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AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 1 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 general description the AAT2512 is a member of skyworks' total power management ic (tpmic?) product family. it is a dual channel synchronous buck converter operating with an input voltage range of 2.7v to 5.5v, making it ideal for applications with single-cell lithium-ion/polymer batter- ies. both regulators have independent input and enable pins. offered with fixed or adjustable output voltages, each channel is designed to operate with 27 a (typical) of quiescent current, allowing for high efficiency under light load conditions. the AAT2512 requires only three external components (c in , c out , and l x ) for each converter, minimizing cost and real estate. both channels are designed to deliver 400ma of load current and operate with a switching fre- quency of 1.4mhz, reducing the size of external compo- nents. the AAT2512 is available in a pb-free, 12-pin tdfn33 package and is rated over the -40c to +85c tempera- ture range. features ? v in range: 2.7v to 5.5v ? output current: ? channel 1: 400ma ? channel 2: 400ma ? 98% efficient step-down converter ? integrated power switches ? 100% duty cycle ? 1.4mhz switching frequency ? internal soft start ? 150 s typical turn-on time ? over-temperature protection ? current limit protection ? available in tdfn33-12 package ? -40c to +85c temperature range applications ? cellular phones ? digital cameras ? handheld instruments ? microprocessor / dsp core/ io power ? pdas and handheld computers typical application AAT2512 4.7f gnd lx1 fb1 vin1 vin2 v bat c in en1 en2 l1 4.7h l2 4.7h c out 4.7f v out1 lx2 fb2 v out2
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 2 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 pin descriptions pin # symbol function 1 en1 enable pin for channel 1. when connected low, it disables the channel and consumes less than 1 a of current. when connected high, normal operation. 2 fb1 feedback input pin for channel 1. this pin is connected to the converter output. it is used to see the output of the converter to regulate to the desired value via an external resistor divider. 3, 6, 7, 10 gnd ground. 4 en2 enable pin for channel 2. when connected low, it disables the channel and consumes less than 1 a of current. when connected high, normal operation. 5 fb2 feedback input pin for channel 2. this pin is connected to the converter output. it is used to see the output of the converter to regulate to the desired value via an external resistor divider. 8 lx2 power switching node for channel 2. output switching node that connects to the output inductor. 9 vin2 input supply voltage for channel 2. must be closely decoupled. 11 lx1 power switching node for channel 2. output switching node that connects to the output inductor. 12 vin1 input supply voltage for channel 1. must be closely decoupled. pin configuration tdfn33-12 (top view) en1 fb1 gnd 1 en2 fb2 gnd vin1 lx1 gnd vin2 lx2 gnd 2 3 4 5 6 12 11 10 9 8 7
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 3 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 1. stresses above those listed in absolute maximum ratings may cause permanent damage to the device. functional operation at co nditions 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. absolute maximum ratings 1 symbol description value units v in input voltages to gnd 6.0 v v lx lx to gnd -0.3 to v p + 0.3 v v fb fb1 and fb2 to gnd -0.3 to v p + 0.3 v v en en1 and en2 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 2.0 w ? ja thermal resistance 2 50 c/w
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 4 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 1. the AAT2512 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 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 2.7 5.5 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 per channel 27 70 a i shdn shutdown current en1 = en2 = gnd 1.0 a i lx_leak lx leakage current v in = 5.5v, v lx = 0 to v in 1.0 a i fb feedback leakage v fb = 1.0v 0.2 a i lim p-channel current limit both channels 1.2 a r ds(on)h high side switch on resistance 0.45 ? r ds(on)l low side switch on resistance 0.40 ? ? v line line regulation v in = 2.7v to 5.5v 0.2 % f osc oscillator frequency 1.4 mhz t s start-up time from enable to output regulation; both channels 150 s t sd over-temperature shutdown threshold 140 c t hys over-temperature shutdown hysteresis 15 c 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 fb = 5.5v -1.0 1.0 a
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 5 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 typical characteristics en1 = v in ; en2 = gnd. efficiency vs. load (v out = 1.8v; l = 4.7 h) output current (ma) efficiency (%) 50 60 70 80 90 100 0.1 1 10 100 100 0 v in = 2.7v v in = 3.6v v in = 4.2v dc regulation (v out = 1.8v) output current (ma) output error (%) -1.0 -0.5 0.0 0.5 1.0 0.1 1 10 100 1000 v in = 4.2v v in = 3.6v v in = 2.7v efficiency vs. load (v out = 2.5v; l = 6.8 h) output current (ma) efficiency (%) 50 60 70 80 90 100 0.1 1 10 100 1000 v in = 5.0v v in = 3.6v v in = 4.2v v in = 2.7v dc regulation (v out = 2.5v) output current (ma) output error (%) -1.0 -0.5 0.0 0.5 1.0 0.1 1 10 100 1000 v in = 5.0v v in = 3.6v v in = 3.0v v in = 4.2v efficiency vs. load (v out = 3.3v; l = 6.8 h) output current (ma) efficiency (%) 50 60 70 80 90 100 0.1 1 10 100 1000 v in = 3.6v v in = 4.2v v in = 5.0v dc regulation (v out = 3.3v; l = 6.8h) output current (ma) output error (%) -1.0 -0.5 0.0 0.5 1.0 0.1 1 10 100 1000 v in = 5.0v v in = 4.2v v in = 3.6v
