 u n i t s / t a p e & r e e l , power analog microelectronics inc www.poweranalog.com 11/2011 rev1.0 PAM2805 3-modes/3w wled driver with 1 or 2 cell battery
9 , power analog microelectronics inc www.poweranalog.com 11/2011 rev1.0 outline dimensions PAM2805 3-modes/3w wled driver with 1 or 2 cell battery l ref. l1 (ref.) m i l l i m e t e r r e f . m i n m a x a - 1 . 3 5 a 1 0 . 0 4 0 . 1 5 a 2 0 . 7 0 1 . 2 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 .
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