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aat1146 fast transient 400ma step-down converter 1146.2006.04.1.3 1 switchreg ? general description the aat1146 switchreg is a member of analogictech's total power management ic? (tpmic?) product family. it is a 1.4mhz 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 aat1146 is available in fixed voltage versions with internal feedback and a programmable ver- sion with external feedback resistors. it can deliver 400ma of load current while maintaining a low 27 a no load quiescent current. the 1.4mhz switching frequency minimizes the size of external components while keeping switching losses low. the aat1146 is designed to maintain high efficien- cy throughout the operating range, which is critical for portable applications. the aat1146 is available in a pb-free, space-saving 2.0x2.1mm sc70jw-8 package and is rated over the -40c to +85c temperature range. features ?v in range: 2.7v to 5.5v ?v out fixed or adjustable from 0.6v to v in ?27 a no load quiescent current ? up to 98% efficiency ? 400ma max output current ? 1.4mhz switching frequency ? 120 s soft start ? fast load transient ? over-temperature protection ? current limit protection ? 100% duty cycle low-dropout operation ?<1 a shutdown current ? sc70jw-8 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 (fixed output voltage) 4.7 h l1 4.7 f c1 4.7 f c2 en 1 out 2 vin 3 lx 4 agnd 5 pgnd 6 pgnd 7 pgnd 8 aat1146 u1 v in v o
pin descriptions pin configuration sc70jw-8 (top view) pin # symbol function 1 en enable pin. 2 out feedback input pin. this pin is connected either directly to the converter output or to an external resistive divider for an adjustable output. 3 vin input supply voltage for the converter. 4 lx switching node. connect the inductor to this pin. it is internally connected to the drain of both high- and low-side mosfets. 5 agnd non-power signal ground pin. 6, 7, 8 pgnd main power ground return pins. connect to the output and input capacitor return. aat1146 fast transient 400ma step-down converter 2 1146.2006.04.1.3 out vin lx pgnd pgnd pgnd agnd en 1 2 3 45 6 7 8
absolute maximum ratings 1 thermal information symbol description value units p d maximum power dissipation 2, 3 625 mw ja thermal resistance 2 160 c/w symbol description value units v in input voltage gnd 6.0 v v lx l x to gnd -0.3 to v in + 0.3 v v out out to gnd -0.3 to v in + 0.3 v v en en to gnd -0.3 to 6.0 v t j operating junction temperature range -40 to 150 c t lead maximum soldering temperature (at leads, 10 sec) 300 c aat1146 fast transient 400ma step-down converter 1146.2006.04.1.3 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. 3. derate 6.25mw/c above 25c.
aat1146 fast transient 400ma step-down converter 4 1146.2006.04.1.3 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 in rising 2.7 v v uvlo uvlo threshold hysteresis 100 mv v in falling 1.8 v v out output voltage tolerance i out = 0 to 400ma, -3.0 +3.0 % v in = 2.7v to 5.5v v out output voltage range 0.6 v in v i q quiescent current no load, 0.6v adjustable 27 70 a version i shdn shutdown current en = agnd = pgnd 1.0 a i lim p-channel current limit 600 ma r ds(on)h high side switch on resistance 0.45 r ds(on)l low side switch on resistance 0.40 i lxleak lx leakage current v in = 5.5v, v lx = 0 to v in , 1 a en = gnd v linereg line regulation v in = 2.7v to 5.5v 0.1 %/v v out out threshold voltage accuracy 0.6v output, no load 591 600 609 mv t a = 25c i out out leakage current 0.6v output 0.2 a r out out impedance >0.6v output 250 k t s start-up time from enable to output 150 s regulation f osc oscillator frequency t a = 25c 1.0 1.4 2.0 mhz t sd over-temperature shutdown threshold 140 c t hys over-temperature shutdown hysteresis 15 c en v en(l) enable threshold low 0.6 v v en(h) enable threshold high 1.4 v i en input low current v in = v out = 5.5v -1.0 1.0 a 1. the aat1146 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 aat1146 fast transient 400ma step-down converter 1146.2006.04.1.3 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
aat1146 fast transient 400ma step-down converter 6 1146.2006.04.1.3 typical characteristics 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 aat1146 fast transient 400ma step-down converter 1146.2006.04.1.3 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 aat1146 fast transient 400ma step-down converter 8 1146.2006.04.1.3 8 1146.2006.04.1.3 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
aat1146 fast transient 400ma step-down converter 1146.2006.04.1.3 9 functional block diagram functional description the aat1146 is a high performance 400ma 1.4mhz monolithic step-down converter. it has been designed with the goal of minimizing external component size and optimizing efficiency over the complete load range. apart from the small bypass input capacitor, only a small l-c filter is required at the output. typically, a 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 version can be programmed with external feedback to any voltage, ranging from 0.6v to the input voltage. an additional feed-forward capacitor can also be added to the external feedback to pro- vide improved transient response (see figure 1). at dropout, the converter duty cycle increases to 100% and the output voltage tracks the input volt- age minus the r dson drop of the p-channel high- side mosfet. the input voltage range is 2.7v to 5.5v. the con- verter efficiency has been optimized for all load conditions, ranging from no load to 400ma. the internal error amplifier and compensation pro- vides excellent transient response, load, and line regulation. soft start eliminates any output voltage overshoot when the enable or the input voltage is applied. en lx err . amp logic dh dl pgnd vin out agnd voltage reference input see note note: for adjustable version, the internal feedback divider is omitted and the out pin is tied directly to the internal error amplifier.
