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1 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 general description the aat2689 provides two independently regulated dc outputs, consisting of a high voltage step-down (buck) regulator and a low input voltage low dropout (ldo) regu- lator. the pmic is optimized for low cost 12v adapter inputs, making the device the ideal system-on-a-chip power solution for consumer communications equipment. channel 1 is a step-down (buck) regulator with an input voltage range of 6v to 24v providing up to 2500ma out- put current. 490khz fixed switching frequency allows small l/c filtering components. channel 1 utilizes volt- age mode control configured for optimum performance across the entire output voltage and load range. channel 2 is a low-dropout (ldo) regulator providing up to 600ma output current. the device provides extremely low output noise, low quiescent current and excellent transient response. the controller includes integrated cycle-by-cycle over- current protection, soft-start and over-temperature dis- able features. independent input and enable pins pro- vide maximum design flexibility. the aat2689 is available in the pb-free 3x4mm 16-pin tdfn package. the rated operating temperature range is -40c to 85c. features ? 2-output step-down converters: ? channel 1 (buck): v in1 = 6v to 24v ? v out1 adjustable from 1.5v to 5.5v ? i out1 up to 2.5a ? high switching frequency ? voltage mode control ? pwm fixed frequency for low-ripple ? channel 2 (ldo): v in2 = 2.7v to 5.5v ? i out2 up to 600ma ? 1v dropout voltage at 600ma ? high accuracy 1.5% ? small solution size ? system on a chip ? ultra-small external l/c ? shutdown current <35 a ? independent enable pins ? adjustable over-current protection ? over-temperature protection ? internal soft start ? 3x4mm 16-pin tdfn low profile thermally enhanced package ? -40c to 85c temperature range applications ? dsl and cable modems ? notebook computers ? satellite settop box ? wireless lan systems typical application c10 2.2f c4 0.1f r2 2k c7 220nf c2 470pf c3 56pf r1 24.3k r3 27.4k r4 6.04k d1 c9,c11 2x22f l1 4.7h/5.3a + c1 220f 25v c8 330pf r5 499 en1 c5 2.2f d2 c6 2.2f c15 1f 25v 1 v in1 6.0v -24.0v v out1 3.3v/2.5a v out2 1.8v/600ma v in2 os1 fb1 comp1 out2 rs1 in2 en1 en2 bst1 vl1 in1 lx1 tdfn34-16 aat2689 gnd
2 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 pin descriptions pin # symbol function 1 in1 input supply voltage pin for channel 1 step-down (buck) regulator. connect both in1 pins together. connect the input capacitor close to this pin for best noise performance. 2 bst1 channel 1 step-down (buck) regulator boost drive input pin. connect the cathode of fast recti er from this pin and connect a 100nf capacitor from this pin to the channel 1 switching node (lx) for internal hi-side mosfet gate drive. 3 en1 channel 1 step-down (buck) regulator enable input pin. active high enables internal linear regulator and channel 1 output. 4 rs1 channel 1 output current sense pin. connect a small signal resistor from this pin to the channel 1 switching node (lx) to enable over-current sense for step-down (buck) converter. 5 os1 channel 1 output sense voltage pin. connect to the output capacitor to enable over-current sense for step- down (buck) converter. 6 comp1 compensation pin for channel 1 step-down (buck) regulator. connect a series resistor and capacitor network to compensate for the voltage mode control loop. 7 fb1 feedback input pin for channel 1 step-down (buck) converter. connect an external resistor divider to this pin to program the output voltage to the desired value. 