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AIC2354 1a synchronous pwm/psm step-down dc/dc converter analog integrations corporation si-soft research center ds-2354g-02 20111101 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 5.5v input voltage range ? 1.0a guaranteed output current ? up to 95% efficiency ? low r ds(on) internal switche: 280m ? ? no schottky diode required ? 100% duty cycle in low dropout operation ? operating frequency: 1.5mhz ? accurate reference 0.6v provides low output voltages ? applications ? lcd tv ? multi-function peripheral ? cellular phones ? cpu i/o supplies ? cordless phones ? pdas and handy-terminals ? battery-operated devices (1 li-ion or 3 nimh/ nicd) ? description the AIC2354 is a low-noise, pulse-width- modulated (pwm), dc-dc step-down converter. the device is available in an adjustable version and fixed output voltages of 1.0v, 1.2v, 1.5v, 1.8v, and 3.3v. the device features an internal synchronous rectifier for high efficiency; it requires no external schottky diode. the AIC2354 is ideally suited for li-ion battery applications. pwm/psm mode extends battery life by switching to a pulse- skipping-modulated mode during light loads. shutdown mode places the device in standby, reducing supply current to under 1a. other features of the AIC2354 include high efficiency, low dropout voltage, short circuit protection, over temperature protection, and over voltage protection. it is available in a small 5 pins sot-23 and a 6 pins dfn package. ? applications circuit fig. 1 fixed step-down dc/dc converter
AIC2354 2 fig. 2 adjustable step-down dc/dc converter ? ordering information exam ple: AIC2354-33gv5tr ? 3.3v output version, in sot-23-5 green package & tape & ree l packing typ e AIC2354gv5tr ? ad jus tab le vers io n, in sot-23-5 green package & tape & ree l packing typ e pin configuration top view vout gnd en 3 21 4 5 lx packing type tr: tape & reel bg: bag package type v5: sot-23-5 da: dfn-6l(2x2) g: green package output voltage default: adj. 1 0: 1.0v 1 2: 1.2v 1 5: 1.5v 1 8: 1.8v 3 3: 3.3v fixed version top view fb gnd en 3 21 4 5 lx a djustable version vin vin s ot-23-5 so t-23-5 dfn-6l ( 2x2 ) top view 1 2 3 6 5 4 nc vin en lx gnd / fb vout AIC2354 -xx x xx xx
AIC2354 3 ? ordering information (continuous) ? marking (fixed version) part no. marking AIC2354-10gv5 gz10g AIC2354-12gv5 gz12g AIC2354-15gv5 gz15g AIC2354-18gv5 gz18g AIC2354-33gv5 gz33g AIC2354-10gda hq10g AIC2354-12gda hq12g AIC2354-15gda hq15g AIC2354-18gda hq18g AIC2354-33gda hq33g ? marking (adjustable version) part no. marking AIC2354gv5 2354g AIC2354gda 2354a
AIC2354 4 ? absolute maximum ratings vin, lx voltage 6v en, fb pin voltage -0.3 v to v in 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 dfn-6l (2x2) 30 ? c/w thermal resistance junction to case sot-23-5 115 ? c/w thermal resistance junction to ambient dfn-6l (2x2) * 165 ? c/w thermal resistance junction to ambient sot-23-5 250 ? c/w (assume no ambient airflow) absolute maximum ratings are those values beyond which the life of a device may be impaired. * the package is placed on a two layers pcb with 2 ounces copper and 2 square in ch, connected by 8 vias.
AIC2354 5 ? electrical characteristics (t a =25 ? c, v in =3.6v unless otherwise specified.) (note 1) parameter conditions symbol min typ max units input voltage range v in 2.5 5.5 v output adjustment range v out 0.6v v in -0.3v v reference voltage v ref 0.588 0.6 0.612 v fb input current v fb = v in i fb -50 50 na p-channel on-resistance i out = 0.2a p rds(on) 280 390 m ? n-channel on-resistance i out = 0.2a n rds(on) 250 390 m ? lx leakage current v lx =0v or v lx =3.6v -1 1 ? a peak inductor current v in = 5v i pk 1.3 1.6 a quiescent current i out = 0ma, v fb =v ref + 5% i q 65 85 ? a shutdown supply current en = gnd i shdn 0.1 1 ? a en high-level input voltage v in =2.5v to 5.5v v en_h 1.5 v en low-level input voltage v in =2.5v to 5.5v v en_l 0.4 v oscillator frequency f osc 1.2 1.5 1.8 mhz maximum duty cycle d max 100 % thermal shutdown temperature 150 c thermal shutdown hysteresis 25 c 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).
