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innovative power tm - 1 - www.active-semi.com copyright ? 2012 active-semi, inc. features ? 7.5v to 36v input voltage ? 40v input voltage surge ? up to 5a output current ? up to 12v output voltage ? dual outputs with independent over current protection ? 7.5% accurate over current protection (ocp) ? integrated 45m ? high side power fet ? 90% efficiency at heavy load ? internal 3ms soft startup ? low standby input current ? sleeping mode at ocp, otp and scp ? zero input and output currents at over current and short circuit protection ? auto recovery into full load after faults ? output cord voltage drop compensation ? stable with low esr ceramic output capacitors ? internal cycle-by-cycle current control ? programmable over current setting ? sop-8ep package applications ? automotive industry ? dual-output car charger ? lcd-tv general description ACT4455 is a wide input voltage step-down dc/dc converter with high-side mosfet integrated. it provides up to 5a continuous output current at 200khz switching frequency. the converter can be configured as single output or dual outputs with independent over current protection. the converter achieves high efficiency and excellent load and line regulation. the converter enters into hiccup and sleeping mode and the converter power consumption is nearly zero when output is overloaded or shorted to ground. other protection features includes cycle-by-cycle current limit, under voltage protection and thermal shutdown. the device is available in sop8-ep package. ACT4455 36v/5a step down dc/dc converter rev 2, 21-nov-12 ACT4455-001 output current (v) efficiency (%) 0 1000 2000 3000 4000 5000 90 80 70 60 50 100 efficiency vs. load current v in = 24v v in = 12v v in = 32v
ACT4455 rev 2, 21-nov-12 innovative power tm - 2 - www.active-semi.com copyright ? 2012 active-semi, inc. ordering information part number operation temperature range package pins packing ACT4455yh-t -40c to 85c sop-8ep 8 tape & reel pin configuration pin descriptions pin name description 1 cs1 the output current of v out1 is sensed by this pin. when the voltage on this pin reaches 116mv for 750s, the ic shuts down for 2. 5 seconds before initiating a restartup. 2 sw switch output. connect this pin to t he switching end of the external inductor. 3 hsb high side bias. this pin acts as the positive rail for the high-side switch?s gate driver. connect a 22nf-100nf capacitor between hsb and sw pins. 4 gnd ground. 5 comp compensation node. comp is used to compensate the voltage regulation loop. 6 fb feedback input. fb senses the output voltage to regulate that voltage. drive fb with a resistive voltage divider from the output voltage. the feedback threshold is 0.808v. see setting the output voltage . 7 in input supply. bypass this pin to gnd with a 10f or greater low esr capacitor. 8 cs2 the output current of v out2 is sensed by this pin. when the voltage on this pin reaches 116mv for 750s, the ic shuts down for 2.5 seconds and then restarts. exposed pad exposed pad. connect this p ad to thick copper plane via copper vias.
ACT4455 rev 2, 21-nov-12 innovative power tm - 3 - www.active-semi.com copyright ? 2012 active-semi, inc. absolute maximum ratings c parameter value unit in to gnd -0.3 to 44 v sw to gnd -0.3 to v in + 0.3 v hsb to gnd v sw - 0.3 to v sw + 7 v fb, cs1, cs2, comp to gnd -0.3 to + 6 v junction to ambient the rmal resistance 50 c/w operating junction temperature -40 to 150 c storage junction temperature -55 to 150 c lead temperature (soldering 10 sec.) 300 c c : do not exceed these limits to prevent damage to the device. exposure to absolute maximum rati ng conditions for long periods m ay affect device reliability.
