innovative power tm - 1 - www.active-semi.com copyright ? 2012 active-semi, inc. ACT4065A high input 2a step down converter features ? 2a output current ? up to 95% efficiency ? 6.0v to 30v input range ? 210khz switching frequency ? adjustable output voltage ? cycle-by-cycle current limit protection ? thermal shutdown protection ? frequency foldback at short circuit ? stability with wide range of capacitors, including low esr ceramic capacitors ? sop-8 package applications ? tft lcd monitors ? portable dvds ? car-powered or battery-powered equip- ments ? set-top boxes ? telecom power supplies ? dsl and cable modems and routers ? termination supplies general description the ACT4065A is a current-mode step-down dc/dc converter that generates up to 2a output current at 210khz switching frequency. the ACT4065A is highly efficient with peak effi- ciency at 95% when in operation. protection fea- tures include cycle-by-cycle current limit, thermal shutdown, and frequency foldback at short circuit. the ACT4065A is available in sop-8 package and requires very few external devices for operation. note: ACT4065A is the drop-in replacement for act4065 with feedback resistance value change. rev 0, 23-apr-12 ? ACT4065A-001 efficiency (%) load current (ma) 10 100 1000 10000 95 90 85 80 75 70 efficiency vs. load current v in = 12v v in = 24v v out = 5v
innovative power tm - 2 - www.active-semi.com copyright ? 2012 active-semi, inc. ACT4065A rev 0, 23-apr-12 ? ordering information part number temperature range package pins packing ACT4065Ash-t -40c to 85c sop-8 8 tape & reel pin configuration pin description sop-8 pin number pin name pin description 1 bs bootstrap. this pin acts as the positive rail for the high-side switch?s gate driver. con- nect a 10nf between this pin and sw. 2 in input supply. bypass this pin to g with a low esr capacitor. see input capacitor in application information section. 3 sw switch output. connect this pin to the switching end of the inductor. 4 g ground. 5 fb feedback input. the voltage at this pin is re gulated to 0.808v. connect to the resistor divider between output and ground to set output voltage. 6 comp compensation pin. see compensation techniques in application information section. 7 en enable input. when higher than 0.8v, this pin turns the ic on. when lower than 0.8v, this pin turn the ic off. out put voltage is discharged when the ic is off. this pin has a small internal pull-up current to a high leve l voltage when pin is not connected. do not allow en pin to exceed 6v. 8 n/c not connected.
innovative power tm - 3 - www.active-semi.com copyright ? 2012 active-semi, inc. ACT4065A rev 0, 23-apr-12 ? absolute maximum ratings 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. parameter value unit in supply voltage -0.3 to 30 v sw voltage -1 to v in + 1 v bs voltage v sw - 0.3 to v sw + 7 v en, fb, comp voltage -0.3 to 6 v continuous sw current internally limited a maximum power dissipation 0.76 w junction to ambient thermal resistance ( ja ) 105 c/w operating junction temperature -40 to 150 c storage temperature -55 to 150 c lead temperature (soldering, 10 sec) 300 c parameter symbol test cond itions min typ max unit input voltage v in v out = 5v, i load = 1a 6 30 v feedback voltage v fb v comp = 1.5v 0.792 0.808 0.824 v high-side switch on resistance r onh 0.22 ? low-side switch on resistance r onl 8 ? sw leakage v en = 0 1 10 a high-side switch current limit i lim duty = 50% 3.5 a comp to current limit transcon- ductance g comp 3.4 a/v error amplifier transconductance g ea i comp = 10a 650 a/v error amplifier dc gain a vea 4000 v/v switching frequency f sw 190 210 240 khz short circuit switching frequency v fb = 0 30 khz maximum duty cycle d max v fb = 0.7v 88 % minimum duty cycle v fb = 1.0v 0 % enable threshold voltage hyster esis = 0.1v 0.75 0.8 0.85 v enable pull-up current pin pulled up to 4.5v typically when left unconnected 4 a supply current in shutdown v en = 0 75 100 a ic supply current in operation v en = 3v, v fb = 1.0v 0.75 ma thermal shutdown temperature hysteresis = 10c 155 c electrical characteristics (v in = 12v, t j = 25 ? c, unless otherwise specified.)
