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1 AAT2148 low-noise, fast transient 1a step-down converter data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 general description the AAT2148 switchreg is a 2mhz step-down converter with an input voltage range of 2.7v to 5.5v and output voltage as low as 0.6v. it is optimized to react quickly to a load variation. the AAT2148 incorporates a unique low noise architecture which reduces ripple and spectral noise. the AAT2148 is available in fixed voltage versions with internal feedback and a programmable version with external feedback resistors. it can deliver 1a of load cur- rent while maintaining a low 37 a no load quiescent current. the 2mhz switching frequency minimizes the size of external components while keeping switching losses low. the AAT2148 is designed to maintain high efficiency throughout the operating range, which is critical for por- table applications. the AAT2148 is available in the pb-free, thermally enhanced 3x3mm qfn-16 package and is rated over the -40c to +85c temperature range. features ? v in range: 2.7v to 5.5v ? low noise light load mode ? low ripple pwm mode ? v out fixed or adjustable from 0.6v to v in ? 37 a no load quiescent current ? up to 98% efficiency ? 1a max output current ? 2mhz switching frequency ? 150 s soft start ? fast load transient ? over-temperature protection ? current limit protection ? 100% duty cycle low-dropout operation ? <1 a shutdown current ? qfn33-16 package ? temperature range: -40c to +85c applications ? cellular phones ? digital cameras ? handheld instruments ? microprocessor / dsp core / io power ? pdas and handheld computers ? usb devices typical application (adjustable output voltage) l1 4.7h r1 118k r2 59k c1 4.7f c2 4.7f v in 2.7v - 5.5v v o 1.8v, 1a vp 11 vp 12 vp 10 lx 13 vcc 9 pgnd 1 fb 4 en 7 pgnd 2 pgnd 3 lx 14 lx 15 u1 AAT2148
skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 2 AAT2148 low-noise, fast transient 1a step-down converter data sheet pin descriptions pin # symbol function 1, 2, 3 pgnd power ground pin 4fb feedback input. this pin is connected either directly to the converter output or to an external resis- tive divider for an adjustable output. 5, 6, 8, 16 n/c not internally connected. 9 vcc bias supply. supplies power for the internal circuitry. connect to input power. 10, 11, 12 vp input supply voltage for the converter power stage. must be closely decoupled to gnd. 13, 14, 15 lx switching node. connect the inductor to this pin. it is internally connected to the drain of both high- and low-side mosfets. ep exposed paddle (bottom); connect to pgnd directly beneath package. pin configuration qfn33-16 (top view) vp vp vp n/c pgnd pgnd pgnd 1 2 3 4 n/c n/c en 16 15 14 13 5 6 7 8 12 11 10 9 n/c vcc lx lx lx fb
skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 3 AAT2148 low-noise, fast transient 1a step-down converter data sheet absolute maximum ratings 1 symbol description value units v in input voltage 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 v in + 0.3 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 2, 3 2w ? ja thermal resistance 2 50 c/w 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. 3. derate 6.25mw/c above 25c.
skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 4 AAT2148 low-noise, fast transient 1a step-down converter data sheet 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 1.8 2.7 v hysteresis 100 mv v out output voltage tolerance i out = 0ma to 1a, 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, 0.6v adjustable version 37 70 a i shdn shutdown current en = agnd = pgnd 1.0 a i lim p-channel current limit 1300 1700 ma r ds(on)h high side switch on resistance 0.35 ? r ds(on)l low side switch on resistance 0.30 ? ? v linereg line regulation v in = 2.7v to 5.5v; i out = 1a 0.1 %/v v fb feedback threshold voltage accuracy 0.6v output, no load; t a = 25c 591 600 609 mv i fb feedback leakage current 0.6v output 1 a t s start-up time from enable to output regulation 150 s f osc oscillator frequency t a = 25c 0.9 2.0 2.6 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 1. the AAT2148 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.
skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 5 AAT2148 low-noise, fast transient 1a step-down converter data sheet typical characteristics efficiency vs. output current (v out = 1.2v; l = 2.2h; c out = 10f) output current (ma) efficiency (%) 0.1 1 10 100 1000 0 10 20 30 40 50 60 70 80 90 100 v in = 2.7v v in = 3.6v v in = 4.2v v in = 5.0v load regulation (v out = 1.2v; l = 2.2h; c out = 10f) output current (ma) output error (%) -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 0.1 1 10 100 1000 v in = 2.7v v in = 3.6v v in = 4.2v v in = 5.0v efficiency vs. output current (v out = 1.8v; l = 4.7h; c out = 4.7f) output current (ma) efficiency (%) 0.1 1 10 100 1000 0 10 20 30 40 50 60 70 80 90 100 v in = 2.7v v in = 3.6v v in = 4.2v v in = 5.0v load regulation (v out = 1.8v; l = 4.7h; c out = 4.7f) output current (ma) output error (%) -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 0.1 1 10 100 1000 v in = 2.7v v in = 3.6v v in = 4.2v v in = 5.0v efficiency vs. output current (v out = 3.3v; l = 6.8h; c out = 4.7f) output current (ma) efficiency (%) 0.1 1 10 100 1000 0 10 20 30 40 50 60 70 80 90 100 v in = 3.6v v in = 4.2v v in = 5.0v load regulation (v out = 3.3v; l = 6.8h; c out = 4.7f) output current (ma) output error (%) -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 0.1 1 10 100 1000 v in = 3.6v v in = 4.2v v in = 5.0v
skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 6 AAT2148 low-noise, fast transient 1a step-down converter data sheet typical characteristics line regulation (v out = 1.8v; c out = 10f; c ff = 100pf) input voltage (v) output error (%) 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 -1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1.00 i out = 1a i out = 500ma i out = 1ma switching frequency vs. temperature temperature (c) switching frequency (mhz) -40 -20 0 20 40 60 80 100 1.8 1.85 1.9 1.95 2 2.05 2.1 2.15 2.2 output error vs. temperature (i out = 500ma) temperature (c) output error (%) -40 -20 0 20 40 60 80 100 -0.015 -0.010 -0.005 0.000 0.005 quiescent current vs. input voltage input voltage (v) quiescent current (a) 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 30 35 40 45 50 55 60 v out = 3.3v v out = 1.8v v out = 1.2v quiescent current vs. temperature (v in = 3.6v) temperature (c) quiescent current (a) -40 -20 0 20 40 60 80 100 20 30 40 50 60 v out = 3.3v v out = 1.8v v out = 1.2v p-channel r ds(on) vs. input voltage input voltage (v) r ds(on)_p (m) 2.7 3.3 3.9 4.5 5.1 200 250 300 350 400 450 500 85c 25c -40c
skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 7 AAT2148 low-noise, fast transient 1a step-down converter data sheet typical characteristics n-channel r ds(on) vs. input voltage input voltage (v) r ds(on)_n (m) 2.7 3.3 3.9 4.5 5.1 150 210 270 330 390 450 85c 25c -40c load transient (v in = 3.6v; v out = 1.8v; c out = 10f; c ff = 100pf) time (40s/div) v out (100mv/div) i out (0.25a/div) 1.8 0a 500ma load transient (v in = 3.6v; v out = 1.8v; c out = 10f; c ff = 100pf) time (16s/div) v out (100mv/div) i out (0.5a/div) 1.8 0a 300ma 1a load transient (v in = 3.6v; v out = 1.8v; c out = 4.7f; c ff = 0pf) time (40s/div) v out (200mv/div) i out (0.25a/div) 1.8 0a 500ma load transient (v in = 3.6v; v out = 1.8v; c out = 4.7f; c ff = 0pf) time (16s/div) v out (200mv/div) i out (0.5a/div) 1.8 0a 300ma 1a line transient (v out = 1.8v; v in = 3.6v to 4.2v; i out = 500ma; c ff = 100pf) time (200s/div) v out (20mv/div) v in (0.5v/div) 3.6 1.8
skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 8 AAT2148 low-noise, fast transient 1a step-down converter data sheet typical characteristics output ripple (v in = 3.6v; v out = 1.2v; i out = 10ma; l = 2.2h; c out = 10f; c ff = 100pf) time (1s/div) v out (20mv/div) lx (2v/div) i lx (0.1a/div) 0 1.2 0a output ripple (v in = 3.6v; v out = 1.2v; i out = 1a; l = 2.2h; c out = 10f; c ff = 100pf) time (0.2s/div) v out (10mv/div) lx (2v/div) i lx (0.2a/div) 0 1.2 1a output ripple (v in = 3.6v; v out = 1.8v; i out = 1a; l = 4.7h; c out = 10f; c ff = 100pf) time (0.2s/div) v out (10mv/div) lx (2v/div) i lx (0.1a/div) 0 1.8 1a soft startup (v in = 3.6v; v out = 1.8v; i out = 1a) time (100s/div) v out (1v/div) v en (2v/div) i in (0.5a/div) 0 0 0
skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 9 AAT2148 low-noise, fast transient 1a step-down converter data sheet functional description the AAT2148 is a high performance 1a 2mhz mono- lithic step-down converter. it has been designed with the goal of minimizing external component size and optimizing efficiency over the complete load range, and produces reduced ripple and spectral noise. 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 values). the fixed output version requires only three external power components (c in , c out , and l). the adjustable ver- sion can be programmed with external feedback to any voltage, ranging from 0.6v to the input voltage. an addi- tional 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 dson 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 all load conditions, ranging from no load to 1a. the internal error amplifier and compensation provides excellent transient response, load, and line regulation. soft start eliminates any output voltage overshoot and input inrush current when the enable or the input volt- age is applied. control loop the AAT2148 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. functional block diagram vp vcc en pgnd pgnd logic 0.6v ref temp. sensing osc op. amp lx fb dh dl cmp 1m
skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 10 AAT2148 low-noise, fast transient 1a step-down converter data sheet 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. for fixed voltage versions, the error amplifier reference volt- age is internally set to program the converter output voltage. for the adjustable output, the error amplifier reference is fixed at 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 AAT2148 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 v in input. under-voltage lockout (uvlo) guarantees sufficient v in bias and proper operation of all internal circuitry prior to activation. l1 4.7h r1 118k r2 59k c1 4.7f c2 10f vin c3 100pf en v in v out 1.8v vin 1 2 3 jp1 vp 11 vp 12 vp 10 lx 13 vcc 9 pgnd 1 fb 4 en 7 ep 0 pgnd 2 pgnd 3 lx 14 lx 15 6 n/c n/c 5 n/c n/c 8 16 u1 AAT2148 figure 1: enhanced transient response schematic.
skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 11 AAT2148 low-noise, fast transient 1a step-down converter data sheet applications information 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 internal slope compensation for the adjustable and low-voltage fixed versions of the AAT2148 is 0.24a/ s. 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 4.7h a s this is the internal slope compensation for the adjust- able (0.6v) version or low-voltage fixed versions. 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 = 7.5h m 0.75 ? v o 0.24a s a s a a s in this case, a standard 6.8 h value is selected. for high-voltage fixed versions ( ? 2.5v), m = 0.48a/ s. table 1 displays inductor values for the AAT2148 fixed and adjustable options. 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 4.7 h sd3118 series inductor selected from coilcraft has a 162m ? typical dcr and a 1.31a saturation cur- rent. at full load, the inductor dc loss is 162mw which gives a 9% loss in efficiency for a 1a, 1.8v output. input capacitor select 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 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. output voltage (v) inductor ( h) output capacitor ( f) 1, 1.2 2.2 10 1.5, 1.8 4.7 4.7 2.5, 3.3 6.8 4.7 table 1: inductor and output capacitor 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 1 2
skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 12 AAT2148 low-noise, fast transient 1a step-down converter data sheet 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 rip- ple 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 AAT2148. 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 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 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 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 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 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.
skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 13 AAT2148 low-noise, fast transient 1a step-down converter data sheet adjustable output resistor selection for applications requiring an adjustable output voltage, the 0.6v version can be externally programmed. resistors r1 and r2 of figure 4 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 current, 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 volt- ages with r2 set to either 59k ? for good noise immu- nity or 221k ? for reduced no load input current. r3 = -1 r4 = - 1 59k = 88.5k v out v ref 1.5v 0.6v the adjustable version of the AAT2148, combined with an external feedforward capacitor (c3 in figure 1), delivers enhanced transient response for extreme pulsed load applications. the addition of the feedforward capac- itor typically requires a larger output capacitor c2 for stability. figure 2: AAT2148 evaluation board figure 3: AAT2148 evaluation board top layer. bottom layer. l1 4.7h r1 267k r2 59k c1 4.7f c2 10f vin c3 100pf en v in v out vin 1 2 3 jp1 vp 11 vp 12 vp 10 lx 13 vcc 9 pgnd 1 fb 4 en 7 ep 0 pgnd 2 pgnd 3 lx 14 lx 15 6 n/c n/c 5 n/c n/c 8 16 u1 AAT2148 figure 4: AAT2148 evaluation board schematic.
skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 14 AAT2148 low-noise, fast transient 1a step-down converter data sheet v out (v) r2 = 59k ? r2 = 221k ? r1 (k ? ) r1 ( ? ) 0.8 19.6 75k 0.9 29.4 113k 1.0 39.2 150k 1.1 49.9 187k 1.2 59.0 221k 1.3 68.1 261k 1.4 78.7 301k 1.5 88.7 332k 1.8 118 442k 1.85 124 464k 2.0 137 523k 2.5 187 715k 3.3 267 1.00m table 2: adjustable resistor values for use with 0.6v step-down converter. thermal calculations there are three types of losses associated with the AAT2148 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 dson(hs) v o + r dson(ls) [v in - v o ]) v in = + (t sw f 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. 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(hs) + 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 qfn33-16 pack- age which is 50c/w. t j(max) = p total ja + t amb layout the suggested pcb layout for the AAT2148 is shown in figures 2, 3, and 4. the following guidelines should be used to help ensure a proper layout. 1. the input capacitor (c1) should connect as closely as possible to v in (pins 9-12) and pgnd (pins 1-3). 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 (pin 4) should be sepa- rate from any power trace and connect as closely as possible to the load point. sensing along a high- current load trace will degrade dc load regulation. the external feedback resistors should be placed as closely as possible to the fb pin (pin 4) to minimize the length of the high impedance feedback trace. 4. the resistance of the trace from the load return to pgnd (pins 1-3) 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.
skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 15 AAT2148 low-noise, fast transient 1a step-down converter data sheet step-down converter design example specifications v o = 1.8v @ 1a (adjustable using 0.6v version), pulsed load ? i load = 300ma v in = 2.7v to 4.2v (3.6v nominal) f s = 2mhz t amb = 85c 1.8v output inductor l1 = 3 v o1 = 3 1.8v = 5.4h s a s a (use 4.7 h; see table 1) for coilcraft inductor sd3118, 4.7 h, dcr = 162m ? . v o v o 1.8 v 1.8v i l1 = 1 - = 1 - = 109m a l1 f s v in 4.7h 2.0mhz 4.2v i pkl1 = i o + i l1 = 1a + 0.055a = 1.055a 2 p l1 = i o 2 dcr = 1a 2 162m = 162mw 1.8v output capacitor v droop = 0.1v 1 23 1 1.8v (4.2v - 1.8v) 4.7h 2.0mhz 4.2v 23 rms i l1 f v in(max) = 3 i load v droop f s 3 0.3a 0.1v 2.0mhz c out = = = 4.5f; use 4.7f = 32marms (v o ) (v in(max) - v o ) = p esr = esr i rms 2 = 5m (32ma) 2 = 6w input capacitor input ripple v pp = 30mv c in = = = 5f; use 4.7f 1 - esr 4 f s v pp i o 1 - 5m w 4 2.0mhz 30mv 1a i o rms i p = esr i rms 2 = 5m (0.5a) 2 = 1.25mw 2 = = 0.5arms
skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 16 AAT2148 low-noise, fast transient 1a step-down converter data sheet AAT2148 losses p total + (t sw f i o + i q ) v in i o 2 (r dson(hs) v o + r dson(ls) [v in -v o ] ) v in = = + (5ns 2.0mhz 1a + 70a) 4.2v = 363mw 1 2 (0.35 1.8v + 0.3 [4.2v - 1.8v]) 4.2v t j(max) = t amb + ja p loss = 85c + (50c/w) 363mw = 103.2c
skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 17 AAT2148 low-noise, fast transient 1a step-down converter data sheet 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 fixed version v out (v) r2, r4 not used r1 (k ? ) l1 ( h) 0.6-3.3v 0 4.7 table 3: evaluation board component values. manufacturer part number inductance ( h) saturation current (a) dcr ( ? ) size (mm) lxwxh type sumida cdrh3d16/hp-2r2 2.2 1.75 47 4.0x4.0x1.8 shielded cdrh5d16-4r7 4.7 2.15 51.3 5.8x5.8x1.8 shielded cdrh5d16-6r8 6.8 1.8 64.7 5.8x5.8x1.8 shielded murata lqh3npn2r2ng0 2.2 1.25 73 3.0x3.0x1.4 shielded lqh32pn2r2nn0 2.2 1.55 76 3.2x2.7x1.55 shielded lqh32pn4r7nn0 4.7 1.0 180 3.2x2.7x1.55 shielded coilcraft sd3118-2r2-r 2.2 2.0 74 3.1x3.1x1.8 shielded sd3118-4r7-r 4.7 1.31 162 3.1x3.1x1.8 shielded sd3118-6r8-r 6.8 1.12 232 3.1x3.1x1.8 shielded table 4: typical surface mount inductors. manufacturer part number value voltage temp. co. case murata grm219r61a475ke19 4.7 f 10v x5r 0805 grm21br60j106ke19 10 f 6.3v x5r 0805 grm21br60j226me39 22 f 6.3v x5r 0805 table 5: surface mount capacitors. 1. for reduced quiescent current, r2 and r4 = 221k ? .
skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202009a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 28, 2012 18 AAT2148 low-noise, fast transient 1a step-down converter data sheet 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 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. ordering information output voltage 1 package marking 2 part number (tape and reel) 3 adj ? 0.6 qfn33-16 6vxyy AAT2148ivn-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 qfn33-16 3.000 all dimensions in millimeters. 1. contact sales for other voltage options. 2. xyy = assembly and date code. 3. sample stock is typically held on part numbers listed in bold .

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