ACT4455 rev 2, 21-nov-12 innovative power tm - 4 - www.active-semi.com copyright ? 2012 active-semi, inc. parameter symbol test cond itions min typ max unit feedback voltage v fb 7.5v v in 40v 798 808 818 mv error amplifier voltage gain a ea 4000 v/v error amplifier transconductance g ea ? i comp = 10a 650 a/v over voltage protection threshold v ovp 41 v max e/a source current i srcmax v fb = 0.5v 120 a max e/a sink current i sinkmax v fb = 1.0v 120 a high-side switch on-resistance r ds(on)1 at 25c 38 m ? low-side switch on-resistance r ds(on)2 5 ? maximum duty cycle d max 80 % switching frequency f sw 180 200 220 khz upper switch current limit i lim duty cycle = 65% 6.5 a comp to current limit transconductance g comp 5 a/v minimum on time t on_min 250 ns input under voltage lockout thresh- old v in_rise v in rising 6.75 7 7.25 v input under voltage lockout hystere- sis v in_falling v in falling 650 mv internal soft startup time t ss 3.0 ms cs1 reference voltage v cs1 113 116 119 mv cs2 reference voltage v cs2 113 116 119 mv frequency foldback threshold v fb_foldback 0.65 v cord compensation v in = 12v, r fb1 =200k, i out = 5a 0.35 v thermal shutdown 150 c electrical characteristics (v in = 12v, t a = 25c, unless otherwise specified.)
ACT4455 rev 2, 21-nov-12 innovative power tm - 5 - www.active-semi.com copyright ? 2012 active-semi, inc. functional block diagram functional description operation as seen in functional block diagram , the ACT4455 is a current mode controlled regulator. the ea output voltage (comp voltage) is proportional to the peak inductor current. a switching cycle starts when the rising edge of the oscillator clock output ca uses the high-side power switch to turn on and the low-side power switch to turn off. with the sw side of the inductor now connected to in, the inductor current ramps up to store energy. the inductor current level is measured by the current sense amplifier and added to the oscillator ramp signal. if the resulting summation is higher than the comp voltage, the output of the pwm comparator goes high. when this happens or when os cillator clock output goes low, the high-side power switch turns off and the inductor freewheels through the schottky diode causing the inductor current to decrease and magnetic energy to be transferred to output. this state continues until the cycle starts again. the high-side power switch is driven by logic using hsb as the positive rail. this pin is charged to v sw + 5v when the low-side power switch turns on. the comp voltage is the integration of the error between fb input and internal 0.808v reference. if fb is lower than the reference voltage, comp tends to go higher to increase current to the output. over current and short circuit protection cs pins are connected to the high side of current sensing resistors to prev ent output over current. with independent cs1 and cs2 pins, two output currents are detected. if the voltage at either cs pins exceeds 116mv for more than 750s. the converter shuts down and goes into sleeping mode. a new soft startup is triggered after 2.5s. if the fault condition is un-cleared, the converter shuts down again until over current condition is cleared. with this long-waiting-time hiccup mode, the power consumption at over loading or outputs short is reduced to nearly zero. thermal shutdown the ACT4455 shuts down when its junction temperature exceeds 150c. the converter triggers a soft-start when the temperature has dropped by 10c. the soft-restart avoi ds output over voltage at thermal hiccup.
