• State Resolved
  • Locked Locked
  • Replies 6 replies
  • Answers 1 answer
  • Subscribers 64 subscribers
  • Views 329 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:

UCC256403: Startup problems with UCC256403

UCC256403: Risk of incorrect start-up sequencing UCC256403

Bastien Bertrand
Prodigy 165 points
Part Number: UCC256403

Tool/software:

Hello,


What is the risk of starting the PFC 400V voltage before the LLC 15V control circuitry?

Since the LLC drivers are not active, is it possible that this could cause the converter to break?

This question is a follow-up to my last request yesterday concerning the breakage of my converter.

The test was carried out at no load, first switching on the 400V (PFC voltage), then switching on a 15V voltage to supply the UCC256403.  


Have a nice day,

  • 0
    TI__Intellectual 2480 points

    Hi Bastien,

     To your question on risk of starting the PFC 400V voltage before the LLC 15V control circuitry - There should not be any risk, in general.

    To further support I have a few questions:

    1. What is the input bulk capacitor are you using? 

    2. Do you have switching waveforms across primary FET D-S and across SR FET D-S at any load? If yes, please share. These are key to understand the issue.

    3. Does the converter startups and operates with load? And only damages when it startups and stays at no-load ?

    Every design is different. It is very important to limit the noise and dampen the ringing due to switching. This is achieved by appropriately selecting the gate drive resistance, RC snubber across D-S (if required) and proper layout. 

    Based on the waveforms you observe:

    1. consider slowing down the primary FETs turn-on transition by increasing the turn-on gate resistance. 

    2. Add RC snubber circuit to dampen the ringing (if any), before the next switching.

    Regards
    Hemanth

  • 0 in reply to Hemanth Sreeperumbudur
    Prodigy 165 points

    Hello Hermanth,

    I'll answer your questions to help you understand my problem :

    1) In input, i just put few ceramic capacitor of 1 uF. I think it's maybe necessary to add an electromistry capacitor for reduce the perturbation accros the switching. Isn't that right ?

    2) I don't have a switching waveform. When i'll starting, the MOSFET shutdown and short-circuit themselves. The gate driver low side shutdown in same time with a low impedance (3 ohms).

    3) I start the converter with any load. I think isn't a problems of load but a problem of switching due to to the 2 problems listed above.

    4) My card is a hole PCB, so wiring + component placement were done by hand. It's a decision of my manager. I think that disturbances between wires + placement can interfere with the assembly and add additional disturbances to the board.

    Thanks for your help,

    Regards,

  • 0 in reply to Hemanth Sreeperumbudur
    Prodigy 165 points

    0412.LLC_DESIGN.pdf

    I'll give tyou my schematic.

    Thanks

  • +1 in reply to Bastien Bertrand
    TI__Intellectual 2480 points

    Hi Bastien,

    Here is my response.

    1. Yes, it needs electrolytic capacitor as well at converter's input.

    2. Without a waveform, it is very difficult to state what could have gone wrong.

    3. Understood.

    4. Any switching converter performance depends on layout. Layout is critical. It is very difficult to guess the problem and recommend a solution. To start with -consider disabling the secondary side synchronous rectifiers and use diodes for rectification until the primary side is proven working.

    I recommend the following:

    1. Refer UCC25640EVM-020 for a reference design. 

    2. Design converter using UCC25640x design sheet with required specification.

    https://dr-download.ti.com/design-tools-simulation/calculation-tool/MD-4q9segeylW/01.00.00.0C/sluc675c.zip 

    3. If concept needs to be proven, use UCC25640EVM-020 Evaluation board | TI.com evaluation board to modify per the above design in #1. Use the modified board to test the performance. 

    Regards

    Hemanth

  • 0 in reply to Hemanth Sreeperumbudur
    Prodigy 165 points

    Hi Hemanth,

    Thank you for your recommendations. I will get back to you as soon as possible so you can get a feedback. Slight smile

    Regards,

    Bastien

  • 0 in reply to Bastien Bertrand
    TI__Intellectual 2480 points

    Hi Bastien,

    Thank you.

    If you have related question, please click on "Ask a related question", otherwise, open a new thread with new test results.

    Regards
    Hemanth