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1 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 typical application 4.7 h l1 118k r1 4.7 f c1 59k r2 4.7 f c2 en 1 out 2 vin 3 lx 4 agnd 5 pgnd 6 pgnd 7 pgnd 8 aat1147 u1 v in v o = 1.8v general description the aat1147 switchreg is a member of skyworks' total power management ic? (tpmic?) product family. it is a fixed frequency 1.4mhz step-down converter with an input voltage range of 2.7v to 5.5v and output voltage as low as 0.6v. the aat1147 is optimized for low noise portable applica- tions, reacts quickly to load variations, and reaches peak efficiency at heavy load. the aat1147 output voltage is programmable with external feedback resistors. it can deliver 400ma of load current while maintaining high power efficiency. the 1.4mhz switching frequency minimizes the size of exter- nal components while keeping switching losses low. the aat1147 is available in a pb-free, space-saving 2.0x2.1mm sc70jw-8 package and is rated over the -40c to +85c temperature range. features v in range: 2.7v to 5.5v v out adjustable from 0.6v to v in 400ma output current up to 98% efficiency low noise, 1.4mhz fixed frequency pwm operation fast load transient 150 s soft start over-temperature and current limit protection 100% duty cycle low dropout operation <1 a shutdown current 8-pin sc70jw package temperature range: -40c to +85c applications cellular phones digital cameras handheld instruments microprocessor/dsp core /io power pdas and handheld computers usb devices downloaded from: http:///
2 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 pin descriptions pin # symbol function 1 en enable pin. 2 out feedback input pin. this pin is connected to an external resistive divider for an adjustable output. 3 vin input supply voltage for the converter. 4l x switching node. connect the inductor to this pin. it is connected internally to the drain of both high- and low-side mosfets. 5 agnd non-power signal ground pin. 6, 7, 8 pgnd main power ground return pins. connect to the output and input capacitor return. pin configuration sc70jw-8 (top view) out vin lx pgndpgnd pgnd agnd en 12 3 45 6 7 8 downloaded from: http:///
3 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 1. stresses above those listed in absolute maximum ratings may cause permanent damage to the device. functional operation at conditions 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. 3. derate 6.25mw/c above 25c. absolute maximum ratings 1 symbol description value units v in input voltage to gnd 6.0 v v lx lx to gnd -0.3 to v in + 0.3 v v out out to gnd -0.3 to v in + 0.3 v v en 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 2 symbol description value units p d maximum power dissipation 3 0.625 w ? ja thermal resistance 160 c/w downloaded from: http:///
4 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 1. the aat1147 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. electrical characteristics 1 t a = -40c to +85c, unless otherwise noted. typical values are t a = 25c, v in = 3.6v. symbol description conditions min typ max units step-down converter v in input voltage 2.7 5.5 v v uvlo uvlo threshold v in rising 2.7 v hysteresis 100 mv v in falling 1.8 v v out output voltage tolerance i out = 0 to 400ma, v in = 2.7v to 5.5v -3.0 3.0 % v out output voltage range 0.6 v in v i q quiescent current no load 160 300 a i shdn shutdown current en = agnd = pgnd 1.0 a i lim p-channel current limit 600 ma r ds(on)h high side switch on resistance 0.45 ? r ds(on)l low side switch on resistance 0.40 ? i lxleak lx leakage current v in = 5.5v, v lx = 0 to v in , en = gnd 1 a ? v linereg line regulation v in = 2.7v to 5.5v 0.1 %/v v out out threshold voltage accuracy 0.6v output, no load, t a = 25c 591 600 609 mv i out out leakage current 0.6v output 0.2 a t s start-up time from enable to output regulation 150 s f osc oscillator frequency 1.0 1.4 2.0 mhz t sd over-temperature shutdown threshold 140 c t hys over-temperature shutdown hysteresis 15 c en v en(l) enable threshold low 0.6 v v en(h) enable threshold high 1.4 v i en input low current v in = v out = 5.5v -1.0 1.0 a downloaded from: http:///
