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LMZ31710: About the difference in design results by WEBENCH

Part Number: LMZ31710

Always I am indebted.
I have purchased your product LMZ31710RVQR.
We are also reconsidering the power supply circuit when revising the board.
Comparing the results of WEBENCH in 2019 with the current results, the value and number of output capacitors are different.
Please tell me the reason why the result of WEBENCH changed.
Also, the value and number of output capacitors were determined from the WEBENCH results in 2019, but should I change them according to the current WEBENCH results?
The value and number of output capacitors seem to be quite different, so I can't tell if it's okay to match the current WEBENCH results.
We apologize for the inconvenience, but please reply as soon as possible.

  • Hi User,

    You are correct. The Webench model has been updated after 2019 (particularly Cout selection). We do these changes to improve upon the current model and to support new features. Here changes were done add new feature (to give more options for cout selection). 

    I will suggest to use above features to adjust the cout for your current design. Kindly use same switching frequency for new design as you have used in 2019. Update switching frequency using below feature in current Webench.

    After adjusting the above parameters for Cout, we can also try and run electrical simulations for the design which will help us to make the decision. We can always change cout to a custom value to meet our requirements (in your case older 2019 values) and run electrical simulations.  

    Electrical Simulation feature:

    Alternate Cout selection:

    The older version of cout selection was also correct and can be used. My suggestion would be running thorough simulations, testing all the operating values (ripple/overshoot/undershoot requirements) before proceeding. Hope this helps. Kindly share older and new design reports if you still need help with this.

    Kind Regards

    Bhushan

     

     

     

  • Always I am indebted.

    2019 results Cout = 100uFx3, Coutx = 47uFx1
    2021 results Cout = 68uFx2

    1. What is the technical reason why the capacity and number of Cout have changed?

    2. Will the impact of the difference between 2019 and 2021 Cout be a lower price?
       What are the other implications?

    3. I think Cout should be changed according to the 2021 results,
       Please tell me the grounds.


    Thank you for your cooperation.2019_WBDesign2.pdf2021_WBDesign13.pdf

  • Always I am indebted.

    2019 results Cout = 100uFx3, Coutx = 47uFx1
    2021 results Cout = 68uFx2

    1. What is the technical reason why the capacity and number of Cout have changed?

    2. Will the impact of the difference between 2019 and 2021 Cout be a lower price?
       What are the other implications?

    3. I think Cout should be changed according to the 2021 results,
       Please tell me the grounds.


    Thank you for your cooperation.

  • Hi,

    We keep improving our tools.
    Last year we went through and improved the calculations for quite a few WEBENCH models.
    The new equation should be better, the older model was a bit too conservative.

    The changes we made were to make the model to pick more reasonable amounts of components and reduce the costs involved.
    We have also enabled advanced options for a user to specify their transient % requirements and pick the cap based on that.

     Hope this addresses your concern.

    Regards,

    Yitzhak Bolurian