UCC256404: UCC256404

Stuart Linzer

Part Number: UCC256404
Other Parts Discussed in Thread: TIDA-010015,

Hi Group,

On reference design PMP30763 inrush limiting circuit consisting of Q8, Q9, Q10 and associated components. Can you talk about the function of this circuit? Interested in why both +12 and +15 are needed and function of C64.

Could just +12 be used to turn on Q10 directly ending the inrush period?

-Stuart

over 2 years ago

0 Ray DiCecco over 2 years ago

TI__Genius 10725 points

Hi Stuart,

Before I attempt to answer your question, I've reached out to the designer of the board so I can make sure I give you the most complete and accurate answer. Since I'm not sure where I am in his queue, please allow several days for me to get back to you.

Ray

0 Roberto S. over 2 years ago in reply to Ray DiCecco

TI__Expert 5585 points

Hi Ray,

The customer is right, we don't need the +15V here. Actually, the section Q8, Q9 and associated components comes from another project, where I needed the +15V to keep Q9 conducting as soon as the capacitor C64 is fully charged. Since in the PMP30763 we have the presence of Q6 (who shuts down U4 if the RVCC voltage (12V) is not present), the +15V follows the 12V as timing. Therefore here it is possible to simplify the schematic and drive Q10 directly from 12V (RVCC). I hope that helps.

Best regards,

Roberto

0 Roberto S. over 2 years ago in reply to Roberto S.

TI__Expert 5585 points

In addition, it is possible also to use the inrush-current circuit shown on TIDA-010015, which is a close design:

https://www.ti.com/tool/TIDA-010015?keyMatch=&tisearch=search-everything&usecase=refdesign

0 Ray DiCecco over 2 years ago in reply to Roberto S.

TI__Genius 10725 points

Hi Roberto, thank you for answering Stuart's question directly.

Stuart, please let me know if this resolves your question.

Regards,

Ray

0 Ray DiCecco over 2 years ago in reply to Ray DiCecco

TI__Genius 10725 points

Hi Stuart, since you've moved on to another question, I'll assume Roberto's response fully answered your question and will close out this thread. If not, please submit another question.

Regards,

Ray

0 Stuart Linzer over 2 years ago in reply to Ray DiCecco

Intellectual 260 points

Yes resolved. Thank you.

+1 Stuart Linzer over 2 years ago in reply to Stuart Linzer

Intellectual 260 points

Hi Ray,

Can I ask another question on this thread or should I open another one. If I can here it is:

PMP30763 and other reference boards includes a capacitor from Vpfc to transformer primary. On PMP30763 the capacitor is C2. Please talk about the function of this capacitor.

Regards,

Stuart Linzer

0 Manikanta Pallantla over 2 years ago in reply to Stuart Linzer

TI__Genius 13245 points

Hi Stuart,

C2 and C3 in PMP30763 form the split resonant capacitor of LLC.

Please see the following e2e post for further details.

UCC25600: UCC256404 Resonant Capacitor Cr - Capacitive Divider? - Power management forum - Power management - TI E2E support forums

Please let me know if you have any further questions.

Regards

Manikanta P

+1 Ray DiCecco over 2 years ago in reply to Stuart Linzer

TI__Genius 10725 points

Hi Stuart,

This question related to the LLC controller. I will assign to the product expert for the UCC256404 as he should be able to give you the best answer.

Ray

0 Ray DiCecco over 2 years ago in reply to Ray DiCecco

TI__Genius 10725 points

I see Manikanta our LLC expert already jumped on this!

0 Stuart Linzer over 2 years ago in reply to Manikanta Pallantla

Intellectual 260 points

Hi Manikanta,

Thank you for resolving my issue. Another question. PMP30763 shows resonant inductor connecting to primary "no-dot" side. Yet a circuit generated from Webench shows resonant inductor connecting to "dot" side of transformer. Please explain which is correct.

Stuart

+1 Manikanta Pallantla over 2 years ago in reply to Stuart Linzer

TI__Genius 13245 points

Hi Stuart,

Since LLC magnetics carries AC currents, it doesn't matter what end connects to the mid point of half bridge.

Regards

Manikanta P

0 Stuart Linzer over 2 years ago in reply to Manikanta Pallantla

Intellectual 260 points

Hi Manikanta,

Using the Excel UCC25640x design tool. With the value for "rated current for resonant capacitor". Is this value halved when using Split Resonant Capacitor configuration?

Regards,

Stuart

0 Stuart Linzer over 2 years ago in reply to Manikanta Pallantla

Intellectual 260 points

Hi Manikanta,

Using the Excel UCC25640x design tool. With the value for "rated current for resonant capacitor". Is this value halved when using Split Resonant Capacitor configuration?

Regards,

Stuart

0 Manikanta Pallantla over 2 years ago in reply to Stuart Linzer

TI__Genius 13245 points

Hi Stuart,

You are correct. Resonant current will be halved if you use the split resonant capacitor configuration.

Regards

Manikanta P