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TMP431: Remote Temperature Readings

Dave Barry
Prodigy 20 points
Part Number: TMP431

I am connecting the TMP431 to a diode-connected PNP transistor inside an ASIC device I want to monitor.  The attached file shows the connections (my design does not use the optional resistors and capacitor so there is a direct connection).  The attached file also contains a typical plot of temperature vs time that I see as the ambient temperature is raised, showing the remote (green)  and local (brown) temperatures reported by the TMP431 along with a heatsink temperature (blue).  The remote temperature reading should track the local temperature curve but with a relatively fixed positive offset. However the remote temperature readings take off at a higher rate and end up maxing out the extended range (the ASIC datasheet says we need to subtract 24C from the remote reading, so the resulting max is 167C).  So the bottom line is that the local temperature readings are good but I don't know what is happening to the remote readings.  Do you have any ideas on what might be going on here?TMP431 Remote Sensing.pdf

  • 0
    TI__Mastermind 28070 points

    Hello,

    Welcome to the E2E Forums!

    The error you are showing is pretty severe. Assuming that the internal diode of your ASIC operates like a normal thermal diode, then the problem is most likely leakage to ground. My first recommendation would be to clean your boards to ensure that there is no leakage current due to flux residue.

    If it persists after cleaning, I would try to repeat the test on an alternate board to ensure that the diode itself is not damaged in some way. 

    Please attempt this and let us know the results. 

    Best Regards,
    Brandon Fisher

  • 0 in reply to Brandon Fisher94
    Prodigy 20 points

    We have seen this on more than one board so I wonder if there is some incompatibility between the ASIC thermal diode and the TMP431?


    For example, the ASIC documentation says that the thermal diode produces an offset in the external temperature sensor that results in a temperature reading that is 24C above the approximate die temperature. That seems odd to me.


    Also, the ASIC documentation recommends a Maxim MAX6657 sensor chip but we wanted a sensor with a wider temperature range. Would compatibility with a MAX6657 somehow explain incompatibility with a TMP431?

  • 0 in reply to Dave Barry
    TI__Mastermind 28070 points

    Hi,

    The MAX6657 should use the same principles for sampling this diode for temperature as the TMP431 and other remote temperature sensors do, so there should not be a compatibility issue. 

    That 24C offset may be from some series resistance of the diode. Do you have series resistance cancellation enabled on the TMP431?

    For reference, what are the other settings of the TMP431 when you are running this test? 

    Best Regards,
    Brandon Fisher

  • 0 in reply to Brandon Fisher94
    Prodigy 20 points

    We are using default settings for all registers except we set the extended temperature range bit in Configuration Register 1.  So resistance correction is enabled.

  • 0 in reply to Dave Barry
    TI__Mastermind 28070 points

    Hi Dave,

    Looking through the MAX6657 datasheet, the biggest differences between how the MAX6657 and TMP431 calculate temperature is going to be the series resistance cancellation, and the Beta compensation features.

    Can you try disabling the resistance cancellation and see if the error persists? This is done in configuration register 2.

    Also, can you try reading back the contents of the beta correction register (register 0x25) to see what kind of transistor configuration the device is detecting?

    Best Regards,
    Brandon Fisher

  • 0 in reply to Brandon Fisher94
    Prodigy 20 points

    We haven’t run the suggested tests yet.  The test engineer is assigned to another task right now and we will get back to this issue when we have a chance.  So please keep this case open.

  • 0 in reply to Dave Barry
    TI__Guru* 91186 points

    Dear Dave - we can keep this open by marking it as "waiting for customer", which I have done - no problem - when you are ready, then you can post again.