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1 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos general description the aat2612 is a multiple rail power management ic. it integrates a 600ma high-frequency switching-converter and three 300ma linear regulators. the switching power supply is a highly-integrated monolithic step-down con- verter operating at 1.5mhz, achieving high efficiency with small external components. the three linear regulators are high psrr low dropout regulators (ldos) providing accurate regulation and excellent transient response. the step down converter is programmable with external feedback resistors, and the three ldos are fixed voltage outputs of six combinations for 1.8v, 2.8v, 3.0v and 3.3v. integrated over-current or over-temperature protection circuitry becomes active as appropriate, when either fault occurs, and the aat2612 recovers automatically when the fault is removed. the aat2612 is available in a pb-free, thermally enhanced 20-pin tqfn33 package. features ? current mode control dc/dc converter: ? programmable output up to 600ma ? ? 1.5mhz switching frequency ? ? up to 90% efficiency ? ? integrated switching power fets ? ? integrated compensation network ? ? internal current limit ? ? 3 low dropout regulators with separate enable pins: ? ? 300ma per channel ? ? high psrr ? ? factory programmable output ? ? integrated soft-start ? ? over-current protection ? ? over-thermal protection ? ? tqfn33-20 package applications ? cellular phones ? i/o power ? memory power ? processor core power ? smart handheld devices typical application pgnd lx fb outl3 inbk agnd 1.2v , 600m a 1.8v 300ma aat2612 inl1 2.2f 2.5v to 5.5v outl1 outl2 2.8 v 300ma 2.8v 300ma enl1 enl2 enl3 enbk inl2 1f 2.5v to 5.5v 1f 1f 2.2f 2.5v to 5.5v 4.7f 2.2h 10f r2 59k r1 59k
2 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos pin descriptions pin # symbol function description 1 inl1 i power input for ldo1. connect a 2.2 f capacitor between this pin and ground. 2, 8, 10, 18, 19 n/c not connected 3 enl1 i active high enable pin. when pulled high, ldo1 regulates its output to the programmed voltage value. 4 inbk i power input pin for the switching converter. connect a 4.7 f capacitor between ground and inbk. 5 lx i/o dc/dc step-down converter switching node. connect lx to the terminal of the inductor. 6 pgnd dc/dc converter power ground. 7 enbk i active high step-down dc/dc converter enable pin. 9fbi dc/dc converter output feedback pin. connect to a resistor divider for an adjustable out- put voltage. 11 enl2 i active high enable pin. when pulled high, ldo2 regulates its output to the programmed voltage value. 12 enl3 i active high enable pin. when pulled high, ldo3 regulates its output to the programmed voltage value. 13,17 agnd analog ground. 14 outl3 o ldo3 output. connect a 1 f capacitor between the pin and ground. 15 outl2 o ldo2 output. connect a 1 f capacitor between the pin and ground. 16 inl2 i power input for ldo2/3. connect a 2.2 f capacitor between the pin and ground. 20 outl1 o ldo1 output. connect a 1 f capacitor between the pin and ground. ep gnd exposed pad. pin configuration tqfn33-20 (top view) enl1 inbk n/c inl1 lx n/c fb enbk pgnd n/c 15 14 13 12 11 agnd enl3 outl3 outl2 enl2 n/c agnd n/c outl1 inl2 1 2 3 4 5 678910 20 19 18 17 16
3 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos 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. 2. mounted on an fr4 board. 3. thermal resistance measured with the device on multi-layer evaluation board in a thermal oven. the amount of power dissipati on which will cause the thermal shutdown to activate will depend on the ambient temperature and the pc board layout ability to dissipate the heat. de-rate 30mw/c above 70 c. absolute maximum ratings 1 symbol description value units inl1, inl2, inbk, outl1, outl2, outl3 -0.3 to 6.0 v enl1, enl2, enl3 -0.3 to 6.0 enbk, fb -0.3 to v inbk lx to pgnd -0.3 to v inbk pgnd to agnd, agnd to agnd -0.3 to +0.3 t a operating ambient temperature range -40 to 85 c t s storage temperature range -65 to 150 t lead maximum soldering temperature (at leads, 10 sec.) 300 thermal information 2 symbol description value units ja thermal resistance 3 50 c/w p d maximum power dissipation 2 w
