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WEBENCH® Tools/TPS54560B: Compensation parameters calculate issue

Gary Jiang
Intellectual 980 points
Part Number: TPS54560B

Tool/software: WEBENCH® Design Tools

Hi team,

Now I'm calculating the compensation parameters of TPS54560B. But I found the parameters(Rcomp, Ccomp, Ccomp2) designed by webench and by excel calculate tool TPS54360-361FAMILY_CALC_TOOL_REVE are totally different. I have changed the Co and Resr in excel tools to be the same in the webench.

Can you tell me why the results are so different? And which one should I choose?  My Vin is range from 18-32V, Vout=12.8V, Iout=5A.

Thanks.

  • 0
    TI__Expert 5830 points

    Hi User,

    The datasheet uses simple approximations to derive the compensation network.

    On the other hand, WEBENCH uses an iterative algorithm for the control loop to find more optimized compensation for the output filter it selects ,hence the results

    are bound to be different.

    We recommend using the one from WEBENCH.

    Thanks and Regards,

    Umayal

  • 0 in reply to Umayal Ramanathan
    TI__Intellectual 980 points

    Hi Umayal,

    But the difference between these two calculated parameters is really huge,  almost up to 17 times. Is that normal?

    Thanks

  • 0 in reply to Umayal Ramanathan
    TI__Intellectual 980 points

    Hi Umayal,

    But the difference between these two calculated parameters is really huge,  almost up to 17 times. Is that normal?

    Thanks

  • 0 in reply to Gary Jiang
    TI__Intellectual 1490 points

    Hi Toaran Jiang,

    Based on your desired phase margin and cross-over frequency, and the calculation method used the exact values of compensation component can be significantly different and this difference is normal.

    In your specific case, please use values suggested by Webench as suggested by Umayal due to the below reason.

    Webench design:

    Excel compensation values: Cross-over frequency 13k Hz, Phase Margin : 91 Degree

    As you can see Webench design gives you a higher cross-over frequency, which means lower overshoot voltage during a load transient. Phase margin in the suggested design is also adequate. Note that the cross-over frequency from the compensation values suggested by excel sheet is very low and this causes very large voltage overshoot during load transient and very slow converter response time. Below is the comparision of load transient response for both designs.

  • 0 in reply to Srikanth Pam
    TI__Intellectual 1490 points

    Sorry missed the below values above.

    In your specific case, please use values suggested by Webench as suggested by Umayal due to the below reason.

    Webench design: Cross-over frequency 45k Hz, Phase Margin: 74 Degree

    Excel compensation values: Cross-over frequency 13k Hz, Phase Margin : 91 Degree

    Best Regards,

    Srikanth Pam

    Online Design Tools