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 6 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 typical characteristics en1 = v in ; en2 = gnd. soft start (v in = 3.6v; v out = 1.8v; i out = 400ma) time (100 s/div) enable and output voltage (top) (v) inductor current (bottom) (a) -5.0 -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 4.0 5.0 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4 1.6 v en i l v o line regulation (v out = 1.8v) input voltage (v) accuracy (%) -0.40 -0.30 -0.20 -0.10 0.00 0.10 0.20 0.30 0.40 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 i out = 10ma i out = 400ma i out = 1ma output voltage error vs. temperature (v in = 3.6v; v o = 1.8v; i out = 400ma) temperature ( c) output error (%) -2.0 -1.0 0.0 1.0 2.0 -40 -20 0 20 40 60 80 100 switching frequency vs. temperature (v in = 3.6v; v out = 1.8v) temperature ( c) variation (%) -15.0 -12.0 -9.0 -6.0 -3.0 0.0 3.0 6.0 9.0 12.0 15.0 -40 -20 0 20 40 60 80 100 frequency vs. input voltage input voltage (v) frequency variation (%) -4.0 -3.0 -2.0 -1.0 0.0 1.0 2.0 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 v out = 1.8v v out = 2.5v v out = 3.3v no load quiescent current vs. input voltage input voltage (v) supply current ( a) 10 15 20 25 30 35 40 45 50 2.7 3.1 3.5 3.9 4.3 4.7 5.1 5.5 85 c 25 c -40 c
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 7 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 typical characteristics en1 = v in ; en2 = gnd. p-channel r ds(on) vs. input voltage input voltage (v) r ds(on) (m ) 300 350 400 450 500 550 600 650 700 750 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 25 c 120 c 100 c 85 c n-channel r ds(on) vs. input voltage input voltage (v) r ds(on) (m ) 300 350 400 450 500 550 600 650 700 750 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 25 c 120 c 100 c 85 c load transient response (1ma to 300ma; v in = 3.6v; v out = 1.8v; c 1 = 10 f; c ff = 100pf) output voltage (top) (v) load and inductor current (200ma/div) (bottom) time (50 1.7 1.8 1.9 2.0 v o 300ma 1ma 0 i o i l load transient response (300ma to 400ma; v in = 3.6v; v out = 1.8v; c 1 = 4.7 f) output voltage (top) (v) load and inductor current (200ma/div) (bottom) time (50 1.75 1.80 1.85 1.90 0.1 0.2 0.3 0.4 v o i o i l 400ma 300ma load transient response (300ma to 400ma; v in = 3.6v; v out = 1.8v; c 1 = 10 f) output voltage (top) (v) load and inductor current (200ma/div) (bottom) time (50 1.75 1.80 1.85 1.90 0.1 0.2 0.3 0.4 v o i o i l 400ma 300ma load transient response (300ma to 400ma; v in = 3.6v; v out = 1.8v; c 1 = 10 f; c 4 = 100pf) output voltage (top) (v) load and inductor current (200ma/div) (bottom) time (50 1.775 1.800 1.825 1.850 0.1 0.2 0.3 0.4 v o i o i l 400ma 300ma
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 8 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 typical characteristics en1 = v in ; en2 = gnd. line response (v out = 1.8v @ 400ma) output voltage (top) (v) input voltage (bottom) (v) time (25 s/div) 1.76 1.77 1.78 1.79 1.80 1.81 1.82 3.0 3.5 4.0 4.5 5.0 5.5 6.0 output ripple (v in = 3.6v; v out = 1.8v; i out = 1ma) time (10s/div) output voltage (ac coupled) (top) (mv) inductor current (bottom) (a) -120 -100 -80 -60 -40 -20 0 20 40 -0.10 -0.05 0.00 0.05 0.10 0.15 0.20 0.25 0.30 v o i l output ripple (v in = 3.6v; v out = 1.8v; i out = 400ma) time (500ns/div) output voltage (ac coupled) (top) (mv) inductor current (bottom) (a) -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 v o i l
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 9 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 functional block diagram en1 lx1 err. amp. dh dl gnd1 vin1 fb1 sgnd2 voltage reference control logic en2 lx2 err. amp. dh dl gnd2 comp. logic logic control logic vin2 fb2 sgnd1 voltage reference comp. see note see note note: internal resistor divider included for 1.2v versions. for low voltage versions, the feedback pin is tied directly to the error amplifier input. functional description the AAT2512 is a high performance power management ic comprised of two buck converters. each channel has independent input voltages and enable/disable pins. designed to operate at 1.4mhz of switching frequency, the converters require only three external components (c in , c out , and l x ), minimizing cost and size of external components. both converters are designed to operate with an input voltage range of 2.7v to 5.5v. typical values of the output filter are 4.7 h and 4.7 f ceramic capacitor. the output voltage operates to as low as 0.6v and is offered as both fixed and adjustable. power devices are sized for 400ma current capability while maintaining over 90% efficiency at full