4 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos electrical characteristics 1 v inbk = v inl1 = v inl2 = 3.6v, l = 2.2 h, c inl1, 2 = 2.2 f, c inbk = 4.7 f, c outbk = 10 f, c outl1, 2, 3 = 1 f, t a = 25c unless otherwise noted. symbol description conditions min typ max units pmu operation v in input voltage 2.5 5.5 v uvlo under-voltage lockout rising 1.9 v hysteresis 150 mv t sd thermal shutdown threshold 140 c hysteresis 15 c i q quiescent current v enbk > 1.5v, v enl1,2,3 >1.5v, no load 220 420 a logic control v ih input logic high threshold enl1, enl2, enl3, enbk 1.5 v inbk v v il input logic low threshold enl1, enl2, enl3, enbk 0.4 v dc-dc step-down converter i shdn shutdown current from inbk pin v enbk < 0.4v, v enl 1, 2, 3 < 0.4v 0.1 1 a i q quiescent current v enl 1, 2, 3 < 0.4v , v enbk >1.5v , i outb = 0ma 120 280 a i lim p-channel current limit v inbk = 2.7v to 5.5v 800 ma v out output voltage range 0.9 85% ? v inbk v v fb_acc feedback voltage accuracy t a = -40c to 85c 0.585 0.600 0.615 v f sw operating switch- ing frequency 1.5 mhz r ds(on)h high-side switch on resistance i outb = 200ma 230 m i outb = 200ma, v inbk = 2.5v 280 r ds(on)l low-side switch on resistance i outb = 200ma 180 m i outb = 200ma, v inbk = 2.5v 220 ldo i shdn shutdown current v enbk = v enl < 0.4v 1 a i lim output current limit r load = 1 450 600 ma v drop dropout voltage i outl = 300ma 500 mv v outl_acc output voltage accuracy t a = -40c to 85c, 1ma load -3 3 % v outl / ? i outl load regulation 1ma < i outl < 300ma 0.3 0.6 % ? v outl / ? v inl line regulation v inl1 = v inl2 = 2.7v to 5.5v 0.2 %/v psrr power supply rejection ratio c out1,2,3 = 1 f, v inl = v outl1,2,3 + 1v f = 100hz i out = 10ma 75 db i out = 150ma 75 f = 1khz i out = 10ma 70 i out = 150ma 70 f = 10khz i out = 10ma 50 i out = 150ma 50 v outl_tc output voltage temperature coef- cient 100 ppm/c
5 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos a at 2 612 step-down dc/dc converter with three high psrr ldos switchreg tm product datasheet 150 170 190 210 230 250 2.5 3.0 3.5 4.0 4.5 5.0 5.5 85c 25c -40c supply current vs supply voltage (v enb , v enl > 1.5v) supply voltage (v) supply current (a) 140.00 130.00 120.00 110.00 85c 100.00 25c -40c 90.00 2.5 3.0 3.5 4.0 4.5 5.0 5.5 buck quiescent current vs supply voltage (v out = 1.2v, v enb > 1.5v,v enl < 0.4v) supply voltage (v) i q (a) 1.35 1.40 1.45 1.50 1.55 1.60 -40 -15 10 35 60 85 switching frequency vs temperature (v inb = 3.6v, i out = 600ma) temperature (c) switching frequency (mhz) 1.44 1.46 1.48 1.50 1.52 1.54 2.5 3 3.5 4 4.5 5 5.5 switching frequency vs input voltage (v outb = 1.2v, i outb = 600ma) input voltage (v) switching frequency (mhz) 0 10 20 30 40 50 60 70 80 90 100 0.1 1 10 100 1000 v in = 2.5v v in = 3.6v v in = 4.2v v in = 5.0v v in = 5.5v buck efficiency vs output current (v out = 1.2v; l = 2.2h) output current (ma) efficiency (%) 1.950 1.910 1.870 1.830 1.790 uvlo_h uvlo_l 1.750 -40 -15 10 35 60 85 uvlo volatge vs temperature temperature (c) v eoc (v)
6 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos a at 2 612 step-down dc/dc converter with three high psrr ldos switchreg tm product datasheet -1.000 -0.600 -0.200 0.200 0.600 1.000 -40 -15 10 35 60 85 buck output voltage vs temperature (v inb = 3.6v; v outb = 1.2v; l = 2.2h) temperature (c) v out error (%) -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 2.533.544.5 55.5 i out = 10ma i out = 100ma i out = 300ma i out = 600ma buck line regulation (v out = 1.2v; l = 2.2h) input voltage (v) output error (%) -1 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1 10 70 130 190 250 310 370 430 490 550 610 v in = 2.5v v in = 3.6v v in = 4.2v v in = 5.0v v in = 5.5v buck load regulation (v out = 1.2v; l = 2.2h) output current (ma) output error (%) 1.20 1.10 1.00 0.90 0.80 -40c 25c 85c 0.70 2.5 3.0 3.5 4.0 4.5 5.0 5.5 en v ih vs supply voltage supply voltage (v) en v ih (v) 0.60 0.70 0.80 0.90 1.00 1.10 1.20 2.5 3.0 3.5 4.0 4.5 5.0 5.5 -40c 25c 85c en v il vs supply voltage supply voltage (v) en v il (v) v in 2v/div v out 1v/div 0 0 i in 0.2a/div 0 softstart (v in = 3.6v; v outb = 1.2v; i outb = 600ma) time 40 s/div
