• State TI Thinks Resolved
  • Locked Locked
  • Replies 3 replies
  • Answers 1 answer
  • Subscribers 63 subscribers
  • Views 196 views
  • Users 0 members are here
Support feedback
Options
Options
Related

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

Original question:

UCC25600: Load regulation.

UCC25600: Issue with Light loads

Dilip Ramgir
Prodigy 90 points
Part Number: UCC25600

Tool/software:

Dear Team,

I'm design a HB- LLC converter with UCC25600, with Input as 665VDC from PFC and the output of the LLC is 30VDC and 8A.

I have selected the Lm=612uH, Lr=120uH and Cr=16.5nF.

I have tested the circuit at full load, it works properly with CC-CV loop as well.

But the problem I'm facing is at lower loads i.e. below 10W, the IC goes into burst mode with switching frequency as 350kHz and the MOSFET's heat up and blows out.

I have tried to

1) Increase the gate turn-ON resistors of the MOSFET's but got the same results.

2) Reducing the Lm/Lr ratio gives trhe same result.

Could you please suggest me some solution for this problem.

Regards,

  • 0
    TI__Intellectual 2480 points

    Hi Dilip,

    Adjust the LL pin voltage to a higher value to increase at what minimum power the converter enters burst mode. Adjust VLLA-VLLB to a higher value for higher HF Burst Entry value. Please see sections 7.5.3.3 and 7.5.3.2 in datasheet.

    Regards
    Hemanth

  • 0 in reply to Hemanth Sreeperumbudur
    Prodigy 90 points

    Hello Hemanth,

    This IC UCC25600 doesn't have LL pin. Pin out is attached below..

    Is there a method to control this with-in this IC.

    Regards,

    Dilip

  • 0 in reply to Dilip Ramgir
    TI__Intellectual 2480 points

    Hi Dilip,


    Sorry, I read the part number wrongly.

    If the MOSFETs damage at very light load or at no-load means, it could be suspected due to reverse recovery or dv/dt.

    Lowering the reverse recovery could help in this situation. This is done by slowing the turn-on of MOSFETs (as you had done). Measure the VGS to look for any ground bounce (VGS rises as the other FET turns-on). If there is any ground bounce, try to reduce the off-resistance (if any).

    Try using split capacitors with lower Ln. Along with these, selecting FETs with low reverse recovery should help.

    Regards
    Hemanth