load. light load efficiency is maintained at greater than 80% down to 500 a of load current. both channels have excellent transient response, load, and line regula- tion. transient response time is typically less than 20 s. the AAT2512 also features soft-start control to limit inrush current. soft start increases the inductor current limit point in discrete steps when power is applied to the input or when the enable pins are pulled high. it limits the current surge seen at the input and eliminates out- put voltage overshoot. the enable input, when pulled low, forces the converter into a low power, non-switching state consuming less than 1 a of current. for overload conditions, the peak input current is limited. as load impedance decreases and the output voltage falls closer to zero, more power is dissipated internally, raising the device temperature. thermal protection completely disables switching when internal dissipation becomes excessive, protecting the device from damage. the junc- tion over-temperature threshold is 140c with 15c of hysteresis. the under-voltage lockout guarantees suffi- cient v in bias and proper operation of all internal circuits prior to activation.
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 10 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 applications information inductor selection the step-down converter uses peak current mode control 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 AAT2512 is 0.24a/ sec. this equates to a slope compensation that is 75% of the inductor cur- rent 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 for the adjust- able (0.6v) version or low-voltage fixed version. when externally programming the 0.6v version to a 2.5v out- put, the calculated inductance would be 7.5 h. 0.75 ? v o l = = 3 ? v o = 3 ? 2.5v = 7.5 h m 0.75v 0.24a / sec sec a sec a in this case, a standard 6.8 h value is selected. for high- voltage fixed versions (2.5v and above), m = 0.48a/ sec. table 1 displays inductor values for the AAT2512 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 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 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 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 this equation provides an estimate for the input capaci- tor required for a single channel. the equation below solves for input capacitor size for both channels. it makes the worst-case assumptions that both converters are operating at 50% duty cycle and are synchronized. c in = 1 ?? - esr ? 4 ? f s ?? v pp i o1 + i o2 because the AAT2512 channels will generally operate at different duty cycles and are not synchronized, the actual ripple will vary and be less than the ripple (v pp ) used to solve for the input capacitor in the equation above. 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 5v dc applied is actually about 6 f. the maximum input capacitor rms current is: ?? i rms = i o1 1 - + i o2 1 - ?? v o1 v in v o1 v in ?? ?? v o2 v in v o2 v in ? ? ?? ?? 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 fixed output 0.6v to 3.3v 4.7 h table 1: inductor values.
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 11 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 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 of both convert- ers combined. i o1(max) + i o2(max) rms(max) i 2 = this equation also makes the worst-case assumption that both converters are operating at 50% duty cycle and are synchronized. since the converters are not syn- chronized and are not both operating at 50% duty cycle, the actual rms current will always be less than this. losses associated with the input ceramic capacitor are typically minimal. the term ?? 1 - ?? v o v in v o v in appears in both the input voltage ripple and input capacitor rms current equations. it 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 AAT2512. low esr/ esl x7r and x5r ceramic capacitors are ideal for this function. to minimize the 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 (c3 and c8) can be seen in the evaluation board layout in figure 4. since decoupling must be as close to the input pins as possible, it is necessary to use two decoupling capaci- tors. c3 provides the bulk capacitance required for both converters, while c8 is a high frequency bypass capaci- tor for the second channel (see c3 and c8 placement in figure 4). 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 during load tran- sients. errors in the loop phase and gain measurements can also result. since the inductance of a short printed circuit board 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 converter performance, a high esr tantalum or alumi- num electrolytic capacitor 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 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. as the loop responds, the induc- tor current increases to match the load current demand. this typically takes two to three switching cycles and can be estimated by: ?? 1 - = d ? (1 - d) = 0.5 2 = 0.2 5 ?? v o v in v o v in 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: c out = 3 i load v droop f s 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.
