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CSD18532Q5B: Psi-JT Thermal characterization parameter

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Replies: 3

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Part Number: CSD18532Q5B

Can you provide the  ΨJT thermal characterization parameter for this part or a similar part in the same package?  It would be helpful to have to estimate junction temperature when I measure my boards.  I note that in a thread earlier this year (e2e.ti.com/.../565594), you mentioned that you did not have this data for the OP's part.  I am hoping that in the interim, your team has started gathering this data. 

Thanks,

Rod

  • Roderick,
    Unfortunately, this is still not a parameter we characterize.

    The junction to base thermal impedance is provided in the datasheet. The junction to top thermal impedance is on the order of 12-15degC/W.

    As for what the real junction to ambient thermal impedance of your application with be, that is something that must be simulated for your end system.

    Best Regards!

    Brett Barr

    Product Marketing Engineer

  • In reply to Brett Barr1:

    Hello Brett,

    I saw the normal parameters reported on all datasheets: junction-to-case and junction-to-ambient.  And I understand their limitations and the need to model or simulate the specific application.

    I had never heard of the Psi parameter until I read about it in TI's application notes.  It was exactly what I was looking for: a way to help estimate Tj in a working prototype.  The "case" temperature at the thermal pad is hard to measure on a PCB because it is underneath the device and heat spreads vertically and horizontally through vias and copper planes.  You don't want to put a thermocouple onto a switching node, and with IR it is so much easier to get the case temperature than the temperature right next to the device.

    Thanks for the rough value, that helps.

    May I recommend that TI become a leader in this area and start providing Psi on datasheets, with an appropriate note as to its use and a link to application notes? 

    Thanks,

    Rod

  • In reply to Brett Barr1:

    Hello Brett,

    My name is Toshio Fukumoto. Im FAE of
    My Customer requests the Psi-JT and Psi-JB of CSD18537NQ5A, CSD18563Q5A, CSD18540Q5B, and CSD18532Q5B.
    They want to use FETs with TPS40171 (DC/DC Controller).
    Package top temperature of CSD18537NQ5A is over 88deg-C.
    They want to estimate janction temperature of FETs.
    Please tell me the better method.

    Thank you.

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