8 en2 channel 2 linear low dropout (ldo) enable input pin. active high. 9 in2 input supply voltage pin for channel 2 linear low dropout (ldo) regulator. connect a 2.2 f ceramic input capacitor close to this pin. 10 out2 output of channel 2 of linear low dropout (ldo) regulator. connect a 2.2 f ceramic capacitor from this pin to the gnd pin. 11 agnd analog ground pin for ldo and buck (step-down) controller. tie to pcb ground plane. 12 vl1 internal linear regulator for channel 1 step-down (buck) converter. connect a 2.2 f/6.3v capacitor from this pin to the gnd pin. 13 gnd ground pin for both channels. power return pin for both channels. connect returns of both channels input and output capacitors close to this pin for best noise performance. 14 in1 input supply voltage pin for channel 1 step-down (buck) regulator. connect both in1 pins together. connect the input capacitor close to this pin for best noise performance. 15 lx1 channel 1 step-down (buck) converter switching pin. connect output inductor to this pin. connect both lx1 pins together. 16 lx1 channel 1 step-down (buck) converter switching pin. connect output inductor to this pin. connect both lx1 pins together. ep1 gnd exposed paddle 1 tied to ground. connect to pcb heatsink for optimum thermal performance of internal ldo device. ep2 in1 exposed paddle 2 tied to drain of internal high side mosfet. connect to pcb heatsink for optimum thermal performance of step-down (buck) regulator. pin configuration tdfn34-16 dual paddle (top view) en1 rs1 os1 in1 bst1 3 comp1 fb1 en2 in1 gnd vl1 lx1 lx1 agnd out2 in2 4 5 1 2 6 7 8 14 13 12 16 15 11 10 9 ep1 ep2
3 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 absolute maximum ratings 1 symbol description value units v in(hi) , v en1 in1, lx, en1 to gnd -0.3 to 30.0 v v in(lo) in2, vl1 to gnd -0.3 to 6.0 v v bst1-lx1 bst1 to lx1 -0.3 to 6.0 v v control fb1, comp1, rs1, os1, out2 to gnd -0.3 to v in(lo) + 0.3 v v en2 en2 to gnd -0.3 to v in2 + 0.3 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 ground plane. 3. derate 20mw/c above 25c ambient temperature.
4 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 electrical characteristics 1 v in1 = 12.0v, v in2 =3.3v; t a = -40c to 85c, unless noted otherwise. typical values are at t a = 25c. symbol description conditions min typ max units channel 1: step-down (buck) converter v in1 input voltage 6.0 24.0 v v uvlo1 uvlo threshold v in1 rising 5.0 v v in1 hysteresis 300 mv v in1 falling 3.0 v v out1 output voltage range 1.5 5.5 v v fb1 feedback pin voltage 0.591 0.600 0.609 v v out1 output voltage accuracy i out1 = 0 to 2.5a -3.0 +3.0 % ( v out1 /v out1 ) / v in1 line regulation v in1 = 6v to 24v, v out1 = 3.3v, i out1 = 0v to 2.5a 0.014 %/v ( v out1 /v out1 ) / i out1 load regulation v in1 = 6v to 24v, v out1 = 3.3v, i out1 = 0a to 2.5a 0.1 %/a i q1 quiescent current v en1 = high, no load 0.6 ma i shdn1 shutdown current v en1 = low, v l1 = 0v 35.0 a v ocp1 over-current offset voltage v en1 = high, v in1 = 6v to 24v, t a = 25c 80 100 120 mv i lx1 lx pin leakage current v in1 = 24.0v, v en1 = low -1.0 1.0 a d max maximum duty cycle 85 % t on(min) minimum on-time v in1 = 6v to 24v 100 ns r dson(h) hi side on-resistance v l1 = 4.5v 70 m f osc1 oscillator frequency 350 490 650 khz f foldback1 short circuit foldback frequency current limit triggered 100 khz t s1 start-up time from enable channel 1 to output regulation 2.5 ms channel 2: 600ma linear low dropout (ldo) regulator v in2 input voltage 2.7 5.5 v v do2 dropout voltage 98% x v out2(nom) , i out2 = 600ma 1000 1300 mv i q2 quiescent (ground) current no load 70 125 a i shdn2 shutdown current v en2 = gnd 1.0 a v out2(tol) output voltage tolerance i out2 = 