7 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos a at 2 612 step-down dc/dc converter with three high psrr ldos switchreg tm product datasheet v outb 200mv/div 1.2 i outb 0.2a/div 0a 600ma 400ma buck load transient (v in = 3.6v, v outb = 1.2v, c inb = 10f, c outb = 10f) time 40 s/div v in 1v/div 4 v out 50mv/div 1.2 buck line transient (v inb = 4v to 5v, i outb = 600ma) v out 20mv/div 1.2 v lx 2v/div 0 output ripple (v in = 3.6v; v out = 1.2v; i out = 600ma; c inb = 4.7f) time 0.4 s/div -0.600 -0.400 -0.200 0.000 0.200 0.400 0.600 -40 -15 10 35 60 85 ldo1 ldo2 ldo3 ldo output voltage vs temperature (v in = 3.6v) temperature (c) v out error (%) 34.00 32.00 30.00 28.00 85c 25c 26.00 - 40c 24.00 2.5 3.0 3.5 4.0 4.5 5.0 5.5 ldo quiescent current vs supply voltage (single channel) supply voltage (v) iq (a) -0.1 -0.08 -0.06 -0.04 -0.02 0 0.02 0.04 0.06 0.08 0.1 2.5 3 3.5 4 4.5 5 5.5 i outb = 10ma i outb = 100ma i outb = 200ma i outb =300ma ldo line regulation (v outl = 1.8v) input voltage (v) output error (%/v)
8 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos a at 2 612 step-down dc/dc converter with three high psrr ldos switchreg tm product datasheet 0 50 100 150 200 250 300 350 20 60 100 140 180 220 260 300 85c 25c -40c dropout voltage vs load current (v out = 2.8v) load current (ma) dropout voltage(mv) v outl 200mv/div 1.8 i outl 0.2a/div 0a 300ma ldo load transient (v in = 3.6v, v outl = 1.8v, c inl = 2.2f, c outl = 1f) time 100 s/div v in 1v/div 4 v out 2.8 20mv/div ldo line transient (v inb = 4v to 5v, i outl = 300ma) time 20 s/div 0 10 20 30 40 50 60 70 80 90 100 100 1000 10000 100000 10ma ldo1 power supply rejection ratio, psrr (i out1 = 10ma, bw = 100~100khz) frequency (hz) magnitude (db)
9 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos block diagram buck inbk lx pgnd inl1 bias, control, and otp, thermal shutdownd fb ldo 2 outl2 ldo 1 outl1 agnd control 1.2v, 600ma enbk 1.8v. 300ma 2.2uh 4.7uf 1uf 1 uf ldo 3 outl3 2.8v. 300ma 2.8v, 300ma 1uf enl1 enl2 enl3 inl2 1uf 1uf 4.7uf r2 59k r1 59k
10 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos functional description the aat2612 is a compact power management solution. it integrates a step-down converter with three high psrr low-dropout regulators to provide power from a wall adapter, usb port, or a single-cell lithium ion/polymer battery or dual cell alkaline battery. the aat2612 uses fixed-frequency peak current control architecture. light load mode is used to enhance light load efficiency. compensation is integrated to reduce the number of external components and achieve excellent transient response and load/line regulation. the ideal 1.5mhz switching frequency allows the use of smaller output filter components for improved power density, reduced external component size, and optimized output voltage ripple. the aat2612 has four separate enable pins to control buck converter and three ldo regulator outputs? startup. also see the ?enable function? section in the applications information section of this datasheet. synchronous step-down converter the aat2612 contains one high performance 600ma, 1.5mhz synchronous step-down converter. the step- down converter operates to ensure high efficiency per- formance over all load conditions. the input voltage range is from 2.5v to 5.5v, and the output voltage is programmable from 85% of v in to as low as 0.9v with external resistor divider. power devices are sized for 600ma current capability while maintaining over 85% efficiency at full load. high efficiency is main- tained at lower currents a high dc gain error amplifier with internal compensa- tion controls the output. it provides excellent transient response and load/line regulation. the converter has soft start control to limit inrush current. apart from the resistor divider and input capacitor, only a small l-c filter is required at the output side for the step-down converter to operate properly. typically, a 2.2 h inductor and a 10 f ceramic capacitor are recom- mended for low output voltage ripple and small compo- nent size. control loop the converter is a peak current mode step-down con- verter. 