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TMP117: Using TMP117AIDRVR for temperature data logging with thermocouples

Martin Holguin
Intellectual 340 points
Part Number: TMP117

Hello,

I'm designing a temperature data logger for thermocouples and I was considering using the TMP117AIDRVR for measuring the cold junction, but I'll be using more than one thermocouple. So, I was thinking of extending an isothermal plane along all the connectors and connecting them to the thermal pad of the TMP117AIDRVR. This means that the thermal pad of the TMP117 isn't directly connected to GND but to a large floating copper mass that extends across all the thermocouple connectors. Would this cause any issues in the normal operation of the IC?

  • +1
    TI__Expert 7170 points

    Hi Martin,

    Extending the thermal plane is ok as long as you take into account the following points:

    • A large thermal plane will increase the thermal mass of the heat source that the TMP117 is thermally coupled to. This would reduce response time and may introduce a slight offset at the cold junction when compared to junction temperature. The larger the plane, the more prominent these will be. Note that this is a setup/system consideration rather than IC behavior.
    • Although the thermal pad of the TMP117 is not electrically connected to the die, this device is not rated for any kind of isolation on the thermal pad and therefore no voltage should be applied to it. Leaving it floating is ok.

    Best regards,

    Simon Rojas

  • 0 in reply to Simon Rojas Avila
    Intellectual 340 points

    Hi ,

    itt's great to read that. I did take into account the thermal issues that could arise if the copper mass were too large. It's possible that the furthest point may be at 20°C and the closest point to the thermal pad could be 20.3°C, but the distances are small, around 40mm, and the device should have a total error of 0.5°C to 0.7°C, which makes me think it should yield good results for my application. Thanks