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general description the AAT2512 is a member of analogictech's total power management ic? (tpmic?) product fam- ily. it is a dual channel synchronous buck convert- er operating with an input voltage range of 2.7v to 5.5v, making it ideal for applications with single- cell lithium-ion/polymer batteries. both regulators have independent input and enable pins. offered with fixed or adjustable out- put voltages, each channel is designed to operate with 27a (typical) of quiescent current, allowing for high efficiency under light load conditions. the AAT2512 requires only three external compo- nents (c in , c out , and l x ) for each converter, mini- mizing cost and real estate. both channels are designed to deliver 400ma of load current and operate with a switching frequency of 1.4mhz, reducing the size of external components. the AAT2512 is available in a pb-free, 12-pin tdfn33 package and is rated over the -40c to +85c temperature 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 ? 150s 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 AAT2512 dual 400ma high frequency buck converter typical application 2512.2006.06.1.4 1 systempower ? 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
pin descriptions pin configuration tdfn33-12 (top view) pin # symbol function 1 en1 enable pin for channel 1. when connected low, it disables the channel and consumes less than 1a 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 1a 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. AAT2512 dual 400ma high frequency buck converter 2 2512.2006.06.1.4 en1 fb1 gnd 1 en2 fb2 gnd vin1 lx1 gnd vin2 lx2 gnd 2 3 4 5 6 12 11 10 9 8 7
absolute maximum ratings 1 thermal information symbol description value units p d maximum power dissipation 2.0 w ja thermal resistance 2 50 c/w 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 AAT2512 dual 400ma high frequency buck converter 2512.2006.06.1.4 3 1. stresses above those listed in absolute maximum ratings may cause permanent damage to the device. functional operation at c ondi- tions 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.
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; 150 s both channels t sd over-temperature shutdown 140 c threshold t hys over-temperature shutdown 15 c hysteresis 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 400ma high frequency buck converter 4 2512.2006.06.1.4 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 correlation with statistical process controls.
typical characteristics en1 = v in ; en2 = gnd. AAT2512 dual 400ma high frequency buck converter 2512.2006.06.1.4 5 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 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 = 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 = 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 = 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 = 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
typical characteristics en1 = v in ; en2 = gnd. AAT2512 dual 400ma high frequency buck converter 6 2512.2006.06.1.4 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 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 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 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 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 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
typical characteristics en1 = v in ; en2 = gnd. AAT2512 dual 400ma high frequency buck converter 2512.2006.06.1.4 7 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 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 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 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 = 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 (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
typical characteristics en1 = v in ; en2 = gnd. AAT2512 dual 400ma high frequency buck converter 8 2512.2006.06.1.4 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 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 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
AAT2512 dual 400ma high frequency buck converter 2512.2006.06.1.4 9 functional block diagram 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 man- agement 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 ), min- imizing 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 4.7h and 4.7f 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 main- taining over 90% efficiency at full load. light load effi- ciency is maintained at greater than 80% down to 500a of load current. both channels have excellent transient response, load, and line regulation. transient response time is typically less than 20s. 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 output voltage overshoot. the enable input, when pulled low, forces the converter into a low power, non-switching state consuming less than 1a of current. for overload conditions, the peak input current is limited. as load impedance decreases and the out- put voltage falls closer to zero, more power is dis- sipated internally, raising the device temperature. thermal protection completely disables switching when internal dissipation becomes excessive, pro- tecting the device from damage. the junction over- temperature threshold is 140c with 15c of hys- teresis. the under-voltage lockout guarantees suf- ficient v in bias and proper operation of all internal circuits prior to activation. 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
