PMP4478: Valley skipping

Andre Strul

Part Number: PMP4478
Other Parts Discussed in Thread: UCC28740, LM5021

Hi to all and thank you in advance for your support.

We have the design of the uCC xxxx smps as per your schemtics

Due to some noise at 400Khz we would like to remove valley skipping . Can you advise us what values we need to change ?

regards

over 7 years ago

0 Richard Yin over 7 years ago

TI__Prodigy 660 points

Hi, From you mention, the "noise" means audio/acoustic noise? If so, where is the noise from?

0 Andre Strul over 7 years ago in reply to Richard Yin

Expert 1330 points

HI and thank you for the reply.

The answer is no... its high frequency electrical noise.

thank you

Andre

0 Richard Yin over 7 years ago in reply to Andre Strul

TI__Prodigy 660 points

Hi,
The valley skipping algorithm is embedded in the UCC28740 controller. Therefore, it is non-removable. However, you can change the current sense resistor value or transformer inductance value to move the valley switching point. Or you could use different controller without the valley skipping function such as LM5021.
Back to the 400kHz noise issue. Is that noise at output? Or EMI noise through conduction line? If it’s output noise, then you should be able to filter it out through an RC or LC filter. If it’s EMI noise, then the problem could be solved with an LC filter at input or a better transformer design (ex: a shielded transformer).

0 Andre Strul over 7 years ago in reply to Richard Yin

Expert 1330 points

OK thank you for now.
regards
Andre

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PMP4478: Valley skipping