general description the AS5422A is a wide input range, high-efficiency, dc- dc step-down switching regulator, capable of delivering up to 2a of output current. current mode pwm control allows the use of small external components, such as ceramic input and output caps, as well as small inductors, while still providing low output ripples. on top of the integrated internal synchronous rectifier that eliminates external schottky diode, AS5422A also employs a proprietary control scheme that switches the device into a power save mode during light load, thereby extending the range of hi gh efficiency operation. therefore, AS5422A is a much superior solution in comparison to other competitions in terms of efficiency and cost. cycle-by-cycle current limit provides output short-circuit protection and an input ovp function guards AS5422A against possible input voltage surge. overall, AS5422A is a highly efficient and robust solution for dc-dc step-down applications that requires wide input ranges. AS5422A is housed in a sop8 package. features ? wide input operating range from 4.5v to 18v ? high efficiency: up to 90%at light load up to 95% at heavy load ? capable of delivering 2a ? input ovp at 20v ? no external schottky diode needed ? current mode control ? 0.923v reference for low output voltages ? logic control shutdown ? thermal shutdown and uvlo applications ? lcd tvs ? notebook computer ? constant current source ? led drivers ? fpga power supplies typical application figure1. typical application circuit AS5422Aver1 .0 1 http://www.a1semi.com a1semi 2a, 18v high efficiency electronics ltd synchronous step-down converter AS5422A a1 a1 a1
package configuration order information pin description absolute maximum ratings (note: exceeding these limits may damage the device. exposure to absolute maximum rating conditions for long periods may affect device reliability.) part number package packing remark AS5422Ad/tr-lf sop 8 tape & reel mpq=2.5k pb free pin# name description 1 bst bootstrap pin. connect a 10nf capacitor from this pin to sw 2 in supply voltage. bypass with a 22 f ceramic capacitor to gnd 3 sw inductor connection. connect an inductor between sw and the regulator output. 4 gnd ground 5 fb feedback input. connect an external resistor divider from the output to fb and gnd to set v out 6 comp regulator compensation. connect series rc network to gnd. 7 en enable pin for the ic. drive this pin to high to enable the part, low to disable. 8 ss soft start pin. connect a 0.1 uf capacitor from this pin to gnd parameter value max input voltage -0.3v to 20v sw, en voltage -0.3v to vin+0.3v bst voltage C 0.3v to sw+6v fb voltage C 0.3v to 6v sw to ground current internally limited operating temperature range C 40c to 85c storage temperature range C 55c to 150c AS5422Aver1 .0 2 http://www.a1semi.com a1semi 2a, 18v high efficiency electronics ltd synchronous step-down converter AS5422A a1 a1 a1
electrical characteristics (vin = 12v, unless otherwise specified. typical values are at ta = 25 o c) parameter test conditions min typ max units input voltage range 5 18 v input uvlo rising, hysteresis=100mv 4.75 v input over voltage lockout 18.5 20 22 v input supply current v fb =0.85v 1 ma input shutdown current 6 a fb feedback voltage 0.904 0.923 0.942 v fb input current 0.01 a error amp transconductance 800 s current sense transresistance 0.2 switching frequency 340 khz high side switch on resistance i sw =200ma 130 m low side switch on resistance i sw =200ma 110 m high side switch current limit 25 3 a sw leakage current v in =12v,v sw =0 or 12v, en= gnd 10 a en input current 1 a en input low voltage 1 1.5 3 v thermal shutdown hysteresis=40c 150 c AS5422Aver1 .0 3 http://www.a1semi.com a1semi 2a, 18v high efficiency electronics ltd synchronous step-down converter AS5422A a1 a1 a1