5 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 typical characteristics efficiency vs. load (v out = 3.3v; l = 6.8h) output current (ma) efficiency (%) 0 20 40 60 80 100 1 10 100 100 0 v in = 3.6v v in = 4.2v v in = 5.0v dc regulation (v out = 3.3v) output current (ma) output error (%) -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 0.1 1 10 100 1000 v in = 3.6v v in = 4.2v v in = 5.0v efficiency vs. load (v out = 2.5v; l = 6.8h) output current (ma) efficiency (%) 0 20 40 60 80 100 1 10 100 1000 v in = 3.6v v in = 4.2v v in = 5.0v dc regulation (v out = 2.5v) output current (ma) output error (%) -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 0.1 1 10 100 1000 v in = 5.0v v in = 4.2v v in = 3.6v efficiency vs. load (v out = 1.8v; l = 4.7h) output current (ma) efficiency (%) 0 20 40 60 80 100 1 10 100 1000 v in = 3.0v v in = 3.6v v in = 4.2v dc regulation (v out = 1.8v) output current (ma) output error (%) -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 0.1 1 10 100 1000 v in = 3.6v v in = 4.2v v in = 3.0v downloaded from: http:///
6 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 typical characteristics line regulation (v out = 3.3v) input voltage (v) accuracy (%) -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 i out = 400ma i out = 10ma i out = 1ma line regulation (v out = 2.5v) input voltage (v) accuracy (%) -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 i out = 400ma i out = 10ma i out = 1ma line regulation (v out = 1.8v) input voltage (v) accuracy (%) -0.5 -0.4 -0.3 -0.2 -0.1 0.0 0.1 0.2 0.3 0.4 0.5 3.0 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 i out = 400ma i out = 10ma i out = 1ma frequency vs. input voltage input voltage (v) frequency variation (%) -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 2.5 2.9 3.3 3.7 4.1 4.5 4.9 5.3 v out = 1.8v v out = 3.3v v out = 2.5v output voltage error vs. temperature (v in = 3.6v; v out = 1.8v; i out = 400ma) temperature ( c) output error (%) -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 -40 -25 -10 5 20 35 50 65 80 95 switching frequency vs. temperature (v in = 3.6v; v out = 1.8v) temperature ( c) variation (%) -15 -12 -9 -6 -3 0 3 6 9 12 15 -40 -25 -10 5 20 35 50 65 80 95 downloaded from: http:///
7 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 typical characteristics no-load quiescent current vs. input voltage input voltage (v) supply current (a) 120 130 140 150 160 170 180 190 200 210 220 2.5 3.0 3.5 4.0 4.5 5.0 5.5 85 c -40 c 25 c line transient response (40ma to 400ma; v in = 3.6v; v out = 1.8v; c 1 = 4.7f; c ff = 100pf) output voltage (top) (v) load and inductor current (bottom) (200ma/div) time (25s/div) 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 40 ma 400 ma line transient response (40ma to 400ma; v in = 3.6v; v out = 1.8v; c 1 = 4.7f) output voltage (top) (v) load and inductor current (bottom) (200ma/div) time (25s/div) 1.0 1.1 1.2 1.3 1.4 1.5 1.6 1.7 1.8 1.9 2.0 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 400ma 40ma soft start (v in = 3.6v; v out = 1.8v; i out = 400ma) enable and output voltage (top) (v) inductor current (bottom) (a) time (25s/div) -2.4 -1.6 -0.8 0.0 0.8 1.6 2.4 3.2 4.0 4.8 5.6 -0.4 0.0 0.4 0.8 1.2 1.6 2.0 2.4 2.8 3.2 3.6 line response (v out = 1.8v @ 400ma) output voltage (top) (v) input voltage (bottom) (v) time (25s/div) 1.40 1.45 1.50 1.55 1.60 1.65 1.70 1.75 1.80 1.85 1.90 3.2 3.4 3.6 3.8 4.0 4.2 4.4 4.6 4.8 5.0 5.2 output ripple (v in = 3.6v; v out = 1.8v; i out = 400ma) output voltage (ac coupled) (top) (mv) inductor current (bottom) (a) time (500ns/div) -120 -100 -80 -60 -40 -20 0 20 40 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 downloaded from: http:///
