AIC2322 2a 550k/1.1mhz synchronous pwm step-down converter analog integrations corporation si-soft research center ds-2322g-03 20121212 3a1, no.1, li-hsin rd. i , science park , hsinchu 300, taiwan , r.o.c. tel: 886-3-5772500 fax: 886-3-5772510 www. analog.com.tw 1 ? features ? 2.5v to 6v input voltage range ? adjustable output voltage from 0.8v to vin ? 2.0a guaranteed output current ? 94% efficiency at heavy load (vin=5v, vout=3.3v, iout=2.0a) ? low r ds(on) internal switches: 110m ? ? no schottky diode required ? 100% duty cycle in low dropout operation ? fixed 550k/1.1mhz operating frequency ? optional soft-start internal fixed 1ms soft- start ? applications ? lcd tv ? multi-function peripheral ? cellular phones ? cpu i/o supplies ? pdas and handy-terminals ? battery-operated devices (1 li-ion or 3 nimh/ nicd). ? description the AIC2322 is a low-noise, pulse-width- modulated (pwm), dc-dc step-down converter. the device features an internal synchronous rectifier for high efficiency; it requires no external schottky diode. shutdown mode places the device in standby, reducing supply current to under 2a. other features of the AIC2322 include high efficiency for all load range, low dropout voltage, short circuit protection, and over temperature protection. ? applications circuit vin 8 vcc 1 en 5 pgnd 6 gnd 3 ref 2 fb 4 lx 7 aic2323 10 ? r1 50k ? r2 16k ? r3 2.2uh l1 0.1uf c4 22uf c3 10uf c1 0.1uf c2 vout vin on off 5v 3.3v typical application circuit AIC2322
AIC2322 2 ? pin configuration packing type tr: tape & reel tb: tube package type s8: sop-8 g: green package a: 1.1mhz b: 550k hz example: AIC2322-ags8tr ? fixed 1.1mhz operating frequency with green sop-8 package and tape & reel packing type pin configuration pgnd vin lx en gnd ref fb vcc 1 3 4 2 8 6 5 7 so p - 8 top view aic232 2 -xxxxxx ? absolute maximum ratings supply input volatge, vcc, vin -0.3v to 6.5v lx pin switch voltage -0.3v to (vin + 0.3v) other i/o pin voltage -0.3v to (vcc + 0.3v) pgnd to gnd +/-0.3 v operating ambient temperature range t a -40? c to 85 ? c operating maximum junction temperature t j 150 ? c storage temperature range t stg -65? c to 150 ? c lead temperature (soldering 10 sec.) 260 ? c thermal resistance junction to case sop-8 40? c/w thermal resistance junction to ambient sop-8 1 60? c/w latch-up 200ma hbm (human body mode) 4kv (assume no ambient airflow, no heatsink) absolute maximum ratings are those values beyond which the life of a device may be impaired.
AIC2322 3 ? electrical characteristics (t a =25 ? c, v in =3.3v, unless otherwise specified.) (note1) parameter conditions symbol min typ max units input voltage range v in 2.5 6 v v cc rising v uvlo(r) 2.3 v under voltage lockout thresh- old v cc falling v uvlo(f) 2.1 v output adjustment range v out 0.8 v in v shutdown current v en = 0v i sd 1 2 ? a quiescent current i out = 0a, v fb = 1v no switching i q 550 ? a standby current i out = 0a, switching i sb 600 900 ? a feedback reference voltage v ref 0.784 0.8 0.816 v v out line regulation v in = 2.5v to 5.5v, i out =0a -2 2 % fb leakage current i fb 0.1 0.2 ? a en supply current i en 3.5 ? a en logic high 1.5 v cc v en logic low 0 0.5 v p-channel on-resistance v in = 3.3v r dsh(on) 110 m ? n-channel on-resistance v in = 3.3v r dsl(on) 80 m ? switch leakage current v en = 0v, v in = 5.5v 0.1 1 ? a peak inductor current i pk 2.6 3.4 a oscillator frequency (a version) f osca 920 1100 1280 khz oscillator frequency (b version) f oscb 468 550 632 khz maximum duty cycle d max 100 % thermal shutdown trip point t otp 150 c thermal shutdown hysteresis t otp_hys 25 c soft-start charge current i ss 4 ? a note 1: specifications are production tested at t a =25 ? c. specifications over the -40 ? c to 85 ? c operating tem- perature range are assured by design, characteriza tion and correlation with statistical quality con- trols (sqc).
