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1 / 16 axelite confidential materials, do not copy or distribute without written consent . rev 1. 1 apr . 28 , 20 1 4 a x 3 7 0 2 1.2mhz , 2a, vfb=0.6v synchronous step - down converter ? general description AX3702 is a high efficiency monolithic synchronous buck regulator using a constant frequency, current mode architecture. the device is available in an adjustable version . supply curr ent with no load is about 2 00 ua and drops to <1ua in shutdown. the 2.5v to 6 v input voltage range makes AX3702 ideally suited for single li - ion, two to four aa battery - powered applications. 100% duty cycle provides low dropout operation, extending battery life in portable systems. pwm pulse skipping mode operation provides very low output ripple voltage for noise sensitive applications. switching frequency is internally set at 1.2m hz, allowing the use of small surface mount inductors and capacitors. the int ernal synchronous switch increases efficiency and decreases need of an external schottky diode. low output voltages are easily supported with the 0.6v feedback reference voltage. AX3702 is available in small sot - 23 - 5l, sot - 23 - 6 l, t dfn - 10 l (3*3) , and sop - 8l - ep package s . ? features - 2.5v to 6 v input voltage range - output voltage from 0.6v to v in - high efficiency: up to 9 5 % - 1.2m hz constant frequency operation - 2 a output current - quiescent current: 2 00 ua (input < 4.2v) - no schottky diode required - 100% duty cycle in dr opout - 0.6v reference allows low output voltages - current mode operation for excellent line and load transient response - current limit, enable function - short circuit protect (scp) - 1 a shutdown current - sot - 23 - 5l , sot - 23 - 6 l, t dfn - 10 l (3*3) , and sop - 8l - ep pb - free package s
2 / 16 axelite confidential materials, do not copy or distribute without written consent . rev 1. 1 apr . 28 , 20 1 4 a x 3 7 0 2 ? b lock d iagram
3 / 16 axelite confidential materials, do not copy or distribute without written consent . rev 1. 1 apr . 28 , 20 1 4 a x 3 7 0 2 ? pin assignment the package s of AX3702 are sot - 23 - 5l, sot - 23 - 6 l, t dfn - 10 l (3*3) , and sop - 8l - ep the pin assig nment is given by : sot - 23 - 5l (a type ) sot - 23 - 5l (b type) sot - 23 - 6l name description en enable pin h pvin power supply input pin svin signal supply input pin sgnd signal ground pin fb output feedback pin sw switch output pin. connect external inductor here. minimize trace area at this pin to reduce emi. pgnd power ground pin gnd ground pin vin power supply input p in nc no connect t d f n - 1 0 l ( 3 * 3 ) e n s w 1 f b 1 0 2 3 4 5 6 7 8 9 p v i n n c n c s g n d s w p g n d p g n d a x 3 7 0 2 ( g n d ) ( t o p v i e w ) 1 2 3 4 8 7 6 5 e n n c s o p - 8 l - e p a x 3 7 0 2 s g n d p v i n p g n d s w f b n c ( t o p v i e w ) e n g n d s w v i n f b 1 2 3 4 s o t - 2 3 - 5 l 5 ( t o p v i e w ) v i n g n d e n f b s w 1 2 3 4 s o t - 2 3 - 5 l 5 ( t o p v i e w ) e n g n d s w v i n f b 1 2 3 4 5 s o t - 2 3 - 6 l 6 g n d
