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1 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 general description the aat1112 switchreg is a 1.5a step-down converter with an input voltage range of 2.4v to 5.5v and an adjustable output voltage from 0.6v to v in . the 1.4mhz switching frequency enables the use of small external components. the small footprint and high efficiency make the aat1112 an ideal choice for portable applications. the aat1112 delivers 1.5a maximum output current while consuming only 42 a of no-load quiescent current. ultra-low r ds(on) integrated mosfets and 100% duty cycle operation make the aat1112 an ideal choice for high output voltage, high current applications which require a low dropout threshold. the aat1112 provides excellent transient response and high output accuracy across the operating range. no external compensation components are required. the aat1112 is designed to maintain high efficiency throughout the load range. pulling the mode/ sync pin high enables ?pwm only? mode, maintaining constant frequency and low output ripple across the operating range. alternatively, the converter may be synchronized to an external clock input via the mode/sync pin. over- temperature and short-circuit protection safeguard the aat1112 and system components from damage. the aat1112 is available in a pb-free, space-saving tdfn33-12 or 2.85 x 3mm tsopjw-12 package. the product is rated over an operating temperature range of -40c to +85c. features ? 1.5a maximum output current ? input voltage: 2.4v to 5.5v ? output voltage: 0.6v to v in ? up to 95% efficiency ? 42 a no load quiescent current ? no external compensation required ? 1.4mhz switching frequency ? synchronizable to external clock ? optional ?pwm only? low noise mode ? 100% duty cycle low-dropout operation ? internal soft start ? over-temperature and current limit protection ? <1 a shutdown current ? tsopjw-12 or tdfn33-12 package ? temperature range: -40c to +85c applications ? cellular phones ? digital cameras ? hard disk drives ? mp3 players ? pdas and handheld computers ? portable media players ? usb devices typical application vp gnd pgnd lx fb v out = 3.3v v in c 10f 2 c 22f 1 l 3.3h 1 en r 267k 1 r 59k 2 vin aat1112 mode/sync
2 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 pin descriptions pin # symbol function tsopjw-12 tdfn33-12 112lx switching node. connect the output inductor to this pin. the switching node is inter- nally connected to the drain of both high- and low-side mosfets. 2 11 vp input voltage for the power switches. 3 10 n/c not connected. 4 9 mode/sync connect to ground for pfm/pwm mode and optimized ef ciency throughout the load range. connect high for low noise pwm operation under all operating conditions. connect to an external clock for synchronization (pwm only). 58en enable pin. a logic low disables the converter and it consumes less than 1 a of cur- rent. when connected high, it resumes normal operation. 6 7 vin power supply. supplies power for the internal circuitry. 76fb feedback input pin. this pin is connected either directly to the converter output or to an external resistive divider for an adjustable output. 8, 9, 10, 11 4, 5 gnd non-power signal ground pin. 12 1, 2, 3 pgnd main power ground return pin. connect to the output and input capacitor return. n/a ep exposed paddle (bottom); connect to ground as closely as possible to the device. pin configuration tsopjw-12 tdfn33-12 (top view) (top view) 1 2 3 4 5 6 12 11 10 9 8 7 lx vp n/c mode/sync en vin pgnd gnd gnd gnd gnd fb pgnd pgnd pgnd 1 gnd gnd fb lx vp n/c mode/sync en vin 2 3 4 5 6 12 11 10 9 8 7
3 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 absolute maximum ratings 1 symbol description value units v in vin, vp to gnd 6.0 v v lx lx pin to gnd -0.3 to v in + 0.3 v v fb fb pin to gnd -0.3 to v in + 0.3 v v n mode/sync, en to gnd -0.3 to 6.0 v t j operating junction temperature range -40 to 150 c t lead maximum soldering temperature (at leads, 10 sec) 300 c thermal information symbol description value units p d maximum power dissipation tsopjw-12 0.625 w tdfn33-12 2.0 ? ja thermal resistance 2 tsopjw-12 160 c/w tdfn33-12 50 1. stresses above those listed in absolute maximum ratings may cause permanent damage to the device. functional operation at c onditions other than the operating conditions specified is not implied. only one absolute maximum rating should be applied at any one time. 2. mounted on an fr4 board.
