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1 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet general description the aat1162 is an 800khz high efficiency step-down dc/dc converter. with a wide input voltage range of 4.0v to 13.2v, the aat1162 is an ideal choice for dual- cell lithium-ion battery-powered devices and mid-pow- er-range regulated 12v-powered industrial applications. the internal power switches are capable of delivering up to 1.5a to the load. the aat1162 is a highly integrated device, simplifying system-level design. minimum external components are required for the converter. the aat1162 optimizes efficiency throughout the entire load range. it operates in a combination pwm/light load mode for improved light-load efficiency. the high switch- ing frequency allows the use of small external compo- nents. the low current shutdown feature disconnects the load from v in and drops shutdown current to less than 1 a. the aat1162 is available in a pb-free, space-saving, thermally-enhanced 16-pin tdfn34 package and is rated over an operating temperature range of -40c to +85c. features ? input voltage range: 4.0v to 13.2v ? up to 1.5a load current ? fixed or adjustable output: ? output voltage: 0.6v to v in ? low 150 a no-load operating current ? less than 1 a shutdown current ? up to 96% efficiency ? integrated power switches ? 800khz switching frequency ? soft start function ? short-circuit and over-temperature protection ? minimum external components ? tdfn34-16 package ? temperature range: -40c to +85c applications ? distributed power systems ? industrial applications ? laptop computers ? portable dvd players ? portable media players ? set-top boxes ? tft lcd monitors and hdtvs typical application lx in ain aat1162 en pgnd fb agnd ldo comp c3 22f r4 10 r5 24k c2 0.1f c8 1f c9 1f c7 330pf l1 2.2 to 4.7h output: 0.6v min, 1.5a max c6 10f input: 4.0v ~ 13.2v dgnd
2 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet pin descriptions pin # symbol function 1, 2, ep2 lx power switching node. lx is the drain of the internal p-channel switch and n-channel synchronous recti- er. connect the output inductor to the two lx pins and to ep2. a large exposed copper pad under the package should be used for ep2. 3, 12 n/c not connected. 4, 5 in power source input. connect in to the input power source. bypass in to dgnd with a 22 f or greater capacitor. connect both in pins together as close to the ic as possible. an additional 100nf ceramic capacitor should also be connected between the two in pins and dgnd, pin 6 6, 13, 14, ep1 dgnd exposed pad 1 digital ground, dgnd. the exposed thermal pad (ep1) should be connected to board ground plane and pins 6, 13, and 14. the ground plane should include a large exposed copper pad under the package for thermal dissipation (see package outline). 7 ain internal analog bias input. ain supplies internal power to the aat1162. connect ain to the input source voltage and bypass to agnd with a 0.1 f or greater capacitor. for additional noise rejection, connect to the input power source through a 10 ? or lower value resistor. 8 ldo internal ldo bypass node. the output voltage of the internal ldo is bypassed at ldo. the internal circuitry of the aat1162 is powered from ldo. do not draw external power from ldo. bypass ldo to agnd with a 1 f or greater capacitor. 9fb output voltage feedback input. fb senses the output voltage for regulation control. for xed output versions, connect fb to the output voltage. for adjustable versions, drive fb from the output voltage through a resistive voltage divider. the fb regulation threshold is 0.6v. 10 comp control compensation node. connect a series rc network from comp to agnd, r = 51k and c = 150pf. 11 agnd analog signal ground. connect agnd to pgnd at a single point as close to the ic as possible. 15 en active high enable input. drive en high to turn on the aat1162; drive it low to turn it off. for automatic startup, connect en to in through a 4.7k ? resistor. en must be biased high, biased low, or driven to a logic level by an external source. do not let the en pin oat when the device is powered. 16 pgnd power ground. connect agnd to pgnd at a single point as close to the ic as possible. pin configuration tdfn34-16 (top view) n/c in in lx lx 3 dgnd ain ldo dgnd dgnd n/c pgnd en agnd comp fb 4 5 1 2 6 7 8 14 13 12 16 15 11 10 9 ep2 ep1
3 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet absolute maximum ratings 1 symbol description value units v in, v ain input voltage -0.3 to 14 v v lx lx to gnd voltage -0.3 to v in + 0.3 v v fb fb to gnd voltage -0.3 to v in + 0.3 v v en en to gnd voltage -0.3 to v in + 0.3 v t j operating junction temperature range -40 to 150 c thermal information 3 symbol description value units p d maximum power dissipation 4 2.7 w ? ja thermal resistance 37 c/w 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. based on long-term current density limitation. 3. mounted on an fr4 board. 4. derate 2.7mw/c above 25c.
