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TPS543C20: TPS543C20 webench sim about output cap

Tsukui Yusuke
Guru 21930 points
Part Number: TPS543C20

Hi,

Could you tell me about TPS543C20 webench sim?
I simulated it under the conditions.

Vin=8V,Vout=0.95V,Iout=16A
webench.ti.com/.../WebenchReportsServlet

However, the output capacitor can not be changed to a ceramic capacitor.
Why is this?
I would like to install 100uF ceramic capacitor in parallel.
I want to know the background of the constraints stated in the red.



Best Regards,
Yusuke/Japan Disty

  • 0
    TI__Guru**** 191445 points
    I tried a different design and Webench would allow me to select a wide variety of capacitor types including polymer and ceramic. Your design seems limited to electrolytic types. I will move this to the Webench forum. Maybe they will know why.
  • 0 in reply to JohnTucker
    Guru 21930 points

    John-san,

    Thank you for your response.
    I also confirm that only electrolytic capacitors can be used.
    I want to make sure the load transients using ceramic capacitor.
    I am looking forward to hearing from WEBENCH team.

    Best Regards,
    Yusuke/Japan Disty

  • 0 in reply to Tsukui Yusuke
    TI__Guru**** 191445 points

    TPS543C20 uses a proprietary control topology.  It will not be possible to share much detail about it due to pending patents.

  • 0 in reply to JohnTucker
    Guru 21930 points

    Hi Team,

    Can I get the information?
    Customers want to use ceramic capacitors for Cout.
    Is it possible to simulate using a ceramic capacitor?
    If you need more information or if  I should  clarify my comment ,
    please let me know.

    Best Regards,
    Yusuke/Japan Disty

  • 0 in reply to Tsukui Yusuke
    TI__Guru**** 191445 points
    I can change it manually as a custom component, but of course I get a warning about ESR being too low. There is not an option to add mixed capacitors for this device, so you have to pick one or the other type of capacitor. I think you best bet is to use the pspice transient model and check the load step response for stability, or better yet, modify and test and EVM.
  • 0 in reply to JohnTucker
    TI__Intellectual 2290 points

    The WEBENCH design is recommending only non-ceramic caps due to a constraint in the minimum esr on the output cap. The esr constraint on the output cap comes from the ripple injection requirement needed by the TPS543C20. One thing that can be done to be able to select ceramic caps is, to go to the select alternate parts page and relax the min and max esr limits for the output cap as shown below highlighted in yellow. Originally those values were 0.1 Ohm for upper bound and 5mOhm for the lower bound respectively.

    By updating the values to 8m and 1u, we start seeing ceramic caps in the list. As John mentioned before, the best is to select a ceramic cap with esr close to 5mOhms and verify with pspice that we are not violating the minimum esr requirement.