typical performance characteristics typical values are at ta = 25 c unless otherwise speciffied. 30 40 50 60 70 80 90 100 20 ? (%) v 200 i out (a ) efficiency v v out =3.3v 2000 ) v s i out vin= 5v vin =12v vin= 4.5v 30 40 50 60 70 80 90 100 20 ? (%) v o 200 i out (a) efficiency v s o u t =5v 2000 s i out vin =12v 0 50 100 150 200 250 300 350 400 450 -40 frequency (khz) 0 4 0 te m p e r a t u r e freq u e ncy v 80 e ( o c) s temp vin=4.5v vin=12v 1 1.02 1.04 1.06 1.08 1.1 1.12 1.14 1.16 1.18 1.2 0 i q (ma) v in v out i sw 51 0 v in ( v i q vs v in start-u p waveform 100ms/ 15 20 v ) iq (ma ) with slow vin div 3.23 3.23 5 3.24 3.24 5 3.25 3.255 3.26 3.26 5 3.27 0 v out (v) i sw v in v out 0.5 1 i out ( a v out vs i out start-u p waveform 100ms/ d 1.5 2 ) vin=4.5v vin=5v vin=12v with fast vin d iv 3.2 3.21 3.22 3.23 3.24 3.25 3.26 3.27 3.28 3.29 3.3 4.5 v out (v) v out i sw 200mv/div 500ma/div 9. 5 v in (v) v out vs v in load transient r 200 ? s/d 14.5 19.5 iou t=0ma iout=300ma es p onse i v 0 AS5422Aver1 .0 4 http://www.a1semi.com a1semi 2a, 18v high efficiency electronics ltd synchronous step-down converter AS5422A a1 a1 a1
functional decriptions loop operation the AS5422A is a wide input range, high-efficiency, dc-to-dc step-down switching regulator, capable of delivering up to 2a of output current, integrated with a 110m synchronous mosfet, eliminating the need for external diode. it uses a pwm current-mode control scheme. an error amplifier integrates error between the fb signal and the internal reference voltage. the output of the integrator is then compared to the sum of a current- sense signal and the slope compensation ramp. this operation generates a pwm signal that modulates the duty cycle of the power mosfets to achieve regulation for output voltage. current limit there is a cycle-by-cycle current limit on the high-side mosfet of 3a(typ). when the current flowing out of sw exceeds this limit, the high-side mosfet turns off and th e synchronous rectifier turns on. unlike the traditional method of current limiting by limiting the voltage at the compensation pin, which usually has large variation due to duty cycle variance, this type of peak current limiti ng scheme provides a relatively more accurate limit for output current, thereby lowering the requirements for system design. light load operation traditionally, a fixed constant frequency pwm dc-dc regulator always switches even when the output load is small. when energy is shuffling back and forth through the power mosfets, power is lost due to the finite rdsons of the mosfets and parasitic capacitances. at light load, this loss is prominent and efficiency is therefore very low. AS5422A employs a proprietary control scheme that improves efficiency in this situation by enabling the device into a power save mode during light load, thereby extending the range of high efficiency operation. application infornation components selection v out (v) c out ( f) l h) 8 22x2 22 5 22x2 15 3.3 22x2 10 2.5 22x2 6.8 1.8 22x2 4.7 1.2 22x2 3.3 AS5422Aver1 .0 5 http://www.a1semi.com a1semi 2a, 18v high efficiency electronics ltd synchronous step-down converter AS5422A a1 a1 a1
package information sop8 symbol min nom max a 1.35 1.55 1.75 a1 0.10 0.15 0.25 a2 1.25 1.40 1.65 a3 0.50 0.60 0.70 b 0.38 - 0.51 b1 0.37 0.42 0.47 c 0.17 0.20 0.23 c1 0.17 - 0.25 d 4.80 4.90 5.00 e 5.80 6.00 6.20 e1 3.80 3.90 4.00 e 1.27bsc l 0.45 0.60 0.80 l1 1.04ref l2 0.25bsc r 0.07 - - r1 0.07 - - h 0.30 0.40 0.50 0 - 8 1 15 17 19 2 11 13 15 3 15 17 19 4 11 13 15 AS5422Aver1 .0 6 http://www.a1semi.com a1 i s r e g i st er ed tr ademar ks o f a1 sem i electronics ltd a1semi a 1 s e m i re se r v e s th e r i g h t to m a ke ch a n g e s w i th out fu r t h e r n o t i ce t o an y pr oducts her ei n. a1semi makes no w a r r a nt y, r epr es ent ation or guar ant ee r egar d i ng t he suit abi l ity of it s products f o r any par t icular pur pos e , nor d o e s a1semi as s u me any li abi l ity arisi ng ou t o f the appli c ation or u s e o f an y product or c i rcu it, and s pec i fically di sc l a im s a n y a n d a l l l i a b il i t y , in c l u d in g w i th o u t l i m i ta t i o n sp e c ia l , c o n s e q u e n t ia l o r in c i de n ta l da m a g e s . . a1semi 2a, 18v high efficiency electronics ltd synchronous step-down converter AS5422A a1 a1 a1
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