unisonic technologies co., ltd uc3656 preliminary cmos ic www.unisonic.com.tw 1 of 7 copyright ? 2011 unisonic technologies co., ltd qw-r502-469.b 1mhz, 800ma synchronous buck controller ? description the utc uc3656 is a synchronous buck controller for a dc/dc converter optimized for high-performance microprocessor applications. it is configured with current mode for excellent line and load transient response. at 1mhz operat ion frequency, the use of small surface mount inductor and capacitor is enabled. the built-in synchronous switch saves the use of an external schottky diode and increases efficiency. the utc uc3656 is a low-noise synchronous step-down dc/dc converter that is ideally suited for systems requiring supplies from a 1-cell li-ion battery or from a 3-ce ll to 4-cell nicd, nimh, or alkaline battery. the utc uc3656 is generally applied in power supply for portable devices and usb-based power system. ? features * high efficiency (95%) possible * input voltage range: 2.5v ~ 5.5v * schottky diode is saved * output current: 800ma (@5v input 3.3v output) * 1.0mhz oscillation frequency * internal on/off * 100% duty cycle allows low dropout operation * stand-by current: 1 a (max.) ? ordering information ordering number package packing lead free halogen free uc3656l-af5-r UC3656G-AF5-R sot-25 tape reel ? marking
uc3656 preliminary cmos ic unisonic technologies co., ltd 2 of 7 www.unisonic.com.tw qw-r502-469.b ? pin configuration ? pin description pin no. pin name description 1 run on/off control 2 gnd power ground 3 sw switch node connection to inductor 4 v in power supply 5 fb output feedback
uc3656 preliminary cmos ic unisonic technologies co., ltd 3 of 7 www.unisonic.com.tw qw-r502-469.b ? block diagram reference oscillator + + - - + - + - + driver lg m2 m1 ug dcc current sense amplifier pwm comparator clock zero-current comparator error amplifier 0.6v slop comp fb en v in sw gnd pwm logic soft start uvlo en logic
uc3656 preliminary cmos ic unisonic technologies co., ltd 4 of 7 www.unisonic.com.tw qw-r502-469.b ? absolute maximum rating parameter symbol ratings unit power supply voltage v ss -0.3 ~ +6.0 v input pin voltage run,fb v in -0.3 ~ v in v sw v in -0.3 ~ v in +0.3 v p-channel switch source current (dc) 1000 ma n-channel switch sink current (dc) 1000 ma peak sw sink and source current 1.5 a ? thermal data parameter symbol ratings unit junction to ambient ja 165 c/w ? electrical characteristics (v in =3.6v, t a =25c, unless otherwise specified.) parameter symbol test conditions min typ max unit input supply range v in 2.5 5.5 v quiescent current (note) i s fb=0.8v, i load =0a, active mode 300 a current in standby mode i st run=0v, v in =5.5v 0.5 1 a feedback voltage v fb t a =-20c ~ +85c 0.588 0.6 0.612 v feedback voltage line-regulation v fb-line v cc =2.5v ~ 5.5v 0.1 0.5 % feedback variation with temperature t a =-20c ~ +85c 0.5 1.0 % feedback current i fb 200 na peak inductor current (note) i pk v in =5v, v out =3.3v 1.10 1.25 1.50 a maximum output current (note) i o v in =5v5%, v out =3.3v, l=4.7h 800 ma oscillator frequency f osc1 fb=0.8v 0.8 1.0 1.2 mh z f osc2 fb=0v 200 kh z r ds ( on ) of p-channel mosfet r pfet i sw =600ma 0.4 0.5 ? r ds ( on ) of n-channel mosfet r nfet i sw =-600ma 0.35 0.45 ? sw leakage current i lsw run=0v, sw=0vor 5v, v in =5v 0.1 1 a run threshold v run 0.3 1.0 1.5 v run leakage current i run 0.1 1 a note: l t ) v v ( i i i i on out in o o pk ? + = + = 2 2
uc3656 preliminary cmos ic unisonic technologies co., ltd 5 of 7 www.unisonic.com.tw qw-r502-469.b ? typical application circuit
uc3656 preliminary cmos ic unisonic technologies co., ltd 6 of 7 www.unisonic.com.tw qw-r502-469.b ? application information capacitor selection proper selection of c apacitors using the utc uc3656 plays a critical role for system performance. the source current of the top mosfet is square wa ve of duty cycle in a continuous mode. the input capacitor is generally us ed to provide a low impedance loop for the edges of pulsed current drawn by the utc uc3656 . a load step at the output can induce ringing at the input v in . this ringing can couple to the output and be mistaken as loop instability. increasing the capaci tance of the input capacit or can great improve the oscillation. a typical value is 4.7~ 22 f ceramic (x5r or x7r), poscap or aluminum polymer. with these capacitors, better high frequency bypassing is achieved; re sistive losses are thus reduced by their low esr for higher efficiency. moreover, the input capacitor rms curr ent changes with the input vo ltage and the output voltage. the maximum rms current in the input capacito r can be expressed in the following formula: ) v v ( v v i i in o in o omax rms ? = 1 the output capacitor depends upon the suitable ripple voltage. low ripple voltage corresponds to lower effective series resistance (esr). the output ripple voltage can be calculated by: ) fc esr ( i v out l out 8 1 + ? the formula as follows shows the output capacitor rms ripple current: in out in out rms v f l ) v v ( v i ? = 3 2 1 for the utc uc3656 , x5r or x7r dielectric formulations have the priority in choosing the input and output ceramic capacitors. this is because these dielectrics prov ide the best temperature and voltage characteristics of all the ceramics for a given value and size. inductor selection selecting an optimum inductor is dependent upon the expected ripple current and large value inductors lower ripple current and small value inductors result in higher ripple current. in addition, the losses associated with the dcr and its effect on the total converter e fficiency should be taken consideration. the inductor is also chosen to limit the ripple current to some pre-fixed value, approx. 20 ~ 40% (typ.) of the full load current at the maximum input voltage. the inductance value can be calculated in the following equation: out(max) l i 0.4 ~ . i = 2 0 ) v v ( i f v l in out l out ? = 1 adjustable output voltage a resistive divider adjusts the output voltage of the utc uc3656 , which divides a 0.6v reference voltage at fb pin. the output voltage can be obtained by the equation as follows: 2 1 0.6 (1 ) out r vv r =+
uc3656 preliminary cmos ic unisonic technologies co., ltd 7 of 7 www.unisonic.com.tw qw-r502-469.b utc assumes no responsibility for equipment failures that result from using products at values that exceed, even momentarily, rated values (such as maximum ratings, operating condition ranges, or other parameters) listed in products specifications of any and all utc products described or contained herein. utc products are not designed for use in life support appliances, devices or systems where malfunction of these products can be reasonably expected to result in personal injury. reproduction in whole or in part is prohibited without the prior written consent of the copyright owner. the information presented in this document does not form part of any quotation or contract, is believed to be accurate and reliable and may be changed without notice.
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