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AIC2359 1a dual synchronous step-down dc/dc converter analog integrations corporation si-soft research center ds-2359g-02 2012020 9 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 ? dual 1a output ? 2.5v to 5.5v input range ? accurate reference 0.6v provides low output voltages ? adjustable output voltage ? up to 95% efficiency ? stable with low esr output ceramic capaci- tors ? no schottky diode required. ? 65a quiescent current per channel. ? 100% duty cycle in low dropout operation. ? 1.5mhz fixed-frequency pwm operation ? applications ? digital still cameras ? cellular phones ? wireless and dsl modems ? notebook chipset supplies. ? pdas and handy-terminals. ? battery-operated devices (1 li-ion or 3 nimh/ nicd). ? description the AIC2359 is a dual output, low-noise, pulse-width-modulated (pwm), dc-dc step- down converter. it powers logic and transmit- ters in small wireless systems such as cellular phones, communicating pdas, and handy- terminals. the device features an internal synchronous rectifier for high efficiency; it requires no exter- nal schottky diode. inte rnally fixed-frequency 1.5mhz operation provides easy post-filtering and allows the use of small inductors and ca- pacitors. the AIC2359 is ideally suited for li- ion battery applications. pwm/psm mode ex- tends 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 AIC2359 include high ef- ficiency, soft start, over temperature protection, and over current protection. it is available in a space-saving 12-pin dfn. ? typical applications circuit vin2 1 lx2 2 gnd 3 fb1 4 nc1 5 en1 6 vin1 7 lx1 8 gnd 9 fb2 10 nc2 11 en2 12 AIC2359 2.2uh l2 2.2uh l1 vin2 4.7uf cin2 vout1 10uf cout1 22pf c11 r12 r11 vout2 10uf cout2 22pf c21 r21 4.7uh cin1 vin1 r22 fig. 1 adjustable output vo ltage step-down dc/dc converter
AIC2359 2 fig. 2 fixed output voltage step-down dc/dc converter
AIC2359 3 ? ordering information packing type tr: tape & reel bg: bag package type df: dfn-12 with heat sink (3x3x0.75-0.45mm ) g: green package output voltage:vout1/vout2 def ault ad jus ta ble -zk:3.3v/1.8v -ze:3.3v/1.2v -rk:2.5v/1.8v AIC2359-xx xxxxx example: AIC2359gdftr ? in green package dfn-12 with heat sink package and tape & r eel packing type AIC2359-zkgdftr ? 3.3v/1.8 v vout ve rsio n in green package dfn-12 w ith heat sink packa ge an d ta pe & ree l packing t ype pin configuration d fn-12 with heat sink t op v iew 1 3 2 5 6 4 vin2 lx2 gnd fb1 nc1 en1 12 10 11 8 7 9 vin1 gnd lx1 en2 nc2 fb2 note: the expo sed pa d m ust be co nn ecte d with gnd pin. ? absolute maximum ratins supply input volatge, v in1 , v in2 6.0v pin voltage for all other pins -0.3v 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-12l (3x3)* 20 ? c/w thermal resistance junction to ambient dfn-12l (3x3)* 50? 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 place on a two layers pcb with 2 ounces copper and 2 square in ch, connected by 8 vias.