4 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet electrical characteristics 1 4.0v < v in < 13.2v. c in = c out = 22 f; l = 2.2 or 3.8 h, t a = -40c to +85c, unless otherwise noted. typical values are at t a = 25c. symbol description conditions min typ max units v in input voltage range 4.0 13.2 v v uvlo input under-voltage lockout rising 4.0 v hysteresis 0.3 i q supply current no load 150 300 a i shdn shutdown current v en = gnd 1 a v out output voltage range 0.6 0.94 v in v v out output voltage accuracy i out = 0a to 1.5a -2.5 2.5 % ? v out / v out / ? v in line regulation v in = 4.5v to 13.2v 0.023 0.100 %/v ? v out / i out load regulation v in = 12v, v out = 5v, i out = 0a to 1.5a 0.4 % v fb feedback reference voltage (adjustable version) no load, t a = 25c 0.59 0.60 0.61 v i fbleak fb leakage current v out = 1.2v adjustable version 0.2 a fixed version 2 f osc pwm oscillator frequency 0.6 0.8 1 mhz foldback frequency 200 khz dc maximum duty cycle 94 % t on minimum turn-on time 100 ns t s soft-start time 2ms r ds(on)h p-channel on resistance v in = 12v 0.12 ? v in = 6v 0.15 r ds(on)l n-channel on resistance v in = 12v 0.06 ? v in = 6v 0.08 ? ef ciency v in = 12v, v out = 5v, i out = 1.5a 90 % i lim pmos current limit 4.0 6.0 a i lxleak lx leakage current v in = 13.2v, v lx = 0 to v in 1 a t sd over-temperature shutdown threshold 140 c t hys over-temperature shutdown hysteresis 25 c v il en logic low input threshold 0.4 v v ih en logic high input threshold 1.4 v i en en input current v en = 0v, v en = 13.2v -1.0 1.0 a 1. the aat1162 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.
5 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet typical characteristics test circuit of figure 2, unless otherwise specified. efficiency vs. output current (v out = 5v) output current (a) efficiency (%) 0 10 20 30 40 50 60 70 80 90 100 0.0001 0.001 0.01 0.1 1 1 0 v in = 6v v in = 8.4v v in = 10v v in = 12v v in = 13.2v load regulation (v out = 5v) output current (a) output voltage difference (%) -0.5 -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 0.5 0.0001 0.001 0.01 0.1 1 10 v in = 6v v in = 8.4v v in = 10v v in = 12v v in = 13.2v efficiency vs. output current (v out = 3.3v) output current (a) efficiency (%) 0 10 20 30 40 50 60 70 80 90 100 0.0001 0.001 0.01 0.1 1 1 0 v in = 5v v in = 8.4v v in = 10v v in = 12v v in = 13.2v load regulation (v out = 3.3v) output current (a) output voltage error (%) -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 1 10 100 1000 10000 v in = 5v v in = 8.4v v in = 10v v in = 12v v in = 13.2v line regulation (v out = 5v) input voltage (v) output voltage difference (%) -0.4 -0.3 -0.2 -0.1 0 0.1 0.2 0.3 0.4 6 7 8 9 10 11 12 1.5a 1ma 10ma 100ma line regulation (v out = 3.3v) input voltage (v) output voltage difference (%) -0.04 -0.03 -0.02 -0.01 0 0.01 0.02 0.03 0.04 0.05 56789101112 1.5a 1ma 10ma 100ma
