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innovative power tm - 1 - www.active-semi.com copyright ? 2012 active-semi, inc. features ? 10v-30v input voltage ? 40v transparent input voltage surge ? up to 1.25a constant output current ? output voltage up to 12v ? good emc performance on single layer pcb ? patent pending activecc constant current control ? integrated current control improves efficiency, lowers cost, and reduces component count ? resistor programmable outputs ? current limit from 500ma to 1250ma patented cable compensation from dc cable compensation from 0 ? to 0.5 ? ? 2% feedback voltage accuracy ? up to 90% efficiency ? 125khz switching frequency eases emi design ? advanced feature set ? integrated soft start ? thermal shutdown ? secondary cycle-by-cycle current limit ? protection against shorted iset pin ? sop-8 package applications ? car charger ? rechargeable portable devices ? general-purpose cc/cv power supply general description act4501 is a dedicated cost-effective dc-dc converter for 5v/1a car charger applications with a wide input voltage and high efficiency. the converter operates in either cv (constant output voltage) mode or cc (constant output current) mode. act4501 provides up to 1.25a output current at 125khz switching frequency. activecc is a patent-pending control scheme to achieve high accuracy sensorless constant current control. activecc eliminates the expensive, high accuracy current sense resistor, making it ideal for battery charging applications and high-brightness led drive for architectural lighting. the act4501 achieves higher efficiency than traditional constant current switching regulators by eliminating the sense resistor and its associated power loss. protection features include cycle-by-cycle current limit, thermal shutdown, and frequency foldback at short circuit. the devices are available in a sop-8 package and require very few external devices for operation. act4501 1.25a cc/cv step-down dc/dc converter rev 2, 14-nov-12 efficiency (%) act4501-001 load current (ma) 10 100 1000 10000 1 100 90 80 70 60 50 40 efficiency vs. load current v in = 12v v out = 5v v in = 24v v in = 16v
act4501 rev 2, 14-nov-12 innovative power tm - 2 - www.active-semi.com copyright ? 2012 active-semi, inc. ordering information part number temperature range package pins packing ACT4501SH-T -40c to 85c sop-8 8 tape & reel pin configuration pin descriptions pin name description 1 hsb high voltage bias pin. this provides po wer to the internal high-side mosfet gate driver. connect a 10nf capacitor from hsb pin to sw pin. 2 in power supply input. bypass this pin with a 10f ceramic capacitor to gnd, placed as close to the ic as possible. 3 sw power switching output to external inductor. 4 gnd ground. connect this pin to a large pcb copper area for best heat dissipation. return fb, comp, and iset to this gnd, and con nect this gnd to power gnd at a single point for best noise immunity. 5 fb feedback input. the voltage at this pin is re gulated to 0.808v. connect to the resistor divider between output and gnd to set the output voltage. 6 comp error amplifier output. this pi n is used to compensate the converter. 7 en enable input. en is pulled up to 5v with a 4 a current, and contains a precise 0.8v logic threshold. drive this pin to a logic-high or leave unconnected to enable the ic. drive to a logic-low to disable the ic and enter shutdown mode. 8 iset output current setting pin. connect a resi stor from iset to gnd to program the output current. sop-8
act4501 rev 2, 14-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 40 v sw to gnd -1 to v in + 1 v hsb to gnd v sw - 0.3 to v sw + 7 v fb, en, iset, comp to gnd -0.3 to + 6 v junction to ambien t thermal resistance 105 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.
act4501 rev 2, 14-nov-12 innovative power tm - 4 - www.active-semi.com copyright ? 2012 active-semi, inc. parameter test conditions min typ max unit input voltage 10 30 v v in uvlo turn-on voltage input vo ltage rising 9.05 9.35 9.65 v v in uvlo hysteresis input voltage falling 1.1 v standby supply current v en = 3v, v fb = 1v 1.0 ma v en = 3v, v o = 5v, no load 2.5 ma shutdown supply current v en = 0v 75 100 a feedback voltage 792 808 824 mv internal soft-start time 800 s error amplifier transconductance v fb = v comp = 0.8v, ? i comp = 10a 650 a/v error amplifier dc gain 4000 v/v switching frequency v fb = 0.808v 115 125 130 khz foldback switching frequency v fb = 0v 10 16 38 khz maximum duty cycle 85 88 93 % minimum on-time 800 ns comp to current limit transconductance v comp = 1.2v 1.75 a/v switch current limit duty = 50% 1.8 a slope compensation duty = d max 0.75 a iset voltage 1 v iset to iout dc room temp current gain iout / iset 25000 a/a en threshold voltage en pin rising 0.75 0.8 0.85 v en hysteresis en pin falling 80 mv en internal pull-up current 4 a high-side switch on-resistance 0.3 ? sw off leakage current v en = v sw = 0v 1 10 a thermal shutdown temperature temperature rising 155 c cc controller dc accuracy r iset = 19.6k ? , v in = 10v - 30v 1020 1200 1380 ma electrical characteristics (v in = 14v, t a = 25c, unless otherwise specified.)
