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1 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 general description the aat1189 is a single output step-down (buck) dc output regulator with an integrated high side mosfet. the input range is 6v to 24v making it the ideal power ic solution for consumer communications equipment oper- ating from a low cost ac/dc adapter with 12v output. the step-down regulator provides up to 2.5a output cur- rent in a small package. 490khz fixed switching fre- quency allows small l/c filtering components. voltage mode control allows for optimum performance across the entire output voltage and load range. the controller includes programmable over-current, inte- grated soft-start and over-temperature protection. the aat1189 is available in the pb-free, low profile 16-pin tdfn34 package. the rated operating tempera- ture range is -40 ? c to 85 ? c. features ? v in = 6.0 to 24.0v ? v out adjustable from 1.5v to 5.5v ? i out up to 2.5a ? small solution size ? low-cost non-synchronous solution ? shutdown current <35 a ? high switching frequency ? voltage mode control ? pwm fixed frequency for lowest noise ? programmable over-current protection ? over-temperature protection ? internal soft start ? low profile 3x4mm tdfn-16 packages ? -40c to 85c temperature range applications ? dsl and cable modems ? notebook computers ? satellite set top box ? wireless lan systems typical application 5v/2.5a d1 bas16 4.7h l1 d2 b340a 6.0v - 24.0v + c1 100f 25v c3 2.2f c7 330pf c4 68nf c6 56pf c2 0.1f c8 22f c5 220pf c9 22f r5 6.04k r4 44.2k r2 24.3k r1 6.34k c11 1f 50v 499 r3 en v in v out en os bst gnd lx rs vl in fb comp aat1189 tdfn 34-16
2 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 pin descriptions pin # symbol function 1, 2, 3, 4, 5, 15, 16 lx step-down converter switching pin. connect output inductor to this pin. connect lx pins together. 6 bst boost drive input pin. connect the cathode of fast recti er from this pin and connect a 100nf ca- pacitor from this pin to the switching node (lx) for internal hi-side mosfet gate drive. 7 en enable input pin. active high. 8rs output current sense pin. connect a small signal resistor from this pin to switching node (lx) to en- able over-current sense for step-down converter. 9os output voltage sense pin. connect to the output capacitor to enable over-current sense for step- down converter. 10 comp compensation pin for step-down regulator. connect a series resistor, capacitor network to compen- sate the voltage mode control loop. 11 fb feedback input pin for step-down converter. connect an external resistor divider to this pin to pro- gram the output voltage to the desired value. 12 gnd ground pin for step-down converter. connect input and output capacitors return terminals close to this pin for best noise performance. 13 vl internal linear regulator. connect a 2.2 f/6.3v capacitor from this pin to gnd pin. 14 in input supply voltage pin for step-down regulator. connect both in pins together. connect the input capacitor close to this pin for best noise performance. ep in exposed paddle connected internally to in. connect to pcb heatsink to ensure maximum thermal dissipation. pin configuration tdfn34-16 (top view) lx lx lx lx lx 3 bst en rs in vl gnd lx lx fb comp os ep 4 5 1 2 6 7 8 14 13 12 16 15 11 10 9
3 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 absolute maximum ratings 1 symbol description value units v in(hi) in, lx to gnd -0.3 to 30.0 v v in(lo) vl to gnd -0.3 to 6.0 v v bst1-lx bst to lx -0.3 to 6.0 v v control fb, comp, os, rs to gnd -0.3 to v in(lo) + 0.3 v v en en to gnd -0.3 to 30.0 v i in(pulsed) in to lx 12.0 a t j operating junction temperature range -40 to 150 ? c t lead maximum soldering temperature (at leads, 10 sec) 300 ? c thermal information symbol description value units ? ja thermal resistance 2 50 c/w p d maximum power dissipation 3 2.0 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. mounted on an fr4 board with exposed paddle connected to single layer pcb plane. 3. derate 20mw/c above 25c ambient temperature for tdfn34-16 package. increased power dissipation is possible with additional pcb heatsinking.