applications information inductor selection the step-down converter uses peak current mode control with slope compensation to maintain stabil- ity for duty cycles greater than 50%. the output inductor value must be selected so the inductor current down slope meets the internal slope com- pensation requirements. the internal slope com- pensation 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 current down slope for a 1.5v output and 4.7h inductor. this is the internal slope compensation for the adjustable (0.6v) version or low-voltage fixed ver- sion. when externally programming the 0.6v ver- sion to a 2.5v output, the calculated inductance would be 7.5h. in this case, a standard 6.8h 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 saturation 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 loss- es 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 4.7h cdrh3d16 series inductor selected from sumida has a 105m dcr and a 900ma dc current rating. 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 4.7f to 10f x7r or x5r ceramic capac- itor for the input. to estimate the required input capacitor size, determine the acceptable input rip- ple 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. this equation provides an estimate for the input capacitor required for a single channel. AAT2512 dual 400ma high frequency buck converter 10 2512.2006.06.1.4 table 1: inductor values. configuration output voltage inductor 0.6v adjustable with 1v, 1.2v 2.2h external feedback 1.5v, 1.8v 4.7h 2.5v, 3.3v 6.8h fixed output 0.6v to 3.3v 4.7h ?? ? 1 - ?? v o v in c in = v o v in ?? - esr ? f s ?? v pp i o 0.75 ? v o l = = 3 ? v o = 3 ? 2.5v = 7.5 h m 0.75v 0.24a / sec sec a sec a 0.75 ? v o m = = = 0.24 l 0.75 ? 1.5v 4.7 h a sec
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. because the AAT2512 channels will generally operate at different duty cycles and are not syn- chronized, 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 coefficient characteristics when selecting the prop- er value. for example, the capacitance of a 10f 6.3v x5r ceramic capacitor with 5v dc applied is actually about 6f. the maximum input capacitor rms current is: 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 converters combined. this equation also makes the worst-case assump- tion that both converters are operating at 50% duty cycle and are synchronized. since the converters are not synchronized 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 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 capacitors. c3 provides the bulk capacitance required for both converters, while c8 is a high frequency bypass capacitor 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 evaluation board input voltage pins. the induc- tance of these wires, along with the low esr ceramic input capacitor, can create a high q net- work that may affect converter performance. this problem often becomes apparent in the form of excessive ringing in the output voltage during load transients. 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 inductance cannot be reduced to a level that does not affect converter performance, a high esr tan- talum or aluminum electrolytic capacitor should be placed in parallel with the low esr, esl bypass ceramic capacitor. this dampens the high q net- work and stabilizes the system. output capacitor the output capacitor limits the output ripple and provides holdup during large load transitions. a 4.7f to 10f x5r or x7r ceramic capacitor typi- cally provides sufficient bulk capacitance to stabi- lize the output during large load transitions and has the esr and esl characteristics necessary for low output ripple. AAT2512 dual 400ma high frequency buck converter 2512.2006.06.1.4 11 ?? 1 - ?? v o v in v o v in i o1(max) + i o2(max) rms(max) i 2 = ?? i rms = i o1 1 - + i o2 1 - ?? v o1 v in v o1 v in ?? ?? v o2 v in v o2 v in ? ? ?? ?? ?? c in = 1 ?? - esr 4 f s ?? v pp i o1 + i o2
the output voltage droop due to a load transient is dominated by the capacitance of the ceramic out- put capacitor. during a step increase in load cur- rent the ceramic output capacitor alone supplies the load current until the loop responds. as the loop responds, the inductor current increases to match the load current demand. this typically takes two to three switching cycles and can be estimated by: once the average inductor current increases to the dc load level, the output voltage recovers. the above equation 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 4.7f. this is due to its effect on the loop crossover frequency (bandwidth), phase margin, and gain margin. increased output capacitance will reduce the crossover frequency with greater phase margin. the maximum output capacitor rms ripple current is given by: 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. adjustable output resistor selection for applications requiring an adjustable output volt- age, the 0.6v version can be programmed exter- nally. resistors r1 through r4 of figure 2 program the output to regulate at a voltage higher than 0.6v. to limit the bias current 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 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 val- ues for various output voltages with r2 and r4 set to either 59k for good noise immunity or 221k for reduced no load input current. the adjustable version of the AAT2512 in combina- tion 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. table 2: adjustable resistor values for use with 0.6v version. r2, r4 = 59k r2, r4 = 221k v out (v) r1, r3 (k ) 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 AAT2512 dual 400ma high frequency buck converter 12 2512.2006.06.1.4 ?? ?? r1 = -1 r2 = - 1 59k = 88.5k v out v ref ?? ?? 1.5v 0.6v 1 23 v out (v in(max) - v out ) rms(max) i l f v in(max) = c out = 3 i load v droop f s