act4501 rev 2, 14-nov-12 innovative power tm - 5 - www.active-semi.com copyright ? 2012 active-semi, inc. functional block diagram functional description cv/cc loop regulation as seen in functional block diagram , the act4501 is a peak current mode pulse width modulation (pwm) converter with cc and cv control. the converter operates as follows: 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 in the magnetic field. 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 oscillator clock output goes low, the high-side power switch turns off. at this point, the sw side of the inductor swings to a diode voltage below ground, 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 the internal 0.808v reference. if fb is lower than the reference voltage, comp tends to go higher to increase current to the ou tput. output current will increase until it reaches the cc limit set by the iset resistor. at this point, t he device will transition from regulating output voltage to regulating output current, and the output voltage will drop with increasing load. the oscillator normally switches at 125khz. however, if fb voltage is less than 0.6v, then the switching frequency decreases until it reaches a typical value of 20khz at v fb = 0.15v. enable pin the act4501 has an enable input en for turning the ic on or off. the en pin contains a precision 0.8v comparator with 75mv hysteresis and a 4a pull-up current source. the comparator can be used with a resistor divider from v in to program a startup voltage higher than the normal uvlo value. it can be used with a resistor divider from v out to disable charging of a deeply discharged battery, or it can be used with a resistor divider containing a thermistor to provide a temperature-dependent shutoff protection for over temperature battery. the thermistor should be thermally coupled to the battery pack for this usage. if left floating, the en pin will be pulled up to roughly 5v by the internal 4a current source. it can be driven from standard logic signals greater than 0.8v, or driven with open-drain logic to provide digital on/off control. thermal shutdown the act4501 disables switching when its junction temperature exceeds 155c and resumes when the temperature has dropped by 20c. en fb bandgap, regulator, & shutdown control + - oscillator v ref = 0.808v emi control pwm controller cc control sw hsb in avin pvin comp iset v ref = 0.808v
act4501 rev 2, 14-nov-12 innovative power tm - 6 - www.active-semi.com copyright ? 2012 active-semi, inc. ? ? ? ? ? ? ? = 1 v 808 . 0 v r r out 2 fb 1 fb (1) 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: cc current setting act4501 constant current value is set by a resistor connected between the iset pin and gnd. the cc output current is linearly proportional to the current flowing out of the iset pin. the voltage at iset is roughly 1v and the current gain from iset to output is roughly 25000 (25ma/1a). to determine the proper resistor for a desired current, please refer to figure 2 below. figure 2: curve for programming output cc current 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: l lim is the internal current limit, which is typically 2.5a, as shown in electrical characteristics table. external high voltage bias diode it is recommended that an external high voltage bias diode be added when the system has a 5v fixed input or the power supply generates a 5v output. this helps improve the efficiency of the regulator. the high voltage bias diode can be a low cost one such as in4148 or bat54. output current vs. r iset act4501-002 1800 1600 1200 1000 800 600 400 200 1400 0 output current (ma) r iset (k ? ) 0 10 20 30 40 50 60 80 90 70 (2) ( ) ripple loadmax sw in out in out k i f v v v v l _ = (3) ( ) sw in out in out pk lpk f v l v v v i = _ _ pk lpk loadmax lpk _ i 2 1 i i + = (4) (5) pk lpk lim outmax i 2 1 i i _ _ =
act4501 rev 2, 14-nov-12 innovative power tm - 7 - www.active-semi.com copyright ? 2012 active-semi, inc. (6) esr ripple outmax ripple r k i v = out 2 sw in lc f 28 v + applications information cont?d figure 3: external high voltage bias diode this diode is also recommended for high duty cycle operation and high output voltage applications. 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 cerami c output capacitors, r esr is very small and does not contribute to the ripple. therefore, a lower capacitance value can be used for ceramic type. in the case of tantalum or electrolytic capacitors, the ripple is dominated by r esr multiplied by the ripple 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.