1 to 600ma, v in2 = 2.7v to 5.5v, t a = 25c -2.0 +2.0 % i out2 = 1 to 600ma, v in2 = 2.7v to 5.5v, t a = -40c to 85c -3.5 +3.5 % e n output noise bw = 300hz to 50khz 250 v rms psrr power supply rejection ratio i out2 = 10ma 1khz 67 db 10khz 47 1mhz 45 i limit2 current limit 700 800 ma t s2 enable start-up delay from enable channel 2 to output regulation 15 s over-temperature, en logic t sd1,2 over-temperature shutdown threshold 135 c over-temperature shutdown hysteresis 15 c v en1,en2(l) enable threshold low 0.6 v v en1(h) enable threshold high 2.5 v v en2(h) enable threshold high 1.4 v i en1,en2 input low current -1.0 1.0 a 1. the aat2689 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 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 typical characteristics step-down converter efficiency vs. load (v out1 = 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 in1 = 6v v in1 = 8v v in1 = 12v v in1 = 18v v in1 = 24v step-down converter dc regulation (v out1 = 3.3v; l = 4.7h) output current (ma) output error (%) 0.1 1 10 100 1000 10000 -2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.0 v in1 = 6v v in1 = 8v v in1 = 12v v in1 = 18v v in1 = 24v step-down converter line regulation (v out1 = 3.3v; l = 4.7h) input voltage (v) accuracy (%) -1.00 -0.75 -0.50 -0.25 0.00 0.25 0.50 0.75 1.00 6 8 10 12 14 16 18 20 22 24 i out1 = 0.1ma i out1 = 1ma i out1 = 1250ma i out1 = 2500ma step-down converter output ripple (v in1 = 12v; v out1 = 3.3v; i out1 = 1ma) time (2s/div) output voltage (ac coupled) (bottom) (v) lx voltage (top) (v) inductor current (middle) (a) 3.29 3.30 3.31 0.0 0.2 0.4 0v 12v step-down converter output ripple (v in1 = 12v; v out1 = 3.3v; i out1 = 2.5a) time (1s/div) output voltage (ac coupled) (bottom) (v) lx voltage (top) (v) inductor current (middle) (a) 3.28 3.30 3.32 2.0 3.0 4.0 0v 12v step-down converter load transient response (i out1 = 1.875a to 2.5a; v in1 = 12v; v out1 = 3.3v; c out1 = 2x22f) time (100s/div) output voltage (ac coupled) (bottom) (v) output current (top) (a) 3.2 3.3 3.4 1.5 2.0 2.5 3.0 2.5a 1.875a
6 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 typical characteristics step-down converter load transient response (i out1 = 1.25a to 2.5a; v in1 = 12v; v out1 = 3.3v; c out1 = 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 line transient response (v in1 = 6v to 10v; v out1 = 3.3v; i out1 = 2.5a) time (2ms/div) input voltage (top) (v) output voltage (bottom) (v) 0 5 10 15 3.2 3.3 3.4 step-down converter soft start (v in1 = 12v; v en1 = 10v; v out1 = 3.3v; i out1 = 2.5a) time (500s/div) enable voltage (top) (v) output voltage (middle) (v) inductor current (bottom) (a) 0 5 10 15 20 0.0 2.0 4.0 step-down converter output voltage error vs. temperature (v in1 = 12v; v out1 = 3.3v) temperature (c) output voltage error (%) -1.0 -0.8 -0.6 -0.4 -0.2 0.0 0.2 0.4 0.6 0.8 1.0 -50 -25 25 50 75 100 0 i out1 = 0.1ma i out1 = 1ma i out1 = 1250ma i out1 = 2500ma step-down converter switching frequency vs. temperature (v in1 = 12v; i out1 = 2.5a) temperature (c) switching frequency (khz) 470 480 490 500 510 520 -40 -20 0 20 40 60 80 100 step-down converter switching frequency vs. input voltage (v out1 = 3.3v; i out1 = 2.5a) temperature (c) frequency variation (%) -40 -20 0 20 40 60 80 100 -8 -6 -4 -2 0 2 4 6 8