AIC2322 4 ? typical performance characteristics (c1=10 f,c3=22 f,l1=2.2 h,t a =25 ,unless otherwise noted) fig. 1 efficiency vs load current fig. 2 efficiency vs load current fig. 3 switching waveform fig. 4 soft start waveform fig. 5 soft start waveform fig. 6 shoutdown waveform vin=vcc=3.3v,vout=1.8v,iload=1.5a vin=vcc=3.3v,vout=1.8v,iload=1.5a vin=vcc=3.3v,vout=0.8v,iload=1.5a ven vout ven out ripple ilx vlx vlx vout ven vin=2.5v vin=3.3v vin=4.2v vin=5.5v vin=4.2v vin=5v vin=5.5v (vcc=vin,vout=1.8v) (vcc=vin,vout=3.3v) vout
AIC2322 5 ? typical performance characteristics (continued) fig. 7 load transient response fig. 8 load transient response fig. 9 switching frequence vs input voltage fig. 10 output voltage deviation vs input voltage out ripple out ripple vin=vcc=5v,vout=2.5v,iload=0.5a to 1a vin=vcc=5v,vout=1.5v,iload=0.5a to 1a iload iload
AIC2322 6 ? block diagram functional block diagram of AIC2322 ? pin descriptions pin no. pin name pin function 1 vcc signal input supply. decouple this pin to g nd with a capacitor. normally vcc is equal to vin. 2 ref internal reference voltage. decouple this pin to gnd with a capacitor. 3 gnd signal ground. all small-signal component s and compensation components should connect to this ground, which in turn connects to pgnd at one point. 4 fb feedback pin. this pin receives the feedba ck voltage from a resistive divider connect across the output. 5 en enable pin. connect to logic high in nor mal operation. forcing this pin to gnd cause the device to be shutdown. 6 pgnd power ground. connect this pin to the negative terminal of c in and c out . 7 lx internal power mosfet switches ou tput. connect this pin to the inductor. 8 vin power input supply. decouple this pin to pgnd with a capacitor.
AIC2322 7 ? application information operation the AIC2322 is a low-noise step-down dc/dc converter with current-mode pwm control architecture. it features an internal synchronous rectifier, which eliminates the external schottky diode and increases efficiency. during normal operation, the AIC2322 can regulate its output voltage through a feedback control circuit, which is composed of an error amplifier; a current comparator and several control signal generators. by comparing the feedback voltage to the reference voltage of 0.8v, the error amplifier varies its output voltage. the output volt age of the error amplifier is compared with the summing signal of current sensing signal and slope compensation signal to determine the duty cycle of internal main power switch (p-channel mosfet). while the main power switch is turned on, the synchronous power switch (n-channel mosfet) will be turned off through anti-short-through block. similarly, when the main power switch is turned off, the synchronous power switch will be turned on until the inductor current starts to reverse or the beginning of the next switching cycle. current limitation the AIC2322 provides current limit function by using an internal sensing resistor. when the main power switch turns on, current follows through the internal sensing resistor. and current amplifier senses the voltage, which crosses the resistor, and amplifies it. while the sensed voltage gets higher than reference voltage, the current limitation function is activated. while the current limitation function is activated, the duty cycle will be reduced to limit the output power to protect the internal power switches. short circuit protection while the output is short ed to ground, the switching frequency of AIC2322 will be reduced to one fourth of the normal switching frequency. this lower switching frequency ensures the inductor current has more time to discharge, thereby pr eventing inductor current runaway. the switching frequency will automatically return to its designed value while short circuit condition is released. shutdown by connecting the en pin to gnd, the AIC2322 can be shut down to reduce the supply current to 2 ? a (typical). at this operation mode, the output voltage of step- down converter is equal to 0v. 100% duty cycle operation when the input voltage approac hes the output voltage, the AIC2322 smoothly transits to 100% duty cycle operation. this allows AIC2322 to regulate the output voltage until AIC2322 completely enters 100% duty cycle operation. in 100% dut y cycle mode, the output voltage is equal to the input voltage minus the voltage, which is the drop across the main power switch. the AIC2322 achieves 100% duty cycle operation by extending the turn-on time of the main power switch. if the summing signal of curr ent sensing signal and slope compensation signal does not reach the output voltage level of the error amplifier at the end of 90% switching period, the main power switch is continuously turned on and the oscillator remains off until the summing signal of current sensing signal and slope compensation signal reaches the output voltage level of the error amplifier. after the summing signal of current sensing signal and slope compensation signal reaches the output voltage leve l of the error amplifier, the main power switch is turned off and the synchronous power switch is turned on for a constant off time. at the end of the constant off time, the next switching cycle is begun. while the input voltage approaches the output voltage, the switching frequency decreases gradually to smoothly transit to 100% duty cycle operation.
