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LP8863-Q1: LEDs is Flicker when use LP8863

Fandy
Expert 2285 points
Part Number: LP8863-Q1

Hello

Please help analysis my LEDs flicker problem,thanks

LED:10s/5p , SCH as attached(actually Rfb3  27Ω is renew to 27K, and Risense is 22mΩ,Rsense is 30mΩ not 20M);

Vin=12V ,VDD_5V and VDD3_3V is powered by external LDO, and its volatge is ok

SDO_PWM was pulled up to 3.3V ,all LP8863's resister is default not be changed, But LEDs is Flicker always.

Vboost about 30V has big ripple(maybe caused by LED current sink shut down) 

GD signal and SW waveform plot as attached

SW_1 with 25KS/s sanning

SW_2 with 500MS/s scaning

 

  • 0
    TI__Prodigy 670 points

    There are two issues in your schematic. First there is no capacitor at input stage boost converter. I would suggset you to add a 47uF capacitor between Q4 and L1 for power input stage. Second, please change R39 to 84.5Kohms from 124kohms. Thank you.

  • 0 in reply to Xianghao Meng
    Expert 2285 points
    Hi Xianghao
    Thanks for your reply.
    Actually,I have added the one 47uF between Q4 and L ,
    I known Vmaxboost=54V based on current value of R39,R43,R67, Limited by resistor value I have, I changed to used Two-Resistor Method of FB Divider, Exg. R67 27K Change to 0Ω，R43 change to 100K, R39 change to 600K,700K,800K, so Vmax Boost should be approximate 30V,35V,40V. But fault still As same As before.