aat1146 fast transient 400ma step-down converter 10 1146.2006.04.1.3 control loop the aat1146 is a peak current mode step-down converter. the current through the p-channel mosfet (high side) is sensed for current loop control, as well as short circuit and overload pro- tection. a fixed slope compensation signal is added to the sensed current to maintain stability for duty cycles greater than 50%. the peak current mode loop appears as a voltage-programmed current source in parallel with the output capacitor. the output of the voltage error amplifier programs the current mode loop for the necessary peak switch current to force a constant output voltage for all load and line conditions. internal loop compen- sation terminates the transconductance voltage error amplifier output. for fixed voltage versions, the error amplifier reference voltage 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 aat1146 into a low-power, non-switching state. the total input current during shutdown is less than 1 a. current limit and over-temperature protection for overload conditions, the peak input current is limited. 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 hysteresis. 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 inter- nal circuitry prior to activation. figure 1: enhanced transient response schematic. l1 cdrh3d16-4r7 4.7 h l1 10 f c1 4.7 f c2 u1 aat1146 sc70jw-8 c2 4.7 f 10v 0805 x5r v out =1.8v gnd v in 1 2 3 enable lx en 1 out 2 vin 3 lx 4 agnd 5 pgnd 6 pgnd 7 pgnd 8 aat1146 u1 gnd2 118k r1 59k r2 c1 10 f 6.3v 0805 x5r 100pf c4 n/a c3
aat1146 fast transient 400ma step-down converter 1146.2006.04.1.3 11 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 induc- tor 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 aat1146 is 0.24a/ sec. this equates to a slope compensation that is 75% of the inductor current down slope for a 1.5v output and 4.7 h inductor. this is the internal slope compensation for the adjustable (0.6v) version or low-voltage fixed ver- sions. when externally programming the 0.6v ver- sion to 2.5v, the calculated inductance is 7.5 h. in this case, a standard 6.8 h value is selected. for high-voltage fixed versions ( 2.5v), m = 0.48a/ sec. table 1 displays inductor values for the aat1146 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 4.7 h 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 4.7 f to 10 f 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. always examine the ceramic capacitor dc voltage coefficient characteristics when selecting the prop- er value. for example, the capacitance of a 10 f, 6.3v, x5r ceramic capacitor with 5.0v dc applied is actually about 6 f. table 1: inductor values. configuration output voltage inductor 0.6v adjustable with 1v, 1.2v 2.2 h external feedback 1.5v, 1.8v 4.7 h 2.5v, 3.3v 6.8 h fixed output 0.6v to 3.3v 4.7 h c in(min) = 1 ?? - esr 4 f s ?? v pp i o ?? 1 - = for v in = 2 v o ?? v o v in v o v in 1 4 ?? 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 0.75 ? v o 0.24a sec a sec a a sec 0.75 ? v o m = = = 0.24 l 0.75 ? 1.5v 4.7 h a sec
aat1146 fast transient 400ma step-down converter 12 1146.2006.04.1.3 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. for v in = 2 x v o the term appears in both the input voltage ripple and input capacitor rms current equations and is a maximum when v o is twice v in . this is why the input voltage ripple and the input capacitor rms current ripple are a maximum at 50% duty cycle. the input capacitor provides a low impedance loop for the edges of pulsed current drawn by the aat1146. low esr/esl x7r and x5r ceramic capacitors are ideal for this function. to minimize stray inductance, the capacitor should be placed as closely as possible to the ic. this keeps the high frequency content of the input current localized, minimizing emi and input voltage ripple. the proper placement of the input capacitor (c2) can be seen in the evaluation board layout in figure 2. a laboratory test set-up typically consists of two long wires running from the bench power supply to the 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 meas- urements 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 inductance cannot be reduced to a level that does not affect the converter performance, a high esr tantalum or aluminum 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 provides holdup during large load transitions. a 4.7 f to 10 f 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. 