innovative power tm - 1 - www.active-semi.com copyright ? 2012 active-semi, inc. typical application circuit act4070b rev 0, 23-apr-12 wide input 3a step down converter features ? 3a output current ? up to 95% efficiency ? 6.5v to 30v input range ? 100a shutdown supply current ? 4ma standby input current ? 300khz switching frequency ? output voltage up to 12v ? cycle-by-cycle current limit protection ? thermal shutdown protection ? internal soft start function ? frequency fold back at short circuit ? stability with wide ra nge of capacitors ? including low esr ceramic capacitors ? sop-8/ep (exposed pad) package applications ? tft lcd monitors or televisions and hdtv ? portable dvd players ? car-powered or battery-powered equipment ? set-top boxes ? telecom power supplies ? dsl and cable modems and routers general description act4070b is a wide input voltage step-down dc/dc converter that provides up to 3a output cur- rent at 300khz switching frequency. act4070b is a replacement part for act4070 with advanced fea- tures such as lower standby current and higher light load efficiency. act4070b can be dropped into act4070 socket with only feedback resistance value changed. act4070b?s protection feat ures include cycle-by- cycle current limit, thermal shutdown, and fre- quency foldback at over current and short circuit. the devices are available in a sop-8ep package and require very few external devices for operation. note: ? act4070b is the replacement part for act4070. act4070b-001 efficiency (%) load current (ma) 10 100 1000 10000 1 100 80 60 40 20 0 efficiency vs. load current v in = 12v v out = 5v v in = 24v
act4070b rev 0, 23-apr-12 innovative power tm - 2 - www.active-semi.com copyright ? 2012 active-semi, inc. ordering information part number temperature range package pins packing act4070byh -40c to 85c sop-8/ep 8 tube ACT4070BYH-T -40c to 85c sop-8/ep 8 tape & reel pin configuration pin description pin number pin name pin description 1 bs bootstrap. this pin acts as the positive ra il for the high-side switch?s gate driver. connect a 10nf between this pin and sw. 2 in input supply. bypass this pin to gnd with a low esr capacitor. see input ca- pacitor in application information section. 3 sw switch output. connect this pin to the switching end of the inductor. 4 gnd ground. 5 fb feedback input. the voltage at this pin is regulated to 0.808v. connect to the resistor divider between output and ground to set output voltage. 6 comp compensation pin. see compensation technique in application information sec- tion. 7 en enable input. when higher than 1.6v, this pin turns the ic on. when lower than 1.5v, this pin turns the ic off. this pin has a small internal pull up current to a high level voltage when pin is not connected. 8 n/c not connected. ep ep exposed pad shown as dashed box. the exposed thermal pad should be con- nected to board ground plane and pin 4. the ground plane should include a large exposed copper pad under the package for thermal dissipation (see package out- line). the leads and exposed pad should be flush with the board, without offset from the board surface. sop-8/ep
act4070b rev 0, 23-apr-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 + 34 v en to gnd -0.3 to v in + 0.3 v bs to sw -0.3 to + 7 v fb, comp to gnd -0.3 to 6 v continuous sw current internally limited a junction to ambient thermal resistance ( ja ) 46 c/w maximum power dissipation 1.8 w operating junction temperature -40 to 150 c storage temperature -55 to 150 c lead temperature (soldering, 10 sec) 300 c sw to gnd -1 to v in + 1 v electrical characteristics (v in = 12v, t a = 25c, unless otherwise specified.) parameter symbol test cond itions min typ max unit input voltage v in v out = 2.5v, i load = 0a to 3a 6.5 30 v feedback voltage v fb 0.792 0.808 0.824 v high-side switch on resistance r onh 130 m ? low-side switch on resistance r onl 7.9 ? sw leakage v en = 0, v in = 12v, v sw = 0v 1 10 a high-side switch peak current limit i lim duty cycle = 50% 3.7 a comp to current limit transcon- ductance g comp i load / i comp 5.25 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 250 300 330 khz short circuit switching frequency v fb = 0v 44 khz maximum duty cycle d max 88 % minimum on time 200 ns enable threshold voltage hyster esis = 0.1v 1.47 1.6 1.73 v enable pull up current pin pulled up to v in when left uncon- nected 4 a supply current in shutdown v en = 0 75 115 a ic supply current in operation v fb = 1.2v, not switching 0.675 1 ma thermal shutdown temperature hysteresis = 20c 150 c v in uvlo turn-on voltage input voltage rising 5.5 v 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.