innovative power tm - 4 - www.active-semi.com copyright ? 2012 active-semi, inc. ACT4065A rev 0, 23-apr-12 ? functional block diagram functional description as seen in, functional block diagram , the ac- t4065a is a current mode pulse width modulation (pwm) converter. the converter operates as fol- lows: a switching cycle starts when the rising edge of the oscillator clock output c auses 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 con- nected to in, the inductor current ramps up to store energy in its magnetic field. the inductor current level is measured by the current sense amplifier and added to the oscillator ramp signal. if the re- sulting summation is higher than the comp volt- age, the output of the pw m comparator goes high. when this happens or when oscillator clock output goes low, the high-side power switch turns off and the low-side power switch turns on. at this point, the sw side of the inductor swings to a diode volt- age below ground, causing the inductor current to decrease and magnetic energy to be transferred to the output. this state conti nues until the cycle starts again. the high-side power switch is driven by logic us- ing the bs bootstrap pin 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 the fb input and the internal 0.808v refer- ence. if fb is lower than the reference voltage, comp tends to go higher to increase current to the output. current limit happens when comp reaches its maximum clamp value of 2.0v. the oscillator normally sw itches at 210khz. how- ever, if the fb voltage is less than 0.6v, then the switching frequency decreases until it reaches a minimum of 30khz at v fb = 0.15v. shutdown control the ACT4065A has an enable input en for turning the ic on or off. when en is less than 0.7v, the ic is in 8 a low current shutdown mode . when en is higher than 0.8v, the ic is in normal operation mode. en is internally pulled up with a 4 a current source and can be left unconnected for always-on operation. en should never be directly connected to in. thermal shutdown the ACT4065A automatically turns off when its junction temperature exceeds 155c.
innovative power tm - 5 - www.active-semi.com copyright ? 2012 active-semi, inc. ACT4065A rev 0, 23-apr-12 ? 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 recom- mended. since a 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 shortest possible traces. in the case of tantalum or electr olytic types, they can be further away if a small parallel 0.1f ceramic ca- pacitor 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 resistance of the output capacitor, f sw is the switching frequency, l is the inductor value, c out is the output capacitance, r esr is very small and does not contribute to the ripple. therefore, a lower ca- pacitance value can be used for ceramic type. in the case of tantalum or electr olytic type, 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 type, typically choose a capacitance of about 22f. for tantalum or electrolytic type, choose a capacitor with less than 50m ? esr. rectifier diode use a schotky diode as the rectifier to conduct cur- rent when the high-side po wer switch is off. the schottky diode must have current rating higher than the maximum output current and the reverse volt- age rating higher than the maximum input voltage. applications information output voltage setting figure 1: output voltage setting figure 1 shows the connections for setting the out- put voltage. select the pr oper ratio of the two feed- back resistors r fb1 and r fb2 based on the output voltage. typically, use r fb2 10k ? and determine r fb1 from the output voltage: inductor selection the inductor maintains a continuous current to the output load. this inductor current has a ripple that is dependent on the inductance value: higher induc- tance 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 outmax is the maximum output 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 output current. with this inductor value (table 1), the peak inductor current is i out (1 + k ripple / 2). make sure that this peak inductor current is less that the 3a current limit. finally, select the inductor core size so that it does not saturate at 3a. table 1. typical inductor values v out 1.5v 1.8v 2.5v 3.3v 5v l 10 h 10 h 15 h 22 h 33 h (1) ? ? ? ? ? ? ? = 1 v 808 . 0 v r r out 2 fb 1 fb (2) () ripple outmax sw in out in out k i f v v v v l ? = ? ? ? ? ? ? ? ? + = out 2 sw in esr ripple outmax ripple lc f 28 v r k i v (3)