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 cur- rent 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 pro- grams the current mode loop for the necessary peak inductor current to force a constant output voltage for all load and line conditions. the voltage feedback resistive divider is external and the error amplifier reference volt- age is 0.6v. the voltage loop has a high dc gain making for excellent dc load and line regulation. the internal voltage loop compensation is located at the output of the transconductance voltage error amplifier. soft-start soft start increases the inductor current limit point lin- early when the input voltage or enable input is applied. it limits the current surge seen at the input and elimi- nates output voltage overshoot. current limit and over-temperature protection for overload conditions the peak input current is limited. as load impedance decreases and the output voltage falls closer to zero, more power is dissipated internally, raising the device temperature. thermal protection com- pletely disables switching when internal dissipation becomes excessive, protecting the device from damage. the junction over-temperature threshold is 140c with 15c of hysteresis. ldo regulator the advanced circuit design of the linear regulator is specifically optimized for very fast start-up and shut- down timing. this proprietary ldo is also tailored for superior transient response characteristics. these traits are particularly important for applications which require fast power supply timing. the high-speed turn-on capability is enabled through the implementation of a fast start control circuit, which accelerates the power up behavior of fundamental con- trol and feedback circuits within the ldo regulator. fast turn-off time response is achieved by an active output pull down circuit, which is enabled when the ldo regula- tor is placed in the shutdown mode. this active fast shutdown circuit has no adverse effect on normal device operation. the ldo regulator output has been specifi- cally optimized to function with low cost, low esr ceram-
11 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos ic capacitors. however, the design will allow for opera- tion over a wide range of capacitor types. the regulator comes with complete short circuit and ther- mal protection. the combination of these two internal protection circuits gives a comprehensive safety system to guard against extreme adverse operating conditions. application information step-down converter input capacitor select a 4.7uf to 10uf x7r or x5r ceramic capacitor for the input. to estimate the required input capacitor value and size, determine the acceptable input ripple voltage level (v pp ) and solve for c in . the calculated value varies with input voltage and is a maximum when v in is double the output voltage. 1 - v o v in c in = v o v in - esr f s v pp i o d = v o v in c in(min) = 1 - esr 4 f s v pp i o where c in is the input capacitance, v in is the input volt- age, v o is the output voltage, f s is the switching fre- quency, i o is the output current, esr is the equivalent series resistor of output capacitor, and d is the duty cycle. 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. i o rms i 2 = the maximum input voltage ripple also appears at 50% duty cycle. the input capacitor provides a low impedance loop for the edges of pulsed current drawn by the aat2612. low esr/esl x7r and x5r ceramic capacitors are ideal for this function. to minimize parasitic inductances, 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 rip- ple. the proper placement of the input capacitors (c1, c2, and c3) is shown 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 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 can also result in the loop phase and gain measurements. since the inductance of a short pcb trace feeding the input voltage is signifi- cantly lower than the power leads from the bench power supply, most applications do not exhibit this problem. in applications where the input power