4 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 electrical characteristics 1 v in = 3.6v; t a = -40c to +85c, unless otherwise noted. typical values are t a = 25c. symbol description conditions min typ max units v in input voltage 2.4 5.5 v v out output voltage range 0.6 v in v v uvlo uvlo threshold v in rising 2.4 v hysteresis 250 mv v in falling 1.8 v v out output voltage tolerance i out = 0a to 1.5a, v in = 2.4v to 5.5v -3.0 3.0 % i q quiescent current no load 42 90 a i shdn shutdown current v en = gnd 1.0 a i lim current limit 1.8 a r ds(on)h high side switch on-resistance 0.120 ? r ds(on)l low side switch on-resistance 0.085 ? i lxleak lx leakage current v in = 5.5v, v lx = 0 to v in 1.0 a i lxlk, r lx reverse leakage current v in unconnected, v lx = 5.5v, v en = gnd 1.0 a ? v loadreg load regulation i load = 0a to 1.5a 0.5 % ? v linereg / ? v in line regulation v in = 2.4v to 5.5v 0.2 %/v v fb feedback threshold voltage accuracy (adjustable version) no load, t a = 25c 0.591 0.60 0.609 v i fb fb leakage current v out = 1.0v 0.2 a f osc internal oscillator frequency 1.12 1.4 1.68 mhz synchronous clock 0.60 3.0 t s start-up time from enable to output regulation 150 s t sd over-temperature shutdown threshold 140 c t hys over-temperature shutdown threshold 15 c en v il enable threshold low 0.6 v v ih enable threshold high 1.4 v i en enable leakage current v in = v en = 5.5v -1.0 1.0 a mode/sync v mode/sync(l) enable threshold low 0.6 v v mode/sync(h) enable threshold high 1.4 v i mode/sync enable leakage current v in = v en = 5.5v -1.0 1.0 a 1. the aat1112 is guaranteed to meet performance specifications over the -40c to +85c operating temperature range and is assu red by design, characterization, and correla- tion with statistical process controls.
5 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 typical characteristics efficiency vs. output current (pfm mode; v out = 3.3v) output current (ma) efficiency (%) 40 50 60 70 80 90 100 0.1 1 10 100 1000 10000 v in = 4.2v v in = 3.6v v in = 5.0v load regulation (pfm mode; v out = 3.3v) output current (ma) v out error (%) -0.50 -0.25 0.00 0.25 0.50 0.1 1 10 100 1000 10000 v in = 3.6v v in = 4.2v v in = 5.0v efficiency vs. output current (pwm mode; v out = 3.3v) output current (ma) efficiency (%) 0 20 40 60 80 100 1.0 10 100 1000 10000 v in = 3.6v v in = 4.2v v in = 5.0v load regulation (pwm mode; v out = 3.3v) output current (ma) v out error (%) -0.50 -0.25 0.00 0.25 0.50 0.1 1 10 100 1000 10000 v in = 3.6v v in = 5.0v v in = 4.2v efficiency vs. output current (pfm mode; v out = 2.5v) output current (ma) efficiency (%) 50 60 70 80 90 100 0.1 1 10 100 1000 10000 v in = 2.7v v in = 3.6v v in = 4.2v load regulation (pfm mode; v out = 2.5v) output current (ma) v out error (%) -0.50 -0.25 0.00 0.25 0.50 0.1 1 10 100 1000 10000 v in = 2.7v v in = 3.6v v in = 4.2v
6 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 typical characteristics output current (ma) efficiency (%) 0 10 20 30 40 50 60 70 80 90 100 1 10 100 1000 10000 v in = 2.7v v in = 3.6v v in = 4.2v v in = 5.0v efficiency vs. output current (pwm mode; v out = 2.5v) load regulation (pwm mode; v out = 2.5v) output current (ma) v out error (%) -0.50 -0.25 0.00 0.25 0.50 0.1 1 10 100 1000 10000 v in = 2.7v v in = 3.6v v in = 5.0v v in = 4.2v efficiency vs. output current (pfm mode; v out = 1.8v) output current (ma) efficiency (%) 40 50 60 70 80 90 100 0.1 1 10 100 1000 10000 v in = 2.7v v in = 3.6v v in = 4.2v load regulation (pfm mode; v out = 1.8v) output current (ma) v out error (%) -0.50 -0.25 0.00 0.25 0.50 0.1 1 10 100 1000 v in = 3.6v v in = 2.7v v in = 4.2v efficiency vs. output current (pwm mode; v out = 1.8v) output current (ma) efficiency (%) 0 10 20 30 40 50 60 70 80 90 100 1 10 100 1000 10000 v in = 2.7v v in = 3.6v v in = 4.2v load regulation (pwm mode; v out = 1.8v) output current (ma) v out error (%) -0.50 -0.25 0.00 0.25 0.50 0.1 1 10 100 1000 10000 v in = 2.7v v in = 3.6v v in = 4.2v
