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aat1156 1mhz 700ma step-down dc-dc converter 1156.2007.01.1.4 1 switchreg ? general description the aat1156 switchreg is a step-down switching converter ideal for applications where high efficien- cy is required over the full range of load conditions. the 2.7v to 5.5v input voltage range makes the aat1156 ideal for single-cell lithium-ion/polymer battery applications. capable of more than 700ma with internal mosfets, the current-mode con- trolled ic provides high efficiency over a wide oper- ating range. fully integrated compensation simpli- fies system design and lowers external parts count. the aat1156 is available in a pb-free, 16-pin, 3x3mm qfn package and is rated over the -40c to +85c temperature range. features ?v in range: 2.7v to 5.5v ? up to 95% efficiency ? 110m r ds(on) internal switches ?<1 a shutdown current ? 1mhz step-down switching frequency ? fixed or adjustable v out 0.8v ? integrated power switches ? current mode operation ? internal compensation ? stable with ceramic capacitors ? internal soft start ? over-temperature protection ? current limit protection ? 16-pin qfn 3x3mm package ? -40c to +85c temperature range applications ? cellular phones ? digital cameras ? mp3 players ? notebook computers ? pdas ? wireless notebook adapters typical application efficiency vs. load current (v out = 2.5v; l = 4.7h) output current (ma) efficiency (%) 50 55 60 65 70 75 80 85 90 95 100 1 10 100 1000 v in = 3.0v v in = 3.6v v in = 4.2v 4.7 h l1 2 x 22 f c3, c4 10 f c1 100 r1 0.1 f c2 c1 murata 10 f 6.3v x5r grm42-6x5r106k6.3 c3-c4 murata 22 f 6.3v grm21br60j226me39l x5r 0805 2.5v in put l1 sumida cdrh3d16-4r7nc 187k r3 59k r4 lx ll en vcc vp nc lx pgnd vp vp fb lx pgnd pgnd sgnd nc aat1156 u1
pin descriptions pin configuration qfn33-16 (top view) pin # symbol function 1, 2, 3 pgnd main power ground return pin. connect to the output and input capacitor return. (see board layout rules.) 4 fb feedback input pin. this pin is connected to the converter output. it is used to set the output of the converter to regulate to the desired value via an internal resistive divider. for an adjustable output, an external resistive divider is connected to this pin on the 1v model. 5 sgnd signal ground. connect the return of all small signal components to this pin. (see board layout rules.) 6 ll mode selector switch. when pulled low, the device enters light load mode. 7 en enable input pin. a logic high enables the converter; a logic low forces the aat1156 into shutdown mode, reducing the supply current to less than 1 a. the pin should not be left floating. 8, 16 nc not internally connected. 9 vcc bias supply. supplies power for the internal circuitry. connect to input power via low pass filter with decoupling to sgnd. 10, 11, 12 vp input supply voltage for the converter power stage. must be closely decoupled to pgnd. 13, 14, 15 lx connect inductor to these pins. switching node internally connected to the drain of both high- and low-side mosfets. ep exposed paddle (bottom); connect to pgnd directly beneath package. aat1156 1mhz 700ma step-down dc-dc converter 2 1156.2007.01.1.4 vp vp vp nc pgnd pgnd pgnd 1 2 3 4 ll sgnd en 16 15 14 13 5 6 7 8 12 11 10 9 nc vc c lx lx lx fb
absolute maximum ratings 1 thermal characteristics recommended operating conditions symbol description value units t ambient temperature range -40 to 85 c symbol description value units ja maximum thermal resistance (qfn33-16) 3 50 c/w p d maximum power dissipation (qfn33-16) 4 (t a = 25c) 2.0 w symbol description value units v cc , v p vcc, vp to gnd 6 v v lx lx to gnd -0.3 to v p + 0.3 v v fb fb to gnd -0.3 to v cc + 0.3 v v en en to gnd -0.3 to 6 v t j operating junction temperature range -40 to 150 c v esd esd rating 2 - hbm 3000 v aat1156 1mhz 700ma step-down dc-dc converter 1156.2007.01.1.4 3 1. stresses above those listed in absolute maximum ratings may cause damage to the device. functional operation at conditions o ther than the operating conditions specified is not implied. only one absolute maximum rating should be applied at any one time. 2. human body model is 100pf capacitor discharged through a 1.5k resistor into each pin. 3. mounted on a demo board (fr4, in still air). 4. derate 20mw/c above 25c.