7 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 typical characteristics step-down converter input current vs. input voltage (v en1 = v in1 ) input voltage (v) input current (ma) 0.40 0.45 0.50 0.55 0.60 0.65 0.70 6 9 12 15 18 21 24 85c 25c -40c ldo dropout voltage vs. temperature temperature (c) dropout voltage (mv) 0 200 400 600 800 1000 1200 1400 -40 -20 0 20 40 60 80 100 i out2 = 600ma i out2 = 500ma i out2 = 300ma i out2 = 150ma i out2 = 50ma ldo dropout characteristics (v out2 = 1.8v) input voltage (v) output voltage (v) 1.5 2 2.5 3 3.5 4 4.5 1.70 1.72 1.74 1.76 1.78 1.80 1.82 1.84 i out2 = 0.1ma i out2 = 10ma i out2 = 50ma i out2 = 100ma i out2 = 300ma i out2 = 600ma ldo dropout voltage vs. output current output current (ma) dropout voltage (mv) 0 100 200 300 400 500 600 0 300 600 900 1200 1500 85c 25c -40c ldo input current vs. input voltage (v en1 = 0v; v en2 = v in2 ) input voltage (v) input current (a) 0 20 40 60 80 100 23 2.5 3.5 4.5 45 85c 25c -40c ldo v ih and v il vs. input voltage input voltage (v) v ih and v il (%) 2.5 3 3.5 4.5 5 5.5 4 1.00 1.05 1.10 1.15 1.20 1.25 1.30 v ih v il
8 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 typical characteristics ldo turn-off response time (v in2 = 3.3v; v en2 = 3.3v; v out2 = 1.8v; i out2 = 600ma) time (5s/div) enable voltage (top) (v) output voltage (bottom) (v) 0 1 2 3 4 -1.0 0.0 1.0 2.0 ldo turn-on time from enable (v in2 = 3.3v; v en2 = 3.3v; v out2 = 1.8v; i out2 = 600ma) time (5s/div) enable voltage (top) (v) output voltage (bottom) (v) 0 1 2 3 4 0 1 2 3 ldo output voltage error vs. temperature (v in2 = 3.3v; v out2 = 1.8v) temperature (c) output voltage error (%) -50 -25 25 50 75 100 0 -3.0 -2.0 -1.0 0.0 1.0 2.0 3.0 i out2 = 0.1ma i out2 = 300ma i out2 = 600ma ldo load transient response (i out2 = 0.3a to 0.6a; v in2 = 3.3v; v out2 = 1.8v; c out2 = 2.2f) time (40s/div) output current (top) (a) output voltage (bottom) (v) 0.3 0.4 0.5 0.6 0.7 1.75 1.80 1.85 1.90 ldo load transient response (i out2 = 0.06a to 0.6a; v in2 = 3.3v; v out2 = 1.8v; c out2 = 2.2f) time (40s/div) output current (top) (a) output voltage (ac coupled) (bottom) (v) 0.0 0.2 0.4 0.6 0.8 1.60 1.70 1.80 1.90 0.06a 0.6a ldo line transient response (v in2 = 3v to 4v; v out2 = 1.8v; i out2 = 600ma; c out2 = 2.2f) time (200s/div) input voltage (top) (v) output voltage (bottom) (v) 2 3 4 5 1.70 1.75 1.80 1.85 v in v out
9 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 typical characteristics ldo output voltage noise (i out2 = 10ma; power bw: 300~50khz) frequency (hz) noise (vrms ) 100 1000 10000 100000 0 5 10 ldo power supply rejection ratio, psrr (i out2 = 10ma; bw: 100khz to 300khz) frequency (hz) magnitude (db) 100 1000 10000 100000 0 10 20 30 40 50 60 70
10 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 functional description the aat2689 provides two independently regulated dc outputs; consisting of a high voltage step-down (buck) regulator and a low input voltage linear low dropout (ldo) regulator. the pmic is optimized for low cost 12v adapter inputs, making the device an ideal system-on-a- chip power solution for consumer communications equipment. channel 1 is a step-down (buck) regulator with an input voltage range 6.0 to 24v; providing up to 2500ma out- put current. 490khz fixed switching frequency allows small l/c filtering components. channel 1 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 resistance (dcr). an external resistor network adjusts the current limit according to the dcr of the desired inductor and the desired output current limit. frequency reduction limits over-current stresses during short-circuit events. the operating frequency returns to the nominal setting when over-current conditions are removed. channel 2 is a linear low-dropout (ldo) regulator provid- ing up to 600ma output current at a factory set output voltage. the device provides extremely low output noise, low quiescent current and excellent transient response. the controllers include integrated over-current, soft- start and over-temperature protection. independent input and enable pins provide maximum design flexibil- ity. the aat2689 is available in the pb-free 3x4mm 16-pin tdfn package. the rated operating temperature range is -40c to 85c. functional block diagram in2 vo2 en2 logic error amp control logic ocp voltage ref 2 ot gnd logic error amp control logic en1 bst1 ot voltage ref vl1 vint comp. in1 reg. lx1 rs1 os1 logic error amp control logic fb1 osc ot voltage ref 1 comp. reg. 20 comp fb_ldo fb_ldo comp1 v ocp1 = 0.1v
