unisonic technologies co., ltd l5101 linear integrated circuit www.unisonic.com.tw 1 of 10 copyright ? 2009 unisonic technologies co., ltd qw-r103-026.b white led step-up converter ? description the utc l5101 is a constant current step-up pwm dc/dc converter optimized to drive white leds. it can drive leds in series with a li-ion cell. the switching frequency of the internal npn is up to 1.2mhz. high frequency allows the use of tiny external components and the current setting resistor has minimum power dissipation for the low feedback voltage of 95mv. the built-in ovp prevents the utc l5101 damage from the open load condition. series connection of leds provides identical led currents which contributes to uniform brightness, saving the use of ballast resistors. the utc l5101 is universally used in cellular phones, pdas , dscs, handheld devices, and white led display backlighting. ? features * open circuit and over voltage protection * high efficiency: 86% typical * switching frequency: 1.2mhz * supply current is 1.0ma * matches led current * requires tiny inductor and capacitors * halogen free sot-26 4 5 3 2 1 6 ? ordering information ordering number package packing L5101G-AG6-R sot-26 tape reel ? marking
l5101 linear integrated circuit unisonic technologies co., ltd 2 of 10 www.unisonic.com.tw qw-r103-026.b ? pin configuration ? pin description pin no. pin name symbol description 1 shutdown shdn tie to higher than 1.5v to e nable device, 0.3v or less to disable device. 2 ground gnd 3 feedback fb reference voltage is 95mv. connect cathode of lowest led and resistor here. calculation formula: r fb =95mv/i led 4 switch sw connect inductor/diode here. minimize trace area at this pin to reduce emi. 5 power input v in bypass v in to gnd with a capacitor sitting as close to v in as possible. 6 over voltage protection ovp the internal npn will turn off when v out >27v.
l5101 linear integrated circuit unisonic technologies co., ltd 3 of 10 www.unisonic.com.tw qw-r103-026.b ? block diagram sw + - 27v over voltage comparator + - pwm comparator + - current amp. rc cc + - error amp v in fb q1 driver control logic gnd rs shdn m ovp 95mv 1.2mhz oscillator ramp generator 6 4 2 1.25v v ref 5 3 1
l5101 linear integrated circuit unisonic technologies co., ltd 4 of 10 www.unisonic.com.tw qw-r103-026.b ? absolute maximum rating parameter symbol ratings unit input voltage v in 6 v sw voltage v sw 33 v fb voltage v fb 6 v shdn voltage v shdn 6 v ovp voltage v ovp 34 v junction temperature t j +125 operating temperature range t opr -20 ~ +85 storage temperature range t stg -40 ~ +150 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. ? electrical characteristics (v shdn =3v, v in =3v, t a =25 , unless otherwise specified.) parameter symbol test conditions min typ max unit operating voltage v in 2.5 5.5 v switching 2 5 non switching 1 2 ma supply current i in v shdn =0v 0.1 1.0 a error amplifier feedback voltage v fb 85 95 105 mv fb input bias current i fb v fb =95mv 100 na oscillator switching frequency f sw 0.8 1.2 1.6 mhz maximum duty cycle dc 85 90 % power switch sw on resistance r on(sw) 1.4 5 ? switch leakage current i leak (sw)) v sw =33v 0.1 1 a control input high v ih(shdn) on 1.5 v shutdown voltage low v il(shdn) off 0.3 v over voltage protection ovp input resistance r in(ovp) 0.6 1.2 1.8 m ? ovp threshold v thr(ovp) 1v hysteresis typical 22 27 32 v
l5101 linear integrated circuit unisonic technologies co., ltd 5 of 10 www.unisonic.com.tw qw-r103-026.b ? test circuit fig.1 test circuit
l5101 linear integrated circuit unisonic technologies co., ltd 6 of 10 www.unisonic.com.tw qw-r103-026.b ? application information recommended component selection * inductor selection: a 10 h inductor is recommended for most applications. * capacitor selection: the small size of ceramic capacitor make s it ideal for utc l5101 applications, x5r and x7r types are recommended because of t heir stable characteristics, 1 f input capacitor with 1 f output capacitor is sufficient for most utc l5101 applications. * diode selection: schottky diode, for its low forward voltag e drop and fast reverse recovery, is an ideal choice for the utc l5101 diode. a schottky diode rated 100ma to 200ma is sufficient for most utc l5101 applications, and the higher current rating us ually have larger diode capacitance which can cause significant switching losses at the 1.2mhz switching frequency. led current control a feedback resistor (precision 1% recommended) as feedback resistor control the led current. (r fb in figure 1) * feedback reference voltage: 95mv. * led current is 95mv/r fb . * the formula for r fb selection: r fb =95mv/i led open-circuit protection the ovp(over voltage protection) pr otects the voltage lower than its ma ximum level under the open circuit condition, which is caused by the failure or disconnection of the leds. the above undesired fault conditions will cause the feedback voltage falling to 0v, then the utc l5101 incr eases duty circle resulting in a high voltage in sw pin. dimming control there are three different ways of dimming control circuits as follows: 1. using a pwm signal sw gnd l1 10h v in shdn ovp fb utc l5101 c1 1f v in r fb 4.7 c2 1f d1 r2 r1 51k 1k pwm fig. 2 dimming control using a pwm signal fig. 3 dimming control with a pwm signal
l5101 linear integrated circuit unisonic technologies co., ltd 7 of 10 www.unisonic.com.tw qw-r103-026.b ? application information(cont.) 2. using a dc voltage sw gnd l1 10h v in shdn ovp fb utc l5101 c1 1f v in r fb 4.7 c2 1f d1 r2 r1 51k 1k v dc 0~5v fig. 4 dimming control using a dc voltage 3. using a filtered pwm signal sw gnd l1 10h v in shdn ovp fb utc l5101 c1 1f v in r fb 4.7 c2 1f d1 r2 51k r1 1k pwm c3 0.1f 5.1k r3 fig. 5 dimming control using a filter pwm signal
l5101 linear integrated circuit unisonic technologies co., ltd 8 of 10 www.unisonic.com.tw qw-r103-026.b ? typical application circuit fig. 6 six white leds application in li-ion battery
l5101 linear integrated circuit unisonic technologies co., ltd 9 of 10 www.unisonic.com.tw qw-r103-026.b ? typical characteristics feedback voltage (mv) switching frequency (mhz) 2.5 supply voltage (v) supply current (ma) 1.29 supply current vs. supply voltage 3.0 3.5 4.0 4.5 5.0 5.5 6.0 1.30 1.31 1.32 1.33 1.34 1.35 fb=v in non-switching 2.5 supply voltage (v) 1.80 supply current vs. supply voltage 3.0 3.5 4.0 4.5 5.0 5.5 6.0 1.85 1.90 1.95 fb=gnd switching 2.5 1.0 1.1 1.2 1.3 1.4 r ds(on) ( ) 3.0 3.5 4.0 4.5 5.0 5.5 6.0 supply voltage (v) r ds(on) vs. supply voltage 0 5 10 15 20 60 65 70 75 80 85 90 led current (ma) efficiency (%) 55 3leds efficiency vs. led current v in =3.0v v in =3.6v v in =4.2v 3leds, l1=10 h
l5101 linear integrated circuit unisonic technologies co., ltd 10 of 10 www.unisonic.com.tw qw-r103-026.b ? typical characteristics 0 5 10 15 20 60 65 70 75 80 85 90 led current (ma) 4leds efficiency vs. led current v in =3.0v v in =4.2v v in =3.6v 4leds, l1=10 h efficiency (%) 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.
|
