unisonic technologies co., ltd uc3666 preliminary cmos ic www.unisonic.com.tw 1 of 8 copyright ? 2010 unisonic technologies co., ltd qw-r502-489.a dual channel 800ma high efficiency step-down dc/dc converter ? description the utc uc3666 is a dual channel high efficiency step-down dc/dc converter with constant frequency and current mode. a main switch and a synchronous rectifier for high efficiency are contained in each converter, and t hus an external schottky diode is saved. supply current is only 300 a during normal operation and is reduced to less than 1 a in shutdown mode. the output voltage can be adjusted to as low as 0. 6v. with input voltage range from 2.5v ~ 5.5v , each converter c an deliver 800ma current to the load. due to the internally fixed 1.8mhz switching frequency , small surface mount inductors and capacitors can be used. it can also run 100% duty cycle for low dropout applications. the utc uc3666 is generally used in digital still cameras, portable instruments, slim-type dvd, microprocessors and dsp core supplies, wireless and dsl card, pdas, smart phones, cellular telephones and so on. ? features * high efficiency * current mode operation * low quiescent current less than 300ua (active mode) * input voltage varying from 2.5v to 5.5v * output current on each channel: 800ma * fixed frequency operation * 0 - 100% full duty ratio in dropout * 0.6v reference allows low output voltages * over-temperature protection circuit * shutdown current less than 0.1 a * rohs compliant (100% green available) * halogen free son-10 1 ? ordering information ordering number package packing lead free halogen free uc3666 l -b10-r UC3666G-B10-R son-10 tape reel note: xx: output voltage, re fer to marking information.
uc3666 preliminary cmos ic unisonic technologies co., ltd 2 of 8 www.unisonic.com.tw qw-r502-489.a ? pin configuration 1 en1 top view 2 3 4 56 7 8 9 10 fb1 vin2 gnd2 sw2 en2 fb2 vin1 gnd1 sw1 exposed pad on backside ? pin description pin no. pin name description 1 en1 channel 1 regulator enable control input pin. drive en1 above 1.5v to turn on channel1. drive en1 below 0.3v to turn it off (shutdown current < 0.1ua). 2 fb1 channel 1 voltage feedback pin 3 vin2 channel 2 supply pin 4 gnd2 channel 2 ground pin 5 sw2 channel 2 power switch output 6 en2 channel 2 regulator enable control input pin. drive en2 above 1.5v to turn on channel2. drive en2 below 0.3v to turn it off (shutdown current < 0.1ua). 7 fb2 channel 2 voltage feedback pin 8 vin1 channel 1 supply pin 9 gnd1 channel 1 ground pin 10 sw1 channel 1 power switch output
uc3666 preliminary cmos ic unisonic technologies co., ltd 3 of 8 www.unisonic.com.tw qw-r502-489.a ? block diagram + + - - + - + - + rs & drive lg m2 m1 ug dcc current sense amplifier pwm comparator clock zero-current comparator oscillator error amplifier 0.6v reference slop comp fb1 fb2 en1 en2 vin1 vin2 sw1 sw2 gnd1 gnd2 pwm logic soft start uvlo en logic
uc3666 preliminary cmos ic unisonic technologies co., ltd 4 of 8 www.unisonic.com.tw qw-r502-489.a ? absolute maximum rating parameter symbol ratings unit input supply voltage v in gnd-0.3 ~ +6.5 v sw voltage -0.3 ~ v in +0.3 v enb, v fb voltage -0.3 ~ v in v sw peak current 1.5 a esd classification class 2 junction temperature t j 125 c operating temperature t orp -20 ~ +85 c storage temperature range t stg -65 ~ +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. the ic has a protection circuit against static electric ity. do not apply high static el ectricity or high voltage that exceeds the performance of the protection circuit to the ic. ? thermal data parameter symbol typ max unit junction ambient ja 50 c/w ? electrical characteristics (recommended operating conditions, unless otherwise specified; v in =3.6v, t a =0 ~ 70c (typical=25c)) parameter symbol test conditions min typ max unit supply voltage v in 2.5 5.5 v feedback current i vfb -30 0.5 30 na t a =25c 0.588 0.6 0.612 v regulated feedback voltage v fb -40c t a 85c 0.582 0.6 0.618 v reference voltage line regulation v fb v in =2.5v ~ 5.5v 0.04 0.4 %v output voltage line regulation v out v in =2.5v ~ 5.5v 0.04 0.4 %v output voltage load regulation v loadrge 0.5 % shutdown current i s v en =0v, v in =5.5v 0.01 1 a sw leakage current i leak v en =0v, v in =5.5v, v sw =0v or 5.5v -1 1 a pmosfet on resistance r dsonp i sw =100ma 0.35 ? nmosfet on resistance r dsonn i sw =100ma 0.24 ? pmosfet current limit i pcl duty cycle=100% current pulse width<1ms 0.9 1.2 1.4 a oscillator frequency f osc 1.2 1.6 2.0 mh z thermal shutdown threshold t s 145 c en high level input voltage v en -40c t a +85c 0.9 v en low level input voltage v en -40c t a +85c 0.3 v en input current i en v en =0v ~ v in -1 1 a
