UCC256404: RVCC function

Sanjay Pusalkar

Part Number: UCC256404
Other Parts Discussed in Thread: UCC28056, , UCC256402

Hi,

In a new 480W design, I intend to use UCC28056 in PFC stage and UCC256404 in LLC stage.

Since UCC28056 does not have a high voltage start up pin, can I use RVCC of UCC256404 to power the UCC28056 ? How do I ensure that LLC will not start unless PFC stage is in operation ?

Regards,

Sanjay

over 4 years ago

0 David Huang33 over 4 years ago

TI__Genius 9140 points

Hi Sanjay,

it is better you can choose UCC256402, and use Blk to sample PFC voltage. in this way, PFC start up and rise the PFC bus voltage to trigger BLK start up threshold, So PFC always start before LLC.

hope this helps you.

0 Sanjay Pusalkar over 4 years ago in reply to David Huang33

Prodigy 130 points

Hi Dave,

Thanks for your suggestion. However, ucc256402 does not have X-cap discharge which I would like to have to reduce no load power consumption.

UCC256404 has it and has "minimal audible noise" too !

Regards,

Sanjay

0 Manikanta Pallantla over 4 years ago in reply to Sanjay Pusalkar

TI__Genius 16155 points

Hi Sanjay,

As David mentioned, LLC controller (UCC256402,403,404 ) will start only after PFC output voltage reaches certain threshold. You can see this in the below pictures.

Here you can observe that RVCC is powering up the PFC controller and then PFC output voltage starts increasing. When it reaches BLK threshold, LLC starts generating pulses.

Regards

Manikanta P

0 Sanjay Pusalkar over 4 years ago in reply to Manikanta Pallantla

Prodigy 130 points

Thank you Manikanta,

This helps a great deal.

Regards,

Sanjay

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UCC256404: RVCC function