ACT4455 rev 2, 21-nov-12 innovative power tm - 6 - www.active-semi.com copyright ? 2012 active-semi, inc. applications information output voltage setting figure 1: output voltage setting figure 1 shows the connections for setting the output voltage. select the proper ratio of the two feedback resistors r fb1 and r fb2 based on the output voltage. typically, use r fb2 10k ? and determine r fb1 from the following equation: over current protection setting the output over current threshold is calculated by: it is recommended that 1% or 0.5% high-accuracy current sensing resistor is selected to achieve high- accuracy over current prot ection. two over current protection thresholds can be different based on different current sensing resistance. inductor selection the inductor maintains a continuous current to the output load. this inductor cu rrent has a ripple that is dependent on the inductance value: higher inductance reduces the peak-to-peak ripple current. the trade off for high inductance value is the increase in inductor core size and series resistance, and the reduction in current handling capability. in general, select an inductance value l based on ripple current requirement: where v in is the input voltage, v out is the output voltage, f sw is the switching frequency, i loadmax is the maximum load current, and k ripple is the ripple factor. typically, choose k ripple = 30% to correspond to the peak-to-peak ripple current being 30% of the maximum load current. with a selected inductor value the peak-to-peak inductor current is estimated as: the peak inductor current is estimated as: the selected inductor should not saturate at i lpk. the maximum output current is calculated as: i lim is the internal current limit, which is typically 6.5a, as shown in electrical characteristics table. input capacitor the input capacitor needs to be carefully selected to maintain sufficiently low ripple at the supply input of the converter. a low esr capacitor is highly recommended. since large current flows in and out of this capacitor during switching, its esr also affects efficiency. the input capacitance needs to be higher than 10f. the best choice is the ceramic type, however, low esr tantalum or electrolytic types may also be used provided that the rms ripple current rating is higher than 50% of the output current. the input capacitor should be placed close to the in and g pins of the ic, with the shortest traces possible. in the case of tantalum or electrolytic types, they can be further away if a small parallel 0.1f ceramic capacitor is placed right next to the ic. output capacitor the output capacitor also needs to have low esr to keep low output voltage ripple. the output ripple voltage is: where i outmax is the maximum output current, k ripple is the ripple factor, r esr is the esr of the output capacitor, f sw is the switching frequency, l is the inductor value, and c out is the output capacitance. in the case of ceramic output capacitors, r esr is very small and does not contribute to the ripple. therefore, a lower capacitance value can be us ed for ceramic type. in the case of tantalum or electrolytic capacitors, the ripple is dominated by r esr multiplied by the ripple (4) ( ) sw in out in out pk lpk f v l v v v i = _ _ pk lpk loadmax lpk _ i 2 1 i i + = (5) (3) ( ) ripple loadmax sw in out in out k i f v v v v l _ = ? ? ? ? ? ? ? = 1 v 808 . 0 v r r out 2 fb 1 fb (1) (6) pk lpk lim outmax i 2 1 i i _ _ = sense 2 ocp 1 ocp r / mv 116 i i = = (2) (7) esr ripple outmax ripple r k i v = +