source lead induc- tance cannot be reduced to a level that does not affect the converter performance, a high esr tantalum or alu- minum electrolytic capacitor should be placed in parallel with the low esr/esl bypass ceramic capacitor. this dampens the high q network and stabilizes the system. output capacitor the output capacitor limits the output ripple and pro- vides holdup during large load transitions. a typical 4.7 f x5r or x7r ceramic capacitor typically provides sufficient bulk capacitance to stabilize the output during large load transitions and has the esr and esl charac- teristics necessary for low output ripple. the output voltage droop due to a load transient is dom- inated by the capacitance of the ceramic output capacitor. during a step increase in load current, the ceramic output capacitor alone supplies the load current until the loop responds. 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: c out = 3 i load v droop f s
12 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos 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. output inductor for most designs, the aat2612 operates with inductor values of 2.2 h to 4.7 h. inductors with low inductance values are physically smaller but generate higher induc- tor current ripple leading to higher output voltage ripple. the inductor value can be derived from the following equation: v out (v in - v out ) v in ? i l f osc l = where i l is inductor ripple current. large value induc- tors result in lower ripple current and small value induc- tors result in high ripple current. choose inductor ripple current approximately 30% of the maximum load cur- rent 0.6a, or ?i l = 180m a 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. the dc current rating of the inductor should be at least equal to the maximum load current plus half the inductor rip- ple current to prevent core saturation (0.6a + 180ma). 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. feedback resistor selection the buck output voltage on the aat2612 is adjustable with external resistors r1 and r2 which program the output to regulate at a voltage in the range of 0.9v to 0.85 ? v inbk . 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 quies- cent current, it will also increase the impedance of the feedback node, making it more sensitive to external noise and interference. the maximum value of r1 should be below 1mohm to keep reference voltage normal and avoid noise coupling. r1 = - 1 r2 v out v ref - 1 r2 v out 0.6v = table 1 shows the standard 1% metal film resistor values for different step-down output voltages v out (v) r2 = 59k , r1 (k ) 1.2 59 2.8 216 3.3 265.5 3.6 259 4.2 354 table 1: v out resistor selection enable function the aat2612 features one buck output enable/disable function for buck converter. this pin (enbk) is active high and is compatible with cmos logic. to assure the buck output will switch on, the enbk turn-on control level must be greater than 1.5v. the buck converter will go into the disable shutdown mode when the voltage on the enbk pin falls below 0.6v. if the enable function is not needed in a specific application, it may be tied to v in to keep the buck output in a continuously on state. low dropout regulator input capacitor typically, a 2.2 f or larger capacitor is recommended for c in in most applications. a c in capacitor is not required for basic ldo regulator operation. however, if the ldo is physically located any distance more than one or two centimeters from the input power source, a c in capacitor will be needed for stable operation. c in should be located as closely to the device v inl pin as practically possible. c in values greater than 1 f will offer superior input line transient response and will assist in maximizing the power supply ripple rejection. ceramic, tantalum, or aluminum electrolytic capacitors may be selected for c in as there is no specific capacitor esr requirement. for better performance, ceramic capacitors are recommended for c in due to their inherent capability over tantalum capacitors to withstand input current surges from low impedance sources such as bat- teries in portable devices.