electrical characteristics v in = v cc = v p = 5v, 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 2.7 5.5 v v out output voltage tolerance v in = v out + 0.2 to 5.5v, -3 3 % i out = 0 to 700ma v il input low voltage 0.6 v v ih input high voltage 1.4 v v uvlo under-voltage lockout v in rising, v en = v cc 2.5 v v in falling, v en = v cc 1.2 v uvlo(hys) under-voltage lockout hysteresis 250 mv i il input low current v in = v fb = 5.5v 1.0 a i ih input high current v in = v fb = 0v 1.0 a i q quiescent supply current no load, ll = 0v; v fb = 0v, 220 350 a v in = 4.2v, t a = 25c i shdn shutdown current v en = 0v, v in = 5.5v 1.0 a i lim current limit t a = 25c 1.2 a r ds(on)h high side switch on resistance t a = 25c 110 150 m r ds(on)l low side switch on resistance t a = 25c 100 150 m v out (v out * v in ) load regulation v in = 4.2v, i load = 0 to 700ma 0.9 % v out /v out line regulation v in = 2.7 to 5.5v 0.1 %/v f osc oscillator frequency t a = 25c 750 1000 1350 khz t sd over-temperature shutdown 140 c threshold t hys over-temperature shutdown 15 c hysteresis aat1156 1mhz 700ma step-down dc-dc converter 4 1156.2007.01.1.4
typical characteristics aat1156 1mhz 700ma step-down dc-dc converter 1156.2007.01.1.4 5 line transient (i out = 500ma; v o = 0.8v) input voltage (top) (v) output voltage (ac coupled) (bottom) (mv) 2.8 3 3.2 3.4 3.6 3.8 4 4.2 4.4 -20 -10 0 10 20 30 40 50 60 time (20 output ripple (0.8v; 700ma; v in = 3.6v) time (250ns/div) output voltage (ac coupled) (top) (mv) inductor current (bottom) (a) -60 -50 -40 -30 -20 -10 0 10 20 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 soft start (0.8v; 700ma; v in = 3.6v) time (100 s/div) enable and output voltage (top) (v) inductor current (bottom) (a) -2 -1.5 -1 -0.5 0 0.5 1 1.5 2 -0.5 0 0.5 1 1.5 2 2.5 3 3.5 output ripple (0.8v; 10ma; v in = 3.6v) time (2 s/div) output voltage (ac coupled) (top) (mv) inductor current (bottom) (a) -60 -50 -40 -30 -20 -10 0 10 20 -0.2 0 0.2 0.4 0.6 0.8 1 1.2 1.4 efficiency vs. load current (v out = 0.8v; l = 2.2h) output current (ma) efficiency (%) 20 30 40 50 60 70 80 90 100 1 10 100 1000 v in = 2.7v v in = 3.6v v in = 4.2v efficiency vs. load current (v out = 2.5v; l = 4.7h) output current (ma) efficiency (%) 50 55 60 65 70 75 80 85 90 95 100 1 10 100 1000 v in = 3.0v v in = 3.6v v in = 4.2v
typical characteristics aat1156 1mhz 700ma step-down dc-dc converter 6 1156.2007.01.1.4 p-channel r ds(on) vs. input voltage input voltage (v) r ds(on) (m ) 0 20 40 60 80 100 120 140 160 180 200 2.5 3.5 345 4.5 5.5 120 c 25 c 85 c 100 c frequency vs. temperature (v in = 3.6v) temperature ( c) frequency (mhz) 0.6 0.7 0.8 0.9 1 1.1 1.2 -40 -20 0 20 40 60 80 100 dc regulation (v out = 0.6v) output current (a) output error (%) -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 0.0001 0.001 0.01 0.1 1 v in = 4.2v v in = 3.6v v in = 2.7v output voltage vs. temperature (v in = 4.2v; v out = 0.8v; 400ma v out ) temperature ( c) output voltage error (%) -0.4 -0.3 -0.2 -0.1 0.1 0.0 -40 -20 0 20 40 60 80 100 no load supply current vs. input voltage input voltage (v) supply current ( a) 0 50 100 150 200 250 300 2.5 3 3.5 4 4.5 5 5.5 -40 c 25 c 85 c load transient response (50ma to 680ma; v in = 3.6v; v out = 0.8v) output voltage (top) (20mv/div) time (10 sec/div) inductor and load current (bottom) (500ma/div) 0.67 0.69 0.71 0.73 0.75 0.77 0.79 0.81 0.83 ? ?