act4070b rev 0, 23-apr-12 innovative power tm - 4 - www.active-semi.com copyright ? 2012 active-semi, inc. functional block diagram functional description as seen in the functional block diagram , the act4070b is a current mode pulse width modula- tion (pwm) converter. the converter operates as follows: a switching cycle starts when the rising edge of the oscillator clock output causes 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 the its magnetic fi eld. the inductor current level is measured by the current sense amplifier and added to the oscillator ramp signal. if the result- ing 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 and the low-side power switch turns on. at this point, the sw side of the inductor swings to a diode voltage below ground, causing the inductor current to de- crease and magnetic energy to be transferred to output. this state continue s until the cycle starts again. the high-side power switch is driven by logic using bs bootstrap pin as the positive rail. this pin is charged to v sw + 6v 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 refer- ence. if fb is lower than the reference voltage, comp tends to go higher to increase current to the output. the oscillator normally switches at 300khz. how- ever, if fb voltage is less than 0.6v, then the switching frequency decreases until it reaches a typical value of 36khz at v fb = 0v. shutdown control the act4070b has an enable input en for turning the ic on or off. when en is less than 1.5v, the ic is in 100 a low current shutdown mode and output is discharged through the low-side power switch. when en is higher than 1.6v, 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. thermal shutdown the act4070b automatically turns off when its junction temperature exceeds 160c and then re- starts once the temperature falls to 150c.
act4070b rev 0, 23-apr-12 innovative power tm - 5 - www.active-semi.com copyright ? 2012 active-semi, inc. 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: 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: v out 1.5v 1.8v 2.5v 3.3v 5v l 6.8 h 6.8 h 8.5 h 15 h 15 h ? ? ? ? ? ? = 1 v 808 . 0 v r r out fb2 1 fb - () ripple outmax sw in out in out k i f v v v v l - = 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 large current flows in and out of this capacitor during switching, its esr also affects effi- ciency. 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 traces possible. 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. 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 in the inductor value, 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. there- fore, a lower capacitance value can be used for ce- ramic type. in the case of tantalum or electrolytic 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, ty pically choose a capaci- tance of about 22f. for tant alum or electrolytic type, choose a capacitor with less than 50m ? esr. out 2 sw in ripple ripple outmax ripple lc f 28 v r k i v + = rectifier diode use a schottky 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. output capacitor inductor selection table 1: typical inductor values input capacitor applications information 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 = between 20% and 30% to correspond to the peak-to-peak ripple current being a percentage 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 5a current limit. finally, select the induct or core size so that it does not saturate at 5a. (1) (2) (3) figure 1: output voltage setting