7 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 typical characteristics efficiency vs. output current (pfm mode; v out = 1.2v) output current (ma) efficiency (%) 30 40 50 60 70 80 90 100 0.1 1 10 100 1000 10000 v in = 2.7v v in = 3.6v v in = 4.2v load regulation (pfm mode; v out = 1.2v) output current (ma) v out error (%) -0.50 -0.25 0.00 0.25 0.50 0.1 1 10 100 1000 10000 v in = 2.7v v in = 3.6v v in = 4.2v efficiency vs. output current (pwm mode; v out = 1.2v) output current (ma) efficiency (%) 0 10 20 30 40 50 60 70 80 90 100 1 10 100 1000 10000 v in = 2.7v v in = 3.6v v in = 4.2v load regulation (pwm mode; v out = 1.2v) output current (ma) v out error (%) -0.50 -0.25 0.00 0.25 0.50 0.1 1 10 100 1000 10000 v in = 2.7v v in = 3.6v v in = 4.2v output voltage vs. temperature (v in = 3.6v; v out = 1.8v; i out = 1a) temperature ( c) output voltage change (%) -1.0 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1.0 -40 -20 0 20 40 60 80 supply current vs. supply voltage (v out = 1.8v; no load; pfm mode) supply voltage (v) supply current (a) 30 35 40 45 50 55 60 65 70 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 85c 25c -40c
8 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 typical characteristics switching frequency vs. temperature (v in = 3.6v; v out = 1.8v; i out = 1a) temperature ( c) switching frequency (mhz) 1.24 1.26 1.28 1.30 1.32 1.34 1.36 1.38 1.40 -40 -20 0 20 40 60 80 line regulation (v out = 1.8v; i out = 1a) supply voltage (v) output voltage error (%) -0.04 -0.02 0.00 0.02 0.04 0.06 0.08 0.10 0.12 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 switching frequency vs. input voltage (i out = 1a) input voltage (v) switching frequency (mhz) 1.32 1.33 1.34 1.35 1.36 1.37 1.38 1.39 1.40 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 v out = 2.5v v out = 3.3v v out = 1.8v enable soft start (v out = 3.6v; i out = 1.5a) time (100s/div) v out (1v/div) en (2v/div) i in (500ma/div) p-channel r ds(on) vs. input voltage input voltage (v) r ds(on) (m ) 90 100 110 120 130 140 150 160 170 180 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 120c 85c 25c n-channel r ds(on) vs. input voltage input voltage (v) r ds(on) (m ) 60 70 80 90 100 110 120 130 140 150 2.7 2.9 3.1 3.3 3.5 3.7 3.9 4.1 4.3 4.5 4.7 4.9 5.1 5.3 5.5 120c 85c 25c
9 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 typical characteristics heavy load switching waveform (pwm mode; v in = 3.6v; v out = 1.8v; 1.5a load) time (2.5s/div) output voltage (ac coupled) (top) (mv) inductor ripple current (bottom) (ma) -12.0 -10.0 -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 2.6 light load switching waveform (pwm mode; v in = 3.6v; v out = 1.8v; 1ma load) time (2.5s/div) output voltage (ac coupled) (top) (mv) inductor ripple current (bottom) (ma) -12.0 -10.0 -8.0 -6.0 -4.0 -2.0 0.0 2.0 4.0 -400 -200 0 200 400 600 800 1000 1200 light load switching waveform (pfm mode; v in = 3.6v; v out = 1.8v; 1ma load) time (100s/div) output voltage (ac coupled) (top) (mv) inductor ripple current (bottom) (ma) -24.0 -20.0 -16.0 -12.0 -8.0 -4.0 0.0 4.0 8.0 -100 0 100 200 300 400 500 600 700 load transient response (v in = 3.6v; v out = 1.8v; c ff = 100pf) time (20s/div) output voltage (top) (v) load current (bottom) (a) 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 0.8 1.0 1.2 1.4 1.6 1.8 2.0 2.2 2.4 load transient response (v in = 3.6v; v out = 1.8v; no c ff ) time (50s/div) output voltage (top) (v) load current (bottom) (a) -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 line transient response (v out = 1.8v; 1.5a load) time (200s/div) input voltage (top) (v) output voltage (bottom) (v) 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 1.4 1.6 1.8 2.0 2.2 2.4 2.6 2.8 3.0
