1 / 9 axelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 may . 0 8 , 20 1 3 ax38 2 1 1.6 a , 1 3 v , 600k hz synchronous rectified step - down converter ? general description the AX3821 is a monolithic synchronous buck regulator. the device integrates two 1 0 0m mosfets, and provides 1.6 a of continuous load current over a wide input voltage of 4. 5v to 1 3 v . current mode control provides fast transient response and cycle - b y - c ycle current limit. internal soft - start prevents inrush current at turn - on, and in shutdown mode the supply current drops to 1 a. this device, available in sot - 23 - 6l package, provi des a very compact solution with minimal external components. ? features - 1.6 a output current - wide 4. 5v to 1 3 v operating input range - integrated 1 0 0m power mosfet switches - output a djust from v fb to 1 1 v - internal compensation - up to 9 4 % efficiency - stable with l ow esr ceramic output capacitors - fixed 600k hz frequency - cycle - by - cycle over current protection - thermal shutdown and short circuit protections ? b lock d iagram - + - + - s r q q + 0 . 6 v i n t e r n a l r e g u l a t o r s i n 5 v i n 5 v g n d m 1 1 0 0 m m 2 1 0 0 m r a m p c l k c u r r e n t s e n s e a m p l i f i e r c u r r e n t c o m p a r a t o r e r r o r a m p l i f i e r 1 0 0 k h z / 6 0 0 k h z g n d b s s w f b + - 1 . 5 v s h u t d o w n c o m p a r a t o r e n o s c i l l a t o r ?
2 / 9 axelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 may . 0 8 , 20 1 3 ax38 2 1 ? pin assignment the package of AX3821 is sot - 23 - 6l ; the pin assignment is given by : name description bs bootstrap. a 10 nf capacitor is connected between sw and bs pins to drive the power switchs gate above the supply gnd ground pin. connect this pin to exposed pad. fb feedback. an e xternal resistor divider from the output to gnd, tapped to the fb pin sets the output voltage. v in power supply input. drive 4.5v to 1 3 v voltage to this pin to power on this chip. connect a 10f ceramic bypass sw switch output. connect this pin to the switch end of the inductor. en enable input. en is a digital input that turns the regulator on or off. drive en high to turn on the regulator, drive it low to turn it off. pull up with 100k resistor ? o rder/marking information order information top marking ( t o p v i e w ) s o t - 2 3 - 6 l 3 6 4 1 g n d e n b s s w 5 f b v i n 2 p a c k i n g a : t a p i n g x x c : s o t - 2 3 - 6 l b l a n k : t u b e p a c k a g e t y p e a x 3 8 2 1 r w w : 0 1 ~ 2 6 ( a ~ z ) 2 7 ~ 5 2 ( a ~ z ) i d c o d e : i n t e r n a l y y x w a x 3 8 2 1 y e a r : a = 2 0 1 0 1 = 2 0 1 1 2 = 2 0 1 2 : : 9 = 2 0 1 9
3 / 9 axelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 may . 0 8 , 20 1 3 ax38 2 1 ? a bsolute maximum ratings (at t a =25 c ) characteristics symbol rating unit input voltage v in C 0.3 to + 1 3 v switch node voltage v sw - 1v to v in +0.3v v boost voltage v bs v sw C 0.3 to v sw + 6 v all other pins C 0.3 to +6 v lead temperature 260 c storage temperature C 65 to +150 c junction temperature t j 150 c output voltage v out 0. 6 to 1 1 v ambient op erating temperature C 40 to +85 c thermal resistance from junction to case jc 180 c/w thermal resistance from junction to ambient ja 250 c/w note : ja is measured with the pcb copper area of approximately 1 in 2 (multi - layer). ? e lectrical c haracteri stics (v in = 12v, t a = +25c, unless otherwise noted.) characteristics symbol conditions min typ max units operating voltage v in 4. 5 - 1 3 v shutdown supply current i sd - 1 - a shutdown current operation v fb =0.6v - 0.5 0.7 ma feedback voltage v fb 4 . 5v v in 13 v 0. 58 0. 6 0. 62 v line regulation v out /v out v cc =5v~ 1 1 v - 0.06 - v load regulation i out = 0 ~ 1.6a - 2 - +2 % high - side switch on resistance ( note ) r ds(on)1 - 10 0 - m low - side switch on resistance ( note ) r ds(on)2 - 10 0 - m high - side switch leakage current v sw = 0v - - 10 a switch current limit 2 - - a oscillation frequency f osc1 - 600 - k hz short circuit oscillation frequency f osc2 v fb = 0v - 1 0 0 - khz maximum duty cycle d max v fb = 0.4 v - 90 - % en high - level input voltage v en_h 2 .5 - - v en low - level input voltage v en_l - - 0. 6 v en shutdown threshold voltage hyster i sis - 1 10 - mv thermal shutdown t sd - 1 5 0 - c thermal shutdown hysterisis t sh - 20 - c note : guaranteed by design.
