TPS92515-Q1: PWM frequency range

hello Elec

the PWM frequency can be down to 30Hz, the only concern is that if PWM is low for too long time, boot UVLO can trip. So Boot cap should be increased a little bit. May I know the PWM duty cycle on your case? Besides, do you mind sharing more information on this project?

Hi Mason,

The duty cycle ranges from 3-45%, which means on time is 1ms~15ms. Do you think there is a problem?

And, the boot UVLO means the boot cap doesn't have enough voltage to turn on the high side MOS, right? Thanks.

BR,

Elec Cheng

hi Elec

your understanding on boot UVLO is right. Let me confirm this internally and then get back to you.

Hi Mason,

Looking forward to your feedback! Thanks.

BR,

Elec Cheng

hi elec

no problem, will share with when it is available.

Hi Mason,

May I get some feedback for this problem. It's been a week. Thanks.

BR,

Elec Cheng

hi Elec

I've applied EVM to test, hopefully, I can get some results within this week.

hi Elec

Pls see below result with 30Hz PWM dimming frequency, 45% duty cycle with Cboot=0.1uF:

from LED current waveform, I think the result is OK. During PWM off, the BOOT UVLO is triggered, SW is internally pulled down by 5mA current sink, Cboot then will be recharged and operate normally at the beginning of next PWM on. So basically, from my side, 30Hz 45% duty operation is OK.

Hi Mason,

Thanks for testing. But in our customer's use case, the duty cycle is as low as 10%. Would that be ok then? Thanks.

BR,

Elec Cheng

hi Elec

so the condition of PWM duty cycle varies between 10%-45%? I checked the result of 3%, it is ok. I can retest and get the waveform for you if needed.

Hi Mason,

Ye thanks. Please send me the test result of 3% duty cycle and 10% duty cycle. And could you please measure the time between EN and output current? Thanks.

BR,

Elec Cheng

hi elec

sure, pls expect the result today or tomorrow.