10 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 functional description the aat1112 is a high performance 1.5a monolithic step-down converter operating at 1.4mhz switching fre- quency. it minimizes external component size and opti- mizes efficiency over the complete load range. apart from the small bypass input capacitor, only a small l-c filter is required at the output. typically, a 3.3 h induc- tor and a 22 f ceramic capacitor are recommended for a 3.3v output (see table of recommended values). at dropout, the converter duty cycle increases to 100% and the output voltage tracks the input voltage minus the r ds(on) drop of the p-channel high-side mosfet (plus the dc drop of the external inductor). the device inte- grates extremely low r ds(on) mosfets to achieve low dropout voltage during 100% duty cycle operation. this is advantageous in applications requiring high output voltages (typically > 2.5v) at low input voltages. the integrated low-loss mosfet switches can provide greater than 95% efficiency at full load. pfm operation maintains high efficiency under light load conditions (typically <150ma). the mode/ sync pin allows option- al ?pwm only? mode. this maintains constant frequency and low output ripple across all load conditions. alternatively, the ic can be synchronized to an external clock via the mode/ sync input. external synchroniza- tion is maintained between 0.6mhz and 3.0mhz. in battery-powered applications, as v in decreases, the converter dynamically adjusts the operating frequency prior to dropout to maintain the required duty cycle and provide accurate output regulation. output regulation is maintained until the dropout voltage, or minimum input voltage, is reached. at 1.5a output load, dropout volt- age headroom is approximately 200mv. the aat1112 typically achieves better than 0.5% out- put regulation across the input voltage and output load range. a current limit of 2.0a (typical) protects the ic and system components from short-circuit damage. typical no load quiescent current is 42 a. functional block diagram en lx err. amp logic dh dl pgnd fb gnd input v ref vin vp mode/sync
11 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 thermal protection completely disables switching when the maximum junction temperature is detected. the junction over-temperature threshold is 140c with 15c of hysteresis. once an over-temperature or over-current fault condition is removed, the output voltage automati- cally recovers. peak current mode control and optimized internal com- pensation provide high loop bandwidth and excellent response to input voltage and fast load transient events. soft start eliminates output voltage overshoot when the enable or the input voltage is applied. under-voltage lockout prevents spurious start-up events. control loop the aat1112 is a peak current mode step-down con- verter. the current through the p-channel mosfet (high side) is sensed for current loop control, as well as short- circuit and overload protection. a fixed slope compensa- tion signal is added to the sensed current to maintain stability for duty cycles greater than 50%. the peak cur- rent mode loop appears as a voltage-programmed cur- rent source in parallel with the output capacitor. the output of the voltage error amplifier programs the current mode loop for the necessary peak switch current to force a constant output voltage for all load and line conditions. internal loop compensation terminates the transconductance voltage error amplifier output. the reference voltage is internally set to program the con- verter output voltage greater than or equal to 0.6v. soft start/enable soft start limits the current surge seen at the input and eliminates output voltage overshoot. when pulled low, the enable input forces the aat1112 into a low-power, non-switching state. the total input current during shut- down is less than 1 a. current limit and over-temperature protection for overload conditions, the peak input current is limit- ed. to minimize power dissipation and stresses under current limit and short-circuit conditions, switching is terminated after entering current limit for a series of