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CAB5R0 NTC location in the power module

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Prathik
Prathik Contributor Level 2
in Module Products

Hello,

I just wanted to find out where in the CAB5R0 SiC MOSFET module the NTC thermistor is placed? Does it measure the hotspot temperature of the power module? How far off is the actual junction temperature from the temperature of the measurement point of the NTC?

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  • Forum_Moderator
    Forum_Moderator Wolfspeed Employee - Contributor Level 5
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    Thank you for your post, it has been approved and we will respond as soon as possible.

  • AustinC
    AustinC Wolfspeed Admin - Contributor Level 4
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    Hi Prathik,

    I've included an image of the internal module layout for the CAB5R0A23GM4 below to make the placement of the thermistor clear in relation to the SiC MOSFET die. As is standard with thermistors in power modules, the temperature of the NTC is more indicative of the substrate/baseplate temperature and is only loosely correlated to the die's junction temperature. For this reason, most users choose to utilize the NTC as a safety limit switch to detect an issue with the cooling system such as coolant flow blockage or heatsink fans not running as opposed to a precise temperature feedback of the die's junction temperature.

    WolfPACK 2.3 kV GM4 NTC Placement.png

    Best Regards,

    Austin C.

  • Prathik
    Prathik Contributor Level 2
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    Hi Austin,

    Thank you for the explanation. I think what this means is the temperature indicated by the NTC is closer to the temperature of the heatsink (or a few degrees above it) and cannot reliably be used for the junction overtemperature protection.

    At full power dissipation, how much hotter can I expect the NTC to be than the temperature of the heatsink that the module sits on so that I can implement some form of overtemperature protection based on what I know will be the maximum heatsink temperature in the worst case scenario?

    Thanks,

    Prathik

  • ChrisN
    ChrisN Wolfspeed Admin - Contributor Level 4
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    Hi Prathik,

    I provided a comparison between NTC thermistor temperature and junction temperature for a liquid-cooled XM3 power module based system using 60ºC coolant. In this example system, the junction temperature is measured at 150ºC while the thermistor measures only ~80ºC. This figure and more information about the example system are provided in PRD-08376.

    The correlation between thermistor and junction temperature is heavily dependent on the power module and cooling solution employed. This can even be observed in the example figure where thermistor temperature decreases as the flow rate is increased, even with the same coldplate as the junction temperature is held constant. For an accurate correlation, it's best to perform simulations or experimental measurements of the entire thermal stackup in example operating conditions.

    image.png

    Thanks,

    Chris N.

    Prathik
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