• State TI Thinks Resolved
  • Locked Locked
  • Replies 5 replies
  • Answers 3 answers
  • Subscribers 63 subscribers
  • Views 220 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.

UCC28910: Output ripple

Nam, Dino
Expert 5775 points
Part Number: UCC28910

Dear team, 

Please review below schematic and let me know your opinion regarding how can i debut output ripple. please refer to the below schematic and waveform. 

<schematic>

- Changed to R185 (91k), R186 (33k) 

<Waveform>

- 12V/ 0.4A output (Red) 

Thank you. 

  • 0
    TI__Guru 66135 points

    Hello,

    You not have enough output capacitance.  Have you checked the design with the Webench design tool?  The design tool can be foud at the following link.  https://www.ti.com/product/UCC28910  There is an excel tool that you can use as well that can be found at the follwoing link. https://www.ti.com/lit/zip/sluc503

    When it comes to output ripple with the UCC28910 increasing the output capacitance and decreasing the output capacitance ESR is the best way to reduce the output ripple voltage.

    Regards,

  • 0 in reply to Mike O'
    TI__Expert 5775 points

    Hello Mike, 

    As your recommendation, we checked output capacitor, so we changed 220uF to 470uF and 1000uF. 

    but the test result is abnormal, the output voltage is drop 12V to 4~5V. 

    Could you review customer schematic again and let me know your opinion regarding this result.

    Thank you.

  • 0 in reply to Nam, Dino
    TI__Guru 66135 points

    Hello,

    If your output is dropping out from 12 V to 4 to 5V you may have a fault or your transformer turns ratio is not correct.

    I have attached and application note that discusses how PSR fault sensing works and the most common issues that arise and techniques to resolve these issues.  I believe this information will be helpful in debugging your issue.

    Regards,

    3581.Clean PSR Sensing App Note 10 5 20B.pdf

  • 0 in reply to Mike O'
    TI__Expert 5775 points

    Hello Mike, 

    Thank you for you comment. I will review app note. 

    BTW,There is quick question

    If turns ratio is not correct or there is OVP  or other issue , Why output is normal(12V) when using 220uF output capacitor? Is it possible? 

    Thank you.  

  • 0 in reply to Nam, Dino
    TI__Guru 66135 points

    Hello,

    You need to figure out why the output is dropping out from 12V to 5V.  By studying the CS, VDD, Out and Aux voltage it should help you determine why the output voltage is dropping.

    When it comes to your output regulating with 220 uF capacitor and then dropping out.   I did not know it was regulating to 12 V.  Now you have to figure out why it is dropping out.  Your CS resistor value could be too large or your RLC resistor may be too large.  These are other things besides what is covered in the application not that could be having issues.  These topics are covered in the data sheet if this ends up being your issue.

    Regards,