uc3666 preliminary cmos ic unisonic technologies co., ltd 5 of 8 www.unisonic.com.tw qw-r502-489.a ? typical application circuit
uc3666 preliminary cmos ic unisonic technologies co., ltd 6 of 8 www.unisonic.com.tw qw-r502-489.a ? function description the uc3666 is a dual channel constant frequency current m ode pwm step-down converter. it is designed for low voltage, li-ion battery powered applications requiring high efficiency and small size. the output voltage can be adjusted from 0.6v to 5.5v by means of an external resist or divider. a main switch a nd a synchronous rectifier are integrated to provide high efficiency, thus an external schottky diode is saved. this device can achieve 100% duty cycle. the duty cycle d of a step-down converter can be calculated as follows: d=t on f osc 100% v P out /v in 100% (where t on is the main switch on time and f osc is the oscillator frequency (1.6mhz)). current mode pwm control slope compensated current mode pwm c ontrol provides stable switching and cycle-by-cycle current limit for superior load and line response and protection of the in ternal main switch and synchronous rectifier. the uc3666 has a constant switching frequ ency of 1.6mhz and can adjust t he output voltage. during each cycle, the pwm comparator modulates the power transferred to the load by changing the inductor peak current based on the feedback error voltage. the main switch is switched on for a certain time to ra mp the inductor current at eac h rising edge of the internal oscillator, and switched off when the peak inductor curr ent exceeds the error voltage during normal operation. when the main switch is turned off, the synchronous rectifier will be tur ned on as soon as possible, and then stay on until either the induct or current drops to zero or the next cycle starts. to get a high efficiency, the device is skipped pulses at light load. dropout operation the uc3666 allows the main switch to keep for more than one switching cycle and increases the duty cycle while the input voltage decreases until nearly equal to the output voltage. when the duty cycle reaches 100%, the main switch is held on continuously to drive the output with current until it is equal to t he p-mosfet current limit. thus, the output voltage can be calculated as the input vo ltage minus the voltage drop across the main switch and the inductor. short circuit protection short circuit protection is incorporated in uc3666 . when the output is shorted to ground, the oscillator frequency is reduced to protect inductor current from being damaged due to it increasing beyond the p-mosfet current limit. in order to make the short circuit current lower, the p-mosfet current limit is also reduced. the values of frequency and current limit are restored unt il the short circuit condition is remo ved as well as the feedback voltage reaches 0.6v. maximum load current the uc3666 ?s input voltage can be of as lo w as 2.5v, however, at lower input voltage, the maximum load current decreases because of the large ir drop on the main switch and synchronous rectifier. the slope compensation signal reduces the peak inductor current as a function of the duty cycle to prevent sub-harmonic oscillations as duty cycles become higher th an 50%. conversely the current limit increases as the duty cycle decreases match other diagrams in this datasheet.
uc3666 preliminary cmos ic unisonic technologies co., ltd 7 of 8 www.unisonic.com.tw qw-r502-489.a soft start/enable soft start limits the current surge seen at the input and eliminates outpu t voltage overshoot. the enable pin is active high. when pulled low, the enable input (en) forces the utc uc3666 into a low-power, non-switching state. the total input current during shutdown is less than 1a. over-temperature thermal protection completely disables switchi ng when internal dissipation becomes excessive. the junction over-temperature threshold is 145 with 10 of hysteresis. once an over-tem perature condition is removed, the output voltage automatically recovers.
uc3666 preliminary cmos ic unisonic technologies co., ltd 8 of 8 www.unisonic.com.tw qw-r502-489.a 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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