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CSD19538Q2: Temperature Rise and Thermal Resistance

Thomas Westrick
Prodigy 20 points
Part Number: CSD19538Q2
Other Parts Discussed in Thread: LM5146,

In my LM5146 design, my high-side FET is the CSD19538Q2 which has around 0.6W of loss in the 2x2mm package. Is this too much loss for that small package to handle? Also, the thermal resistance is 65W/C, but that is under the ideal conditions stated in the datasheet. In my buck application, the high and low-side FETs will have to be close together and the overall board size will be quite small (probably around 1in2 or less). For this reason, we estimated that the thermal resistance under these conditions would be around double that of the value in the datasheet. Are there more accurate ways to estimate this, or do you have a better estimate for the temp rise in the CSD19538Q2?

Thanks,

Thomas

  • +1
    TI__Mastermind 29525 points

    Hi Thomas,

    Thanks for the inquiry. Estimating thermal impedance and temperature rise for a particular application and PCB layout is difficult. It can be modeled using tools such as Flotherm. Below you will find links to technical articles on how TI specs and tests thermal impedance and the max power that our various FET packages can dissipate. With a good layout on a multi-layer PCB, the 2x2mm SON can dissipate 2.2W max. This is a "rule of thumb" number and the actual performance is highly dependent on the PCB layout and stackup as well as the ambient conditions (temperature and airflow). I think the FET should be able to dissipate 0.6W. I hope this helps. Let me know if I can be of further assistance.

    http://e2e.ti.com/blogs_/b/powerhouse/archive/2016/06/10/understanding-mosfet-data-sheets-part-6-thermal-impedance

    https://e2e.ti.com/blogs_/b/powerhouse/archive/2019/10/29/selecting-the-right-power-mosfet-power-block-package-for-your-application

    Best Regards,

    John Wallace

    TI FET Applications