LP8867C-Q1: High frequency buzzing sound coming from the boost section.

Hi Manu,

Our expert is currently out of office. She will reply to you later when back to office. Thanks for your understanding.

Best Regards,

Steven

Hi Manu,

What's the PWM frequency?

BR, Gracie

Hi Gracie,

Th PWM frequency when i measured using a oscilloscope was 15kHz.

Yes it is in the range of a audible frequency but if that is the case then the sound should come at all the scenarios rit?

But here the sound comes only when the display is connected.

Hi Manu,

You mean when the backlight is lit up alone, there is no audible noise?

BR, Gracie

Hi Gracie,

When the Backlight is lit up the audible noise comes , when there is no display or no backlight lit up there is no audible noise.

TnR Manu

Hi Manu,

It makes sense. PWM frequency really affects the audible noise. You can increase it to 20kHz to see if it still exists.

BR, Gracie

Hi Gracie,

How should I increase the PWM frequency? Do I need to edit it from the Driver side, if so could you please guide to locate the code line.

Or is it possible to change the PWM frequency by making any hardware changes?

Hi Manu,

It's from outside PWM input.

BR, Gracie

Hi Gracie,

I tried applying the PWM wave using a function generator instead of giving it from the processor. I DNP the R313 thus isolating the system from the PWM generated from the microprocessor.

So  my doubt is if the sound was caused by the processor then while applying the PWM using function generator it should produce the sound rit. But in this case it was still producing and that to in respective to the frequency we set on the generator ie, if higher frequency than 15khz the sound was not all audible.

Basically some component is resonating in the frequency of the PWM.

Could you please check in the schematic if any components are of not right values as per suggested design.

And please let me know if you require any component's part code.

Regards,

Manu Thomas

Hi Manu,

Our expert is currently out of office. She will reply to you later when back to office. Thanks for your understanding.

Best Regards,

Steven