6 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet typical characteristics test circuit of figure 2, unless otherwise specified. supply current vs. input voltage (v out = 5v) input voltage (v) quiescent current (a) 110 120 130 140 150 160 170 6 7 8 9 10 11 1 2 85c 25c -40c switching current vs. temperature (v out = 5v) temperature (c) on time (ns) 110 120 130 140 150 160 170 -40 -15 10 35 60 85 v in = 12v v in = 6v n-channel r ds(on) vs. temperature temperature (c) resistance (m ) 0 20 40 60 80 100 120 -40 -15 10 35 60 85 v in = 12v v in = 6v p-channel r ds(on) vs. temperature (v in = 6v) temperature (c) resistance (m ) 0 20 40 60 80 100 120 140 160 180 200 -40 -15 10 35 60 85 v in = 6v v in = 12v switching frequency vs. temperature temperature (c) switching frequency (hz) 770 775 780 785 790 795 800 805 810 -40 -15 10 35 60 85 v in = 6v v in = 12v start-up time (v out = 5.0v; c ff = 100pf; r load = 1.5a; c in = 10f; c out = 22f; l = 3.8h) time (500s/div) enable voltage (top) (v) input current (bottom) (a) 0 1 2 3 4 5 6 0 1 2 3 4 5 6 v out i load v en
7 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet typical characteristics test circuit of figure 2, unless otherwise specified. line transient (v out = 5.0v; c ff = 100pf; v in = 7.6v to 11v; i out = 1.5a; c in = 10f; c out = 22f; l = 3.8h) time (100s/div) input voltage (top) (v) output voltage (bottom) (v) 4 5 6 7 8 9 10 11 12 4.90 4.95 5.00 5.05 5.10 5.15 5.20 5.25 5.30 load transient (v out = 3.3v; c ff = 100pf; c out = 66f) time (50s/div) output voltage (top) (v) load and inductor current (bottom) (1a/div) 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 10ma 1.5a load transient (v out = 3.3v; c out = 66f; no c ff ) time (50s/div) output voltage (top) (v) load and inductor current (bottom) (1a/div) 2 2.2 2.4 2.6 2.8 3 3.2 3.4 3.6 10ma 1.5a load transient (v out = 5v; c ff = 100pf; c out = 66f) time (50s/div) output voltage (top) (v) load and inductor current (bottom) (1a/div) 3 3.3 3.6 3.9 4.2 4.5 4.8 5.1 5.4 10ma 1.5a load transient (v out = 5v; c out = 66f; no c ff ) time (50s/div) output voltage (top) (v) load and inductor current (bottom) (1a/div) 3 3.3 3.6 3.9 4.2 4.5 4.8 5.1 5.4 10ma 1.5a v out vs. temperature (v out = 3.3v; i load = 1.5a) temperature (c) output voltage difference (%) -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 -40-30-20-100 102030405060708090
8 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet typical characteristics test circuit of figure 2, unless otherwise specified. load transient (v out = 3.3v; c ff = 100pf; c out = 22f) time (50s/div) output voltage (top) (v) load and inductor current (bottom) (1a/div) 1.5 1.8 2.1 2.4 2.7 3 3.3 3.6 3.9 10ma 1.5a load transient (v out = 3.3v; c out = 22f; no c ff ) time (50s/div) output voltage (top) (v) load and inductor current (bottom) (1a/div) 0.5 0.9 1.3 1.7 2.1 2.5 2.9 3.3 3.7 10ma 1.5a load transient (v out = 5v; c ff = 100pf; c out = 22f) time (50s/div) output voltage (top) (v) load and inductor current (bottom) (1a/div) 3 3.3 3.6 3.9 4.2 4.5 4.8 5.1 5.4 10ma 1.5a load transient (v out = 5v; c out = 22f; no c ff ) time (50s/div) output voltage (top) (v) load and inductor current (bottom) (1a/div) 3 3.3 3.6 3.9 4.2 4.5 4.8 5.1 5.4 10ma 1.5a
9 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet functional description the aat1162 is a current-mode step-down dc/dc con- verter that operates over a wide 4v to 13.2v input volt- age range and is capable of supplying up to 1.5a to the load with the output voltage regulated as low as 0.6v. both the p-channel power switch and n-channel syn- chronous rectifier are internal, reducing the number of external components required. the output voltage is adjusted by an external resistor divider; fixed output voltage versions are available upon request. the regula- tion system is externally