• State Resolved
  • Locked Locked
  • Replies 4 replies
  • Subscribers 63 subscribers
  • Views 406 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

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.

UCC2897A: Output Unstable

Kuan Wei Chen (Kevin Chen)
Genius 9710 points
Part Number: UCC2897A
Other Parts Discussed in Thread: TL431, ATL431, , UCC28740

Dear Team,

My customer's output is unstable depending on the load current.

When the output voltage drop, the TL431 also not maintain at 2.5V.

Originally I thought is because of competitor's TL431 sink too much current.

So I suggest them to use ATL431, but the issue is the same.

Do you think smaller PR62 will help here?

I am worried if smaller PR62 solve the customer the issue, they will still use competitor's TL431.

Do you have any suggestion on it?

0304.pdf

BR

Kevin

  • 0
    TI__Genius 13660 points
    Hi Kevin,

    PR62 here is used for power supply and offer the bias current for TL431. Decrease PR62, the bandwidth of voltage will increase and dynamic response will become better, but from the test data, I don' t think it will help this issue.
    I assume that which protection was activated maybe current limit protection, which limited the duty cycle, since the maximum power was limited at 33W.
    So I suggest that
    1. Try to lower the input voltage, then to find out that if the maximum limited power will be smaller than 33W?
    2. You can observe the CS pin voltage to find whether the over current protection (CS Pin arrived at 0.5 V ) was activated, and try to decrease the current sense resister PR50 to find out that if it works?

    Regards,
    Teng
  • 0 in reply to Teng Feng
    TI__Genius 9710 points
    Dear Teng,

    Thanks for the information.
    The engineer will provide the CS pin information soon.

    Besides, the customer is wondering transformer 20uH is enough?
    Because we don't have calculation tool available on the web.
    So the only available way will be using Webench, right?
    But it seems I can't force the webench use flyback topology, it use forward to calculate.
    Can you check 20uH is enough?

    BR
    Kevin
  • 0 in reply to Kuan Wei Chen (Kevin Chen)
    TI__Genius 13660 points

    UCC28740 design tools.xlsxHi Kevin,

    Is there any update from customers?

    Yes, it is not available to calculate parameters within flyback topology for UCC2897A on the web.

    However, for the DCM flaback, you can also use UCC28740 design tools to estimate primary inductance. for the CCM flyback, you can use WENBENCH tool within UCC38C4X to estimate primary inductance.

    Regards,

    Teng

  • 0 in reply to Teng Feng
    TI__Genius 13660 points
    Hi Kevin,

    I am going to close this post for now, but if you still need our help, just post a reply below (or create a new thread if the thread has locked due to time-out). Thanks.

    Regards,
    Teng