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 12 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 adjustable output resistor selection for applications requiring an adjustable output voltage, the 0.6v version can be programmed externally. resistors r1 through r4 of figure 2 program the output to regu- late at a voltage higher than 0.6v. to limit the bias cur- rent required for the external feedback resistor string, the minimum suggested value for r2 and r4 is 59k ? . although a larger value will reduce the 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 and r4 set to either 59k ? for good noise immunity or 221k ? for reduced no load input current. 1 23 v out (v in(max) - v out ) rms(max) i l f v in(max) = the adjustable version of the AAT2512 in combination with an external feedforward capacitor (c4 and c5 of figure 2) delivers enhanced transient response for extreme pulsed load applications. the addition of the feedforward capacitor typically requires a larger output capacitor (c1 and c2) for stability. v out (v) r2, r4 = 59k ? r1, r3 (k ? ) r2, r4 = 221k ? r1, r3 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 version. thermal calculations there are three types of losses associated with the AAT2512 converter: switching losses, conduction losses, and quiescent current losses. conduction losses are associated with the r ds(on) characteristics of the power output switching devices. switching losses are dominat- ed by the gate charge of the power output switching devices. at full load, assuming continuous conduction mode (ccm), a simplified form of the dual converter losses is given by: ?? ?? r1 = -1 r2 = - 1 59k = 88.5k v out v ref ?? ?? 1.5v 0.6v i q is the AAT2512 quiescent current for one channel and t sw is used to estimate the full load switching losses. for the condition where channel one is in dropout at 100% duty cycle, the total device dissipation reduces to: p total i o1 2 (r dson(hs) v o1 + r dson(ls) [v in -v o1 ]) v in = + + (t sw f [i o1 + i o2 ] + 2 i q ) v in i o2 2 (r dson(hs) v o2 + r dson(ls) [v in -v o2 ]) 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 tdfn33-12 pack- age which is 50c/w. t j(max) = p total ? ja + t am b
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 13 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 pcb layout the following guidelines should be used to insure a proper layout. 1. due to the pin placement of v in for both converters, proper decoupling is not possible with just one input capacitor. the large input capacitor c3 should con- nect as closely as possible to v p and gnd, as shown in figure 4. the additional input bypass capacitor c8 is necessary for proper high frequency decoupling of the second converter. 2. the output capacitor and inductor should be con- nected as closely as possible. the connection of the inductor to the lx pin should also be as short as possible. 3. the feedback trace should be separate 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. if external feedback resistors are used, they should be placed as closely as possible to the fb pin. this prevents noise from being coupled into the high impedance feedback node. 4. the resistance of the trace from the load return to gnd 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. for good thermal coupling, pcb vias are required from the pad for the tdfn paddle to the ground plane. the via diameter should be 0.3mm to 0.33mm and positioned on a 1.2mm grid.