act4501 rev 2, 14-nov-12 innovative power tm - 8 - www.active-semi.com copyright ? 2012 active-semi, inc. v out c out r comp c comp c comp2 c 2.5v 47 f sp cap 25k ? 1.5nf none 3.3v 47 f sp cap 25k ? 1.8nf none 5v 47 f sp cap 25k ? 2.2nf none 2.5v 220 f/6.3v/30m ? 25k ? 1.5nf 100pf 3.3v 220 f/6.3v/30m ? 25k ? 1.8nf 100pf 5v 220 f/6.3v/30m ? 25k ? 2.2nf 100pf ? ? ? ? ? ? ? ? ? out out 6 esrcout v 012 . 0 , c 10 1 . 1 min r (15) ( ? ) (16) comp esrcout out 2 comp r r c c = out out 5 comp c v 10 2 . 1 c ? = (f) (14) (13) (f) comp 5 comp r 10 8 . 1 c ? = (12) ( ? ) out out 8 c v 10 75 . 2 = v 808 . 0 g g 10 f c v 2 r comp ea sw out out comp = (11) comp2 comp 3 p c r 2 1 f = (10) comp2 comp 1 z c r 2 1 f = (9) out out out 2 p c v 2 i f = (8) comp vea ea 1 p c a 2 g f = (7) comp vea out vdc g a i v 808 . 0 a = stability compensation figure 4: 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 3. 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 3.4 / (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 2 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. c comp2 47pf is recommended. cc loop stability the constant-current control loop is internally compensated over the 400ma-1500ma output range. no additional external compensation is required to stabilize the cc current. output cable resistance compensation to compensate for resistive voltage drop across the charger's output cable, the act4501 integrates a simple, user-programmable cable voltage drop compensation using the impedance at the fb pin. use the curve in figure 4 to choose the proper
act4501 rev 2, 14-nov-12 innovative power tm - 9 - www.active-semi.com copyright ? 2012 active-semi, inc. stability compensation cont?d feedback resistance values for cable compensation. r fb1 is the high side resistor of voltage divider. in the case of high r fb1 used, the frequency compensation needs to be adjusted correspondingly. as show in figure 6, adding a capacitor in paralled with r fb1 or increasing the compensation capacitance at comp pin helps the system stability. figure 5: cable compensation at various resistor divider values figure 6: 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. 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 figure 7 shows an example of pcb layout. figure 8 gives one typical car charger application schematics and associated bom list. figure 7: pcb layout act4501-003 0.3 0.25 0.2 0.15 0.1 0.05 0 delta output voltage (v) output current (ma) 0 200 400 600 800 1000 delta output voltage vs. output current v in = 12v v 0ut = 5v 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 = 100k r f b 1 = 5 1 k
act4501 rev 2, 14-nov-12 innovative power tm - 10 - www.active-semi.com copyright ? 2012 active-semi, inc. figure 8: typical application circuit for 5v/1a car charger table 2: bom list for 5v/1a car charger item reference description manufacturer qty 1 u1 ic, act4501sh, sop-8 active-semi 1 2 c1 capacitor, electrolytic, 47f/50v, 6.3 7mm murata, tdk 1 3 c2 capacitor, ceramic, 2.2f/50v, 1206, smd murata, tdk 1 4 c3 capacitor, ceramic, 2.2nf/6.3v, 0603, smd murata, tdk 1 5 c4 capacitor, ceramic, 10nf/50v, 0603, smd murata, tdk 1 6 c5 capacitor, electrolytic, 100f/10v, 6.3 7mm murata, tdk 1 9 l1 82h, 1.4a, 20%, smd cdrh125-820m sumida 1 10 d1 diode, schottky, 40v/2a, b240a, sma diodes 1 12 r1 chip resistor, 20k ? , 0603, 1% murata, tdk 1 13 r2 chip resistor, 52k ? , 0603, 1% murata, tdk 1 14 r3 chip resistor, 25k ? , 0603, 5% murata, tdk 1 15 r4 chip resistor, 10k ? , 0603, 1% murata, tdk 1 11 d2 diode, 75v/150ma, ll4148 good-ark 1 7 c6 capacitor, ceramic, 1f/10v, 0603, smd murata, tdk 1 8 c7 (optional) capacitor, ceramic, 100pf/6.3v, 0603 murata, tdk 1
