AIC2823 3a 23v synchronous pwm step-down converter analog integrations corporation si-soft research center ds-2823g-05 20131025 3a1, 1 li-hsin 1 st rd., science park, hsinchu 300, taiwan, r.o.c. tel: 886-3-5772500 f ax: 886-3- 5772510 www. analog.com.tw 1 ? features ? 3a continuous output current ? wide 4.75v to 23v operating input range ? ouput adjustable from 0.925v to 12v (v ref =0.925v version) ? ouput adjustable from 0.8v to 12v (v ref =0.8v version) ? up to 95% efficiency ? low rds(on) internal switches: 100m ? and 85m ? ? <3a supply current in shutdown mode ? 340khz/550khz frequency ? programmable soft start ? thermal shutdown ? cycle by cycle over current protection ? under voltage lockout ? short circuit protection ? over voltage protection ? applications ? networking systems ? distributed power systems ? pre-regulator for linear regulators ? set-top box ? description the AIC2823 is a monolithic synchronous step- down converter. the devic e can provide 3a output current from a 4.75v to 23v input supply. the AIC2823?s current mode architecture and ex- ternal compensation allow the transient response to be optimized over a wide range of loads and capaci- tors. current mode control also provides cycle-by- cycle current limit. the AIC2823 provides over voltage protection and thermal shutdown. an adjus table soft-start prevents inrush current during turn on. this device is available in a sop-8 package, pro- vides a very compact system solution with minimal external components and pcb area. ? typical applications circuit AIC2823 typical application circuit
AIC2823 2 ? ordering information packing type tr: tape & reel tb: tube packaging type r8: sop-8 exposed pad (heat sink) g: green package 3: fs=340khz 5: fs=550khz default: v ref =0.925v k: v ref =0.8v example: AIC2823-3gr8tr ? v ref =0.925v, fs=340khz with green sop-8 exposed pad (heat sink) package and tape & reel packing type AIC2823-k5gr8tr ? v ref =0.8v, fs=550khz with green sop-8 exposed pad (heat sink) package and tape & reel packing type pin configuration comp ss en fb sw in gnd bs a ic2823-xxxxx xx 1 3 4 2 8 6 5 7 so p -8 expose d p ad ( hea t s ink ) top view note: the e xpos ed p ad sh ou ld b e con ne cte d with gnd pi n exposed pad ? absolute maximum ratings input voltage (v in )???????????????????????????????. - 0.3v to 26v sw pin voltage (vsw) ???????????????????????.???? -1v to v in + 0.3v bs pin voltage ?????????????????????????.???vsw ? 0.3v to vsw + 6v en pin voltage????????????????????????????????.... - 0.3v to v in all other pins voltage?????????????????????????????..? - 0.3v to 6v operating ambient temperature range t a ???...............................??.?..................... - 40 ? c ~ 85 ? c operating maximum junction temperature t j ???.?????...????.??????........... 150 ? c storage temperature range t stg ......................................................................................... -65o c~150oc lead temperature (soldering 10 sec.)???????????????????..?????? 260 ? c thermal resistance junction to case sop-8 exposed pad*?????????????..15 ? c/w thermal resistance junction to ambient sop-8 exposed pad*?????????????..60 ? 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.
AIC2823 3 ? electrical characteristics (v in =12v, t a =25? c, unless otherwise specified.) (note1) parameter symbol conditions min typ max units supply voltage range 4.75 23 v under voltage lockout threshold v in rising 3.7 4.05 v uvlo hysteresis 210 mv shutdown supply current v en = 0v 0.3 3 ? a standby current (switching) v en = 3.0v; sw = nc 0.7 1.5 ma reference voltage (default version) (note2) v ref 0.900 0.925 0.950 v reference voltage (k version) (note2) v ref 0.779 0.8 0.821 v feedback over voltage threshold v fb rising 123 % en shutdown threshold voltage v en rising 1.1 1.5 2.2 v en shutdown hysteresis 220 mv high-side switch on-resistance r ds(on)1 100 m ? low-side switch on-resistance r ds(on)2 85 m ? high-side switch leakage current v en = 0v, v sw = 0v 0 10 ? a high-side switch current limit peak current 4.0 5.8 a oscillation frequency (3 version) (note2) fs 300 340 380 khz oscillation frequency (5 version) (note2) fs 485 550 615 khz short circuit oscillation frequency v fb = 0v 110 khz maximum duty cycle d max 90 % minimum on time t on 220 ns soft-start current v ss = 0v 6 ? a soft-start period v ss = 0.1 ? f 15 ms thermal shutdown trip point 160 ? c note 1: specifications are production tested at t a =25 ? c. specifications over the -40? c to 85 ? c operating temperature range are assured by design, characte rization and correlation with statistical quality controls (sqc). note 2: referring to the ordering information.