pulses. switching is terminated for seven consecutive clock cycles after a current limit has been sensed for a series of four consecutive clock cycles. thermal protection completely disables switching when internal dissipation becomes excessive. the junction over-temperature threshold is 140c with 15c of hys- teresis. once an over-temperature or over-current fault conditions is removed, the output voltage automatically recovers. under-voltage lockout internal bias of all circuits is controlled via the vin input. under-voltage lockout (uvlo) guarantees sufficient v in bias and proper operation of all internal circuitry prior to activation. pgnd 1 fb 6 vp 11 lx 12 en 8 n/c 4 pgnd 3 pgnd 2 vcc 7 sync 9 gnd 5 n/c 10 aat1112 tdfn33-12 u1 v in 3.3v 1 2 3 enable 10f c1 22 f c2 r2 59k r3 (optional) c3 3.3h l1 1 2 3 sync figure 1: aat1112 schematic.
12 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 component selection inductor selection the step-down converter uses peak current mode con- trol with slope compensation to maintain stability for duty cycles greater than 50%. the output inductor value must be selected so the inductor current down slope meets the internal slope compensation requirements. the inductor should be set equal to the output voltage numeric value in h. this guarantees that there is suf- ficient internal slope compensation. manufacturer?s specifications list both the inductor dc current rating, which is a thermal limitation, and the peak current rating, which is determined by the satura- tion characteristics. the inductor should not show any appreciable saturation under normal load conditions. some inductors may meet the peak and average current ratings yet result in excessive losses due to a high dcr. always consider the losses associated with the dcr and its effect on the total converter efficiency when selecting an inductor. the 3.3 h cdrh4d28 series sumida inductor has a 49.2m ? worst case dcr and a 1.57a dc current rating. at full 1.5a load, the inductor dc loss is 97mw which gives less than 1.5% loss in efficiency for a 1.5a, 3.3v output. input capacitor select a 10 f to 22 f x7r or x5r ceramic capacitor for the input. to estimate the required input capacitor size, determine the acceptable input ripple level (v pp ) and solve for c. the calculated value varies with input volt- age and is a maximum when v in is double the output voltage. ?? 1 - ?? v o v in c in = v o v in ?? - esr f s ?? v pp i o ?? 1 - = for v in = 2 v o ?? v o v in v o v in 1 4 c in(min) = 1 ?? - esr 4 f s ?? v pp i o always examine the ceramic capacitor dc voltage coef- ficient characteristics when selecting the proper value. for example, the capacitance of a 10 f, 6.3v, x5r ceramic capacitor with 5.0v dc applied is actually about 6 f. the maximum input capacitor rms current is: ?? i rms = i o 1 - ?? v o v in v o v in the input capacitor rms ripple current varies with the input and output voltage and will always be less than or equal to half of the total dc load current. ?? 1 - = d (1 - d) = 0.5 2 = ?? v o v in v o v in 1 2 for v in = 2 v o i o rms(max) i 2 = the term ? ? 1 - ? ? v o v in v o v in appears in both the input voltage ripple and input capacitor rms current equations and is a maximum when v o is twice v in . this is why the input voltage ripple and the input capacitor rms current ripple are a maximum at 50% duty cycle. the input capacitor provides a low impedance loop for the edges of pulsed current drawn by the aat1112. low esr/esl x7r and x5r ceramic capacitors are ideal for this function. to minimize stray inductance, the capacitor should be placed as closely as possible to the ic. this keeps the high frequency content of the input current localized, minimizing emi and input voltage ripple. the proper placement of the input capacitor (c1) can be seen in the evaluation board layout in the layout section of this datasheet (see figure 2). a laboratory test set-up typically consists of two long wires running from the bench power supply to the evalu- ation board input voltage pins. the inductance of these wires, along with the low-esr ceramic input capacitor, can create a high q network that may affect converter performance. this problem often becomes apparent in the form of excessive ringing in the output voltage dur- ing load transients. errors in the loop phase and gain measurements can also result. since the inductance of a short pcb trace feeding the