4 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 electrical characteristics 1 v in = 12v; t a = -40c to 85c, unless noted otherwise. typical values are at t a = 25c. symbol description conditions min typ max units v in input voltage 6.0 24.0 v v uvlo uvlo threshold v in rising 5.0 v v in hysteresis 300 mv v in falling 3.0 v v out output voltage range 1.5 5.5 v output voltage accuracy i out = 0a to 2.5a -2.5 2.5 % v fb feedback pin voltage 0.591 0.600 0.609 v v linereg / v in line regulation v in = 6v to 24v, v out = 3.3v, i out = 2.5a 0.028 %/v v in = 6v to 24v, v out = 5.0v, i out = 2.5a 0.17 v loadreg / i in load regulation v in = 12v, v out = 3.3v, i out = 0a to 2.5a 0.064 %/a v in = 12v, v out = 5v, i out = 0a to 2.5a 0.08 i q quiescent current v en = high, no load 0.6 ma i shdn shutdown current v en = low, v l = 0v 35.0 a v ocp over-current offset voltage v en = high, v in = 6.0v to 24.0v, t a = 25c 80 100 120 mv i lx lx pin leakage current v in = 24.0v, v en = low -1.0 1.0 a d max maximum duty cycle 85 % t on(min) minimum on-time v in = 6.0 to 24.0v 100 ns r dson(h) hi side on-resistance v l = 4.5v 70 m f osc oscillator frequency 350 490 650 khz f foldback short circuit foldback frequency current limit triggered 100 khz t ss soft-start time from enable to output regulation 2.5 ms t sd over-temperature shutdown threshold 135 c over-temperature shutdown hysteresis 15 c v en(l) enable threshold low 0.6 v v en(h) enable threshold high 2.5 v i en input low current -1.0 1.0 a 1. the aat1189 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 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 typical characteristics step-down converter efficiency vs. load (v out = 3.3v; l = 4.7h) output current (ma) efficiency (%) 0 10 20 30 40 50 60 70 80 90 100 0.1 1 10 100 1000 10000 v in = 6v v in = 8v v in = 12v v in = 18v v in = 24v step-down converter efficiency vs. load (v out = 5v; l = 4.7h) output current (ma) efficiency (%) 0 10 20 30 40 50 60 70 80 90 100 0.1 1 10 100 1000 10000 v in = 6v v in = 8v v in = 12v v in = 18v v in = 24v step-down converter dc regulation (v out = 3.3v; l = 4.7h) output current (ma) output error (%) -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 0.1 1 10 100 1000 10000 v in = 6v v in = 8v v in = 12v v in = 18v v in = 24v step-down converter dc regulation (v out = 5v; l = 4.7h) output current (ma) output error (%) 0.1 1 10 100 1000 10000 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 2.5 3.0 v in = 6v v in = 8v v in = 12v v in = 18v v in = 24v step-down converter line regulation (v out = 3.3v; l = 4.7h) input voltage (v) accuracy (%) -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 6 8 10 12 14 16 18 20 22 24 i out = 0.10ma i out = 10ma i out = 100ma i out = 1250ma i out = 2500ma step-down converter line regulation (v out = 5v; l = 4.7h) input voltage (v) accuracy (%) 6 8 10 12 14 16 18 20 22 24 -4.0 -3.5 -3.0 -2.5 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 i out = 0.10ma i out = 10ma i out = 100ma i out = 1250ma i out = 2500ma
6 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 typical characteristics step-down converter output ripple (v in = 12v; v out = 3.3v; i out = 1ma) time (2s/div) output voltage (ac coupled) (bottom) (v) lx voltage (top) (v) inductor current (middle) (a ) 3.28 3.29 3.30 0.0 0.2 0.4 0v 12v step-down converter output ripple (v in = 12v; v out = 5v; i out = 1ma) time (2s/div) output voltage (ac coupled) (bottom) (mv) lx voltage (top) (v) inductor current (middle) (a ) 4.99 5.00 -0.1 0.0 0.1 0v 12v step-down converter output ripple (v in = 12v; v out = 3.3v; i out = 2.5a) time (1s/div) output voltage (ac coupled) (bottom) (v) lx voltage (top) (v) inductor current (middle) (a ) 3.29 3.30 3.31 1.0 2.0 3.0 0v 12v step-down converter output ripple (v in = 12v; v out = 5v; i out = 2.5a) time (1s/div) output voltage (ac coupled) (bottom) (v) lx voltage (top) (v) inductor current (middle) (a ) 4.98 5.00 5.02 2.0 3.0 4.0 12v 0v step-down converter load transient response (i out = 1.875a to 2.5a; v in = 12v; v out = 3.3v; c out = 2x22f) time (100s/div) output voltage (ac coupled) (bottom) (v) output current (top) (a) 3.2 3.3 3.4 1.0 1.5 2.0 2.5 3.0 2.5a 1.875a step-down converter load transient response (i out = 1.875a to 2.5a; v in = 12v; v out = 5v; c out = 2x22f) time (100s/div) output voltage (ac coupled) (bottom) (v) output current (top) (a) 4.9 5.0 5.1 1.0 1.5 2.0 2.5 3.0 2.5a 1.875a