AIC2823 4 ? typical performance characteristics v in 10v/div v out 2v/div v sw 10v/div i l 2a/div time(20ms/div) v in =12v,v out =3.3v,i out =3a v in 10v/div v out 2v/div v sw 10v/div i l 2a/div time(20ms/div) v in =12v,v out =3.3v,i out =3a fig. 1 efficiency vs. load current fig. 2 start-up waveform at v out =3.3v, i out =3a v in 5v/div v out 2v/div v sw 10v/div i l 5a/div time(4ms/div) v in =12v,v out =3.3v,i out =3a v in 5v/div v out 2v/div v sw 10v/div i l 5a/div time(4ms/div) v in =12v,v out =3.3v,i out =3a v in 5v/div v out 2v/div v sw 10v/div i l 5a/div time(4ms/div) v in =12v,v out =3.3v,i out =3a v in 5v/div v out 2v/div v sw 10v/div i l 5a/div time(4ms/div) v in =12v,v out =3.3v,i out =3a fig. 3 start-up waveform at v out =3.3v, i out =3a fig. 4 shutdown waveform at v out =3.3v, i out =3a v out ac 500mv/div i l 2a/div time(1ms/div) v in =12v,v out =3.3v,i out =0.5a~2.5a v out ac 500mv/div i l 2a/div time(1ms/div) v in =12v,v out =3.3v,i out =0.5a~2.5a v out ac 500mv/div i l 2a/div time(1ms/div) v in =12v,v out =3.3v,i out =1a~3a v out ac 500mv/div i l 2a/div time(1ms/div) v in =12v,v out =3.3v,i out =1a~3a fig. 5 load transient at v out =3.3v, i out =0.5a to 2.5a fig. 6 load transient at v out =3.3v, i out =1a to 3a
AIC2823 5 ? typical performance characteristics (continued) v sw 5v/div v out ac 20mv/div i l 1a/div time(2 s/div) v in =12v,v out =3.3v,i out =1a v sw 5v/div v out ac 20mv/div i l 1a/div time(2 s/div) v in =12v,v out =3.3v,i out =1a v sw 5v/div v out ac 20mv/div i l 2a/div time(2 s/div) v in =12v,v out =3.3v,i out =3a v sw 5v/div v out ac 20mv/div i l 2a/div time(2 s/div) v in =12v,v out =3.3v,i out =3a fig. 7 stability waveform at v out =3.3v, i out =1a fig. 8 stability waveform at v out =3.3v, i out =3a
AIC2823 6 ? block diagram functional block diagram of AIC2823 (v ref =0.925v version) functional block diagram of AIC2823 (v ref =0.8v version)
AIC2823 7 ? pin descriptions sop-8 pin no. pin name pin function 1 bs high side gate drive boost input. bs supplies the drive for the high-side n- channel mosfet switch. connect a 10nf or greater capaitor from sw to bs to power the high-side switch. 2 in power input. in supplies power to the ic , as well as the step-down converter switches.by pass in to gnd with a suitabl ey large capacitor to eliminate noise on the input to the ic. 3 sw power switching output. sw is the sw itching node that supplies power to the output. connect the output lc filter from sw itch to the output load. note that a capacitor is required from sw to bs to power the high-side switch. 4 gnd ground. connect the exposed pad on backside to pin 4. 5 fb feedback input. fb senses the output voltage to regulate that voltage. drive feedback with a resistive voltage di vider from the output voltage. 6 comp compensation node. comp is used to co mpensate the regulation control loop. connect a series rc network form comp to gnd to compensate the regula- tion control loop. in some cases, an addi tional capacitor from comp to gnd is required. 7 en enable input. en is a digital input that turns the regulator on or off. drive en high to turn on the regulator. drive it low to turn it off. for automatic strat-up, attach to in with a 100k ? pull up resistor. 8 ss soft star contol input. ss controls t he soft star period. connect a capacitor from ss to gnd to set the soft-star peri od. to disable the soft-star feature, leave the ss pin unconnected.