13 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 input voltage is significantly lower than the power leads from the bench power supply, most applications do not exhibit this problem. in applications where the input power source lead induc- tance cannot be reduced to a level that does not affect the converter performance, a high esr tantalum or alu- minum electrolytic should be placed in parallel with the low esr/esl bypass ceramic capacitor. this dampens the high q network and stabilizes the system. output capacitor the output capacitor limits the output ripple and pro- vides holdup during large load transitions. a 10 f to 22 f x5r or x7r ceramic capacitor typically provides sufficient bulk capacitance to stabilize the output during large load transitions and has the esr and esl charac- teristics necessary for low output ripple. the output voltage droop due to a load transient is dominated by the capacitance of the ceramic output capacitor. during a step increase in load current, the ceramic output capacitor alone supplies the load current until the loop responds. within two or three switching cycles, the loop responds and the inductor current increases to match the load current demand. the rela- tionship of the output voltage droop during the three switching cycles to the output capacitance can be esti- mated by: c out = 3 i load v droop f s once the average inductor current increases to the dc load level, the output voltage recovers. the above equa- tion establishes a limit on the minimum value for the output capacitor with respect to load transients. the internal voltage loop compensation also limits the minimum output capacitor value to 10 f. this is due to its effect on the loop crossover frequency (bandwidth), phase margin, and gain margin. increased output capac- itance will reduce the crossover frequency with greater phase margin. adjustable output resistor selection the output voltage on the aat1112 is programmed with external resistors r1 and r2. to limit the bias current required for the external feedback resistor string while maintaining good noise immunity, the minimum sug- gested value for r2 is 59k ? . although a larger value will further reduce quiescent current, it will also increase the impedance of the feedback node, making it more sensi- tive to external noise and interference. table 1 sum- marizes the resistor values for various output voltages with r2 set to either 59k ? for good noise immunity or 221k ? for reduced no load input current. v out (v) r2 = 59k ?? r1 (k ? ) r2 = 221k ?? r1 (k ? ) 0.8 19.6 75 0.9 29.4 113 1.0 39.2 150 1.1 49.9 187 1.2 59.0 221 1.3 68.1 261 1.4 78.7 301 1.5 88.7 332 1.8 118 442 1.85 124 464 2.0 137 523 2.5 187 715 3.0 237 887 3.3 267 1000 table 1: aat1112 resistor values for various output voltages. thermal calculations there are three types of losses associated with the aat1112 step-down converter: switching losses, con- duction losses, and quiescent current losses. conduction losses are associated with the r ds(on) characteristics of the power output switching devices. switching losses are dominated by the gate charge of the power output switching devices. at full load, assuming continuous con- duction mode (ccm), a simplified form of the losses is given by: p total i o 2 (r ds(on)h v o + r ds(on)l [v in - v o ]) v in = + (t sw f s i o + i q ) v in i q is the step-down converter quiescent current. the term t sw is used to estimate the full load step-down con- verter switching losses.
