TPS92690: LOW duty PWM doesn't work

Peter Zha

Prodigy 200 points

Part Number: TPS92690

Hello Sir,

if apply PWM 200Hz 0.5% duty to PIN1 nDIM， the backlight turns on after 22seconds,

if apply PWM 200Hz grater than 10% to PIN1 nDIM, the backlight turns on in 3 seconds,

is any suggestion of it.

the attached picture shows PMW and ouput voltage,

10 LEDs in serial, 6 in Parellel, current 242mA, LED voltage 56V.

the yellow curve is 200Hz 0.5% PWM,

the green curev is LEDvoltage.

thanks!

Wiht best regards,

over 3 years ago

0 Peter Zha over 3 years ago

Prodigy 200 points

Low duty PWM works, but too slow to boot.

+1 Peter Zha over 3 years ago in reply to Peter Zha

Prodigy 200 points

the valu of the parts are same as EVM

0 Tuan Tran74 over 3 years ago

TI__Mastermind 18890 points

Hello Peter,

The reason low duty cycle is slow to boot up is that the regulator main FET is only enable during the PWM enable period. So if PWM cycle is only 0.5% of the time then it will take 200 times longer to power up versus PWM being100% duty cycle.

Thanks Tuan

0 Peter Zha over 3 years ago in reply to Tuan Tran74

Prodigy 200 points

HI Tuan,

thanks, we will increase duty cycle for boot normally.

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TPS92690: LOW duty PWM doesn't work