8 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 functional description the aat1147 is a high performance 400ma 1.4mhz monolithic step-down converter. it has been designed with the goal of minimizing external component size and optimizing efficiency at heavy load. apart from the small bypass input capacitor, only a small l-c filter is required at the output. typically, a 4.7 h inductor and a 4.7 f ceramic capacitor are recommended (see table of val- ues). only three external power components (c in , c out , and l) are required. output voltage is programmed with exter- nal resistors and ranges from 0.6v to the input voltage. an additional feed-forward capacitor can also be added to the external feedback to provide improved transient response (see figure 1). 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. the input voltage range is 2.7v to 5.5v. the converter efficiency has been optimized for heavy load conditions up to 400ma. the internal error amplifier and compensation provide excellent transient response, load, and line regulation. soft start eliminates any output voltage overshoot when the enable or the input voltage is applied. functional block diagram en lx err . amp logic dh dl pgnd vin agnd voltage reference input out downloaded from: http:///
9 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 l1 cdrh3d16-4r7 4.7 h l1 10 f c1 4.7 f c2 u1 aat1147 sc70jw-8 c2 4.7 f 10v 0805 x5r v out =1.8v gnd v in 1 2 3 enable lx en 1 out 2 vin 3 lx 4 agnd 5 pgnd 6 pgnd 7 pgnd 8 aat1147 u1 gnd2 118k r1 59k r2 c1 10 f 6.3v 0805 x5r 100pf c4 n/a c3 figure 1: enhanced transient response schematic. control loop the aat1147 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 error amplifier reference is 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 aat1147 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. downloaded from: http:///
10 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 applications informationinductor 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 internal slope compensation for the aat1147 is 0.24a/ sec. this equates to a slope compensation that is 75% of the inductor current down slope for a 1.5v output and 4.7 h inductor. 0.75 ? v o m = = = 0.24 l 0.75 ? 1.5v 4.7 h a sec this is the internal slope compensation. when externally programming the 0.6v version to 2.5v, the calculated inductance is 7.5 h. 0.75 ? v o l = = 3 ? v o = 3 ? 2.5v = 7.5 h m 0.75 ? v o 0.24a sec a sec a a sec in this case, a standard 6.8 h value is selected. table 1 displays inductor values for the aat1147. manufacturers 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 4.7 h cdrh3d16 series inductor selected from sumida has a 105m ? dcr and a 900ma dc current rat- ing. at full load, the inductor dc loss is 17mw which gives a 2.8% loss in efficiency for a 400ma, 1.5v output. input capacitorselect a 4.7 f to 10 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 voltage 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 14 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 ceram- ic capacitor with 5.0v dc applied is actually about 6 f. con ? guration output voltage inductor 0.6v adjustable with external feedback 1v, 1.2v 2.2 h 1.5v, 1.8v 4.7 h 2.5v, 3.3v 6.8 h table 1: inductor values. 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 12 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. downloaded from: http:///
11 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 figure 2: aat1147 evaluation board figure 3: exploded view of evaluation top side. board top side layout. figure 4: aat1147 evaluation board bottom side. the input capacitor provides a low impedance loop for the edges of pulsed current drawn by the aat1147. 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 (c2) can be seen in the evaluation board layout in 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. downloaded from: http:///