act4501 rev 2, 14-nov-12 innovative power tm - 11 - www.active-semi.com copyright ? 2012 active-semi, inc. typical performanc e characteristics input voltage (v) 5 10 15 20 25 30 35 act4501-005 switching frequency vs. input voltage switching frequency (khz) 125 120 115 110 105 100 130 act4501-006 switching frequency vs. feedback voltage switching frequency (khz) 100 80 60 40 20 0 120 140 feedback voltage (v) 0 0.2 0.4 0.6 0.8 1 act4501-007 1000 900 800 700 600 500 400 cc current (ma) temperature (c) -40 -25 0 25 50 75 80 act4501-008 cc current vs. input voltage cc current (ma) 1000 900 800 700 600 500 400 act4501-009 peak current limit vs. duty cycle maximum cc current (ma) 2500 2250 2000 1750 1500 1250 1000 750 500 250 0 duty cycle 0 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 cc current vs. temperature input voltage (v) 10 12 18 24 30 v in = 12v r iset = 33k ? r iset = 33k ? (circuit of figure 7, i iset = 1a, l = 82h, c in = 10f, c out = 22f, t a = 25c, unless otherwise specified.) efficiency (%) act4501-004 load current (ma) 10 100 1000 10000 1 100 90 80 70 60 50 40 efficiency vs. load current v in = 12v v out = 5v v in = 24v v in = 16v
act4501 rev 2, 14-nov-12 innovative power tm - 12 - www.active-semi.com copyright ? 2012 active-semi, inc. typical performance ch aracteristics cont?d act4501-011 standby supply current vs. input voltage input current (ma) 5 4 3 2 1 0 act4501-012 reverse leakage current (v in floating) reverse leakage current (a) 100 80 60 40 20 0 v out (v) 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 input voltage (v) 5 15 25 35 sw vs. output voltage ripples act4501-013 v in = 12v v 0ut = 5v i 0ut = 1a ch1 ch2 ch1: v out , 50mv/div ch2: v sw , 5v/div time: 4s/div (circuit of figure 7, i iset = 1a, l = 82h, c in = 10f, c out = 22f, t a = 25c, unless otherwise specified.) shutdown current vs. input voltage (en pulled low) act4501-010 140 120 100 80 60 40 20 0 shutdown current (a) input voltage (v) 5 10 15 20 25 30 sw vs. output voltage ripples act4501-014 v in = 24v v 0ut = 5v i 0ut = 1a ch1 ch2 ch1: v out , 50mv/div ch2: v sw , 10v/div time: 4s/div act4501-015 start up with en v in = 12v v 0ut = 5v i 0ut = 1a ch1 ch2 ch1: en, 1v/div ch2: v out , 1v/div time: 2ms/div
act4501 rev 2, 14-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, i iset = 1a, l = 82h, c in = 10f, c out = 22f, t a = 25c, unless otherwise specified.) load step waveforms act4501-017 v in = 12v v 0ut = 5v i iset = 1a ch1 ch2 ch1: v out , 200mv/div ch2: i out , 1a/div time: 400 s/div act4501-018 load step waveforms v in = 24v v 0ut = 5v i iset = 1a ch1 ch2 ch1: v out , 200mv/div ch2: i out , 1a/div time: 400 s/div act4501-016 start up with en ch1 ch2 ch1: en, 1v/div ch2: v out , 1v/div time: 2ms/div v in = 24v v 0ut = 5v i iset = 1a
act4501 rev 2, 14-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, i iset = 1a, l = 82h, c in = 10f, c out = 22f, t a = 25c, unless otherwise specified.) act4501-022 short circuit recovery v in = 24v v 0ut = 5v i iset = 1a ch1 ch2 ch3 ch1: v out , 2v/div ch2: i out , 1a/div ch3: v sw , 20v/div time: 40s/div act4501-020 short circuit recovery v in = 12v v 0ut = 5v i iset = 1a ch1 ch2 ch1: v out , 2v/div ch2: i out , 1a/div ch3: v sw , 10v/div time: 40s/div ch3 short circuit act4501-019 v in = 12v v 0ut = 5v i iset = 1a ch1 ch2 ch1: v out , 2v/div ch2: i out , 1a/div ch3: v sw , 10v/div time: 40s/div ch3 act4501-021 short circuit v in = 24v v 0ut = 5v i iset = 1a ch1 ch2 ch1: v out , 2v/div ch2: i out , 1a/div ch3: v sw , 20v/div time: 40s/div ch3
act4501 rev 2, 14-nov-12 innovative power tm - 15 - www.active-semi.com copyright ? 2012 active-semi, inc. package outline sop-8 package outline and dimensions symbol dimension in millimeters dimension in inches min max min max a 1.350 1.750 0.053 0.069 a1 0.100 0.250 0.004 0.010 a2 1.350 1.550 0.053 0.061 b 0.330 0.510 0.013 0.020 c 0.190 0.250 0.007 0.010 d 4.700 5.100 0.185 0.201 e 3.800 4.000 0.150 0.157 e1 5.800 6.300 0.228 0.248 e 1.270 typ 0.050 typ l 0.400 1.270 0.016 0.050 0 8 0 8 a a2 a1 l ? c e d e1 b e 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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