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 14 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 design example specifications v o1 = 2.5v @ 400ma (adjustable using 0.6v version), pulsed load ? i load = 300ma v o2 = 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 = 1.4 mhz t amb = 85c 2.5v v o1 output inductor l1 = 3 ? v o1 = 3 ? 2.5v = 7.5 h sec a sec a (see table 1) for sumida inductor cdrh3d16, 10 h, dcr = 210m ? . v o v o1 2.5 v 2.5v i1 = ? 1 - = ? 1 - = 72.3ma l1 ? f v in 10 h ? 1.4mhz 4.2v i pk1 = i o1 + i1 = 0.4a + 0.036a = 0.44a 2 p l1 = i o1 2 ? dcr = 0.4a 2 ? 210m = 34mw ? ? ? ? ? ? ? ? 1.8v v o2 output inductor l2 = 3 ? v o2 = 3 ? 1.8v = 5.4 h sec a sec a (see table 1) for sumida inductor cdrh3d16, 4.7 h, dcr = 105m ? . v o2 v o2 1.8 v 1.8v i2 = ? 1 - = ? 1 - = 156ma l ? f v in 4.7 h ? 1.4mhz 4.2v i pk2 = i o2 + i2 = 0.4a + 0.078a = 0.48a 2 p l2 = i o2 2 ? dcr = 0.4a 2 ? 105m = 17mw ? ? ? ? ? ? ? ? 2.5v output capacitor 1 23 1 2.5v (4.2v - 2.5v) 10 h 1.4mhz 4.2v 23 rms(max) i l f v in(max) = 3 i load v droop f s 3 0.3a 0.2v 1.4mhz c out = = = 3.2 f = 21marms (v out ) (v in(max) - v out ) = p esr = esr i rms 2 = 5m (21ma) 2 = 2.2 w
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 15 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 1.8v output capacitor 1 23 1 1.8v (4.2v - 1.8v) 4.7 h 1.4mhz 4.2v 23 rms(max) i l f v in(max) = 3 i load v droop f s 3 0.3a 0.2v 1.4mhz c out = = = 3.2 f = 45marms (v out ) (v in(max) - v out ) = p esr = esr i rms 2 = 5m (45ma) 2 = 10 w input capacitor input ripple v pp = 25mv. c in = = = 6.8 f 1 ?? - esr ? 4 ? f s ?? v pp i o1 + i o2 1 ?? - 5m ? 4 ? 1.4mhz ?? 25mv 0.8a i o1 + i o2 rms(max) i p = esr i rms 2 = 5m (0.4a) 2 = 0.8mw 2 = = 0.4arms AAT2512 losses the maximum dissipation occurs at dropout where v in = 2.7v. all values assume an ambient temperature of 85c and a junction temperature of 120c. p total + (t sw f i o2 + 2 i q ) v in i o1 2 (r dson(hs) v o1 + r dson(ls) (v in -v o1 )) + i o2 2 (r dson(hs) v o2 + r dson(ls) (v in -v o2 )) v in = = + 5ns 1.4mhz 0.4a + 60 a) 2.7v = 239mw 0.4 2 (0.725 2.5v + 0.7 (2.7v - 2.5v)) + 0.4 2 (0.725 1.8v + 0.7 (2.7v - 1.8v)) 2.7v t j(max) = t amb + ja ? p loss = 85 c + (50 c/w) ? 239mw = 97 c
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 16 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 1. for enhanced transient configuration c5, c4 = 100pf and c1, c2 = 10 f. see table 3 l2 4.7 f c2 1 v o1 gnd see table 3 r1 59.0k r2 c4 1 fb1 2 en1 1 lx1 11 gnd2 7 lx2 8 gnd1 10 sgnd1 3 vin1 12 vin2 9 sgnd2 6 fb2 5 en2 4 AAT2512 u1 10 f c3 see table 3 l1 v o2 gnd lx2 see table 3 r3 59.0k r4 c5 1 4.7 f c1 1 lx1 123 output 1 enable 321 output 2 enable v in 0.01 f c7 0.01 f c6 0.1 f c8 figure 3: AAT2512 evaluation board schematic. figure 4: AAT2512 evaluation board top side. figure 5: AAT2512 evaluation board bottom side.
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 17 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 1. for reduced quiescent current, r2 and r4 = 221k . adjustable version (0.6v device) r2, r4 = 59k ? r2, r4 = 221k ? 1 l1, l2 ( h) v out (v) r1, r3 (k ? ) r1, r3 (k ? ) 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 r2, r4 not used l1, l2 ( h) v out (v) r1, r3 (k ? ) 0.6-3.3v 0 4.7 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 10uf 6.3v x5r 0805 murata grm21br60j226me39 22uf 6.3v x5r 0805 table 5: surface mount capacitors.
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 18 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 2013 1. xyy = assembly and date code. 2. sample stock is generally held on part numbers listed in bold . ordering information package voltage marking 1 part number (tape and reel) 2 channel 1 channel 2 tdfn33-12 0.6v 0.6v qkxyy AAT2512iwp-aa-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. legend voltage code adjustable (0.6v) a 0.9 b 1.2 e 1.5 g 1.8 i 1.9 y 2.5 n 2.6 o 2.7 p 2.8 q 2.85 r 2.9 s 3.0 t 3.3 w 4.2 c
AAT2512 dual 1.4mhz, 400ma synchronous buck dc/dc converter data sheet 19 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202022b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 19, 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. 1. 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 c onnection. package information tdfn33-12 1 top view bottom view detail "a" side view 3.00 all dimensions in millimeters.

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