12 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 since the inductance of a short pcb trace feeding the 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. 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 4.7 f to 10 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 dom- inated 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 relationship of the output volt- age droop during the three switching cycles to the output capacitance can be estimated 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 4.7 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. the maximum output capacitor rms ripple current is given by: 1 23 v out (v in(max) - v out ) rms(max) i l f s v in(max) = dissipation due to the rms current in the ceramic output capacitor esr is typically minimal, resulting in less than a few degrees rise in hot-spot temperature. output resistor selection the output voltage of the aat1147 0.6v version can be externally programmed. resistors r1 and r2 of figure 5 program the output to regulate at a voltage higher than 0.6v. to limit the bias current required for the external feedback resistor string while maintaining good noise immunity, the minimum suggested value for r2 is 59k ? . although a larger value will further reduce quiescent cur- rent, it will also increase the impedance of the feedback node, making it more sensitive to external noise and interference. table 2 summarizes 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. ???? r1 = -1 r2 = - 1 59k = 88.5k v out v ref ???? 1.5v 0.6v the aat1147, combined with an external feedforward capacitor (c4 in figure 1), delivers enhanced transient response for extreme pulsed load applications. the addi- tion of the feedforward capacitor typically requires a larger output capacitor c1 for stability. 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 3.3 267 1000 table 2: resistor values for use with 0.6v step-down converter. downloaded from: http:///
13 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 l1 cdrh3d16-4r7 4.7 h l1 10 f c1 4.7 f c2 u1 aat1147 sc70jw-8 c1 10 f 10v 0805 x5r c2 4.7 f 10v 0805 x5r v out gnd v in 1 2 3 enable lx en 1 out 2 vin 3 lx 4 agnd 5 pgnd 6 pgnd 7 pgnd 8 aat1147 u1 gnd2 118k r1 59k r2 figure 5: aat1147 evaluation board schematic. thermal calculations there are three types of losses associated with the aat1147 step-down converter: switching losses, conduc- tion 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 switch- ing devices. at full load, assuming continuous conduction mode (ccm), a simplified form of the losses is given by: 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. p total i o 2 (r dson(h) v o + r dson(l) [v in - v o ]) v in = + (t sw f s i o + i q ) v in 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 dson(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 sc70jw-8 pack- age which is 160c/w. t j(max) = p total ja + t amb downloaded from: http:///
14 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 layout the suggested pcb layout for the aat1147 is shown in figures 2, 3, and 4. the following guidelines should be used to help ensure a proper layout. 1. the input capacitor (c2) should connect as closely as possible to v in (pin 3) and pgnd (pins 6-8). 2. c1 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 out pin (pin 2) should be separate from any power trace and connect as close- ly as possible to the load point. sensing along a high-current load trace will degrade dc load regula- tion. external feedback resistors should be placed as closely as possible to the out pin (pin 2) to minimize the length of the high impedance feedback trace. 4. the resistance of the trace from the load return to the pgnd (pins 6-8) should be kept to a minimum. this will help to minimize any error in dc regulation due to differences in the potential of the internal signal ground and the power ground. a high density, small footprint layout can be achieved using an inexpensive, miniature, non-shielded, high dcr inductor. an evaluation board is available with this induc- tor and is shown in figure 6. the total solution footprint area is 40mm 2 . figure 6: minimum footprint evaluation board using 2.0mm x 1.6mm x 0.95mm inductor. downloaded from: http:///