4 / 16 axelite confidential materials, do not copy or distribute without written consent . rev 1. 1 apr . 28 , 20 1 4 a x 3 7 0 2 ? order/marking information order information top marking ( t dfn - 10l) top marking (sot - 23 - 5l) to p marking ( sot - 23 - 6 l) top marking ( sop - 8 l - ep ) p a c k a g e t y p e a x 3 7 0 2 p a c k i n g a : t a p i n g x x x x b : s o t - 2 3 - 5 l e s : s o p - 8 l - e p x p i n t y p e a : a t y p e b : b t y p e ( f o r s o t - 2 3 - 5 l o n l y ) b l a n k : b a g c : s o t - 2 3 - 6 l j 1 0 : t d f n - 1 0 l ( 3 x 3 ) 3 p a r t n u m b e r i d c o d e : i n t e r n a l w w : 0 1 ~ 5 2 y e a r : 1 0 = 2 0 1 0 1 1 = 2 0 1 1 y y w w x 7 0 2 : : 1 9 = 2 0 1 9 x w w : 0 1 ~ 2 6 ( a ~ z ) 2 7 ~ 5 2 ( a ~ z ) y e a r : a = 2 0 1 0 1 = 2 0 1 1 2 = 2 0 1 2 i d c o d e : i n t e r n a l z q : a x 3 7 0 2 ( a t y p e ) x y w x : : 9 = 2 0 1 9 z r : a x 3 7 0 2 ( b t y p e ) z a x 3 7 0 2 w w : 0 1 ~ 2 6 ( a ~ z ) 2 7 ~ 5 2 ( a ~ z ) y e a r : a = 2 0 1 0 1 = 2 0 1 1 i d c o d e : i n t e r n a l g y w x : : 9 = 2 0 1 9 l o g o y a x 3 p a r t n u m b e r i d c o d e : i n t e r n a l w w : 0 1 ~ 5 2 y e a r : 1 0 = 2 0 1 0 1 1 = 2 0 1 1 7 0 2 y w w x : : 1 9 = 2 0 1 9
5 / 16 axelite confidential materials, do not copy or distribute without written consent . rev 1. 1 apr . 28 , 20 1 4 a x 3 7 0 2 ? a bsolute m aximum r atings (at t a = 25 c ) characteristics symbol rating unit v in pin voltage v in v ss - 0.3 to v ss + 8 v 2ms p ulse width vin tolerance v pluse v ss - 0.3 to v ss + 10 v feedback pin voltage v fb v ss - 0.3 to v cc + 0.3 v en pin voltage v en v ss - 0.3 to v cc + 0.3 v switch pin voltage v sw v ss - 0.3 to v cc + 0.3 v peak sw sink and source current i psw 2.4 a power dissip ation pd ( t j - t a ) / ja mw storage temperature range t st - 40 to +150 c operating temperature range t op - 4 0 to + 8 5 c junction temperature t j +125 c esd hbm hbm 2 kv esd mm mm 200 v thermal resistance from junction to case t d fn - 10 l (3x3) jc 7.8 c/w sot - 23 - 6 l 13 0 sot - 23 - 5l 13 0 so p - 8l - ep 15 thermal resistance from junction to ambient t d fn - 10 l (3x3) ja 105 c/w sot - 23 - 6 l 250 sot - 23 - 5l 250 so p - 8l - ep 75 note: ja is measured with the pcb copper area of approximately 1 in 2 (multi - layer). that need connect to gnd pin of the AX3702 .
