PMP22764: Need help to resolve issue with audible noise

Miteshkumar Dalabhai Patel

Intellectual 1970 points

Part Number: PMP22764
Other Parts Discussed in Thread: LM5156

Hi David,

Refer e2e thread -

https://e2e.ti.com/support/tools/simulation-hardware-system-design-tools-group/sim-hw-system-design/f/simulation-hardware-system-design-tools-forum/1047679/pmp22764-lm51561h

Heating issue is resolved & able to load the output up to 70Watt & board are working with stable output. One of the observation with present design - when we turn off the dithering option by connecting the pin to VCC, design is working ok & no issue observed. when we enabling the dither option, we are hearing the audible noise from transformer. We raised the frequency from 150KHz to 200KHz but we didn't find much improvement on audible noise. Output is showing more ripple at output compare to non-dither option but design is able to load up to 70watt.

How to remove the audible noise while using Dithering option?

Mitesh

over 2 years ago

0 Darwin Fernandez over 2 years ago

TI__Mastermind 40415 points

Hi Mitesh, usually there is a modulation frequency in the dithering function of some PWM controllers. I don't see that it is adjustable in this controller. I'll loop in the apps engineer who can give some recommendations. Thanks!

0 EM over 2 years ago in reply to Darwin Fernandez

TI__Genius 11215 points

Hello Mitesh,

Like Darwin said, the LM5156 does not have adjustable modulation frequency. If the Flyback is actually performing well under all operating conditions, this noise might also just be coming from the core of the transformer due to the change in its magnetic field. What type of transformer are you currently testing on your board (did it undergo potting/varnishing/gluing)? We're looking forward to hearing from you.

Kind regards,
EM

0 Miteshkumar Dalabhai Patel over 2 years ago in reply to EM

TI__Intellectual 1970 points

Darwin, EM,

At present, transformer is made with EFD30 core & not varnished nor undergo with Potting/gluing. How much frequency variation is expected with Dithering?

Mitesh

0 EM over 2 years ago in reply to Miteshkumar Dalabhai Patel

TI__Genius 11215 points

Hello Mitesh,

Thank you for you answer. Do you have a second transformer that you can test on your board? At page 18 of the datasheet in Figure 9-10 you can see the frequency variation due to the dual random spread spectrum:

Kind regards,
EM

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PMP22764: Need help to resolve issue with audible noise