15 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 step-down converter design examplespecifications v o = 1.8v @ 400ma (adjustable using 0.6v version), pulsed load ? i load = 300ma v in = 2.7v to 4.2v (3.6v nominal) f s = 1.4mhz t amb = 85c 1.8v output inductor l1 = 3 ? v o2 = 3 ? 1.8v = 5.4 h sec a sec a (use 4.7 h; see table 1) for sumida inductor cdrh3d16, 4.7 h, dcr = 105m ? . v o v o 1.8 v 1.8v i l1 = ? 1 - = ? 1 - = 156ma l1 ? f s v in 4.7 h ? 1.4mhz 4.2v i pkl1 = i o + i l1 = 0.4a + 0.068a = 0.468a 2 p l1 = i o 2 ? dcr = 0.4a 2 ? 105m = 17mw ?? ?? ?? ?? 1.8v output capacitorv droop = 0.1v 1 23 1 1.8v (4.2v - 1.8v) 4.7 h 1.4mhz 4.2v 23 rms i l1 f s v in(max) = 3 i load v droop f s 3 0.3a 0.1v 1.4mhz c out = = = 6.4 f; use 10f = 45marms (v o ) (v in(max) - v o ) = p esr = esr i rms 2 = 5m (45ma) 2 = 10 w downloaded from: http:///
16 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 input capacitorinput ripple v pp = 25mv c in = = = 3.11 f; use 4.7 f 1 ?? - esr 4 f s ?? v pp i o 1 ?? - 5m 4 1.4mhz ?? 25mv 0.4a i o rms ip = esr i rms 2 = 5m (0.2a) 2 = 0.2mw 2 = = 0.2arms aat1147 losses p total + (t sw f s i o + i q ) v in i o 2 (r dson(h) v o + r dson(l) [v in -v o ] ) v in = t j(max) = t amb + ja p loss = 85 c + ( 160 c/w ) 126mw = 105.1 c downloaded from: http:///
17 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 1. for reduced quiescent current, r2 and r4 = 221kw. adjustable version (0.6v device) v out (v) r2 = 59k r1 (k ) r2 = 221k 1 r1 (k ) l1 ( h) 0.8 19.6 75.0 2.2 0.9 29.4 113 2.2 1.0 39.2 150 2.2 1.1 49.9 187 2.2 1.2 59.0 221 2.2 1.3 68.1 261 2.2 1.4 78.7 301 4.7 1.5 88.7 332 4.7 1.8 118 442 4.7 1.85 124 464 4.7 2.0 137 523 6.8 2.5 187 715 6.8 3.3 267 1000 6.8 table 3: evaluation board component values. manufacturer part number inductance ( h) max dc current (a) dcr ( ) size (mm) lxwxh type sumida cdrh3d16-2r2 2.2 1.20 0.072 3.8x3.8x1.8 shielded sumida cdrh3d16-4r7 4.7 0.90 0.105 3.8x3.8x1.8 shielded sumida cdrh3d16-6r8 6.8 0.73 0.170 3.8x3.8x1.8 shielded murata lqh2mcn4r7m02 4.7 0.40 0.80 2.0x1.6x0.95 non-shielded murata lqh32cn4r7m23 4.7 0.45 0.20 2.5x3.2x2.0 non-shielded coilcraft lpo3310-472 4.7 0.80 0.27 3.2x3.2x1.0 1mm coiltronics sd3118-4r7 4.7 0.98 0.122 3.1x3.1x1.85 shielded coiltronics sd3118-6r8 6.8 0.82 0.175 3.1x3.1x1.85 shielded coiltronics sdrc10-4r7 4.7 1.30 0.122 5.7x4.4x1.0 1mm shielded table 4: typical surface mount inductors. manufacturer part number value voltage temp. co. case murata grm219r61a475ke19 4.7 f 10v x5r 0805 murata grm21br60j106ke19 10 f 6.3v x5r 0805 murata grm21br60j226me39 22 f 6.3v x5r 0805 table 5: surface mount capacitors. downloaded from: http:///
18 aat1147 high efficiency, low noise, fast transient 400ma step-down converter data sheet skyworks solutions, inc. phone [781] 376-3000 fax [781] 376-3100 sales@skyworksinc.com www.skyworksinc.com 201986a skyworks proprietary information products and product information are subject to change without notice. may 23, 2012 copyright ? 2012 skyworks solutions, inc. all rights reserved. information in this document is provided in connection with skyworks solutions, inc. (skyworks) products or services. these materials, including the information contained herein, are provided by sky works 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 information 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 informatio n provided here- under, including the sale, distribution, reproduction or use of skyworks products, information or materials, except as may be provided 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. skyworks 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 conditions, posted at www.skyworksinc.com, are incorporated by reference. 1. xyy = assembly and date code. 2. sample stock is generally held on part numbers listed in bold . ordering information package marking 1 part number (tape and reel) 2 sc70jw-8 scxyy aat1147ijs-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 sc70jw-8 0.225 0.075 0.45 0.10 0.05 0.05 2.10 0.30 2.00 0.20 7 3 4 4 1.75 0.10 0.85 0.15 0.15 0.05 1.10 max 0.100 2.20 0.20 0.048ref 0.50 bsc 0.50 bsc 0.50 bsc all dimensions in millimeters. downloaded from: http:///

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