compensated, allowing the cir- cuit to be optimized for each application. the aat1162 includes cycle-by-cycle current limiting, frequency fold- back for improved short-circuit performance, and ther- mal overload protection to prevent damage in the event of an external fault condition. control loop the aat1162 regulates the output voltage using con- stant frequency current mode control. the aat1162 monitors current through the high-side p-channel mosfet and uses that signal to regulate the output volt- age. this provides improved transient response and eases compensation. internal slope compensation is included to ensure the current ?inside loop? stability. functional block diagram control logic + - ldo + - reference note 1 fb en agnd dgnd pgnd lx in ain ldo comp note 1: for fixed output voltage versions, fb is connected to the error amplifier through the resistive voltage divider shown. . + - current sense amp error amp current mode comparator
10 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet high efficiency is maintained under light load conditions by automatically switching to variable frequency light load control. in this condition, transition losses are reduced by operating at a lower frequency at light loads. short-circuit protection the aat1162 uses a cycle-by-cycle current limit to pro- tect itself and the load from an external fault condition. when the inductor current reaches the internally set 3.0a current limit, the p-channel mosfet switch turns off and the n-channel synchronous rectifier is turned on, limiting the inductor and the load current. during an overload condition, when the output voltage drops below 50% of the regulation voltage (0.3v at fb), the aat1162 switching frequency drops by a factor of 4. this gives the inductor current ample time to reset dur- ing the off time to prevent the inductor current from rising uncontrolled in a short-circuit condition. thermal protection the aat1162 includes thermal protection that disables the regulator when the die temperature reaches 140oc. it automatically restarts when the temperature decreas- es by 25oc or more. applications information setting the output voltage figure 1 shows the basic application circuit for the aat1162 and output setting resistors. resistors r1 and r2 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 5.9k . although a larger value will further reduce quies- cent current, it will also increase the impedance of the feedback node, making it more sensitive to external noise and interference. table 1 summarizes the resistor values for various output voltages with r2 set to either 5.9k for good noise immunity or 59k for reduced no load input current. pgnd agnd lx lx in in en dgnd fb aat 1162 c6 10f vin 4.5v- 13.2v l1 3.8h c1 100pf c3 22f r3 432k r6 59k vout 5v, 1.5a 3 5 4 6 9 2 1 11 10 ain 7 dgnd ldo dgnd comp lx dgnd r5 24k c7 330pf c9 1 f c2 0.1 f r4 10 14 8 13 16 ep1 ep2 c8 1 f figure 1: typical application circuit. the adjustable feedback resistors, combined with an external feed forward capacitor (c1 in figure 1), deliver enhanced transient response for extreme pulsed load applications. the addition of the feed forward capacitor typically requires a larger output capacitor c3 for stabil- ity. larger c1 values reduce overshoot and undershoot during startup and load changes. however, do not exceed 470pf to maintain stable operation.