6 / 16 axelite confidential materials, do not copy or distribute without written consent . rev 1. 1 apr . 28 , 20 1 4 a x 3 7 0 2 ? electrical characteristics (v in = v en =3. 6 v , t a =25c, unless otherwise specified) (not e ) characteristics symbol conditions min typ max units input voltage range v in 2.5 - 7.5 v under voltage l ock out threshold v uvlo v in rising 1.8 2 . 1 2.3 v hysteresis 100 250 400 mv feedback voltage v fb v fb = 0.6 v 0.5880 0.6000 0.6120 v feedback bias current i fb v fb =0.65v - 30 - + 30 na quiescent current i cc v fb = 1 v - 200 4 00 ua shutdown supply current i sd v en =0v - 0.1 1 ua switching current limit i limit i out =2a 3.2 3.5 3.7 a line regulation v out /v out v in = 2.5v~5.5v - 0.04 0.4 %/v load regulation v out /v out i out = 0.01 to 2 a - 0.5 0.6 % oscillation frequency f osc sw pin 1. 0 1. 2 1.4 mhz r ds(on) of p - ch mosfet r dson i out = 2 a - 0. 1 4 0. 17 r ds(on) of n - ch mosfet r dson i out = 2 a - 0. 10 0. 15 efficiency effi v in =5v, v out =3.3v, i out =0.5a 92 - - % en pin logic input threshold voltage v enl - - 0.6 v v enh 1.2 - - en pin input current i en - 0.1 1 ua s oft - start interval t ss 1.2 ms note: 100% production test at +25c. specifications over the temperature range are guaranteed by design and char acterization. ? a pplication c ircuit v i n e n g n d s w f b c 1 4 . 7 u f r 1 6 0 k r 2 3 0 k c 3 3 3 0 p f ( o p t i o n ) c 2 2 2 u f v o u t = 1 . 8 v l 1 2 . 2 u h v i n
7 / 16 axelite confidential materials, do not copy or distribute without written consent . rev 1. 1 apr . 28 , 20 1 4 a x 3 7 0 2 ? f unction d escriptions operation ax370 2 is a m onolithic switching mode step - down dc - dc converter. it utilizes internal mosfets to achieve high efficiency and can generate very low output voltage by using internal reference at 0.6v. it operates at a fixed switching frequency, and uses the slope compensated current mode architecture. this step - down dc - dc converter suppli es 2a output current at v out = 1.8v with input voltage range from 2.5v to 6v. current mode pwm control slope compensated current mode pwm control provides stable switching an d cycle - by - cycle current limit for excellent load and line responses and protection of the internal main switch (p - ch mosfet) and synchronous rectifier (n - ch mosfet). during normal operation, the internal p - ch mosfet is turned on for a certain time to ramp the inductor current at each rising edge of the internal oscillator, and switched off when the peak inductor current is above the error voltage. the current comparator, i comp, limits the peak inductor current. when the main switch is off, the synchronou s rectifier will be turned on immediately and stay on until either the inductor current starts to reverse, as indicated by the current reversal comparator, i zero , or the beginning of the next clock cycle. the ovdet comparator controls output transient over shoots by turning the main switch off and keeping it off until the fault is no longer present. idle mode operation at very light loads, AX3702 automatically enters pulse skipping mode. in the pulse skipping mode, the inductor current may reach zero or reverse on each pulse. the pwm control loop will automatically skip pulses to maintain output regulation. the bottom mosfet is turned off by the current reversal comparator, i zero, and the switch voltage will ring. this is discontinuous mode operation, and is normal behavior for the switching regulator. maximum load current AX3702 will operate with input supply voltage as low as 2.5v, however, the maximum load current decreases at lower input due to large ir drop on the main switch and synchronous rectifier. the slope compensation signal reduces the peak inductor current as a function of the duty cycle to prevent sub - harmonic oscillations at duty cycles greater than 50%. conversely the current limit increases as the duty cycle decreases.
8 / 16 axelite confidential materials, do not copy or distribute without written consent . rev 1. 1 apr . 28 , 20 1 4 a x 3 7 0 2 ? a pp lication i nformation setting the output voltage application circuit item shows the basic application circuit with AX3702 adjustable output version. the external resistor sets the output voltage according to the following equation: table 1 resistor select for output voltage setting v out r2 r1 1.2v 30k 30k 1.5v 30k 45k 1.8v 30k 60k 2.5v 30k 95k 3.3v 30k 135k inductor selection for most designs, the AX3702 operates with inductors of 1h to 4.7h. low inductance values are physically smaller but require faster switching, which results in some efficiency loss. the inductor value can be derived from the following equation: where is inductor ripple current. large value inductors lower ripple current and small value inductors result in high ripple currents. choose inductor ripple current approximately 35% of the maximum load current . table 2 inductor select for output voltage setting (v cc = 5 v) v out 1.2v 1.5v 1.8v 2.5v 3.3v inductor 2. 2 uh 2. 2 uh 2. 2 uh 2.2 u h 2.2uh note: part type mh or m (www.we - online.com) for output voltages above 2.0v, when light - load efficiency is important, the minimum recommended inductor is 2.2h. for optimum voltage - positioning load transients, choose an inductor with dc series res istance in the 50m? to 150m? range. for higher efficiency at heavy loads (above 200ma), or minimal load regulation (but some transient overshoot), the resistance should be kept below 100m?. the dc current rating of the inductor should be at least equal to the maximum load current plus half the ripple curr ent to prevent core saturatio n . ) 2 r 1 r + 1 ( v 6 . 0 = v out ? ? f i v v v v l osc l in out in out ? ? ? ? ? ?