AIC2823 8 ? application informations the AIC2823 is a synchronous high voltage buck converter that can support the input voltage range from 4.75v to 23v and the output current can be up to 3a. setting the output voltage the output voltage is set by using a resistive voltage divider connected from the output voltage to fb. the voltage divider divides the output voltage down to the feedback voltage by the ratio: 2r1r 2r vv out fb ? ?? thus the output voltage is: 2r 2r1r vv ref out ? ?? for example, for a 3.3v output voltage and v ref =0.925v, r2 is 10k
, and r1 is 25.6k
. inductor the inductor selection depends on the current ripple of inductor, the input voltage and the output voltage. ? ? ? ? ? ? ? ? ? ?? ? in out ls 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 s out maxout peak v v 1 lf2 v ii soft-start the AIC2823 provides the soft- start function. initially, the voltage at ss pin is 0v. then an internal current source of 6 ? a (typ.) charges an external soft-start ca- pacitor. during the soft-start period, the voltage at ss pin will limit the feedback thre shold voltage at fb pin. when the voltage at ss pin is higher than reference voltage, the feedback threshold voltage at fb pin reaches the desired value. the soft-start time can be calculated in accordance with the following equation. a6 v 5ct ref ss ? ?? the soft-start capacitor is discharged to gnd when the en pin is connected to gnd. optional schottky diode a schottky diode with low forward drop voltage and fast reverse recovery is the ideal choice for better efficiency. the forward drop voltage of a schottky diode will result in the conduction losses in the diode, and the diode capacitance (c t or c d ) will cause the switching losses. therefore, it is necessary to consider both forward voltage drop and diode capacitance for diode selection. in addition, the rating of selected schottky diode should be able to handle the input voltage and the maximum peak diode current. 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
AIC2823 9 required output voltage ripple. the output voltage ripple can be expressed as: l s l out iesr )4c//3cf8 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. loop compensation in order to avoid the poor output voltage ripple and low efficiency caused by instability, AIC2823 requires a proper external compensation network to compensate its feedback loop. in this external compensation network, the compensation resistor, r c , and the compensation capacitor, c c , are used to set the high- frequency integrator gain and the integrator zero. c7 is used to cancel the zero caused by the output capacitor and it?s esr. while using the ceramic capacitor as the output capacitor, c7 can be omitted due to the small esr. the system has one pole of importance, due to the output capacitor, c3//c4 and the load resistor. this poles is located at: load 1p r)4c//3c( 2 1 =f the system has one zero of importance, due to the compensation capacitor, cc and the compensation resistor, rc. this zero is located at: rccc 2 1 =f 1z the system may have another zero of importance, if the output capacitor has a large capacitance and/or a high esr value. the zero, due to the esr and capaci- tance of the output capacitor, is located at: esr esr r)4c//3c( 2 1 =f in this case, a third pole set by the compensation ca- pacitor, c7 and the compensation resistor, rc is used to compensate the effect of the esr zero on the loop gain. this pole is located at: rc7c 2 1 =f 2p the values of the compensation components are given in the AIC2823 demo board user manual. layout consideration in order to ensure a proper operation of AIC2823, 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 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. in order to prevent the effect from noise, the ic?s gnd pin should be placed close to the ground of the input bypass capacitor. 6. the fb pin should be connected to the feedback resistors directly and t he route should be away from the noise sources.
AIC2823 10 ? physical dimensions ? sop-8 exposed pad(heat sink) 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 result from its use. we reserve the right to change t he circuitry and specificat ions 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 sys- tems are devices or systems which, (i) are intended for surgical implant into the body or (ii) support or sustain life, and who se failure to perform, when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to res ult in a significant injury to the user. note : 1. refer to jedec ms-012e. 2. dimension "d" does not include mold flash, protru sions or gate burrs. mold flash, protrusion or gate bu rrs shall not exceed 6 mil per side . 3. dimension "e" does no t include inter-lead flash o r protrusions. 4. controlling dimension is millimeter, converted in ch dimensions are not necessarily exact. a d ? l view b 0.25 seating plane section a-a base metal gauge plane with plating a1 b c e aa h e d1 e1 exposed thermal pad(heat sink) (bottom center of package) h x 45 see view b h l d e h e c b a1 0 8 1.27 bsc 4.80 3.80 0.31 0.17 0.00 5.00 4.00 0.51 0.25 0.15 s y m b o l a sop-8 exposed pad(heat sink) millimeters 1.35 min. 1.75 max. d1 e1 3.50 1.50 1.0 2.55 5.80 6.20 0.25 0.50 0.40 1.27
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