UCC2897A: VDD issue

Sam Shyu36

Part Number: UCC2897A

Dear Sir,

Our customer use UCC2897A to design 48Vin to 12Vout/5A application. But the VDD voltage will over rating 16.5V. Could you help to double check schematic or components have any wrong? (VDD, POE_12V, AUX pin and out pin waveform as below.)

over 6 years ago

0 John Griffin1 over 6 years ago

TI__Mastermind 34465 points

Hi Sam,
The scope wave forms show that the bias voltage starts up at about 12V which is what you expect from the UCC2897A internal regulator.
Once the ic starts switching the internal regulator is turned off and the ic gets its power from the auxiliary winding on the main transformer.
This seems to be very high at 20V and it will damage the ic. So you can either reduce the number of turns or use a linear regulator on the output of this winding.
Regards
John

0 Sam Shyu36 over 6 years ago in reply to John Griffin1

Intellectual 735 points

Dear John,

Thanks for your suggestion.

Regards

Sam Shyu

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UCC2897A: VDD issue