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WEBENCH® Tools/LMR23625-Q1: please check the thermal simulation result right or not?

Alpha Han
Expert 3750 points
Part Number: LMR23625-Q1

Tool/software: WEBENCH® Design Tools

Hi, Team:

when we design power with webench such as LMR23625-Q1, we found the IC die temperature and top temperature are the same. IC die and IC top power dissipation are also the same.

But I think the top and die temperature should be different. Can you help to check and advise what's the reason and how to understand these result?

https://webench.ti.com/appinfo/webench/scripts/SD2.cgi?ID=208521::power::alpha.han@ti.com

https://webench.ti.com/appinfo/webench/scripts/SD2.cgi?ID=208521::power::alpha.han@ti.com

  • 0
    TI__Expert 6245 points
    Hello Alpha,

    Could you please use Webench to share your projects with me, robert.blattner@ti.com? Currently, I cannot look at them.
  • 0 in reply to Robert Blattner
    TI__Expert 3750 points

    Have share you the design. Please check the thermal performance.

    Now, Ttop=Tdie，which seems  not real.

  • 0 in reply to Alpha Han
    TI__Expert 6245 points
    Hello Alpha,

    It appears that the simulation is OK. Almost all of the heat is running from the die, through the pins, then into the PCB. The top of the die is small and there is no air flow assumed, so the top of the package is the thermal equivalent of an open circuit. Like an electrical Kelvin sense, the top of the package remains at almost the same temperature as the die. In the datasheet, the relevant parameter is called RthJC(top) but should be called PsiJT (These two specifications are swapped in this datasheet) which is listed as 0.3 C/W. For a detailed description of what these numbers mean, see that app note referenced in the note below the thermal characteristics table in the datasheet. For a non JEDEC board like the one simulated this number can be 2x larger. This times 2.3 W generated in the die gives about 2 C drop from die temperature. It is also a little confusing that they list total power for the top of the die. Looking at the rest of your project, 2.3 W is the total heat generated in the die.

    If I have answered your questions please click “resolved”, otherwise, please reply to this thread