9 / 16 axelite confidential materials, do not copy or distribute without written consent . rev 1. 1 apr . 28 , 20 1 4 a x 3 7 0 2 input capacitor selection the input capacitor reduces the surge current drawn from the input and switching noise from the device. the input capacitor impedance at the swi tching frequency shall be less than input source impedance to prevent high frequency switching current passing to the input. a low esr input capacitor sized for maximum rms current must be used. ceramic capacitors with x5r or x7r dielectrics are highly rec ommended because of their low esr and small temperature coefficients. a 4.7f ceramic capacitor for most applications is sufficient. output capacitor selection the output capacitor is required to keep the output voltage ripple small and to ensure regul ation loop stability. the output capacitor must have low impedance at the switching frequency. ceramic capacitors with x5r or x7r dielectrics are recommended due to their low esr and high ripple current. compensation capacitor selection the compensation capacitors for increasing phase margin provide additi onal stability. it is required and more than 22pf , refer to demo board schematic, the optimum values for c 3 (option) is 330 p f .
10 / 16 axelite confidential materials, do not copy or distribute without written consent . rev 1. 1 apr . 28 , 20 1 4 a x 3 7 0 2 pcb layout recommendations when laying out the pr inted circuit board, the following checking should be used to ensure proper operation of the ax370 2 . check the following in your layout: 1. the power traces, consisting of the gnd trace, the sw trace and the v in trace should be kept short, direct and wide. 2. does the (+) plates of cin connect to v in as closely as possible. this capacitor provides the ac current to the internal power mosfets. 3. keep the switching node sw away from the sensitive v out node. 4. keep the ( - ) plates of c in and c out as close as possible. AX3702 1 2 3 4 5 vin fb en gnd sw c1 r2 r1 c2 c3 l1 net vin net vin vin vout gnd gnd AX3702 1 2 3 nc pgnd vin pgnd sw c1 r2 r1 c2 c3 l1 vin vout gnd gnd 10 9 8 en 4 5 fb nc sw sgnd 7 6 AX3702 1 2 3 nc pgnd vin sw nc c1 r2 r1 c2 c3 l1 vin vout gnd gnd 8 7 6 en 4 sgnd fb 5
11 / 16 axelite confidential materials, do not copy or distribute without written consent . rev 1. 1 apr . 28 , 20 1 4 a x 3 7 0 2 ? typical characteristics 5 v ~1 0 v v in overshoot test, no load, 1.8v out 100ma~ 2 a load transient test, 5v in to 1.8v out , c3=330pf no load start up and shutdo wn, 5v in to 1.8v out 2 a load start up and shutdown, 5v in to 1.8v out output short circuit test, 5v in to 1.8v out 150 c thermal shutdown, 5v in to 1.8v out , 1a load
12 / 16 axelite confidential materials, do not copy or distribute without written consent . rev 1. 1 apr . 28 , 20 1 4 a x 3 7 0 2 ? typical characteristics (continuous) no load switching waveform, 5v in to 1.8v out 2 a load switching waveform, 5v in to 1.8v out i out vs efficiency, v in =5 v
