unisonic technologies co., ltd p1786 linear integrated circuit www.unisonic.com.tw 1 of 8 copyright ? 2011 unisonic technologies co., ltd qw-r103-038.c pwm control 3a step-down converter ? description utc p1786 consists of 3a step-down switching regulator control which includes a reference voltage source, oscillation circuit, error amplifier, internal pmos and etc with pwm. utc p1786 can provide low-ripple power, high efficiency, and excellent transient characteristi cs. an enable function, an over current protect and short circuit prot ect function are built inside, so the operation frequency can be r educed from 300khz to 30khz when ocp or scp happens. the pwm control circuit can vary the duty ratio linearly from 100 down to 0%. this converter also includes an error amplifier circuit as well as a soft-start circuit that prevents overshoot at startup. also, to minimum external component counts for an internal compensati on block is built in. these ics can work as step-down switching regulators with the addition of an internal p-channel po wer mos, a coil, capacitors, and a diode connected externally. they provide such outstanding features: low current consumption. it is also suitable for the operation via an ac adapter because this converter accommodate an input voltage up to 23v. ? features * input voltage: 4.0v ~ 23v * output voltage: 0.8v ~ v cc * duty ratio: 0% to 100% pwm control * oscillation frequency: 300khz typ. * soft-start, current limit, enable function * thermal shutdown function * built-in internal sw p-channel mos ? ordering information ordering number package packing lead free halogen free p1786l-s08-r p1786g-s08-r sop-8 tape reel p1786l-s08-t P1786G-S08-T sop-8 tube (1) r: tape reel, t: tube (2) s08: sop-8 (3) g: halogen free, l: lead free p1786l -s08 -r (1)packing type (2)package type (3)lead free
p1786 linear integrated circuit unisonic technologies co., ltd 2 of 8 www.unisonic.com.tw qw-r103-038.c ? pin configuration ? pin descriptions pin no. pin name i/o description 1 fb i feedback pin. 2 en i chip enable, h: enable step-down function l: chip disable 3 ocset i add an external resist or to set max output current. 4 v cc ic power supply pin 5, 6 output o switch pin. connect external inductor/di ode here. minimize trace area at this pin to reduce emi. 7, 8 v ss gnd pin
p1786 linear integrated circuit unisonic technologies co., ltd 3 of 8 www.unisonic.com.tw qw-r103-038.c ? block diagram
p1786 linear integrated circuit unisonic technologies co., ltd 4 of 8 www.unisonic.com.tw qw-r103-038.c ? absolute maximum ratings parameter symbol rating unit v cc pin voltage v cc v ss - 0.3 ~ v ss + 25 v feedback pin voltage v fb v ss - 0.3 ~ v cc v en pin voltage v en v ss - 0.3 ~ v in + 0.3 v switch pin voltage v out v ss - 0.3 ~ v in + 0.3 v power dissipation p d internally limited operating temperature t opr -20 ~ +125 c storage temperature t stg -40 ~ +150 c note: absolute maximum ratings are those values beyond which the device could be permanently damaged. absolute maximum ratings are stress ratings only and functional device oper ation is not implied. ? thermal data parameter symbol rating unit junction to ambient ja 65 c/w ? electrical characteristics (v in = 12v, t a =25c, unless otherwise specified) parameter symbol conditions min typ max unit input voltage v in 4 23 v feedback voltage v fb i out =0.1a 0.784 0.8 0.816 v feedback bias current i fb ( bias ) i out =0.1a 0.1 0.5 a switch current i sc 3.5 a standby current i stn-by v en =0v 10 a line regulation out out v v v in = 5v~23v, i out =0.2a 1 2 % load regulation out out v v i out = 0.1 to 3a 0.2 0.5 % oscillation frequency f osc measure waveform at sw pin 240 300 360 khz frequency of current limit or short circuit protect f osc1 measure waveform at sw pin 10 30 60 khz en pin input voltage v sh evaluate oscillation at sw pin 2.0 v v sl evaluate oscillation stop at sw pin 0.7 v en pin input leakage current i sh 20 a i sl -10 a ocset pin bias current i ocset 75 90 105 a soft-start time t ss 0.3 2 5 ms internal mosfet r ds(on) r ds(on) v in =5v, v fb =0v 110 150 m ? v in =12v, v fb =0v 70 100 m ? efficiency v in = 12v, v out = 5v, i out = 3a 91 %
p1786 linear integrated circuit unisonic technologies co., ltd 5 of 8 www.unisonic.com.tw qw-r103-038.c ? function description pwm control the utc p1786 consists of dc/dc converters which employ a pwm system. in this dc/dc converter, the pulse width varies in a range from 0 to 100% which is according to the load current. cause the switching frequency remains constant the ripple voltage which produced by t he switching can be removed easily through a filter. therefore, these converters provi de a low-ripple power over broad ranges of input voltage and load current. under voltage lockout the under voltage lockout circuit makes su re that the outputs of hi gh-side mosfet driver remain in the off state after the supply voltage drops below 3.3v. when v cc rises above 3.5v normal operation resumes. r ds(on) current limiting the current limit threshold is fixed by the external resistor which is connected from v cc supply to ocset. an over-current condition is triggered when the pwm voltage is less than the voltage at ocset. i load r ds(on) = i ocset r ocset above formula is setting the current limit value.
p1786 linear integrated circuit unisonic technologies co., ltd 6 of 8 www.unisonic.com.tw qw-r103-038.c ? test circuits + - ? typical application circuit v in =12v, i ma x =3a v out 2.5v 3.3v 5v l1 value 15uh 18uh 22uh
p1786 linear integrated circuit unisonic technologies co., ltd 7 of 8 www.unisonic.com.tw qw-r103-038.c ? typical characteristics 0 340 310 input voltage, v in (v) oscillation freque ncy, fosc (khz) input voltage vs. frequency 25 10 520 300 315 335 350 325 305 320 330 345 15 0 0.82 0.76 fb (v) input voltage vs. fb 25 10 520 0.74 0.77 0.81 0.84 0.79 0.75 0.78 0.80 0.83 15 input voltage, v in (v) v out =3.3v i out =0.2a v out =3.3v i out =0.2a 0 3.35 3.15 input voltage, v in (v) output voltage, v out (v) line regulation 25 10 520 3.10 3.20 3.40 3.25 3.30 15 v out =3.3v i out =0.2a 0.0 5.08 5.02 output current, i out (a) output voltage, v out (v) load regulation 4.0 2.0 1.0 3.0 5.00 5.03 5.07 5.10 5.05 5.01 5.04 5.06 5.09 v in =12v efficiency (%)
p1786 linear integrated circuit unisonic technologies co., ltd 8 of 8 www.unisonic.com.tw qw-r103-038.c ? typical characteristics(cont.) 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 writ ten 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.
|