7 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 typical characteristics step-down converter load transient response (i out = 1.25a to 2.5a; v in = 12v; v out = 3.3v; c out = 2x22f) time (100s/div) output voltage (ac coupled) (bottom) (v) output current (top) (a) 3.2 3.3 3.4 1.0 1.5 2.0 2.5 3.0 2.5a 1.25a step-down converter load transient response (i out = 1.25a to 2.5a; v in = 12v; v out = 5v; c out = 2x22f) time (100s/div) output voltage (ac coupled) (bottom) (v) output current (top) (a) 4.9 5.0 5.1 1.0 1.5 2.0 2.5 3.0 2.5a 1.25a step-down converter load transient response (i out = 0.25a to 2.5a; v in = 12v; v out = 3.3v; c out = 2x22f) time (100s/div) output voltage (ac coupled) (bottom) (v) output current (top) (a) 3.2 3.3 3.4 3.5 0.0 1.0 2.0 3.0 2.5a 0.25a step-down converter load transient response (i out = 0.25a to 2.5a; v in = 12v; v out = 5v; c out = 2x22f) time (100s/div) output voltage (ac coupled) (bottom) (v) output current (top) (a) 4.9 4.8 5.0 5.1 5.2 0.0 1.0 2.0 3.0 2.5a 0.25a step-down converter line transient response (v in = 6v to 10v; v out = 3.3v; i out = 2.5a) time (100ms/div) input voltage (top) (v) output voltage (bottom) (v) 0 5 10 15 3.25 3.30 3.35 step-down converter line transient response (v in = 6v to 10v; v out = 5v; i out = 2.5a) time (100ms/div) input voltage (top) (v) output voltage (bottom) (v) 0 5 10 15 4.8 5.0 5.2
8 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 typical characteristics step-down converter soft start (v in = 12v; v en = 10v; v out = 3.3v; i out = 2.5a) time (500s/div) enable voltage (top) (v) output voltage (middle) (v) inductor current (bottom) (a) 0 5 10 15 0.0 2.0 4.0 step-down converter soft start (v in = 12v; v en = 10v; v out = 5v; i out = 2.5a) time (500s/div) enable voltage (top) (v) output voltage (middle) (v) output current (bottom) (a) 0 5 10 15 0.0 2.0 4.0 step-down converter switching frequency vs. temperature (v out = 5v; l = 4.7h) temperature (c) switching frequency (khz) 440 450 460 470 480 490 500 -40 -20 0 20 40 60 80 100 step-down converter switching frequency vs. input voltage (v in = 6v to 24v; v out = 3.3v; i out = 2.5a) input voltage (v) frequency variation (%) -8 -6 -4 -2 0 2 4 6 8 6 8 10 12 14 16 18 20 22 24 v ih and v il vs. input voltage input voltage (v) v ih and v il (%) 1.00 1.05 1.10 1.15 1.20 1.25 1.30 1.35 510152025 v ih v il no load step-down converter input current vs. input voltage (v en = v in ) input voltage (v) input current (a) 300 350 400 450 500 550 600 650 6 9 12 15 18 21 24 85c 25c -40c
9 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 typical characteristics step-down converter output voltage error vs. temperature (v in = 12v; v out = 5v) temperature (c) output voltage error (%) -50 -25 0 25 75 100 50 -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 i out = 0.10ma i out = 10ma i out = 100ma i out = 1250ma i out = 2500ma step-down converter output voltage error vs. temperature (v in = 12v; v out = 3.3v) temperature (c) output voltage error (%) -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 -50 -25 0 25 75 100 50 i out = 0.10ma i out = 10ma i out = 100ma i out = 1250ma i out = 2500ma
10 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 functional description the aat1189 is a high voltage step-down (buck) regula- tor with input voltage range from 6.0v to 24.0v, provid- ing high output current in a small package. the output voltage is user-programmable from 1.5v to approxi- mately 85% of v in voltage. the device is optimized for low-cost 12v adapter inputs. the device utilizes voltage mode control configured for optimum performance across the entire output voltage and load range. the controller includes integrated over-current, soft- start and over-temperature protection. over-current is sensed through the output inductor dc winding resis- tance (dcr). an external