14 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 for the condition where the step-down converter is in dropout at 100% duty cycle, the total device dissipation reduces to: p total = i o 2 r ds(on)h + i q v in since r ds(on) , quiescent current, and switching losses all vary with input voltage, the total losses should be inves- tigated over the complete input voltage range. given the total losses, the maximum junction tempera- ture can be derived from the ? ja for the tdfn3-12 and tsopjw-12 packages, which is 50c/w and 160c/w respectively. t j(max) = p total ja + t amb layout the suggested pcb layout for the aat1112 is shown in figures 2 and 3. the following guidelines should be used to help ensure a proper layout. 1. the input capacitor (c1) should connect as closely as possible to vp and pgnd. 2. c2 and l1 should be connected as closely as possi- ble. the connection of l1 to the lx pin should be as short as possible. 3. the feedback trace or fb pin should be separate from any power trace and connect as closely as pos- sible to the load point. sensing along a high-current load trace will degrade dc load regulation. 4. the resistance of the trace from the load return to pgnd should be kept to a minimum. this will help to minimize any error in dc regulation due to differ- ences in the potential of the internal signal ground and the power ground. 5. connect unused signal pins to ground to avoid unwanted noise coupling. figure 2: aat1112 evaluation board top side layout.
15 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 figure 3: aat1112 evaluation board bottom side layout.
16 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 design example specifications v o 3.3v @ 1.5a, pulsed load ? i load = 1.5a v in 2.7v to 4.2v (3.6v nominal) f s 1.2mhz t amb 85c in tdfn33-12 package output inductor l1 = v o ( h) = 3.3 h; see table 2. for sumida inductor cdrh4d28 3.3 h dcr = 49.2m ? max. v o v o1 3.3 v 3.3v i 1 = ? 1 - = ? 1 - = 179m a l1 ? f s v in 3.3h ? 1.2mhz 4.2v i pk1 = i o1 + i 1 = 1.5a + 0.089a = 1.59a 2 p l1 = i o1 2 ? dcr = 1.5a 2 ? 49.2m = 110mw ? ? ? ? ? ? ? ? output capacitor v droop = 0.2v 1 23 1 3.3v (4.2v - 3.3v) 3.3h 1.2mhz 4.2v 23 rms(max) i l f s v in(max) = 3 i load v droop f s 3 1.5a 0.2v 1.2mhz c out = = = 18.8f; use 22f = 52marms (v out ) (v in(max) - v out ) = p esr = esr i rms 2 = 5m (52ma) 2 = 13.3w input capacitor input ripple v pp = 50mv c in = = = 7.3f; use 10f 1 ?? - esr 4 f s ?? v pp i o1 + i o2 1 ?? - 5m 4 1.2mhz ?? 50mv 1.5a i o rms(max) i p = esr i rms 2 = 5m (0.75a) 2 = 3mw 2 = = 0.75arms
17 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 aat1112 losses total losses can be estimated by calculating the dropout (v in = v o ) losses where the power mosfet r ds(on) will be at the maximum value. all values assume an 85c ambient temperature and a 120c junction temperature with the tdfn 50c/w package. p loss = i o1 2 r ds(on)h = 1.5a 2 0.16 = 0.36w t j(max) = t amb + ja p loss = 85 c + (50 c/w) 360mw = 103 c the total losses are also investigated at the nominal lithium-ion battery voltage (3.6v). the simplified version of the r ds(on) losses assumes that the n-channel and p-channel r ds(on) are equal. p total = i o 2 r ds(on) + (t sw f s i o + i q ) v in = 1.5a 2 152m + (5ns 1.2mhz 1.5a + 50 a) 3.6v = 375mw t j ( max ) = t amb + ja p loss = 85 c + (50 c/w) 375mw = 104 c v out (v) inductance ( h) part number manufacturer size (mm) rated current (a) i rms (a) i sat (a) dcr ( ? ) 3.3 3.3 cdrh4d28 sumida 5x5x3 1.57 36.4 2.5 2.2 cdrh4d28 sumida 5x5x3 2.04 23.2 1.8 1.8 cdrh4d28 sumida 5x5x3 2.2 20.4 1.5 1.8 cdrh4d28 sumida 5x5x3 2.2 20.4 1.2 1.2 cdrh4d28 sumida 5x5x3 2.56 17.5 1.0 1.0 sd3114-1.0 cooper 3.1x3.1x1.45 1.67 2.07 0.042 0.8 1.0 sd3114-1.0 cooper 3.1x3.1x1.45 1.67 2.07 0.042 0.6 1.0 sd3114-1.0 cooper 3.1x3.1x1.45 1.67 2.07 0.042 table 2: surface mount inductors. manufacturer part number value voltage temp. co. case murata grm21br60j106ke19 10 f 6.3v x5r 0805 murata grm21br60j226me39 22 f 6.3v x5r 0805 table 3: surface mount capacitors.