11 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 applications information output 1 is a high voltage dc/dc buck (step-down) con- verter providing an output voltage from 1.5v to 5.5v. the integrated high-side n-channel mosfet device pro- vides up to 2.5a output current. input voltage range is 6.0v to 24.0v. the step-down converter utilizes constant frequency (pwm-mode) voltage mode control to achieve high operating efficiency while maintaining extremely low output noise across the operating range. high 490khz (nominal) switching frequency allows small external filtering components, achieving minimum cost and solution size. external compensation allows the designer to optimize the transient response while achiev- ing stability across the operating range. output 2 is a low voltage, low dropout (ldo) linear regulator providing 1.8v with up to 600ma output cur- rent. the input voltage range is 2.7v to 5.5v. the ldo provides very low noise output which can be derived directly from the output 1 channel. output voltage and current output 1 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 maximum duty cycle is 85%. v out (v) r 4 = 6.04k ? r 3 (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 alternately, the feedback resistor may be calculated using the following equation: r 3 = (v out - 0.6) r 4 0.6 r3 is rounded to the nearest 1% resistor value. channel 1 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. channel 1 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. channel 1 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. channel 1 input capacitor selection for low cost applications, a 100 f/25v electrolytic capac- itor 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 max- imum input voltage is connected as close as possible to the input pin (pin 14) for high frequency decoupling.
12 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 channel 1 feedback and compensation networks r4 r3 r1 r5 c8 c2 c3 fb1 v out1 comp1 ref figure 1: aat2689 feedback and compensation networks for type iii voltage-mode control loop. 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 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. equation 3, 4, 5 and 6 relate the compensation network?s poles and zeros to the components r1, r3, r5, c2, c3, and c8: eq. 3: f z1 = 1 2 r 1 c 2 eq. 4: f z2 = 1 2 ( r 3 + r 5 ) c 8 eq. 5: 1 f p1 = 2 r 1 c 2 c 3 c 2 + c 3 eq. 6: f p2 = 1 2 r 5 c 8 components of the feedback, feed-forward, compensa- tion, and current limit networks need to be adjusted to maintain the systems stability for different input and output voltages applications as shown in table 2. network components v out = 3.3v v in = 12v xed v out = 3.3v v in = 6v to 24v v out = 5.0v v in = 6v to 24v feedback r3 6.04k ? 6.04k ? 6.04k ? r4 27.4k ? 27.4k ? 44.2k ? feed-forward c8 470pf 330pf 330pf r5 1.37k ? 499 ? 499 ? compensation c2 1nf 470pf 220pf c3 56pf 56pf 56pf r1 11.8k ? 24.3k ? 24.3k ? current limit c7 22nf 220nf 220nf r2 10k ? 2k ? 2k ? r6 open open open r7 11k ? 2k ? 2k ? r8 600k ? 133k ? 133k ? table 2: aat2689 feedback, feed-forward, compensation, and current limit components for v out = 3.3v and v out = 5.0v.