ACT4455 rev 2, 21-nov-12 innovative power tm - 7 - www.active-semi.com copyright ? 2012 active-semi, inc. applications information cont?d current. in that case, the output capacitor is chosen to have sufficiently low esr. for ceramic output capacitor, typically choose a capacitance of about 22f. for tantalum or electrolytic capacitors, choose a capacitor with less than 50m ? esr. rectifier diode use a schottky diode as the rectifier to conduct current when the high-side power switch is off. the schottky diode must have current rating higher than the maximum output current and a reverse voltage rating higher than the maximum input voltage.
ACT4455 rev 2, 21-nov-12 innovative power tm - 8 - www.active-semi.com copyright ? 2012 active-semi, inc. stability compensation figure 2: stability compensation c : c comp2 is needed only for high esr output capacitor the feedback loop of the ic is stabilized by the components at the comp pin, as shown in figure 2. the dc loop gain of the system is determined by the following equation: the dominant pole p1 is due to c comp : the second pole p2 is the output pole: the first zero z1 is due to r comp and c comp : and finally, the third pole is due to r comp and c comp2 (if c comp2 is used): the following steps should be used to compensate the ic: step 1. set the cross over frequency at 1/10 of the switching frequency via r comp : step 2. set the zero f z1 at 1/4 of the cross over frequency. if r comp is less than 15k ? , the equation for c comp is: if r comp is limited to 15k ? , then the actual cross over frequency is 6.36 / (v out c out ). therefore: step 3. if the output capacitor?s esr is high enough to cause a zero at lower than 4 times the cross over frequency, an additional compensation capacitor c comp2 is required. the condition for using c comp2 is: and the proper value for c comp2 is: though c comp2 is unnecessary when the output capacitor has sufficiently low esr, a small value c comp2 such as 100pf may improve stability against pcb layout parasitic effects. table 1 shows some calculated results based on the compensation method above. table 1: typical compensation for different output voltages and output capacitors c : c comp2 is needed for high esr output capacitor. output cable resistance compensation to compensate for resistive voltage drop across the charger's output cable, the ACT4455 integrates a simple, user-programmable cable voltage drop compensation using the impedance at the fb pin. use the curve in figure 3 to choose the proper feedback resistance values for cable compensation. r fb1 is the high side resistor of voltage divider. c (8) comp vea out vdc g a i v 808 . 0 a = 2 g f = (10) out out out 2 p c v 2 i f = (11) comp1 comp 1 z c r 2 1 f = (12) comp2 comp 3 p c r 2 1 f = (13) ( ? ) out out 8 c v 10 48 . 0 = v 808 . 0 g g 10 f c v 2 r comp ea sw out out comp = (14) (f) comp 5 comp r 10 18 . 3 c ? = out out 6 comp c v 10 67 . 6 c ? = (f) (15) ? ? ? ? ? ? ? ? ? out out 6 esrcout v 012 . 0 , c 10 1 . 1 min r (16) ( ? ) (17) comp esrcout out 2 comp r r c c = v out c out r comp c comp c comp2 c 2.5v 47 f sp cap 5.6k ? 5.6nf none 3.3v 47 f sp cap 7.5k ? 4.7nf none 5v 47 f sp cap 11k ? 3.3nf none 2.5v 680 f/6.3v/30m ? 15k ? 3.3nf 220pf 3.3v 680 f/6.3v/30m ? 15k ? 3.3nf 220pf 5v 680 f/6.3v/30m ? 15k ? 4.7nf 220pf
ACT4455 rev 2, 21-nov-12 innovative power tm - 9 - www.active-semi.com copyright ? 2012 active-semi, inc. stability compensation cont?d in the case of high r fb1 used, the frequency compensation needs to be adjusted correspondingly. as show in figure 4, adding a capacitor in paralled with r fb1 or increasing the compensation capacitance at comp pin helps the system stability. figure 3: cable compensation at various resistor divider values figure 4: frequency compensation for high r fb1 pc board layout guidance when laying out the printed circuit board, the following checklist should be used to ensure proper operation of the ic. 1) arrange the power components to reduce the ac loop size consisting of c in , in pin, sw pin and the schottky diode. 