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. within two or three switching cycles, the loop responds and the inductor current increases to match the load current demand. the relationship of the output volt- age droop during the three switching cycles to the output capacitance can be estimated by: 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 4.7 f. 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. c out = 3 i load v droop f s ?? 1 - ?? v o v in v o v in i o rms(max) i 2 = ?? 1 - = d (1 - d) = 0.5 2 = ?? v o v in v o v in 1 2 ?? i rms = i o 1 - ?? v o v in v o v in
aat1146 fast transient 400ma step-down converter 1146.2006.04.1.3 13 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 externally pro- grammed. resistors r1 and r2 of figure 5 program the output to regulate at a voltage higher than 0.6v. to limit the bias current required for the external feedback resistor string while maintaining good noise immunity, the minimum suggested value for r2 is 59k . although a larger value will further reduce quiescent 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 voltages with r2 set to either 59k for good noise immunity or 221k for reduced no load input current. figure 2: aat1146 evaluation board figure 3: exploded view of evaluation top side. board top side layout. figure 4: aat1146 evaluation board bottom side. ?? ?? 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) =
aat1146 fast transient 400ma step-down converter 14 1146.2006.04.1.3 the adjustable version of the aat1146, combined with an external feedforward capacitor (c4 in figure 1), delivers enhanced transient response for extreme pulsed load applications. the addition of the feedforward capacitor typically requires a larg- er output capacitor c1 for stability. table 2: adjustable resistor values for use with 0.6v step-down converter. thermal calculations there are three types of losses associated with the aat1146 step-down 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, assuming continuous conduction mode (ccm), a simplified form of the losses is given by: i q is the step-down converter quiescent current. the term t sw is used to estimate the full load step- down converter switching losses. r2 = 59k r2 = 221k v out (v) 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 figure 5: aat1146 adjustable evaluation board schematic. 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 l1 cdrh3d16-4r7 4.7 h l1 10 f c1 4.7 f c2 u1 aat1146 sc70jw-8 c1 10 f 10v 0805 x5r c2 4.7 f 10v 0805 x5r v out gnd v in 1 2 3 enable lx en 1 out 2 vin 3 lx 4 agnd 5 pgnd 6 pgnd 7 pgnd 8 aat1146 u1 gnd2 118k r1 59k r2
aat1146 fast transient 400ma step-down converter 1146.2006.04.1.3 15 for the condition where the step-down converter is in dropout at 100% duty cycle, the total device dis- sipation 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 sc70jw-8 package which is 160c/w. layout the suggested pcb layout for the aat1146 is shown in figures 2, 3, and 4. the following guide- lines should be used to help ensure a proper layout. 1. the input capacitor (c2) should connect as closely as possible to v in (pin 3) and pgnd (pins 6-8). 2. c1 and l1 should be connected as closely as possible. the connection of l1 to the lx pin should be as short as possible. 