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TPS709: The expected device temperature with a corresponding performance

Ralph Holzmann
Prodigy 10 points
Part Number: TPS709

Dear experts,

I use the device "TPS70933DBVR". I simulate my requirements for the device in the Webench. Vin is 24V for me and my current is 20mA. According to the result of the simulation, the "IC junction temperature" is 113.11°C. Does this actually mean the temperature of the device or does it mean the heating of the environment (Junction-to-ambient).

When I want to calculate the temperature of the device, I use the formula for "Junction-to-ambient thermal resistance" or the "Junction-to case (top) thermal resistance"?

Thank you for your help.

Best regards

  • 0
    TI__Mastermind 37005 points

    Hi Ralph,

    You should use the junction to ambient specification unless you have a thermal heat sink of some kind dissipating the heat, in which case you would use the junction to case thermal resistance parameter.  The junction to ambient thermal resistance listed in the datasheet is based on the industry standard JEDEC standard.  Please see the following application note for additional details on the thermal metrics.

    https://www.ti.com/lit/an/spra953c/spra953c.pdf?ts=1611605531135

    The junction to ambient thermal resistance is heavily dependent on the board layout, and your layout may perform better than the JEDEC standard layout.  To that end, we also have an app note which you can use to determine your board specific junction to ambient temperature.  Please see the following link:

    https://www.ti.com/lit/an/slvae85/slvae85.pdf

    For reference, we've found that our EVMs perform on par with the "thermally saturated" board shown in this app note which would result in an expected Rja which is ~54% of the JEDEC number listed in the PDS (Rja=212.1C/W).

    Thanks,

    - Stephen