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WEBENCH® Tools/TPS54540: IC ThetaJA Effective

K.Hamamoto
Guru 12155 points

Part Number: TPS54540

Tool/software: WEBENCH® Design Tools

Hi

Our customer are going to simulate a thermal situation by WEBENCH. The result are as the following,

https://webench.ti.com/appinfo/webench/scripts/SD2.cgi?ID=207497::power::hamamoto-k@clv.macnica.co.jp

At the above result , the thermal resistance was 26degC/W (ICthetaJA Effective) but the thetaJA is as below on the datasheet.

(ThetaJA is 42degC/W.)

(I understand the thetaJA from WEBENCH is calculated from (59.6C-25C)/1.33W.)

Why and What is the difference?

And if the Ta is 104C, how can we estimate the junction temp? (ThetaJA=26C ? or 42C?. If it is 42C , Tj will be over Abs max.)

Best Regards,

Koji Hamamoto

  • 0
    TI__Intellectual 1625 points

    Hi Koji,

    We are not able to open the above shared link.

    Could you please send us the correct link so that we look at the exact issue you are mentioning.

    Below image describes the steps to share the design.

    Thanks,

    Kiran Kumar

  • 0 in reply to Kiran Kumar10
    Guru 12155 points
    Hi Kiran-san,

    Thank you for your prompt reply.

    Here is a public link,
    webench.ti.com/.../SDP.cgi

    If you can not link the above design,please let me know.

    Best Regards,
    Koji Hamamoto
  • 0 in reply to K.Hamamoto
    TI__Mastermind 29010 points
    Hi Koji-san,

    Thanks for your question. We are using 26degC/W to better match the EVM board layout. We used efficiency and junction temp measurements from the EVM board and found out the effective thetaJA that matches the data closely is around 26degC/W. That is the reason for the lower value of thetaJA. I would use 26degC/W if your board is very similar to the EVM board though it might be slightly different from board to board. So, for higher ambient temperatures, it would be hard to estimate exactly if the junction temperature will tip over and cause issues related to thermal shutdown. Only way to find out would be to build a test board and see if there are thermal issues.

    Regards,
    Amod
  • 0 in reply to Amod Vaze
    Guru 12155 points
    Hi Amod-san,

    Thank you.

    Best Regards,
    Koji Hamamoto