11 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet the external resistors set the output voltage according to the following equation: ?? v out = 0.6v 1 + ?? r1 r2 or ?? ?? r1 = -1 r2 v out v ref table 1 shows the resistor selection for different output voltage settings. v out (v) r2 = 5.9(k ) r1 (k ) r2 = 59(k ) r1 (k ) 0.8 1.96 19.6 0.9 2.94 29.4 1.0 3.92 39.2 1.1 4.99 49.9 1.2 5.90 59.0 1.3 6.81 68.1 1.4 7.87 78.7 1.5 8.87 88.7 1.8 11.8 118 1.85 12.4 124 2.0 13.7 137 2.5 18.7 187 3.3 26.7 267 5.0 43.2 432 table 1: resistor selection for different output voltage settings. standard 1% resistors are substituted for calculated values. inductor selection for most designs, the aat1162 operates with inductors of 2 h to 4.7 h. low inductance values are physically smaller, but require faster switching, which results in some efficiency loss. the inductor value can be derived from the following equation: v out 3.3 l1 = 3.8h where ? i l is inductor ripple current. large value induc- tors lower ripple current and small value inductors result in high ripple currents. choose inductor ripple current approximately 32% of the maximum load current 1.5a, or ? i l = 480ma. for output voltages above 3.3v, the minimum recommended inductor is 3.8 h. for 3.3v and below, use a 2 to 3.8 h inductor. for optimum voltage- positioning load transients, choose an inductor with dc series resistance in the 15m to 20m range. for higher efficiency at heavy loads (above 1a), or minimal load regulation (but some transient overshoot), the resistance should be kept below 18m . the dc current rating of the inductor should be at least equal to the maximum load current plus half the ripple current to prevent core saturation (1.5a + 280ma). table 2 lists some typical surface mount inductors that meet target applications for the aat1162. 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. for example, the 4.7 h we-tpc series inductor selected from wurth has an 38m dcr and a 2.4adc current rating. at full load, the inductor dc loss is 85mw which gives only a 1.1% loss in efficiency for a 1.5a, 5v output. input capacitor selection the input capacitor reduces the surge current drawn from the input and switching noise from the device. the input capacitor impedance at the switching frequency shall be less than the input source impedance to prevent high frequency switching current passing to the input. a low esr input capacitor sized for maximum rms current must be used. ceramic capacitors with x5r or x7r dielectrics are highly recommended because of their low esr and small temperature coefficients. a 10 f ceramic capacitor is sufficient for most applications.
12 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet manufacturer part number l ( h) max dcr (m ) rated dc current (a) size wxlxh (mm) sumida cdrh103rnp-2r2n 2.2 16.9 5.10 10.3x10.5x3.1 sumida cdr7d43mnnp-3r7nc 3.7 18.9 4.3 7.6x7.6x4.5 coilcraft mss1038-382nl 3.8 13 4.25 10.2x7.7x3.8 cooper bussman dr73-4r7-r 4.7 29.7 3.09 6.0x7.6x3.55 wurth 7440530047 4.7 38 2.40 5.8x5.8x2.8 table 2: typical surface mount inductors. 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 osc ?? v pp i o ?? 1 - = for v in = 2 v o ?? v o v in v o v in 1 4 c in(min) = 1 ?? - esr 4 f osc ?? v pp i o always examine the ceramic capacitor dc voltage coef- ficient characteristics when selecting the proper value. for example, the capacitance of a 10 f, 16v, x5r ceram- ic capacitor with 12v dc applied is actually about 8.5 f. the maximum input capacitor rms current is: ?? i rms = i o 1 - ?? v o v in v o v in the input capacitor rms ripple current varies with the input and output voltage and will always be less than or equal to half of the total dc load current: ?? 1 - = d (1 - d) = 0.5 2 = ?? v o v in v o v in 1 2 for v in = 2 v o i o rms(max) i 2 = the term ?? 1 - ?? v o v in v o v in appears in both the input voltage ripple and input capacitor rms current equations and is at 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 aat1162. 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 (c6) can be seen in the evaluation board layout in figure 3. additional noise fil- tering for proper operation is accomplished by adding a small 0.1 f capacitor on the in pins (c2). a laboratory test set-up typically consists of two long wires running from the bench power supply to the eval- uation board input voltage pins. the inductance of these wires, along with the low-esr ceramic input capacitor, can create a high q network that may affect converter performance. this problem often becomes apparent in the form of excessive ringing in the output voltage dur- ing load transients. errors in the loop phase and gain measurements can also result. since the inductance of a short pcb trace feeding the input voltage is significantly lower than the power leads from the bench power sup- ply, most applications do not exhibit this problem. in applications where the input power source lead induc- tance cannot be reduced to a level that does not affect the converter performance, a high esr tantalum or alu- minum electrolytic should be placed in parallel with the low esr, esl bypass ceramic. this dampens the high q network and stabilizes the system.