13 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 channel 1 thermal protection the aat2689 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. over-current protection the output 1 controller provides true-load dc output current sensing which protects the load and limits com- ponent stresses. the output current is sensed through the dc resistance in the output inductor (dcr). the con- troller reduces the operating frequency when an over- current condition is detected; limiting stresses and pre- venting 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 rs1 to os1 exceeds 100mv (nominal). r2 2k c7 220nf 3.3v/2.5a 4.7h 5.3a l1 r7 r8 v out1 os1 5 rs1 4 lx1 figure 2: resistor network to adjust the current limit less than the pre-set over-current threshold (add r7, r8). r2 2k c7 220nf 3.3v/2.5a 4.7h 5.3a l1 r7 r6 v out1 os1 5 rs1 4 lx1 figure 3: resistor network to adjust the current limit greater than the pre-set over-current level (add r6, r7). channel 2 input capacitor typically, a 1 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 aat2689 is physically located more than three centimeters from an input power source, a c in capacitor will be needed for stable operation. c in should be located as close to the device v in pin as pos- sible. c in values greater than 1 f will offer superior input line transient response and will assist in maximizing the highest possible power supply ripple rejection. ceramic, tantalum, or aluminum electrolytic capacitors may be selected for c in . there is no specific capacitor esr require- ment for c in . however, for 150ma ldo regulator output operation, 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 batteries in portable devices. channel 2 output capacitor for proper load voltage regulation and operational stabil- ity, a capacitor is required between pins vout and gnd. the c out capacitor connection to the ldo regulator ground pin should be connected as close as possible for maximum device performance. the aat2689 ldo has been specifically designed to function with very low esr ceramic capacitors. for best performance, ceramic capacitors are recommended.
14 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 typical output capacitor values for maximum output cur- rent conditions range from 1 f to 10 f. applications utilizing the exceptionally low output noise and optimum power supply ripple rejection characteristics of channel 2 should use 2.2 f or greater for c out . if desired, c out may be increased without limit. in low output current applications where output load is less than 10ma, the minimum value for c out can be as low as 0.47 f. channel 2 enable function the aat2689 features an ldo regulator enable/disable function. this pin (en) is active high and is compatible 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 disable shutdown mode when the voltage on the en pin falls below 0.6v. if the enable function is not needed in a specific applica- tion, it may be tied to v in to keep the ldo regulator in a continuously on state. when the ldo regulator is in shutdown mode, an internal 1.5k ? resistor is connected between v out and gnd. this is intended to discharge c out when the ldo regulator is disabled. the internal 1.5k ?? has no adverse effect on device turn-on time. channel 2 short-circuit protection the aat2689 ldo contains an internal short-circuit pro- tection circuit that will trigger when the output load cur- rent exceeds the internal threshold limit. under short- circuit conditions, the output of the ldo regulator will be current limited until the short-circuit condition is removed from the output or ldo regulator package power dissi- pation exceeds the device thermal limit. channel 2 thermal protection the aat2689 ldo has an internal thermal protection circuit which will turn on when the device die tempera- ture exceeds 150c. the internal thermal protection circuit will actively turn off the ldo regulator output pass device to prevent the possibility of over tempera- ture damage. the ldo regulator output will remain in a shutdown state until the internal die temperature falls back below the 150c trip point. the combination and interaction between the short circuit and thermal protec- tion systems allows the ldo regulator to withstand indefinite short-circuit conditions without sustaining per- manent damage. channel 2 no-load stability the