innovative power tm - 6 - www.active-semi.com copyright ? 2012 active-semi, inc. ACT4065A rev 0, 23-apr-12 ? the feedback system of the ic is stabilized by the components at 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): follow the following steps to compensate the ic: step 1. set the cross over frequency at 1/5 of the switching frequency via r comp : but limit r comp to 15k ? maximum. 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 6.1/ (v out c out ). therefore: step 3. if the output capacitors 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 required. the condition for using c comp2 is: and the proper value for c comp2 is: though c comp2 is unnecessary when the output ca- pacitor 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 2: typical compensation for different output volt- ages and output capacitors figure 3 shows a sample ACT4065A application circuit generating a 2.5v/2a output. v out c out r comp c comp c comp2 c 2.5v 22 f ceramic 12k ? 2.2nf none 3.3v 22 f ceramic 12k ? 1.5nf none 5v 22 f ceramic 15k ? 2.2nf none 2.5v 47 f sp cap 15k ? 1.5nf none 3.3v 47 f sp cap 15k ? 1.8nf none 5v 47 f sp cap 15k ? 2.7nf none 2.5v 470f/6.3v/30m ? 15k ? 1.5nf 47pf 3.3v 470f/6.3v/30m ? 15k ? 2.2nf 47pf 5v 470f/10v/30m ? 15k ? 2.7nf 47pf c : c comp2 is needed only for high esr output capacitors c : c comp2 is needed only for high esr output capacitors stability compensation figure 2: stability compensation comp vea out vdc g a i v 808 . 0 a = (4) comp vea ea 1 p c a 2 g f = (5) out out out 2 p c v 2 i f = (6) comp comp 1 z c r 2 1 f = (7) comp2 comp 3 p c r 2 1 f = (8) (9) v 808 . 0 g g 10 f c v 2 r comp ea sw out out comp = ( ? ) (10) (f) (11) (f) (12) ? ? ? ? ? ? ? ? ? out out 6 esrout v 012 . 0 , c 10 1 . 1 min r ( ? ) comp esrout out 2 comp r r c c = (13) out out 8 c v 10 75 . 2 = out out 5 comp c v 10 2 . 1 c = comp 5 comp r 10 8 . 1 c ? =
innovative power tm - 7 - www.active-semi.com copyright ? 2012 active-semi, inc. ACT4065A rev 0, 23-apr-12 ? figure 3: typical application circuit for 5v/2a car charger table 3: bom list for 5v/2a car charger item reference description manufacturer qty 1 u1 ic, ACT4065Ash, sop-8ep active-semi 1 2 c1 capacitor, electrolytic, 47f/35v, 6.3 7mm murata, tdk 1 3 c2 capacitor, ceramic, 10f/35v, 1210, 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 7 c6 capacitor, ceramic, 1f/10v, 0603, smd murata, tdk 1 8 l1 inductor,33h, 3.0a sumida 1 9 d1 diode, schottky, 40v/2a, sb240 diodes 1 10 r1 chip resistor, 52k ? , 0603, 1% murata, tdk 1 11 r3 chip resistor, 8.2k ? , 0603, 5% murata, tdk 1 12 r2 chip resistor, 10k ? , 0603, 1% murata, tdk 1
innovative power tm - 8 - www.active-semi.com copyright ? 2012 active-semi, inc. ACT4065A rev 0, 23-apr-12 ? typical performanc e characteristics (circuit of figure 3, unless otherwise specified .) input voltage (v) 10 15 20 25 30 8 6 ACT4065A-002 switching frequency vs. input voltage switching frequency (khz) 250 230 210 190 170 150 130 110 ACT4065A-003 switching frequency vs. feedback voltage switching frequency (khz) 260 210 160 110 60 10 feedback voltage (mv) 0 100 200 300 400 500 600 700 800 900 ACT4065A-004 maximum peak current vs. duty cycle maximum cc current (ma) 3.8 3.4 3.3 3.2 3.1 3 3.7 3.6 3.5 duty cycle 20 30 40 50 60 70 ACT4065A-005 start up with en v in = 12v v 0ut = 5v i load = 2a ch1 ch2 ch1: en, 1v/div ch2: v out , 1v/div time: 10ms/div
innovative power tm - 9 - www.active-semi.com copyright ? 2012 active-semi, inc. ACT4065A rev 0, 23-apr-12 ? 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 4.780 5.000 0.188 0.197 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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