2) place input decoupling c eramic capacitor c in as close to in pin as possible. c in is connected power gnd with vias or short and wide path. 3) return fb, comp and iset to signal gnd pin, and connect the signal gnd to power gnd at a single point for best noise immunity. connect exposed pad to power ground copper area with copper and vias. 4) use copper plane for power gnd for best heat dissipation and noise immunity. 5) place feedback resistor close to fb pin. 6) use short trace connecting hsb-c hsb -sw loop 7) sw pad is noisy node switching from v in to gnd. it should be isolated away from the rest of circuit for good emi and low noise operation. ACT4455-002 delta output voltage vs. output current delta output voltage (v) 0.6 0.5 0.4 0.3 0.2 0.1 0 output current (ma) 0 1000 2000 3000 4000 5000 v r f b 1 = 3 0 0 k r f b 1 = 2 7 0 k r f b 1 = 2 4 0 k r f b 1 = 2 0 0 k r f b 1 = 1 5 0 k r f b 1 = 1 0 0 k r f b1 = 5 1 k
ACT4455 rev 2, 21-nov-12 innovative power tm - 10 - www.active-semi.com copyright ? 2012 active-semi, inc. figure 5: typical application circuit for 5v/4.2a dual-output car charger table 2: bom list for 5v/4.2a dual-output car charger item reference description manufacturer qty 1 u1 ic ACT4455yh, sop-8ep active-semi 1 2 c1 capacitor, electrolytic, 150f/50v, 88mm koshin 1 3 c2 capacitor, electrolytic, 680f/10v, 811.5mm koshin 1 4 c3 capacitor, ceramic, 10f/50v, 1206, smd murata, tdk 1 5 c4 capacitor, ceramic, 4.7nf/25v, 0603, smd murata, tdk 1 12 l1 inductor, 18h, 5a, 20%, dip electronic-magnetics 1 13 d1 diode, schottky, 45v/10a, v10l45 vishay 1 14 r1, r2 chip resistor, 50m ? , 1206, 1% murata, tdk 2 15 r3 chip resistor, 9.7k ? , 0603, 1% murata, tdk 1 16 r4 chip resistor, 51k ? , 0603, 1% murata, tdk 1 17 r5 chip resistor, 15k ? , 0603, 5% murata, tdk 1 18 r6 chip resistor, 5.1 ? , 1206, 5% murata, tdk 1 7 c6 capacitor, ceramic, 2.2nf/25v, 0603, smd murata, tdk 1 6 c5 capacitor, ceramic, 220pf/25v , 0603, smd (optional) murata, tdk 1 8 c7 capacitor, ceramic, 1000pf/25v, 0603, smd (optional) murata, tdk 1 9 c8 capacitor, ceramic, 100pf/25v , 0603, smd (optional) murata, tdk 1 10 c9 capacitor, ceramic, 2200pf/25v, 0805, smd murata, tdk 1 11 c10 capacitor, ceramic, 2.2f/16v, 0603, smd murata, tdk 1
ACT4455 rev 2, 21-nov-12 innovative power tm - 11 - www.active-semi.com copyright ? 2012 active-semi, inc. typical performanc e characteristics (circuit of figure 7, r cs1 = r cs2 = 50m ? , l = 18h, c in = 150f, c out = 680f, t a = 25c, unless otherwise specified.) input voltage (v) 5 10 15 20 25 40 30 35 ACT4455-004 switching frequency vs. input voltage switching frequency (khz) 250 200 150 100 50 0 ACT4455-005 switching frequency vs. feedback voltage switching frequency (khz) 250 200 150 100 50 0 feedback voltage (mv) 0 0.2 0.4 0.6 0.8 1 ACT4455-007 standby current vs. input voltage standby current (a) 940 880 860 840 820 800 900 920 input voltage (v) 5 10 15 20 25 40 30 35 maximum peak current vs. duty cycle 9 8.5 8 7.5 7 6.5 6 pk current limit (ma) duty cycle 0.15 0.25 0.35 0.45 0.55 0.65 0.75 0.85 ACT4455-006 ACT4455-008 12 10 8 6 4 2 0 14 input current (ma) input voltage (v) 5 10 15 20 25 30 35 40 input current vs. input voltage at no load ACT4455-002 output current (v) efficiency (%) 0 1000 2000 3000 4000 5000 90 80 70 60 50 100 efficiency vs. load current v in = 24v v in = 12v v in = 32v