13 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet output capacitor selection the output capacitor is required to keep the output volt- age ripple small and to ensure regulation loop stability. the output capacitor must have low impedance at the switching frequency. ceramic capacitors with x5r or x7r dielectrics are recommended due to their low esr and high ripple current. the output ripple v out is deter- mined by: ?? esr + v out ?? v out (v in - v out ) v in f osc l 1 8 f osc c out the output capacitor limits the output ripple and pro- vides holdup during large load transitions. a 10 f to 47 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 volt- age 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 capac- itor 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 voltage droop during the three switching cycles to the output capacitance can be estimated by: c out = 3 i load v droop f osc 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 mini- mum output capacitor value to 22 f. this is due to its effect on the loop crossover frequency (bandwidth), phase margin, and gain margin. increased output capac- itance will reduce the crossover frequency with greater phase margin. the maximum output capacitor rms ripple current is given by: 1 23 v out (v in(max) - v out ) rms(max) i l f osc v in(max) = dissipation due to the rms current in the ceramic output capacitor esr is typically minimal, resulting in less than a few degrees rise in hot-spot temperature. compensation the aat1162 step-down converter uses peak current mode control with slope compensation scheme to main- tain stability with lower value inductors for duty cycles greater than 50%. the regulation feedback loop in the ic is stabilized by the components connected to the comp pin, as shown in figure 1. to optimize the compensation components, the following equations can be used. the compensation resistor r comp (r5) is calculated using the following equation: 2 v out c out f osc 10g ea g comp v fb r comp (r5)= where v fb = 0.6v, g comp = 40.1734 and g ea = 9.091 10 -5 . f osc is the switching frequency and c out is based on the output capacitor calculation. the c comp value can be determined from the following equation: c comp (c7) = 4 ?? 2 r comp (r5) ?? f osc 10 the feed forward capacitor cff (c1) provides faster transient response for pulsed load applications. the addition of the feed forward capacitor typically requires a larger output capacitor c1 for stability. larger c1 val- ues reduce overshoot and undershoot during startup and line/load changes. the cff value can be from 100pf to 470pf, but do not exceed 470pf to maintain stable operation.
14 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet layout guidance figure 2 is the schematic for the evaluation board. when laying out the pc board, the following layout guideline should be followed to ensure proper operation of the aat1162: 1. exposed pad ep1 must be reliably soldered to pgnd/ dgnd/agnd. the exposed thermal pad should be connected to board ground plane and pins 6, 11, 13, 14 and 16. the ground plane should include a large exposed copper pad under the package for thermal dissipation. 2. the power traces, including gnd traces, the lx traces and the vin trace should be kept short, direct and wide to allow large current flow. the l1 connec- tion to the lx pins should be as short as possible. use several via pads when routing between layers. 3. exposed pad pin ep2 must be reliably soldered to the lx pins 1 and 2. the exposed thermal pad should be connected to the board lx connection and the induc- tor l1 and also pins 1 and 2. the lx plane should include a large exposed copper pad under the pack- age for thermal dissipation. 4. the input capacitors (c9 and c1) should be con- nected as close as possible to in (pins 4 and 5) and dgnd (pin 6) to get good power filtering. 5. keep the switching node lx away from the sensitive fb node. 6. the feedback trace for the fb pin should be separate from any power trace and connected as closely as possible to the load point. sensing along a high- current load trace will degrade dc load regulation. the feedback resistors should be placed as close as possible to the fb pin (pin 9) to minimize the length of the high impedance feedback trace. 7. the output capacitors c3, 4, and 5 and l1 should be connected as close as possible and there should not be any signal lines under the inductor. 8. the resistance of the trace from the load return to the pgnd (pin 16) should be kept to a minimum. this will help to minimize any error in dc regulation due to differences in the potential of the internal signal ground and the power ground.
