UCC29950: About UCC29950 Application Question

Wen Yung

Part Number: UCC29950

Hi Sir,

My customer interested our PFC with LLC combo IC UCC29950 now. But have some question need you help. Thanks.
1. Why UCC29950 switching frequency spec design up to 350kHz?
In general, LLC switching frequency design rang from 70kHz to 100kHz.. So, I think 150kHz enough.

2. Have some document can explain UCC29950 have build in ditheing function for PFC?

over 8 years ago

0 John Stevens over 8 years ago

TI__Expert 7395 points

Wen,
Thanks for your interest in TI here. I've contacted the relevant product group and you should hear from them soon.
As always we ask that unreleased part information is not discussed publicly but we will assess your questions on ucc29950.

Regards
John

0 Yunsheng Qu over 8 years ago

TI__Genius 9790 points

Hi, Wen

1. For LLC design, the switching frequency would be high at light load, short load. The maximum frequency is 2 or 3 times of resonant frequency normally.
2.Per datasheet, the dithering function of PFC is integrated inside UCC29950. Dithering range is +-2kHz, dithering rate is 333Hz.

Regards,
Yunsheng

0 Wen Yung over 8 years ago in reply to Yunsheng Qu

Expert 1220 points

Hi Sir,

Have any document can explain Dithering function benefit and behavior?

Wen

0 Yunsheng Qu over 8 years ago in reply to Wen Yung

TI__Genius 9790 points

Hi, Wen

please refer to first page in below link.
emlab.ee.ntou.edu.tw/.../AppEMC-13-P3.pdf

Regards,
Yunsheng

0 Colin Gillmor over 8 years ago in reply to Yunsheng Qu

TI__Mastermind 25570 points

Hi Wen

The dithering function in the UCC29950 changes the PFC stage switching frequency from f_nom to f_nom+2kHz and to f_nom-2kHz at a 343Hz rate. The pattern is shown in the screenshot below.

Dithering can be effective in reducing the Average detector EMI response but in practice it has little if any effect on the response of the Peak detector. Careful layout and attention to transformer design is more important in reducing the EMI signature of your design.

Regards
Colin

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UCC29950: About UCC29950 Application Question