AIC2322 8 if input voltage is very close to output voltage, the switching mode goes from pure pwm mode to 100% duty cycle operation. duri ng this transient state mentioned above, large output ripple voltage may appear on output terminal. components selection inductor the inductor selection depends on the current ripple of inductor, the input voltage and the output voltage. ? ? ? ? ? ? ? ? ? ?? ? in out l osc out v v if v l 1 accepting a large current ripple of inductor allows the use of a smaller inductance. however, higher current ripple of inductor can cause higher output ripple voltage and large core loss. by setting an acceptable current ripple of inductor, a suitable inductance can be obtained from above equation. in addition, it is important to ensure the inductor saturation current exceeds the peak value of inductor current in application to prevent core saturation. the peak value of inductor current can be calculated according to the following equation. ?? ? ? ? ? ? ? ? ? ? ?? ?? in out osc out out peak v v lf v ii 1 2 max input capacitor and output capacitor to prevent the high input voltage ripple and noise resulted from high frequency switching, the use of low esr ceramic capacitor for the maximum rms current is recommended. the approximated rms current of the input capacitor can be calculated according to the following equation . ?? 12 2 2 2 )( l in out inout maxout cinrms i v vvv ii ? ? ? ? ? the selection of output capacitor depends on the required output voltage ripple. the output voltage ripple can be expressed as: l out osc l out iesr cf i v ??? ?? ? ?? 8 for lower output voltage ripple, the use of low esr ceramic capacitor is recommended. the tantalum capacitor can also be used well, but its ers is larger than that of ceramic capacitor. when choosing the input and output ceramic capacitors, x5r and x7r types are recommended because they retain their capacitance over wider ranges of voltage and temperature than other types. output voltage programming by connecting a resistive divider r 2 and r 3, the output voltage of AIC2322 step-down converter can be set. v out can be calculated as: ? ? ? ? ? ? ? ? ??? 3 2 18.0 r r v out the resistive divider should sit as close to vfb pin as possible. layout consideration in order to ensure a proper operation of AIC2322, the following points should be managed comprehensively. 1. the input capacitor and v in should be placed as close as possible to each other to reduce the input voltage ripple and noise. 2. the output loop, which is consisted of the inductor, the internal main power switch, the internal synchronous power switch and the output capaci- tor, should be kept as small as possible. 3. the routes with large current should be kept short and wide. 4. logically the large current on the converter should flow at the same direction. 5. the vfb pin should be connected to the feedback resistors directly and the route should be away from the noise sources.
AIC2322 9 ? physical dimensions (unit: mm) ? sop-8 package note : information provided by aic is believed to be accurate and reliabl e. however, we cannot assume responsibility for use of any ci rcuitry other than circuitry entirely embodied in an aic product; nor for any infringement of patents or other rights of third parties that may re sult from its use. we reserve the right to change the circuitr y and specifications without notice. life support policy: aic does not authorize any aic product for us e in life support devices and/or systems. life support device s or systems are devices or systems which, (i) are intended for surgical implant into the body or (ii) support or sustain life, and whose failur e to perform, when properly used in accordance with instructi ons for use provided in the labeling, can be reasonably expected to result in a significant injury to the user. note: 1. refer to jedec ms-012aa. 2. dimension "d" does not include mold flash, protrus ions or gate burrs. mold flas h, protrusion or gate bur rs shall not exceed 6 mil per side . 3. dimension "e" does not i nclude inter-lead flash or protrusions. 4. controlling dimensi on is millimeter, converted inc h dimensions are no t necessarily exact. a l view b 0.25 seating plane section a-a base metal gauge plane with plating a1 b c d e aa h e h x 45 see view b h l d e h e c b a1 0.50 0.25 0.40 0 1.27 8 1.27 bsc 4.80 5.80 3.80 0.33 0.19 0.10 5.00 6.20 4.00 0.51 0.25 0.25 s y m b o l a sop-8 millimeters 1.35 min. 1.75 max.
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