resistor and capacitor network adjusts the current limit according to the dcr of the inductor and the desired output current limit. frequency reduction limits the over-current stress during overload and short-circuit events. the operating frequency returns to the nominal setting when over-current conditions are removed. the aat1189 is available in the pb-free 16-pin tdfn34 package with rated operating temperature range of -40c to 85c. the tdfn34-16's exposed paddle (ep) can be soldered to the pcb plane(s) for maximum ther- mal performance. functional block diagram gnd logic error amp control logic en ot voltage ref vl vint comp. reg. lx bst in rs os logic error amp control logic fb osc ot voltage ref comp. reg. 20 comp comp v ocp = 0.1v
11 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 applications information the high voltage dc/dc step-down converter provides an output voltage from 1.5v to 5.5v. the integrated high-side n-channel mosfet device provides up to 2.5a output current 1 . input voltage range is 6.0v to 24.0v. the step-down converter utilizes constant frequency (pwm-mode) voltage mode control to achieve high oper- ating efficiency while maintaining extremely low output noise across the operating range. high 490khz (nominal) switching frequency allows small external filtering com- ponents, achieving minimum cost and solution size. external compensation allows the designer to optimize the transient response while achieving stability across the operating range. output voltage and current the output voltage is set using an external resistor divider as shown in table 1. minimum output voltage is 1.5v and maximum output voltage is 5.5v. typical max- imum duty cycle is 85%. v out (v) r 5 = 6.04k ? r 4 (k ? ) 1.5 9.09 1.8 12.1 1.85 12.4 2.0 14.0 2.5 19.1 3.0 24.3 3.3 27.4 5.0 44.2 table 1: feedback resistor values. alternatively, the feedback resistor may be calculated using the following equation: (v out - 0.6) r 5 0.6 r 4 = r 4 is rounded to the nearest 1% resistor value. buck regulator output capacitor selection two 22 f ceramic output capacitors are required to filter the inductor current ripple and supply the load transient current for i out = 2.5a. the 1206 package with 10v minimum voltage rating is recommended for the output capacitors to maintain a minimum capacitance drop with dc bias. output inductor selection the step-down converter utilizes constant frequency (pwm-mode) voltage mode control. a 4.7 h inductor value is selected to maintain the desired output current ripple and minimize the converter?s response time to load transients. the peak switch current should not exceed the inductor saturation current, the mosfet or the external schottky rectifier peak current ratings. rectifier selection when the high-side switch is on, the input voltage will be applied to the cathode of the schottky diode. the recti- fier's rated reverse breakdown voltage must be chosen at least equal to the maximum input voltage of the step- down regulator. when the high-side switch is off, the current will flow from the power ground to the output through the schottky diode and the inductor. the power dissipation of the schottky diode during the time-off can be deter- mined by the following equation: v out p d = i out v d 1 - v in where v d is the voltage drop across the schottky diode. input capacitor selection for low cost applications, a 100 f/25v electrolytic capacitor is selected to control the voltage overshoot across the high side mosfet. a small ceramic capacitor with voltage rating at least 1.05 times greater than the maximum input voltage is connected as close as possible to the input pin (pin 14) for high frequency decoupling. feedback and compensation networks the transfer function of the error amplifier is dominated by the dc gain and the l c out output filter of the regula- tor. this output filter and its equivalent series resistor (esr) create a double pole at f lc and a zero at f esr in the following equations: eq. 1: f lc = 1 2 l c out 1. output current capability may vary and is dependent on package selection, maximum ambient temperature, airflow and pcb heats inking.