ACT4455 rev 2, 21-nov-12 innovative power tm - 12 - www.active-semi.com copyright ? 2012 active-semi, inc. typical performance ch aracteristics cont?d (circuit of figure 7, r cs1 = r cs2 = 50m ? , l = 18h, c in = 150f, c out = 680f, t a = 25c, unless otherwise specified.) vcs vs. temperature ACT4455-010 start up ACT4455-011 v out = 5v r lord = 1.5 ? i iset = 2a v in = 12v ch1: v out , 2v/div ch2: v in , 5v/div time: 1ms/div ch1 ch2 v in = 12v i out = 1a ch1: ripper, 50mv/div ch2: sw, 10v/div time: 2s/div sw vs. output ripples ACT4455-012 ch1 ch2 v in = 12v i out = 0a load step waveforms ACT4455-014 ch1 ch2 ch1: v out ripple, 200mv/div ch2: i out , 2a/div time: 400s/div v in = 12v i out1 = 0.08-2.1a i out2 = 0a ACT4455-009 input current at output short output input current (ma) 1.2 1 0.8 0.6 0.4 0.2 0 input voltage (v) 5 10 15 20 25 30 35 40 temperature (c) -25 0 25 50 75 100 125 150 vcs (v) 0.18 0.17 0.16 0.15 0.14 0.13 v cs1 v cs2 ch1: ripper, 50mv/div ch2: sw, 10v/div time: 2s/div sw vs. output ripples ACT4455-013 ch1 ch2 v in = 12v i out = 4.2a
ACT4455 rev 2, 21-nov-12 innovative power tm - 13 - www.active-semi.com copyright ? 2012 active-semi, inc. typical performance ch aracteristics cont?d (circuit of figure 7, r cs1 = r cs2 = 50m ? , l = 18h, c in = 150f, c out = 680f, t a = 25c, unless otherwise specified.) ACT4455-016 short circuit ch1 ch2 ch1: v out , 5v/div ch2: il, 2a/div ch3: sw, 10v/div time: 400s/div ch3 v in = 12v i out1 = 2.1a i out2 = 0a ACT4455-017 short circuit ch1 ch2 ch1: v out , 5v/div ch2: il, 2a/div ch3: sw, 10v/div time: 400s/div ch3 v in = 12v i out1 = 2.1a i out2 = 2.1a short circuit recovery ACT4455-018 ch1 ch2 ch1: v out , 2v/div ch2: il, 2a/div ch3: sw, 10v/div time: 1ms/div ch3 v in = 12v i out1 = 2.1a i out2 = 0a ACT4455-019 short circuit recovery ch1 ch2 ch1: v out , 2v/div ch2: il, 2a/div ch3: sw, 10v/div time: 1ms/div ch2 v in = 12v i out1 = 2.1a i out2 = 2.1a hiccup mode ACT4455-020 ch1 ch2 ch1: v out , 5v/div ch2: sw, 5v/div time: 1s/div v in = 12v i out1 = 2.1a i out2 = 2.1a ch1: v out ripper, 200mv/div ch2: i out , 2a/div time: 400s/div load step waveforms ACT4455-015 ch1 ch2 v in = 12v i out1 = 0-2.1a i out2 = 2.1a
ACT4455 rev 2, 21-nov-12 innovative power tm - 14 - www.active-semi.com copyright ? 2012 active-semi, inc. typical performance ch aracteristics cont?d (circuit of figure 7, r cs1 = r cs2 = 50m ? , l = 18h, c in = 150f, c out = 680f, t a = 25c, unless otherwise specified.) ACT4455-022 input surge ch1 ch2 ch1: v in , 10v/div ch2: v out ripper, 200mv/div time: 10ms/div v in = 8v-40v i out1 = 2.1a i out2 = 2.1a ACT4455-021 input surge v in = 24v v out = 5v i iset = 2.1a ch1 ch2 ch1: v in , 10v/div ch2: v out ripper, 200mv/div time: 10ms/div v in = 8v-40v i out1 = 2.1a i out2 = 0 a
ACT4455 rev 2, 21-nov-12 innovative power tm - 15 - www.active-semi.com copyright ? 2012 active-semi, inc. package outline sop-8ep package ou tline and dimensions symbol dimension in millimeters dimension in inches min max min max a 1.350 1.700 0.053 0.067 a1 0.000 0.100 0.000 0.004 a2 1.350 1.550 0.053 0.061 b 0.330 0.510 0.013 0.020 c 0.170 0.250 0.007 0.010 d 4.700 5.100 0.185 0.200 d1 3.202 3.402 0.126 0.134 e 3.800 4.000 0.150 0.157 e1 5.800 6.200 0.228 0.244 e2 2.313 2.513 0.091 0.099 e 1.270 typ 0.050 typ l 0.400 1.270 0.016 0.050 0 8 0 8 active-semi, inc. reserves the right to modify the circuitry or specifications without notice. user s should evaluate each product to make sure that it is suitable for their applicat ions. active-semi products are not intended or authorized for use as critical components in life-support dev ices or systems. active-semi, inc. does not assume any liability arising out of the use of any product or circuit described in this datasheet, nor does it convey any patent license. active-semi and its logo are trademarks of active-semi, inc. for more information on this and other products, contact sales@active-semi.com or visit http://www.active-semi.com . is a registered trademark of active-semi.

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