act4070b rev 0, 23-apr-12 innovative power tm - 6 - www.active-semi.com copyright ? 2012 active-semi, inc. stability compensation the feedback system of t he 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: comp vea out vdc g a i v 808 . 0 a = the dominant pole p1 is due to c comp : comp vea ea 1 p c a 2 g f = comp comp 1 z c r 2 1 f = and finally, the third pole is due to r comp and c comp2 (if c comp2 is used): comp2 comp 3 p c r 2 1 f = follow the following steps to compensate the ic: step 1. set the cross over frequency at 1/10 of the switching frequency via r comp : but limit r comp to 15k ? maximum. out out out 2 p c v 2 i f = the first zero z1 is due to r comp and c comp : the second pole p2 is the output pole: 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 4.8/(v out c out ). therefore: out out 6 comp c v 10 x 45 . 6 c ? = 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 us- ing c comp2 is: and the proper value for c comp2 is: comp esrout out comp r r c c = though c comp2 is unnecessary when the output capacitor has sufficiently low esr, a small value c comp2 such as 220pf 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 voltages and output capacitors v out c out r comp c comp c comp2 c 1.8v 22 f ceramic 4k ? 3.3nf 220pf 2.5v 22 f ceramic 5.6k ? 3.3nf 220pf 5v 22 f ceramic 12k ? 1.5nf 220pf 1.8v 100 f sp cap 15k ? 1.5nf 220pf 2.5v 100 f sp cap 15k ? 2.2nf 220pf 5v 100 f sp cap 15k ? 4.7nf 220pf figure 3 shows a sample act4070b application circuit generating a 2.5v/3a output. (11) (13) (4) (5) (6) (7) (8) out out 7 comp ea sw out out comp c v 10 x 12 . 5 v 808 . 0 g g 10 f c v 2 r = = ( ? ) (9) v 006 . 0 , c 10 x 77 . 1 min r out out 6 esrout ? ? ? ? ? ? ? ? ? (12) ( ? ) comp 5 comp r 10 x 83 . 2 c = (10) (f) (f) c : c comp2 is needed for board parasitic and high esr output capacitor. c : c comp2 is needed only for high esr output capacitor figure 2: stability compensation c
act4070b rev 0, 23-apr-12 innovative power tm - 7 - www.active-semi.com copyright ? 2012 active-semi, inc. figure 3: act4070b 5v/3a output application c table 3: bom list for 5v/3a car charger item reference description manufacturer qty 1 u1 ic, act4070b, sop-8ep active-semi 1 2 c1 capacitor, ceramic, 10f/50v, 1206, smd murata, tdk 1 3 c2 capacitor, ceramic, 4.7nf/25v, 0603, smd murata, tdk 1 4 c3 capacitor, ceramic, 10nf/25v, 0603, smd murata, tdk 1 5 c4 capacitor, ceramic, 22f/10v, 0805, smd murata, tdk 1 6 l1 inductor, 15h, 4a, 20%, smd sunlord 1 7 d1 diode, schottky, 40v/3a, sk34 diodes 1 8 r1 chip resistor, 51k ? , 0603, 1% murata, tdk 1 9 r2 chip resistor, 9.76k ? , 0603, 1% murata, tdk 1 10 r3 chip resistor, 12k ? , 0603, 5% murata, tdk 1
act4070b rev 0, 23-apr-12 innovative power tm - 8 - www.active-semi.com copyright ? 2012 active-semi, inc. typical performanc e characteristics (circuit of figure 3, unless otherwise specified.) act4070b-002 efficiency (%) load current (ma) 10 100 1000 10000 1 100 80 60 40 20 0 efficiency vs. load current v in = 12v v out = 5v v in = 24v shutdown current vs. input voltage act4070b-003 shutdown current (a) 100 80 60 40 20 0 120 input voltage (v) 10 15 20 30 5 25 load transient response load transient response act4070b-004 act4070b-005 ch1 ch1 ch2 ch2 v in = 24v v 0ut = 5v v in = 12v v 0ut = 5v ch1: i out , 1a/div ch2: v out , 200mv/div time: 400s/div ch1: i out , 1a/div ch2: v out , 200mv/div time: 400s/div act4070b-006 maximum peak current vs. duty cycle maximum cc current (a) 4.5 4.2 3.9 3.6 3.3 3 duty cycle 20 30 40 50 60 70
act4070b rev 0, 23-apr-12 innovative power tm - 9 - www.active-semi.com copyright ? 2012 active-semi, inc. 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 package outline sop-8/ep package outline and dimensions 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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