12 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 eq. 2: f esr = 1 2 esr c out the feedback and compensation networks provide a closed loop transfer function with the highest 0db cross- ing frequency and adequate phase margin for system stability. equations 3, 4, 5 and 6 relate the compensa- tion network?s poles and zeros to the components r2, r3, r4, c5, c6, and c7: eq. 3: f z1 = 1 2 r 2 c 5 eq. 4: f z2 = 1 2 ( r 3 + r 4 ) c 7 eq. 5: 1 f p1 = 2 r 2 c 5 c 6 c 5 + c 6 eq. 6: f p2 = 1 2 r 3 c 7 components of the feedback, feed forward, compensa- tion, and current limit networks need to be adjusted to maintain system stability for different input and output voltage applications as shown in table 2. r5 r4 r2 r3 c7 c5 c6 fb v out comp ref figure 1: aat1189 feedback and compensation networks for type iii voltage-mode control loop. network components v out = 3.3v v out = 5.0v feedback r4 27.4k ? 44.2k ? r5 6.02k ? 6.02k ? feed-forward c7 330pf 330pf r3 499 ? 499 ? compensation c5 470pf 220pf c6 56pf 56pf r2 24.3k ? 24.3k ? current limit c4 68nf 68nf r1 6.34k ? 6.34k ? r6 6.34k ? 6.34k ? r7 453k ? 649k ? r8 open open table 2: aat1189 feedback and compensation network components for v out =3.3v and v out = 5.0v.
13 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 thermal protection the aat1189 has an internal thermal protection circuit which will turn on when the device die temperature exceeds 135c. the internal thermal protection circuit will actively turn off the high side regulator output device to prevent the possibility of over temperature damage. the buck regulator output will remain in a shutdown state until the internal die temperature falls back below the 135c trip point. the combination and interaction between the short circuit and thermal protection sys- tems allows the buck regulator to withstand indefinite short-circuit conditions without sustaining permanent damage. thermal calculations there are two types of losses associated with the aat1189 step-down converter: 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, assuming continuous con- duction mode (ccm), a simplified form of the synchro- nous step-down converter losses is given by: p total i out 2 (r ds(on)h v out + r ds(on)l [v in - v out ]) + (t sw f s i out + i q ) v in v in = i q is the step-down converter and ldo quiescent cur- rents respectively. the term t sw is used to estimate the full load step-down converter switching losses. for asynchronous step-down converter, the power dis- sipation is only in the internal high side mosfet during the on time. when the switch is off, the power dissipates on the external schottky diode. total package losses for aat1189 reduce to the following equation: p total = i out 2 r ds(on)h d + (t sw f s i out + i q ) v in where d = v out is the duty cycle. v in 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. given the total losses, the maximum junction tempera- ture can be derived from the ja for the tdfn34-16 package, which is 50c/w. t j(max) = p total ja + t amb r1 6.34k c4 68nf 5v/2.5a l1 4.7h r6 r7 v out os rs lx r1 6.34k c4 68nf 5.0v/2.5a l1 4.7h r6 r8 os rs lx figure 2: resistor network to adjust the figure 3: resistor network to adjust the current limit less than the pre-set current limit greater than the pre-set over-current threshold (add r6, r7). over-current level (add r6, r8).
14 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 over-current protection the controller provides true-load dc output current sensing which protects the load and limits component stresses. the output current is sensed through the dc resistance in the output inductor (dcr). the controller reduces the operating frequency when an over-current condition is detected; limiting stresses and preventing inductor saturation. this allows the smallest possible inductor for a given output load. a small resistor divider may be necessary to adjust the over-current threshold and compensate for variation in inductor dcr. the preset current limit threshold is triggered when the differential voltage from rs to os exceeds 100mv (nominal). layout considerations the suggested pcb layout for the aat1189 is shown in figures 5 and 6. the following guidelines should be used to help ensure a proper layout. 1. the power input capacitors (c1 and c12) should be connected as close as possible to high voltage input pin (in) and power ground. 2. c2, l1, d2, c8 and c9 should be placed as close as possible to minimize any parasitic inductance in the switched current path which generates a large volt- age spike during the switching interval. the connec- tion of inductor to switching node should be as short as possible. 3. the feedback trace or fb pin should be separated from any power trace and connected as close 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 returns to pgnd should be kept 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. 5. connect unused signal pins to ground to avoid unwanted noise coupling. 6. the critical small signal components include feed- back components, and compensation components should be placed close to the fb and comp pins. the feedback resistors should be located as close as pos- sible to the fb pin with its ground tied directly to the signal ground plane which is separated from power ground plane. 7. c4 should be connected close to the rs and os pins, while r1 should be connected close to the inductor. 8. for good thermal coupling, pcb vias are required from the exposed pad (ep) for the tdfn paddle to the bottom plane. the ep is internally connected to in.