13 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos output capacitor for proper load voltage regulation and operational sta- bility, a capacitor is required between pins vout and gnd. the c out capacitor connection to the ldo regulator ground pin should be made as direct as practically pos- sible for maximum device performance. the aat2612 ldos have been specifically designed to function with very low esr ceramic capacitors. although the device is intended to operate with these low esr capacitors, it is stable over a very wide range of capacitor esr, thus it will also work with some higher esr tantalum or alumi- num electrolytic capacitors. for best performance, ceramic capacitors are recommended. the value of c out typically ranges from 1 f to 10 f. 1 f is sufficient for most operating conditions. enable function the aat2612 features three ldo regulator enable/dis- able function for ldo1/2/3 respectively. these pins (enl1, enl2, and enl3) are active high and are compat- ible with cmos logic. to assure the ldo regulator will switch on, the en turn-on control level must be greater than 1.5v. the ldo regulator will go into the disable shutdown mode when the voltage on the en pin falls below 0.6v. if the enable function is not needed in a specific application, it may be tied to v in to keep the ldo regulator in a continuously on state. short-circuit and thermal protection the aat2612 ldos are protected by both current-limiting and over-temperature protection circuitry. the internal short-circuit current limiting circuit is designed to activate when the output load demand exceeds the maximum rated output. if a short-circuit condition were to continu- ally draw more than the current limit threshold, the ldo regulator?s output voltage would drop to a level necessary to supply the current demanded by the load. under short- circuit or other over-current operating conditions, the output voltage would drop and the aat2612?s die tem- perature would rapidly increase. once the regulator?s power dissipation capacity has been exceeded and the internal die temperature reaches approximately 140c, the system thermal protection circuit will become active. the internal thermal protection circuit will actively turn off the ldo regulator output pass device to prevent the pos- sibility of over-temperature damage. the ldo regulator output will remain in a shutdown state until the internal die temperature falls back below the 140c trip point. the interaction between the short-circuit and thermal protection systems allows the ldo regulator to with- stand indefinite short-circuit conditions without sustain- ing permanent damage. no-load stability the aat2612 ldo is designed to maintain output voltage regulation and stability under operational no-load condi- tions. this is an important characteristic for applications where the output current may drop to zero. an output capacitor is required for stability under no-load operating conditions. refer to the output capacitor section of this datasheet for recommended typical output capacitor val- ues. internal power supply the aat2612 internal circuitry uses inl1 as the internal power supply. the buck output will have no output when inl1 is not connected to power. thermal calculations there are three types of losses associated with the aat2612 step-down converters: switching losses, con- duction 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, with continuous conduction mode (ccm), a simplified form of the losses is given by: p buck = i o 2 r ds(on)p + r ds(on)n 1 - + t sw f s i o v in + i q v in v o v in v o v in where i q is the step-down converter quiescent current, t sw is the switching time, r ds(on)p and r ds(on)n are the high side and low side switching mosfets? on-resistance. v in , v o and i o are the input voltage, the output voltage and the load current. since r ds(on) , quiescent current and switching losses all vary with input voltage, the total losses should be inves- tigated over the complete input voltage range. for all the ldos, p d(max) = (v in ? v out ) i out(max) . the total power losses of both step-down converter and ldos can be expressed as p total = p buck + p d(max) . given the total losses, the maximum junction tempera- ture can be derived from the ja for the package. t j(max) = p total ja + t a
14 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos inl1 2.5v to 5.5v 2.2f c1 2.2h l1 bo1 1.2v 600m a 10f c8 ldo2 2.2f c2 4.7f c3 ldo1 ldo3 1f c5 1f c6 1f c7 enbk enl1 enl2 enl3 agnd lx ldo3 ldo2 ldo1 fb pgnd lx 5 ep 0 fb 9 inbk 4 outl3 14 inl2 16 inl1 1 enbk 7 enl3 12 enl2 11 enl1 3 n/c 2 outl1 20 outl2 15 pgnd 6 agnd 17 agnd 13 u1 aat2612 59k r1 59k r2 n/c c4 inl2 2.5v to 5.5v inbk 2.5v to 5.5v enbk enl1 enl2 enl3 j_in1 j_in2 gnd figure 1: aat2612idg evaluation board schematic. layout considerations the suggested pcb layout for the aat2612 is shown in figures 2(a) - 2(d). the following guidelines are recom- mended to ensure a proper layout: 1. connect the input capacitors (c1, c2, c3) and out- put capacitors (c5, c6, c7, c8 ) as close as possible to the pins (inl1, inl2, inbk, vout) and power ground (agnd, pgnd) to minimize any parasitic inductance in the switched current path which gen- erates a large voltage spike during the switching interval. 2. keep the power traces (gnd, lx, and inbk) short, direct, and wide to allow large current flow. place sufficient multiple-layer pads when needed to change the trace layer. 3. connect the output capacitor c8 and inductor l1 as close as possible to the device. keep the connection of l1 to the lx pins as short as possible and route no signal lines under the inductor. 4. separate the feedback traces or fb pin (pin 9) from any power trace and connect as close as possible to the load point. sensing along a high-current load trace will degrade dc load regulation. 5. keep the resistance of the trace from the load returns to pgnd to a minimum. this will help to minimize any error in dc regulation due to differ- ences in the potential of the internal signal ground and the power ground. 6. connect the ground pin of the exposed pad to agnd internal plane with multiple vias to decrease the effect of large power ground pgnd noise on the ana- log ground. 7. connect the ground pins of ldo output capacitors to agnd.