15 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet vin vout in 5 ain 7 pgnd 16 ldo 8 lx 2 n/c 3 n/c 12 in 4 dgnd 13 fb 9 en 15 dgnd 14 agnd 11 lx 1 comp 10 dgnd 6 lx ep2 gnd ep1 u1 aat1162 dgnd *note: connect gnd, dgnd, and agnd at ic ep1 r1 4.75k r2 4.75k r4 10 r5 24k r3 432k r6 59k c6 10f c8 1f c2 0.1f c9 1f c3 22f c4 np c5 np c7 330pf c1 100pf jp1 enable tp3 enable tp2 lx tp4 vout tp6 vout tp12 gnd tp8 gnd tp11 gnd tp9 gnd tp13 gnd tp5 vin tp7 vin tb2 vout tb1 vin tp1 gnd l1 3.8h * tp14 gnd figure 2: aat1162 evaluation board schematic. figure 3: aat1162 evaluation board figure 4: aat1162 evaluation board component side layout. solder side layout.
16 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet design example specifications v out 5v @ 1.5a, pulsed load ? i load = 1.5a v in 12v nominal f osc 800khz t amb 85c in tdfn34-16 package output inductor v out 3.3 l = 3.8h = 5.75h; use 4.7h (see table 2) i l = 0.32 i load = 480ma for cooper bussman inductor dr73-4r7-r 4.7 h dcr = 29.7mw max. v out v o1 5 v 5v i 1 = ? 1 - = ? 1 - = 480m a l1 ? f osc v in 4.7h ? 800khz 12v i pk1 = i load + i 1 = 1.5a + 0.480a = 1.98a 2 p l1 = i load 2 ? dcr = 3a 2 ? 13m = 117mw ? ? ? ? ? ? ? ? output capacitor v droop = 0.2v 1 23 1 5v (12v - 5v) 4.7h 800khz 12v 23 rms(max) i l f osc v in(max) = 3 i load v droop f osc 3 1.5a 0.2v 800khz c out = = = 28f; use 22f = 139marms (v out ) (v in(max) - v out ) = p esr = esr i rms 2 = 5m (277ma) 2 = 384w input capacitor input ripple v pp = 50mv c in = = = 11f; use 10 f 1 ?? - esr 4 f osc ?? v pp i load 1 ?? - 5m 4 800khz ?? 50mv 1.5a i load rms(max) i p = esr i rms 2 = 5m (0.75a) 2 = 2.81mw 2 = = 0.75arms
17 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet aat1162 losses total losses can be estimated by calculating the dropout (v in = v o ) losses where the power mosfet r ds(on) will be at the maximum value. all values assume an 85c ambient temperature and a 140c junction temperature with the tdfn 37c/w package. p loss = i load 2 r ds(on)h = 1.5a 2 0.158 = 0.355w t j(max) = t amb + ja p loss = 85 c + (37 c/w) 355mw = 96.6 c the total losses are also investigated at the nominal input voltage (12v). the simplified version of the r ds(on) losses assumes that the n-channel and p-channel r ds(on) are equal. p total = i load 2 r ds(on) + [(t sw f osc i load + i q ) v in ] = 1.5a 2 100m + [(5ns 800khz 1.5a + 150a) 12v] = 299mw t j(max) = t amb + ja p loss = 85 c + (37 c/w) 299mw = 96 c
18 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet ordering information package marking 1 part number (tape and reel) 2 tdfn34-16 yyxyy aat1162irn-0.6-t1 skyworks green? products are compliant with all applicable legislation and are halogen-free. for additional information, refer to skyworks de?ition of green , document number sq04-0074. package information tdfn34-16 3 top view bottom view side view 3.000 all dimensions in millimeters. 1. xyy = assembly and date code. 2. sample stock is generally held on part numbers listed in bold . 3. 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.
19 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 201998b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat1162 12v, 1.5a step-down dc/dc converter data sheet 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.

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