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TMP75C-Q1: Potting affects on temperature sensor

Natalie
Prodigy 10 points
Part Number: TMP75C-Q1
Other Parts Discussed in Thread: TMP75, TMP75C

Tool/software:

I'm using TMP75 to measure PCB temperature and it's accurate when the device is in open air but when the pcb is in its plastic enclosure and is fully potted its now reading 7C lower than it was before. I think it is reading the temperature of the potting. Is the affects of potting on a temperature sensor known and are is there anyway I can insulate the sensor from the potting? 

  • 0
    TI__Expert 6240 points

    Hello Natalie,

    Thank you addressing your issue. When it comes to protective coating TMP75, the stress could be a concern. What process are you using to coat your devices? What is the thickness of the plastic on top of the device? 

    Best Regards,

    Meredith McKean

  • 0 in reply to Meredith McKean
    Prodigy 10 points

    Hi Meredith, I'm potting the device in a polyurethane potting material (epoxies 20-2183) where it covers the sensor about 1mm and the plastic enclosure is also about 1mm. 

  • 0 in reply to Natalie
    TI__Expert 6240 points

    Hello Natalie,

    We do not have data on how TMP75C will preform with coated polyurethane potting material. When coating the devices, there are two sources of error. The first error is strain sensitivity where the device could be sensitive to strain which will vary depending on the molding material and thickness. The second error is added thermal mass which affects the thermal response of the device and will add a delta in junction vs ambient temperature.

    Best Regards,

    Meredith McKean

  • 0 in reply to Meredith McKean
    Prodigy 10 points

    Do you have any recommendations for something I can use to insulate the sensor from the potting material? 

  • 0 in reply to Natalie
    TI__Expert 6240 points

    Hello Natalie,

    Can you please clarify what you are trying to insulate from? What exactly is the temperature sensor measuring? Can you provide for details about the setup? Can you change the potting material? If you believe the coating on temperature sensor is causing the accuracy issue, I would recommend to reduce the thickness and choose a material with a good thermal conductivity for better thermal response. 

    Best Regards,

    Meredith McKean