AIC2359 4 ? electrical characteristics (v in =3.6v, v out =2.5v, unless otherwise specified. typical values are at ta=25 ? c) parameter symbol conditions min typ max units input voltage range v in 2.2 5.5 v reference voltage v ref 0.588 0.6 0.612 v fb input current i fb v fb = 0.62v -50 50 na quiesecnt current i q i out = 0ma, v fb = v ref + 5% 65 85 ua shutdown supply current i shdn 0.1 1 ua enable high input voltage v en_h 1.5 v in v enable low input voltage v en_l 0.4 v output adjustment range v out ( v = iout x p rds(on) ) v ref v in - v v output voltage accuracy v out -3 v out 3 % p-channel on-resistance p rds(on) i out =200ma 0.28 0.39 ? n-channel on-resistance n rds(on) i out =200ma 0.25 0.39 ? p-channel current-limit threshold 1.3 1.6 a oscillator frequency f osc i out =100ma 1.2 1.5 1.8 mhz maximum duty cycle duty max 100 % thermal shutdown tempera- ture t sd 150 c lx leakage current i lx v lx =0v or v lx =3.6v -1 1 ua
AIC2359 5 ? 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
AIC2359 6 ? 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
AIC2359 7 ? typical performance characteristics (continuous) fig. 15 load transient response fig. 16 load transient response fig. 17 load transient response fig. 18 psm operation
AIC2359 8 ? block diagram ? pin descriptions pin number pin name pin function 1 vin2 power input of channel 2. 2 lx2 pin for switching of channel 2. 3, 9, exposed pad (13) gnd ground. the exposed pad must be soldered to a large pcb and connected to gnd for maximum power dissipation. 4 fb1 feedback of channel 1. 5, 11 nc1, nc2 no connection or connect to vin. 6 en1 chip enable of channel 1 (active high). ven1 vin1. Q 7 vin1 power input of channel 1. 8 lx1 pin for switching of channel 1. 10 fb2 feedback of channel 2. 12 en2 chip enable of channel 2 (active high). ven2 vin2. Q
AIC2359 9 ? application information operation the AIC2359 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 AIC2359 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 0.6v, the error amplifier varies its output voltage. the output voltage of the error amp lifier is compared with the summing signal of current sensing signal and slope compensation signal to det ermine 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 swit ching cycle. in order to achieve better efficiency and prevent overcharging the output capacitor, AIC2359 will enter pulse-skipping- modulated mode (psm) operation while working at light load conditions. current limitation the AIC2359 provides current lim it function by using an in- ternal 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 re- sistor, and amplifies it. while the sensed voltage gets higher than reference voltage, the current limitation function is acti- vated. while the current limitat ion 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 AIC2359 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 preventi ng 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 AIC2359 can be shut down to reduce the supply current to 0.1 a (typical). at this operation mode, t he output voltage of step-down converter is equal to 0v. 100% duty cycle operation when the input voltage approac hes the output voltage, the AIC2359 smoothly transits to 100% duty cycle operation. this allows AIC2359 to regulate the output voltage until AIC2359 complete ly enters 100% duty cycle operation. in 100% duty cycle mode, the output voltage is equal to the input voltage minus the voltage, which is the drop across the main power switch. the AIC2359 achieves 100% dut y cycle operation by ex- tending the turn-on time of the main power switch. if the summing signal of current sensing signal and slope com- pensation 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 oscilla- tor 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 level 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, t he next switching cycle is begun. while the input voltage approac hes the output voltage, the switching frequency decreases gr adually to smoothly transit to 100% duty cycle operation.
AIC2359 10 if input voltage is very close to output voltage, the switching mode goes from pure pwm mode to 100% duty cycle operation. during 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 rippl e of inductor allows the use of a smaller inductance. howe ver, 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 vo ltage ripple and noise resulted from high frequency switching, the use of low esr ceramic capacitor for the maximum rms current is recommended. the approximat ed 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 out put 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 (AIC2359 adjustable version only) by connecting a resistive divider r 11 and r 12 (r 21 and r 22 ) , the output voltage of aic 2359 step-down converter can be set. v out1 and v out2 can be calculated as: ? ? ? ? ? ? ? ? ??? ? ? ? ? ? ? ? ? ??? 22 21 2 12 11 1 16.0 16.0 r r v r r v out out the resistive divider should sit as close to vfb pin as possible. layout consideration in order to ensure a proper operation of AIC2359, the fol- lowing 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 synchro- nous 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 resis- tors directly and the rout e should be away from the noise sources.
AIC2359 11 ? physical dimensions (unit: mm) ? dfn 12l-3x3x0.75-0.45mm package outline drawing 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 patent s or other rights of third parties that may result from its use. we reserve the right to change the circuitry and specif ications 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 t he body or (ii) support or sustain life, and whose failure to per form, when properly used in accordance with instructions for use provi ded in the labeling, can be reasonably expected to result in a significant injury to the user. 12 pin#1 d 7 e2 e 61 b a3 a seating plane l d2 e millimeters min. s y m b o l a3 a 0.70 max. 0.20 bsc 0.80 dfn 12l-3x3x0.75-0.45mm e e l e2 0.30 1.40 d2 d b 2.20 0.18 2.90 3.10 0.45 bsc 0.50 1.80 2.90 3.10 2.70 0.30 note : 1. dimension and tolerancing conform to asme y14.5m-1994 . 2.controlling dimensionsmillimeterconverted inch dimension are not necessarily exact.

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