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 dominated by the gate charge of the power output switching devices. at full load, assum- ing continuous conduction mode (ccm), a simplified form of the dual converter losses is given by: i q is the AAT2512 quiescent current for one chan- nel and t sw is used to estimate the full load switch- ing losses. for the condition where channel one is in dropout at 100% duty cycle, the total device dissipation reduces to: since r ds(on) , quiescent current, and switching losses all vary with input voltage, the total losses should be investigated over the complete input voltage range. given the total losses, the maximum junction tem- perature can be derived from the ja for the tdfn33-12 package which is 50c/w. pcb layout the following guidelines should be used to insure a proper layout. 1. due to the pin placement of v in for both con- verters, proper decoupling is not possible with just one input capacitor. the large input capaci- tor c3 should connect as closely as possible to v p and gnd, as shown in figure 4. the addi- tional input bypass capacitor c8 is necessary for proper high frequency decoupling of the second converter. 2. the output capacitor and inductor should be connected as closely as possible. the connec- tion 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 differences in the potential of the internal sig- nal 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 1.2 mm grid. AAT2512 dual 400ma high frequency buck converter 2512.2006.06.1.4 13 t j(max) = p total ja + t amb p total = i o1 2 r dson(hs) + + (t sw f i o2 + 2 i q ) v in i o2 2 (r dson(hs) v o2 + r dson(ls) [v in -v o2 ]) v in 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
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 (see table 1) for sumida inductor cdrh3d16, 10h, dcr = 210m . 1.8v v o2 output inductor (see table 1) for sumida inductor cdrh3d16, 4.7h, dcr = 105m . AAT2512 dual 400ma high frequency buck converter 14 2512.2006.06.1.4 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 ? ? ? ? ? ? ? ? l2 = 3 ? v o2 = 3 ? 1.8v = 5.4 h sec a sec a 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 ? ? ? ? ? ? ? ? l1 = 3 ? v o1 = 3 ? 2.5v = 7.5 h sec a sec a
2.5v output capacitor 1.8v output capacitor input capacitor input ripple v pp = 25mv. AAT2512 dual 400ma high frequency buck converter 2512.2006.06.1.4 15 i o1 + i o2 rms(max) i p = esr i rms 2 = 5m (0.4a) 2 = 0.8mw 2 = = 0.4arms c in = = = 6.8 f 1 ?? - esr 4 f s ?? v pp i o1 + i o2 1 ?? - 5m 4 1.4mhz ?? 25mv 0.8a 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 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 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. figure 3: AAT2512 evaluation board schematic. AAT2512 dual 400ma high frequency buck converter 16 2512.2006.06.1.4 1. for enhanced transient configuration c5, c4 = 100pf and c1, c2 = 10f. 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 t j(max) = t amb + ja p loss = 85 c + (50 c/w) 239mw = 97 c 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
table 3: evaluation board component values. figure 4: AAT2512 evaluation board top side. figure 5: AAT2512 evaluation board bottom side. adjustable version r2, r4 = 59k r2, r4 = 221k 1 (0.6v device) v out (v) r1, r3 (k ) r1, r3 (k ) l1, l2 (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 r2, r4 not used v out (v) r1, r3 (k ) l1, l2 (h) 0.6-3.3v 0 4.7 AAT2512 dual 400ma high frequency buck converter 2512.2006.06.1.4 17 1. for reduced quiescent current, r2 and r4 = 221k .
table 4: typical surface mount inductors. table 5: surface mount capacitors. manufacturer part number value voltage temp. co. case murata grm219r61a475ke19 4.7f 10v x5r 0805 murata grm21br60j106ke19 10uf 6.3v x5r 0805 murata grm21br60j226me39 22uf 6.3v x5r 0805 inductance max dc dcr size (mm) manufacturer part number (h) current (a) ( ) 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 AAT2512 dual 400ma high frequency buck converter 18 2512.2006.06.1.4
AAT2512 dual 400ma high frequency buck converter 2512.2006.06.1.4 19 ordering information voltage package channel 1 channel 2 marking 1 part number (tape and reel) 2 tdfn33-12 0.6v 0.6v qkxyy AAT2512iwp-aa-t1 tdfn33-12 1.8v 1.6v qyxyy AAT2512iwp-ih-t1 1. xyy = assembly and date code. 2. sample stock is generally held on part numbers listed in bold . legend voltage code adjustable a (0.6v) 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 all analogictech products are offered in pb-free packaging. the term ?pb-free? means semiconductor products that are in compliance with current rohs standards, including the requirement that lead not exceed 0.1% by weight in homogeneous materials. for more information, please visit our website at http://www.analogictech.com/pbfree.
AAT2512 dual 400ma high frequency buck converter 20 2512.2006.06.1.4 advanced analogic technologies, inc. 830 e. arques avenue, sunnyvale, ca 94085 phone (408) 737-4600 fax (408) 737-4611 tdfn33-12 all dimensions in millimeters. ? advanced analogic technologies, inc. analogictech cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in an analogictech pr oduct. no circuit patent licenses, copyrights, mask work rights, or other intellectual property rights are implied. analogictech reserves the right to make changes to their products or specifi cations or to discontinue any product or service without notice. customers are advised to obtain the latest version of relevant information to verify, before placing orders, that information b eing relied on is current and complete. all products are sold sub- ject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warranty, patent infringement, and limitation of liability. analogictech warrants performance of its semiconductor products to the specifications applicable at the time of sale in accordance with anal ogictech?s standard warranty. testing and other quality con- trol techniques are utilized to the extent analogictech deems necessary to support this warranty. specific testing of all param eters of each device is not necessarily performed. analogictech and the analogictech logo are trademarks of advanced analogic technologies incorporated. all other brand and produ ct names appearing in this document are regis- tered trademarks or trademarks of their respective holders. top view bottom view detail "b" detail "a" side view 3.00 2.40 +

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