15 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 vcc l1 4.7h + c1 100f 25v c3 2.2f c6 56pf c8 22f c9 22f c10 open c5 220pf c7 330pf r2 24.3k r8 open r6 6.34k r7 649k r5 6.04k r4 44.2k r3 499 r1 6.34k c4 68nf d2 b340a c2 0.1f d1 bas16 en 7 os 9 bst 6 lx 4 lx 3 lx 1 lx 5 lx 2 lx 16 gnd 12 lx 15 rs 8 vl 13 in 14 fb 11 comp 10 aat1189 tdfn34-16 u1 1 2 3 en c11 1f 50v v in 6.0v - 25.0v v out 5v/2.5a ep u1 aat1189 skyworks, hi-voltage buck, tdfn34-16 c1 cap, mlc, 100f/25v, electrolytic c2 cap, mlc, 0.1f/6.3v, 0402 c3 cap, mlc, 2.2f/6.3v, 0805 c4 cap, mlc, 68nf/16v, 0402 c5, c6, c7 cap, mlc, misc, 0402 c8, c9 cap, mlc, 22f/10v, 1206 c11 cap, mcl, 1f/50v, 0805 d1 bas16, generic, rectifier, 0.2a/85v, ultrafast, sot23 d2 b340a, generic, schottky rectifier, 3a/40v, sma l1 rch108np-4r7m, 4.7h, sumida, i sat = 5.3a, or 7447789004, 4.7h, wurth, i sat = 3.9a r1-r8 carbon film resistor, 0402 figure 4: aat1189irn evaluation board schematic. figure 5: aat1189irn evaluation board figure 6: aat1189irn evaluation board top layer. bottom layer.
16 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 aat1189 design example specifications v out = 5.0v @ 2.5a, pulsed load ? i load = 2.5a v in = 12v f s = 490khz t amb = 85c in tdfn34-16 package output inductor for sumida inductor rch108np-4r7m, 4.7 h, dcr = 11.7m ? max. i = 1 - = 1 - = 1.2 a i pk = i out + = 2.5a + 0.6a = 3.1a p l1 = i out 2 dcr = 3.1a 2 11.7m = 112mw v out l 1 f s i 2 v out v in 5v 12v 5v 4.7h 490khz output capacitor v droop = 0.33v (10% output voltage) 1 23 1 5.0v (24v - 5.0v) 4.7h 490khz 24v 23 rms(max) = i l f s v in1(max) 3 i load v droop f s 3 2.5a 0.33v 490khz c out = = = 46.4f; use 2x22f = 496ma rms v out (v in(max) - v out1 ) = p rms = esr i rms 2 = 5m (496ma) 2 = 1.2mw input capacitor input ripple v pp = 25mv c in = = = 102f 1 - esr 4 f s v pp i out 1 - 5m 4 490khz 25mv 2.5a for low cost applications, a 100 f/25v electrolytic capacitor in parallel with a 1 f/25v ceramic capacitor is used to reduce the esr. i out1 2 rms i p = esr ( i rms ) 2 = 5m (1.25a) 2 = 7.8mw = = 1.25a
17 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 current limit over-current offset voltage: v ocp = 100mv total trace parasitic resistor and inductor dcr is 10m ? i limit = 5a 100mv i preset = = = 10a > i limit 10m v ocp dcr v out r 1 v ocp - i limit dcr r 7 == 5v 6.34k 0.1v - 5a 10m = 634k r 1 r 7 r 7 - r 1 r 6 = 6.34k 634k 634k - 6.34k = = 6.40k aat1189 losses all values assume an 85c ambient temperature and thermal resistance of 50c/w in the tdfn34-16 package. p total = i out 2 r ds(on)h d + (t sw f s i out + i q ) v in p total = + (5ns 490khz 2.5a + 70a) 12v p total = 257mw t j(max) = t amb + ja p loss = 85c + (50c/w) 257mw = 98c 2.5a 2 70m 5v 12v
18 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 ordering information package voltage marking 1 part number (tape and reel) 2 tdfn34-16 0.6 3rxyy aat1189irn-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 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 aat1189 high voltage step-down regulator data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202002a ? skyworks proprietary information ? products and product information are subject to change without notice. ? may 31, 2012 copyright ? 2012 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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