aat2689 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. channel 2 reverse output-to-input voltage conditions and protection under normal operating conditions, a parasitic diode exists between the output and input of the ldo regula- tor. the input voltage should always remain greater than the output load voltage, maintaining a reverse bias on the internal parasitic diode. conditions where v out might exceed v in should be avoided since this would forward bias the internal parasitic diode and allow excessive cur- rent flow into the v out pin, possibly damaging the ldo regulator. in applications where there is a possibility of v out exceeding v in for brief amounts of time during nor- mal operation, the use of a larger value c in capacitor is highly recommended. a larger value of c in with respect to c out will effect a slower c in decay rate during shut- down, thus preventing v out from exceeding v in . in appli- cations where there is a greater danger of v out exceed- ing v in for extended periods of time, it is recommended to place a schottky diode across v in to v out (connecting the cathode to v in and anode to v out ). the schottky diode forward voltage should be less than 0.45v. thermal calculations there are three types of losses associated with the aat2689 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 and ldo losses is given by: p total i out1 2 (r ds(on)h v out1 + r ds(on)l [v in1 - v out1 ]) + (t sw f s i out1 + i q1 ) v in1 + (v in2 - v out2 ) i out2 v in1 = i q1 and i q2 are the step-down converter and ldo quies- cent currents respectively. the term t sw is used to esti- mate the full load step-down converter switching losses.
15 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 for asynchronous step-down converter operation, the power dissipation 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 loss for aat2689 reduces to the following equation: p total = i out1 2 r ds(on)h d + (t sw f s i out1 + i q1 ) v in1 + (v in2 - v out2 ) i out2 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 layout considerations the suggested pcb layout for the aat2689 is shown in figures 4, 5, and 6. the following guidelines should be used to help ensure a proper layout. 1. the power input capacitors (c1 and c15) should be connected as close as possible to high voltage input pin (in1) and power ground. 2. c1, l1, d2, c9 and c11 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 fb1 pin should be separated from any power trace and connected as close as pos- sible 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 fb1 and comp1 pins. the feedback resistors should be located as close as possible to the fb1 pin with its ground tied straight to the signal ground plane which is separated from power ground plane. 7. c7 should be connected close to the rs1 and os1 pins, while r2 should be connected directly to the output pin of the inductor. for the best current limit performance, c7 and r2 should be placed on the bot- tom layer to avoid noise coupling from the inductor. 8. for good thermal coupling, pcb vias are required from exposed pad 1 (ep1) to the bottom ground plane and from exposed pad 2 (ep2) to the bottom vin plane.
16 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 u1 aat2689 skyworks, hi-voltage buck/ldo, tdfn34-16 c1 cap, mlc, 100f/25v, electrolytic cap c5, c6, c10 cap, mlc, 2.2f, 6.3v, 0805 c4 cap, mlc, 0.1f/6.3v, 0603 c2, c3, c7, c8 cap, mlc, misc., 0603 c9, c11 cap, mlc, 22f/10v, 1206 d1 bas16, g eneric, rectifier, 0.2a/85v, ultrafast, sot23 d2 b340a, generic, schottky rectifier, 3a/40v, sma l1 rch108np-4r7m, 4.7f, i sat = 5.3a, dcr = 11.7m or wurth 744 778 900 4, 4.7h, i sat = 3.9a, dcr = 35m r1 - r8 carbon film resistor, 0402 c15 cap, mlc,1f/25v, 0603 r2 2k r6 open r7 2k r1 24.3k l1 4.7h/5.3a r5 499 3.3v/2.5a 6.0v - 24.0v + c1 100f 25v c15 1f 25v 1 2 3 en1 1 2 3 en2 c5 2.2f c10 2.2f c9 22f c11 22f c12, c13 open c14 open c7 220nf c2 470pf c3 56pf c8 330pf c6 2.2f c4 0.1f d1 bas16 1 2 j1 d2 r8 133k r4 6.04k r3 27.4k v out2 v out1 v in1 v in2 os 1 5 fb1 7 comp1 6 out2 10 rs1 4 in2 9 en1 3 en 2 8 bst1 2 agnd 11 vl 1 12 in1 1 lx1 15 lx1 16 tdfn34-16 aat2689 in1 14 gnd 13 u1 1.8v/600ma ep2 ep1 figure 4: aat2689irn evaluation board schematic for v in = 6v to 24v and v out = 3.3v. figure 5: aat2689irn evaluation figure 6: aat2689irn evaluation board top layer. board bottom layer.