typical characteristics aat1156 1mhz 700ma step-down dc-dc converter 1156.2007.01.1.4 7 1156.2007.01.1.4 7 n-channel r ds(on) vs. input voltage input voltage (v) r ds(on) (m ) 0 20 40 60 80 100 120 140 160 180 200 2.5 3.5 345 4.5 5.5 120 c 25 c 85 c 100 c frequency vs. input voltage input voltage (v) frequency (mhz) 0.94 0.95 0.96 0.97 0.98 0.99 1 1.01 1.02 2.7 3.2 3.7 4.2 4.7 5.2 5.7
aat1156 1mhz 700ma step-down dc-dc converter 8 1156.2007.01.1.4 functional block diagram operation control loop the aat1156 is a peak current mode step-down converter. the inner wide bandwidth loop controls the inductor peak current. the inductor current is sensed through the p-channel mosfet (high side) and is also used for short-circuit and overload protection. a fixed slope compensation signal is added to the sensed current to maintain stability for duty cycles greater than 50%. the loop appears as a voltage-programmed current source in paral- lel with the output capacitor. the voltage error amplifier output programs the current loop for the necessary inductor current to force a constant output voltage for all load and line conditions. the external voltage feedback resistive divider divides the output voltage to the error ampli- fier reference voltage of 0.6v. the voltage error amplifier dc gain is limited. this eliminates the need for external compensation components, while still providing sufficient dc loop gain for good load regulation. the voltage loop crossover frequency and phase margin are set by the output capacitor. soft start/enable soft start increases the inductor current limit point in discrete steps once the input voltage or enable input is applied. it limits the current surge seen at the input and eliminates output voltage overshoot. when pulled low, the enable input forces the aat1156 into a non-switching shutdown state. the total input current during shutdown is less than 1 a. power and signal source separate small signal ground and power supply pins isolate the internal control circuitry from the noise associated with the output mosfet switch- ing. the low pass filter r1 and c2 (shown in the schematic in figure 1) filters the input noise asso- ciated with the power switching. vp = 2.7v to 5.5v vcc en sgnd pgnd logic 1.0v ref temp. sensing osc op. amp l x fb dh dl cmp 1m ll
current limit and over-temperature protection for overload conditions, the peak input current is lim- ited. as load impedance decreases and the output voltage falls closer to zero, more power is dissipated internally, raising the device temperature. thermal protection completely disables switching when inter- nal dissipation becomes excessive, protecting the device from damage. the junction over-temperature threshold is 140c with 15c of hysteresis. inductor the output inductor is selected to limit the ripple cur- rent to a predetermined value, typically 20% to 40% of the full load current at the maximum input voltage. 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 losses due to a high dcr. always consider the losses asso- ciated with the dcr and its effect on the total con- verter efficiency when selecting an inductor. for a 0.7a, 1.5v output with the ripple set to 40% at a maximum input voltage of 4.2v, the maximum peak-to-peak ripple current is 280ma. the induc- tance value required is 3.44 h. the factor "k" is the fraction of full load selected for the ripple current at the maximum input voltage. for ripple current at 40% of the full load current, the peak current will be 120% of full load. selecting a standard value of 3.3 h gives 42% ripple current. a 3.3 h inductor selected from the sumida cdrh3d16 series has a 63m dcr and a 1.1a dc current rating. at full load, the inductor dc loss is 31mw which amounts to less than 3% loss in efficiency for a 0.7a, 1.5v output. input capacitor the primary function of the input capacitor is to pro- vide a low impedance loop for the edges of pulsed current drawn by the aat1156. a low esr/esl ceramic capacitor is ideal for this function. to mini- mize stray inductance, the capacitor should be placed as closely as possible to the ic. this keeps the high frequency content of the input current local- ized, minimizing radiated and conducted emi while facilitating optimum performance of the aat1156. ceramic x5r or x7r capacitors are ideal for this function. the size required will vary depending on aat1156 1mhz 700ma step-down dc-dc converter 1156.2007.01.1.4 9 figure 1: aat1156 evaluation board schematic ? lithium-ion to 2.5v converter. v out i o ? k ? f s v out v in 1.5 v 1.5v l = ? 