high effi ciency integrated driver for 4-strings of 150ma leds SC441 power management april 26, 2007 1 features applications description wide input voltage range from 4.5v to 21v 36v maximum output voltage drives up to 40 wleds in 4 strings programmable led current for up to 150ma per string +/- 2% string-to-string current matching up to 90% effi ciency wide 0.2% to 100% pwm dimming range possible analog dimming integrated 2.5a power switch 800khz switching frequency for small size adjustable ovp for cost-eff ective output cap selection open/short led protection thermal protection with auto-recovery thermally enhanced tssop-20 edp package fully weee and rohs compliant ? ? ? ? ? ? ? ? ? ? ? ? ? ? ? medium-sized lcd panel notebook display automotive car navigation display sub-notebook and tablet computer displays portable media players ? ? ? ? ? the SC441 is a high-effi ciency multiple string wled driver with an integrated boost converter. it operates over a wide input range from 4.5v to 21v with a maximum out- put voltage of 36v and a 2.5a internal power switch. it can drive up to forty wleds in 4 strings with current up to 150ma per string. the string-to-string current match- ing is 2% typical, 3% maximum. the overall effi ciency is greater than 90% due to the low current sense voltage and a low-impedance internal power switch. the wide pwm dimming range boasts a ratio of 500: 1. the 800khz switching frequency enables the user to op- timize the external component sizes for effi ciency. when there are fewer than 10 leds in each string, users can ad- just the output voltage protection yielding an allowable reduction in associated costs, size and voltage ratings of the output capacitor. the SC441 also features comprehensive open and short- circuit led protection functions. it disables the corre- sponding strings with led open or led short conditions while maintaining normal operation of other, unaff ected led strings. this feature allows lcd panels to remain view- able even under led failure, wire disconnect, or short-cir- cuit conditions. the internal thermal shutdown protects the ic from overheating at abnormal conditions. the SC441 is available in a thermally-enhanced tssop-20 edp package. 4 vout ss pgnd ioset io1-4 comp ovpin agnd vin sw pwm en ovprtn sw fflag pgnd iognd SC441 4 strings 1 10 vin (4.5v -21v) 2 edp pgnd ioset io1- 4 comp ss agnd vout ovpin typical application circuit
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