15 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos a: top side b: internal plane 1 (agnd) c: internal plane 2 (pgnd) d: bottom side figure 2: aat2612idg evaluation board layout.
16 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos component part number description manufacturer u1 aat2612 step-down dc/dc converter with three high psrr ldos skyworks c1, c2 grm188r71a225ke15 cap ceramic 2.2 f 0603 x7r 10v 10% murata c3 grm188r60j475ke19 cap ceramic 4.7 f 0603 x5r 6.3v 10% c8 grm188r60j106me47 cap ceramic 10 f 0603 x5r 6.3v 10% c4, c5, c6, c7 grm188r71c105ka12 cap ceramic 1 f 0603 x7r 6.3v 10% l1 lqh3npn2r2mm0 2.2 h, 73m , 1.25a, 20% r1, r2 rc0603fr-0759kl res, 59k , 1/10w, 1%, 0603, smd yageo table 2: aat2612idg evaluation board bill of materials (bom). manufacturer part number l ( h) max dcr (m ) saturation current (a) size wxlxh (mm) murata lqh3np2r2ng0 2.2 140 1.27 3.0x3.0x0.9 lqh3np3r3ng0 3.3 180 0.85 lqh3np4r7ng0 4.7 260 0.8 coilcraft lpa3015-222mlc 2.2 110 1.1 3.1x3.1x1.5 lpa3015-332mlc 3.3 130 1.1 lpa3015-472mlc 4.7 200 0.9 table 3: surface mount inductors. manufacturer part number value ( f) voltage (v) tolerance temp. co. case murata grm188r70j105k 1 6.3 10% x7r 0603 grm188r70j106k 10 6.3 10% x7r 0603 grm188r71a225k 2.2 10 10% x7r 0603 grm188r71a475k 4.7 10 10% x7r 0603 avx 06036c105kat 1 6.3 10% x7r 0603 06036c106kat 10 6.3 10% x7r 0603 0603zc225kat 2.2 10 10% x7r 0603 0603zc475kat 4.7 10 10% x7r 0603 kemet c0603c105k9rac 1 6.3 10% x7r 0603 c0603c106k9rac 10 6.3 10% x7r 0603 c0603c225k8rac 2.2 10 10% x7r 0603 c0603c475k8rac 4.7 10 10% x7r 0603 table 4: surface mount capacitors.
17 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos ordering information dc-dc step-down (v) ldo1 (v) ldo2 (v) ldo3 (v) part marking 1 part number (tape and reel) 2 adj 2.8 2.8 1.8 s2xyy aat2612idg-1-t1 adj 2.8 1.8 1.8 tbd aat2612idg-2-t1 adj 2.8 2.8 2.8 tbd aat2612idg-3-t1 adj 2.8 1.8 3.0 tbd aat2612idg-4-t1 adj 2.8 1.8 3.3 t5xyy aat2612idg-5-t1 adj 3.0 1.8 3.3 t6xyy AAT2612IDG-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 tqfn33-20 3 1.700 0.050 1.700 0.050 3.00 0.05 0.75 0.05 3.00 0.05 0 + 0.10 -0.00 0.203 ref 0.400 bsc 0.210 0.040 0.400 0.050 index area top view (saw type) bottom view side view (saw type) detail "a" detail "a" r(5x) all dimensions in millimeters. 1. a = assembly house code, y = year, w = week. 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
18 skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202407b ? skyworks proprietary information ? products and product information are subject to change without notice. ? mar ch 20, 2013 aat2612 data sheet step-down dc/dc converter with three high psrr ldos 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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