1 - l = 3.44 h l = ? 1 - 0.7a ? 0.4 ? 1mhz 4.2v ? ? ? ? ? ? ? ? 4.7 h l1 2 x 22 f c3, c 4 10 f c1 100 r1 0.1 f c2 c1 murata 10 f 6.3v x5r grm42-6x5r106k6.3 c3, c4 murata 22 f 6.3v grm21br60j226me396 x5r 0805 vout+ vin+ l1 sumida cdrh3d16-4r7nc ll en vcc vp n/c vp vp sgnd pgnd lx n/c lx pgnd fb lx pgnd aat1156 u1 100k r6 200k r3 59k r4 enable 100k r2 ll
aat1156 1mhz 700ma step-down dc-dc converter 10 1156.2007.01.1.4 the load, output voltage, and input voltage source impedance characteristics. values range from 1 f to 10 f. the input capacitor rms current varies with the input voltage and output voltage. the equa- tion for the rms current in the input capacitor is: the input capacitor rms ripple current reaches a maximum when v in is two times the output voltage, where it is approximately one half of the load cur- rent. losses associated with the input ceramic capacitor are typically minimal and are not an issue. proper placement of the input capacitor is shown in the reference design layout in figure 2. output capacitor since there are no external compensation compo- nents, the output capacitor has a strong effect on loop stability. larger output capacitance will reduce the crossover frequency with greater phase margin. for the 1.5v, 0.7a design using the 3.3 h inductor, two 22 f capacitors provide a stable output. in addition to assisting in stability, the output capacitor limits the output ripple and provides holdup during large load transitions. the output capacitor rms ripple current is given by: for an x7r or x5r ceramic capacitor, the esr is so low that dissipation due to the rms current of the capacitor is not a concern. tantalum capacitors with sufficiently low esr to meet output voltage rip- ple requirements also have an rms current rating well beyond that actually seen in this application. layout figures 2 and 3 display the suggested pcb layout for the aat1156. the following guidelines should be used to help ensure a proper layout. 1. the input capacitor (c1) should connect as closely as possible to vp (pins 10, 11, and 12) and pgnd (pins 1, 2, and 3). 2. c3, c4, and l1 should be connected as closely as possible. the connection from l1 to the lx node should be as short as possible. 3. the feedback trace (pin 4) 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. 4. the resistance of the trace from the load return to pgnd (pins 1, 2, and 3) should be kept to a minimum. this will help to minimize any error in dc regulation due to differences in the potential of the internal signal ground and the power ground. 5. low pass filter r1 and c2 provide a cleaner bias source for the aat1156 active circuitry. c2 should be placed as closely as possible to sgnd (pin 5) and vcc (pin 9). figure 2: aat1156 evaluation figure 3: aat1156 evaluation board top side. board bottom side. v out ? (v in - v out ) 1 i rms = ? l ? f s ? v in 2 ? 3 v o ? v o ? i rms = i o ? ? 1 - v in ? v in ?