18 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 ordering information package marking 1 part number (tape and reel) 2 tsopjw-12 yvxyy aat1112itp-0.6-t1 tdfn33-12 sbxyy aat1112iwp-0.6-t1 skyworks green? products are compliant with all applicable legislation and are halogen-free. for additional information, refer to skyworks de?ition of green , document number sq04-0074. package information 3 tsopjw-12 0.20 + 0.10 - 0.05 0.055 0.045 0.45 0.1 5 7 nom 4 4 3.00 0.10 2.40 0.10 2.85 0.20 0.50 bsc 0.50 bsc 0.50 bsc 0.50 bsc 0.50 bsc 0.15 0.05 0.9625 0.0375 1.00 + 0.10 - 0.065 0.04 ref 0.010 2.75 0.25 all dimensions in millimeters. 1. xyy = assembly and date code. 2. sample stock is generally held on part numbers listed in bold . 3. the leadless package family, which includes qfn, tqfn, dfn, tdfn and stdfn, has exposed copper (unplated) at the end of the lead terminals due to the manufacturing process. a solder fillet at the exposed copper edge cannot be guaranteed and is not required to ensure a proper bottom solder connection.
19 aat1112 1.5a, 1.4mhz step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201972b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 15, 2013 copyright ? 2012, 2013 skyworks solutions, inc. all rights reserved. information in this document is provided in connection with skyworks solutions, inc. (?skyworks?) products or services. these m aterials, including the information contained herein, are provided by skyworks as a service to its customers and may be used for informational purposes only by the customer. skyworks assumes no responsibility fo r errors or omissions in these materials or the information contained herein. sky- works may change its documentation, products, services, speci cations or product descriptions at any time, without notice. skyworks makes no commitment to update the materials or informati on and shall have no responsibility whatsoever for con icts, incompatibilities, or other dif culties arising from any future changes. no license, whether express, implied, by estoppel or otherwise, is granted to any intellectual property rights by this document . skyworks assumes no liability for any materials, products or information provided here- under, including the sale, distribution, reproduction or use of skyworks products, information or materials, except as may be p rovided in skyworks terms and conditions of sale. the materials, products and information are provided ?as is? without warranty of any kind, whether express, implied, statutory, or otherwise, including fitness for a particular purpose or use, merchantability, performance, quality or non-infringement of any intellectual property right; all such warranti es are hereby expressly disclaimed. skyworks does not warrant the accuracy or completeness of the information, text, graphics or other items contained within these materials. sk yworks shall not be liable for any damages, in- cluding but not limited to any special, indirect, incidental, statutory, or consequential damages, including without limitation , lost revenues or lost profits that may result from the use of the materials or information, whether or not the recipient of materials has been advised of the possibility of such damage. skyworks products are not intended for use in medical, lifesaving or life-sustaining applications, or other equipment in which the failure of the skyworks products could lead to personal injury, death, physical or en- vironmental damage. skyworks customers using or selling skyworks products for use in such applications do so at their own risk and agree to fully indemnify skyworks for any damages resulting from such improper use or sale. customers are responsible for their products and applications using skyworks products, which may deviate from published speci cations as a result of design defects, errors, or operation of products outside of pub- lished parameters or design speci cations. customers should include design and operating safeguards to minimize these and other risks. skyworks assumes no liabi lity for applications assistance, customer product design, or damage to any equipment resulting from the use of skyworks products outside of stated published speci cations or parameters. skyworks, the skyworks symbol, and ?breakthrough simplicity? are trademarks or registered trademarks of skyworks solutions, inc ., in the united states and other countries. third-party brands and names are for identi cation purposes only, and are the property of their respective owners. additional information, including relevant terms and co nditions, posted at www.skyworksinc.com, are incorporated by reference. tdfn33-12 top view bottom view detail "a" side view 3.00 all dimensions in millimeters.

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