13 / 16 axelite confidential materials, do not copy or distribute without written consent . rev 1. 1 apr . 28 , 20 1 4 a x 3 7 0 2 ? p ackage o utlines (1) t dfn - 10 l (3*3mm 2 ) symbol dimensions in millimeters dimensions in inches min. nom. max. min. nom. max. a 0.7 0.75 0.8 0.028 0.03 0.031 a1 0 0.02 0.05 0 0.001 0.002 a3 0.20 ref. 0.008 ref. b 0.18 0.25 0.3 0.007 0.01 0.012 d 2.9 3 3.1 0.114 0.118 0.122 d2 2.2 2.4 2.5 0.087 0.094 0.098 e 2.9 3 3.1 0.114 0.118 0.122 e2 1.5 1.6 1.7 0. 059 0.063 0.07 e 0.50 bsc. 0.020 bsc. l 0.3 0.4 0.5 0.012 0.016 0.02 e d a a 1 a 3 d 2 e e 2 l ( t o p v i e w ) ( b o t t o m v i e w ) b p i n 1 s e a t i n g p l a n e ( s i d e v i e w )
14 / 16 axelite confidential materials, do not copy or distribute without written consent . rev 1. 1 apr . 28 , 20 1 4 a x 3 7 0 2 (2) sot - 23 - 6 l symbol dimensions in millimeters dimensions in inches min. nom. max. min. nom. max. a - - 1.45 - - 0.057 a1 0 - 0.15 0 0.003 0.006 a 2 0.9 1.1 1.3 0.035 0.043 0.051 b 0.3 0.4 0.5 0.012 0.016 0.02 c 0.08 - 0.22 0.003 0.006 0.009 d 2.7 2.9 3.1 0.106 0.114 0.122 e1 1.4 1.6 1.8 0.055 0.063 0.071 e 2.6 2.8 3 0.102 0.11 0.118 l 0.3 0.45 0.6 0.012 0.018 0.024 l1 0.5 0.6 0.7 0.02 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 d e t a l a l 1 e g a u g e p l a n e c d e t a l a
15 / 16 axelite confidential materials, do not copy or distribute without written consent . rev 1. 1 apr . 28 , 20 1 4 a x 3 7 0 2 (3) sop - 8l - ep symbol dimensions in millimeters dimensions in inches min. nom. max. min. nom. max. a - - 1.75 - - 0.069 a1 0 - 0.15 0 - 0.06 a2 1.25 - - 0.049 - - c 0.1 0. 2 0.25 0.0075 0.008 0.01 d 4.7 4.9 5.1 0.185 0.193 0.2 e 3.7 3.9 4.1 0.146 0.154 0.161 h 5.8 6 6.2 0.228 0.236 0.244 l 0.4 - 1.27 0.015 - 0.05 b 0.31 0.41 0.51 0.012 0.016 0.02 e 1.27 bsc 0.050 bsc y - - 0.1 - - 0.004 x - 2.34 - - 0.092 - y - 2.34 - - 0.092 - 0 o - 8 o 0 o - 8 o mold flash shall not exceed 0.25mm per side jedec outline: ms - 012 ba d e t a i l a l h e a a 2 a 1 e d 7 ( 4 x ) b y c d e t a i l a y x e x p o s e p a d
16 / 16 axelite confidential materials, do not copy or distribute without written consent . rev 1. 1 apr . 28 , 20 1 4 a x 3 7 0 2 (4) sot - 23 - 5l symbol dimensions in millimeters dimensions in inches min. nom. max. min. nom. max. a - - 1.45 - - 0.057 a1 0 0. 08 0.15 0 0.003 0.006 a2 0.9 1.1 1.3 0.035 0.043 0.051 b 0.3 0.4 0.5 0.012 0.016 0.02 c 0.08 0.15 0.22 0.003 0.006 0.009 d 2.7 2.9 3.1 0.106 0.114 0.122 e1 1.4 1.6 1.8 0.055 0.063 0.071 e 2.6 2.8 3 0.102 0.11 0.118 l 0.3 0.45 0.6 0.012 0.018 0.024 l1 0.5 0.6 0.7 0.02 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 1 5 o 10 o 15 o 5 o 10 o 15 o 2 5 o 10 o 15 o 5 o 10 o 15 o jedec outline: mo - 178 aa l e 1 e 1 e d a 2 a 1 b ( 5 x ) a d e t a l a l 1 1 ( 4 x ) 2 ( 4 x ) e g a u g e p l a n e c d e t a l a

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