AIC2354 6 ? typical performance characteristics fig. 3 efficiency vs. input voltage fi g. 4 efficiency vs. output current fig. 5 efficiency vs. output current fig. 6 efficiency vs. output current fig. 7 output voltage vs. temperature fig. 8 oscillator frequency vs. temperature
AIC2354 7 ? typical performance characteristics (continuous) fig. 9 oscillator frequency vs. input voltage fig. 10 r ds(on) vs. input voltage fig. 11 supply current vs. input voltage fig. 12 current limit vs. input voltage fig. 13 load transient response fig. 14 load transient response
AIC2354 8 ? typical performance characteristics (continuous) fig. 15 load transient response fig. 16 load transient response fig. 17 load transient response fig. 18 psm operation
AIC2354 9 ? block diagram functional block diagram of AIC2354 ? pin descriptions pin dfn-6l pin sot-23 pin name pin function 1 nc no internal connect (floating or connecting to gnd). 2 1 en chip enable (active high). 3 4 vin power input. 4 3 lx pin for switching. 5 2 gnd ground. 6 5 fb/vout feedback/output voltage pin.
AIC2354 10 ? application information operation the AIC2354 is a low-noise step-down dc/dc converter with current-mode pwm/psm control architecture. it features an internal synchronous rectifier, which eliminates the external schottky diode and increases efficiency. during normal operation, the AIC2354 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 com paring the feedback voltage to the reference voltage of 0.6v, the error amplifier varies its output voltage. the output voltage 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 switch ing cycle. in order to achieve better efficiency and prevent overcharging the output capacitor, AIC2354 will enter pulse-skipping- modulated mode (psm) operation while working at light load conditions. current limitation the AIC2354 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 AIC2354 will be reduced to one third 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 AIC2354 can be shut down to reduce the supply current to 0.1 ? a (typical). at this operati on 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 AIC2354 smoothly transits to 100% duty cycle operation. this allows AIC2354 to regulate the output voltage until AIC2354 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 AIC2354 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
AIC2354 11 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. 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 losc out v v 1 if v l 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 maxout peak v v 1 lf2 v ii 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 i v vvv i i 2 l 2 in out inout 2 )max(out cinrms ? ? ? ? ? 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 cf8 i v ??? ?? ? ?? 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 (AIC2354 adjustable version only) by connecting a resistive divider r 1 and r 2, the output voltage of AIC2354 step-down converter can be set. v out can be calculated as: ? ? ? ? ? ? ? ? ??? 2 1 out r r 16.0v the resistive divider should sit as close to vfb pin as possible. layout consideration in order to ensure a proper operation of AIC2354, 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 syn- chronous power switch and the output capacitor, 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.
AIC2354 12 ? physical dimensions ? sot-23-5 c a a2 b with plating view b l1 l seating plane gauge plane 0.25 a1 section a-a base metal e1 d e aa e1 see view b e note : 1. refer to jedec mo-178aa. 2. dimension "d" does not include mold flash, protru sions or gate burrs. mold flash, protrusion or gate bu rrs shall not exceed 10 mil per side. 3. dimension "e1" does not include inter-lead flash or protrusions. 4. controlling dimens ion is millimeter, converted in ch dimensions are not necessarily exact. 0 0.90 0.30 1.50 2.60 2.80 0.08 0.30 0.00 e l1 l e1 c e e1 d b a2 a1 0.95 bsc 8 0.60 1.90 bsc 0.60 ref 1.30 1.70 3.00 3.00 0.22 0.50 0.15 0.95 min. s y m b o l a 1.45 max. sot-23-5 millimeters
13 e l d2 b a3 top view bottom view side view e 31 a seating plane 6 pin#1 d 4 e2 ? dfn 6l-2x2 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 infri ngement of patents or other rights of third parties that m ay result from its use. we reserve the right to change the circ uitry 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 impl ant into the body or (ii) support or sustain life, and whose fa ilure to perform, when properly used in accordance with instructions for use prov ided in the labeling, can be reasonably expected to result in a significant in- jury to the user. note : 1. dimension and tolerancing conform to asme y14.5m-1994 . 2.controlling dimensionsmillimeterconverted inch dimension are not necessarily exact. 3.dimension b applies to metallized terminal and is measured between 0.10 and 0.25 mm from terminal tip. millimeters min. s y m b o l a3 a0.70 max. 0.20 bsc 0.80 dfn 6l-2x2x0.75-0.65mm e e l e2 0.25 0.55 d2 d b 1.20 0.25 0.65 bsc 0.45 0.85 1.60 0.35 2.00 bsc 2.00 bsc

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