3. the feedback trace or out pin (pin 2) should be separate from any power trace and connect as closely as possible to the load point. sensing along a high-current load trace will degrade dc load regulation. if external feed- back resistors are used, they should be placed as closely as possible to the out pin (pin 2) to minimize the length of the high impedance feedback trace. 4. the resistance of the trace from the load return to the pgnd (pins 6-8) should be kept to a minimum. this will help to minimize any error in dc regulation due to differences in the poten- tial of the internal signal ground and the power ground. a high density, small footprint layout can be achieved using an inexpensive, miniature, non- shielded, high dcr inductor. an evaluation board is available with this inductor and is shown in figure 6. the total solution footprint area is 40mm 2 . figure 6: minimum footprint evaluation board using 2.0mm x 1.6mm x 0.95mm inductor. t j(max) = p total ja + t amb p total = i o 2 r dson(hs) + i q v in
aat1146 fast transient 400ma step-down converter 16 1146.2006.04.1.3 step-down converter design example specifications v o = 1.8v @ 400ma (adjustable using 0.6v version), pulsed load i load = 300ma v in = 2.7v to 4.2v (3.6v nominal) f s = 1.4mhz t amb = 85c 1.8v output inductor (use 4.7 h; see table 1) for sumida inductor cdrh3d16, 4.7 h, dcr = 105m . 1.8v output capacitor v droop = 0.1v 1 23 1 1.8v (4.2v - 1.8v) 4.7 h 1.4mhz 4.2v 23 rms i l1 f v in(max) = 3 i load v droop f s 3 0.3a 0.1v 1.4mhz c out = = = 6.4 f; use 10f = 45marms (v o ) (v in(max) - v o ) = p esr = esr i rms 2 = 5m (45ma) 2 = 10 w v o v o 1.8 v 1.8v i l1 = ? 1 - = ? 1 - = 156ma l1 ? f v in 4.7 h ? 1.4mhz 4.2v i pkl1 = i o + i l1 = 0.4a + 0.068a = 0.468a 2 p l1 = i o 2 ? dcr = 0.4a 2 ? 105m = 17mw ? ? ? ? ? ? ? ? l1 = 3 ? v o2 = 3 ? 1.8v = 5.4 h sec a sec a
aat1146 fast transient 400ma step-down converter 1146.2006.04.1.3 17 input capacitor input ripple v pp = 25mv aat1146 losses t j(max) = t amb + ja p loss = 85 c + (160 c/w) 126mw = 105.1 c 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 1.4mhz 0.4a + 70 a) 4.2v = 126mw 0.4 2 (0.725 1.8v + 0.7 [4.2v - 1.8v]) 4.2v i o rms i p = esr i rms 2 = 5m (0.2a) 2 = 0.2mw 2 = = 0.2arms c in = = = 3.11 f; use 4.7 f 1 ?? - esr 4 f s ?? v pp i o 1 ?? - 5m 4 1.4mhz ?? 25mv 0.4a
table 3: evaluation board component values. table 4: typical surface mount inductors. 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 adjustable version r2 = 59k r2 = 221k 1 (0.6v device) v out (v) r1 (k ) 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 r2, r4 not used v out (v) r1 (k ) l1 ( h) 0.6-3.3v 0 4.7 aat1146 fast transient 400ma step-down converter 18 1146.2006.04.1.3 1. for reduced quiescent current, r2 and r4 = 221k .
table 5: surface mount capacitors. manufacturer part number value voltage temp. co. case murata grm219r61a475ke19 4.7 f 10v x5r 0805 murata grm21br60j106ke19 10 f 6.3v x5r 0805 murata grm21br60j226me39 22 f 6.3v x5r 0805 aat1146 fast transient 400ma step-down converter 1146.2006.04.1.3 19
aat1146 fast transient 400ma step-down converter 20 1146.2006.04.1.3 advanced analogic technologies, inc. 830 e. arques avenue, sunnyvale, ca 94085 phone (408) 737-4600 fax (408) 737-4611 1. contact sales for other voltage options. 2. xyy = assembly and date code. 3. sample stock is generally held on part numbers listed in bold . ? 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 subject to the terms and conditions of sale supplied at the time of order acknowledgement, including those pertaining to warran ty, 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. ordering information package information sc70jw-8 all dimensions in millimeters. output voltage 1 package marking 2 part number (tape and reel) 3 1.875 sc70jw-8 qmxyy aat1146ijs-1.875-t1 adj 0.6 sc70jw-8 oxxyy aat1146ijs-0.6-t1 0.225 0.075 0.45 0.10 0.05 0.05 2.10 0.30 2.00 0.20 7 3 4 4 1.75 0.10 0.85 0.15 0.15 0.05 1.10 max 0.100 2.20 0.20 0.048ref 0.50 bsc 0.50 bsc 0.50 bsc all 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.

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