thermal calculations there are three types of losses associated with the aat1156: mosfet switching losses, conduction losses, and quiescent current losses. the conduction losses are due to the r ds(on) characteristics of the internal p- and n-channel mosfet power devices. at full load, assuming continuous conduction mode (ccm), a simpli- fied form of the total losses is given by: where i q is the aat1156 quiescent current. once the total losses have been determined, the junction temperature can be derived from the ja for the qfn33-16 package. adjustable output resistors r3 and r4 of figure 1 force the output to regulate higher than 0.6v. the optimum value for r4 is 59k . values higher than this may cause problems with stability, while lower values can degrade light load efficiency. for a 2.5v output with r4 set to 59k , r3 is 187k . figure 4: r3 vs. v out for adjustable output using the aat1156. aat1156 1mhz 700ma step-down dc-dc converter 1156.2007.01.1.4 11 output voltage (v) r3 (k ) 0 50 100 150 200 250 300 350 400 450 500 1 1.5 2 2.5 3.5 3 4 4.5 5 5. 5 r4=59k ?? ?? r3 = -1 r4 = - 1 59k = 187k v o v ref ?? ?? 2.5v 0.6v t j = p ja + t amb i o 2 ? ( r ds(on)h ? v o + r ds(on)l ? ( v in - v o )) p = + (t sw ? f s ? i o ? v in + i q ) ? v in v in
aat1156 1mhz 700ma step-down dc-dc converter 12 1156.2007.01.1.4 design example specifications i out 0.7a i ripple 40% of full load at max v in v out 2.5v v in 2.7v to 4.2v (3.6v nominal) f s 1mhz t amb 85c maximum input capacitor ripple: inductor selection: select sumida inductor cdrh3d16 or cdrh4d28 4.7 h. v o v o 2.5 v 2.5v i = ? 1 - = ? 1- = 220ma l ? f s v in 4.7 h ? 1mhz 4.2v i pk = i out + i = 0.7a + 0.11a = 0.81a 2 p = i o 2 ? dcr = (0.7a) 2 ? 80m = 40mw ? ? ? ? ? ? ? ? v out v out 2.5 v 2.5v l = ? 1 - = ? 1 - = 4.82 h i o ? k ? f s v in 0.7a ? 0.3 ? 1mhz 4.2v ? ? ? ? ? ? ? ? 1 0.34arms, v in = 2 v o oo rms o in in vv ii vv ?? = -= ?? p = esr i rms 2 = 5m 0.34 2 a = 0.6mw
aat1156 1mhz 700ma step-down dc-dc converter 1156.2007.01.1.4 13 output capacitor ripple current: aat1156 dissipation: figure 5: 0.8v solution. efficiency vs. load current (v out = 0.8v; l = 2.2h) output current (ma) efficiency (%) 20 30 40 50 60 70 80 90 100 1 10 100 1000 v in = 2.7v v in = 3.6v v in = 4.2v 2.2 h l1 2 x 22 f c3, c4 10 f c1 100 r1 0.1 f c2 c1 murata 10 f 6.3v x5r grm42-6x5r106k6.3 c3, c4 murata 22 f 6.3v grm21br60j226me39l x5r 0805 0.8v in put l1 sumida cdrh3d16-2r2nc 19.6k r3 59k r4 ll en vcc vp n/c vp vp sgnd pgnd lx n/c lx pgnd fb lx pgnd aat1156 u1 t j(max) = t amb + ja ? p loss = 85 c + 50 c/w ? 0.141w = 92 c p total + (t sw ? f s ? i o + i q ) ? v in i o 2 ? (r ds(on)h ? v o + r ds(on)l ? (v in -v o )) v in = = + (20nsec ? 1mhz ? 0.7a + 300 a) ? 4.2v = 0.141w (0.7a) 2 ? (0.17 ? 2.5v + 0.16 ? (4.2v - 1.5v)) 4.2v 1 23 1 2.5v (4.2v - 2.5v) 4.7 h 1mhz 4.2v 23 rms i l f s v in = = 62marms v out (v in - v out ) = pesr = esr i rms 2 = 5m (62 ma) 2 = 19 w
aat1156 1mhz 700ma step-down dc-dc converter 14 1156.2007.01.1.4 surface mount inductors surface mount capacitors manufacturer part number value voltage temp. co. case murata grm40 x5r 106k 6.3 10 f 6.3v x5r 0805 murata grm42-6 x5r 106k 6.3 10 f 6.3v x5r 1206 murata grm21br60j226me39l 22 f 6.3v x5r 0805 max dc size (mm) manufacturer part number value current dcr l x w x h type taiyoyuden npo5db4r7m 4.7 h 1.4a 0.038 5.9x6.1x2.8 shielded toko a914byw-3r5m-d52lc 3.5 h 1.34a 0.073 5.0x5.0x2.0 shielded sumida cdrh4d28-4r7 4.7 h 1.32a 0.072 4.7x4.7x3.0 shielded sumida cdrh3d16-2r2 2.2 h 1.2a 0.050 3.8x3.8x1.8 shielded sumida cdrh3d16-3r3 3.3 h 1.1a 0.063 3.8x3.8x1.8 shielded sumida cdrh3d16-4r7 4.7 h 0.9 0.080 3.8x3.8x1.8 shielded sumida cdrh5d28-4r2 4.2 h 2.2a 0.031 5.7x5.7x3.0 shielded sumida cdrh5d18-4r1 4.1 h 1.95a 0.057 5.7x5.7x2.0 sielded murata lqh55dn4r7m03 4.7 h 2.7a 0.041 5.0x5.0x4.7 non-shielded murata lqh66sn4r7m03 4.7 h 2.2a 0.025 6.3x6.3x4.7 shielded
aat1156 1mhz 700ma step-down dc-dc converter 1156.2007.01.1.4 15 ordering information package information 3 all dimensions in millimeters. output voltage package marking 1 part number (tape and reel) 2 0.6v (adj vout 0.8v) qfn33-16 luxyy AAT1156IVN-T1 advanced analogic technologies, inc. 830 e. arques avenue, sunnyvale, ca 94085 phone (408) 737- 4600 fax (408) 737- 4611 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 re quired to ensure a proper bottom solder connection. ? 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. 3.000 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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