17 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 aat2689 design example specifications v o1 = 3.3v @ 2.5a, pulsed load ? i load = 2.5a v o2 = 1.8v @ 600ma v in1 = 12v f s = 490khz t amb = 85c in tdfn34-16 package channel 1 output inductor for sumida inductor rch108np-4r7m, 4.7 h, dcr = 11.7m ? max. i = 1 - = 1 - = 1 a i pk1 = i out1 + = 2.5a + 1a = 3.5a p l1 = i out1 2 dcr = 3.5a 2 11.7m = 143mw v out1 l 1 f s i 2 v out1 v in 3.3v 12v 3.3v 4.7h 490khz channel 1 output capacitor v droop = 0.33v (10% output voltage) 1 23 1 3.3v (24v - 3.3v) 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 = 357ma rms v out1 (v in(max) - v out1 ) = p rms = esr i rms 2 = 11.7m (357ma) 2 = 1.5w channel 1 input capacitor input ripple v pp = 25mv c in1 = = = 102f 1 - esr 4 f s v pp1 i out1 1 - 5m 4 490khz 25mv 2.5a for low cost applications, 100 f/25v electrolytic capacitor in parallel with 1 f/25v ceramic capacitor are used to reduce the esr. i out1 2 rms i p = esr ( i rms ) 2 = 5m (1.25a) 2 = 7.8mw = = 1.25a
18 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 channel 1 current limit voltage sense v s = 100mv total trace parasitic resistor and inductor dcr is 10m ? 100mv i lim = = = 10a > 5a 10m v s dcr v out1 r 2 v ocp - i limit dcr r 8 == 3.3v 2k 0.1v - 5a 10m = 133k r 2 r 8 r 8 - r 2 r 7 = 2k 133k 133k - 2k == 2k aat2689 losses all values assume a 25c ambient temperature and thermal resistance of 50c/w in the tdfn34-16 package. p total = i out1 2 r ds(on)h d + (t sw f s i out1 + i q1 ) v in1 + (v in2 - v out2 ) i out2 p total = + (5ns 490khz 2.5a + 70a) 12v (3.3v - 1.8v) 600ma p total = 1.1w t j(max) = t amb + ja p loss = 25c + (50c/w) 1.1w = 80c 2.5a 2 70m 3.3v 12v
19 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 2012 ordering information package voltage marking 1 part number (tape and reel) 2 channel 1 channel 2 tdfn34-16 adj (0.6) 1.8 3pxyy AAT2689IRN-AI-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. legend voltage code adjustable (0.6) a 1.8 i 1. xyy = assembly and date code. 2. sample stock is generally held on part numbers listed in bold .
20 aat2689 pmic solution for 12v adapter systems with 2-output high performance step-down converters data sheet skyworks solutions, inc. ? phone [781] 376-3000 ? fax [781] 376-3100 ? sales@skyworksinc.com ? www.skyworksinc.com 202035a ? skyworks proprietary information ? products and product information are subject to change without notice. ? jun e 8, 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. package information 1 tdfn34-16 top view bottom view side view 3.000 all dimensions in millimeters. 1. 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 connection.

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