4 / 9 axelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 may . 0 8 , 20 1 3 ax38 2 1 ? application circuit v out =v fb ( ) , v fb = 0. 6 v , r2 suggest 10k~30 k table recommended component selection v out r h r l l c out 5 110k 15k 4.7uh 22uf*2 3.3 54k 12k 4.7uh 22uf*2 2.5 47k 15k 4.7uh 22uf*2 1.8 60k 30k 4.7uh 22uf*2 1.5 45k 30k 2.2uh 22uf*2 ? f unction d escriptions the AX3821 is a synchronous rectifi ed, current - mode, step - down regulator. it r egulates input voltages from 4. 5v to 1 3 v down to an output voltage as low as 0. 6 v, and supplies up to 1.6 a of load current. the AX3821 uses current - mode control to regulate the output voltage. the output voltage i s measured at fb through a resistive voltage divider and amplified through the internal tr an conductance error amplifier. the converter uses internal n - channel mosfet switches to step - down the input voltage to the regulated output voltage. since the high s ide mosfet requires a gate voltage greater than the input voltage, a boost capacitor connected between sw and bs is needed to drive the high side gate. the boost capacitor is charged from the internal 5v rail when sw is low. g n d v i n b s f b s w v i n v o u t 3 . 3 v 1 a c 1 1 0 f / 2 5 v c e r a m i c c 2 2 2 f / 6 . 3 v 2 c e r a m i c l 1 4 . 7 h c 3 1 0 n f r 2 1 2 k ? / 1 % r 1 5 4 k ? / 1 % c 4 ( o p t i o n ) r 3 1 0 0 k e n a x 3 8 2 1 d 1 ( o p t i o n ) 4 . 5 v t o 1 3 v 2 r 1 r + 1
5 / 9 axelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 may . 0 8 , 20 1 3 ax38 2 1 ? t ypical character istics output voltage = 3.3v output voltage = 5v
6 / 9 axelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 may . 0 8 , 20 1 3 ax38 2 1 ? t ypical characteristics (c ountinous ) en able on waveform en able on waveform v in =12v, v out =3.3v, i load =no load v in =12v, v out =3.3v, i load =1.6a en able off waveform en able off waveform v in =12v, v out =3.3v, i load =no load v in =12v, v out =3.3v, i load =1.6a load transient waveform v in =12v, v out =3.3v, i out =0.5a~1.6a
7 / 9 axelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 may . 0 8 , 20 1 3 ax38 2 1 ? application information component selection setting the output voltage the output voltage is set using a resistive voltage divider from the output voltage to fb pin. the voltage divider divides the output voltage down to the feedback voltage by the ratio: v fb = v out where vfb is the feedback voltage and v out is the output voltage. thus the output voltage is: v out = 0. 6 r2 can be as high as 100k, but a typical value is 10k. using the typical value for r2, r1 is determined by: r1= 20 (v out 0. 6 ) (k ) for example, for a 3.3v output volt age, r2 is 12 k, and r1 is 54 k. 2 1 2 r r r ? 2 2 1 r r r ?
8 / 9 axelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 may . 0 8 , 20 1 3 ax38 2 1 layout guidance when laying out the pc board, the following suggestions should be taken to ensure proper operation of the AX3821 . these items are also illustrated graphically in below . 1. the po wer traces, including the gnd trace, the sw trace and the v in trace should be kept short, direct and wide to allow large current flow. put enough multiply - layer pads when they need to change the trace layer. 2. connect the input capacitor c1 to the v in pin a s closely as possible to get good power filter effect. 3. keep the switching node, sw, away from the sensitive fb node. 4. do not trace signal line under inductor. sot - 23 - 6 l layout guide b s g n d f b s w c 1 v i n v o u t c 2 r 1 r 2 s w s h o u l d b e c o n n e c t e d t o i n d u c t o r b y w i d e a n d s h o r t t r a c e , k e e p s e n s i t i v e c o m p o n e n t s a w a y f r o m t h i s t r a c e c 4 c 2 ' s g r o u n d m u s t b e a s c l o s e r t o i c ' s g n d p i n a s p o s s i b l e c 1 ' s g r o u n d m u s t b e a s c l o s e r t o i c ' s g n d p i n a s p o s s i b l e c 4 , r 1 a n d r 2 m u s t b e a s c l o s e r t o i c ' s f b p i n a s p o s s i b l e a x 3 8 2 1 6 c 3 l 1 v i n v i n 1 2 3 4 5 e n r 3
9 / 9 axelite confidential materials, do not copy or distribute without written consent . rev. 1. 2 may . 0 8 , 20 1 3 ax38 2 1 ? p ackage o utlines symbol dimensions in millimeters dimensions in inches min. nom. max. min. nom. max. a - - 1.45 - - 0.057 a1 0.00 - 0.15 0 0.003 0.006 a2 0.90 1.10 1.30 0.035 0.043 0.051 b 0.30 0.40 0.50 0.012 0.016 0.020 c 0.08 - 0.22 0.003 0.006 0.009 d 2.70 2.90 3.10 0.106 0.114 0.122 e1 1.40 1.60 1.80 0.055 0.063 0.071 e 2.60 2.80 3.00 0.102 0.110 0.118 l 0.30 0.45 0.60 0.012 0.018 0.024 l1 0.50 0.60 0.70 0.020 0.024 0.028 e1 1.9 bsc 0.075 bsc e 0.95 bsc 0.037 bsc 0 o 4 o 8 o 0 o 4 o 8 o jedec outline: mo - 178 ab l e 1 e 1 e d a 2 a 1 b a detal a l 1 e gauge plane c detal a
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