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TMP431: Question about Beta compensation

Go
Genius 4220 points
Part Number: TMP431


Hi,

Now my customer have been evaluating TMP431 for measuring internal temperature of some processor.

As a result, the temperature value of TMP431 remote sensing was about 3 degrees lower than the surface temperature of the processor that was measured by themocouple when the processor was at work (around 120 degrees)

when the processor was under suspention, both measured result were almost same (about 25 degrees).

In light of these result, I'd like to know the following questions,

1. When automatic beta correction (data: 0x08) beta setting is enabled,
Will nFactor setting value (Reg: 0x18) be ignored?

2. Related to the above, can we set nFactor value(Reg:0x18) to desired value with automatic beta correction enabled?

3. Is it possible to compensate the gap l told above with any register settings?

4. When automatic beta correction is enabled, TMP431 will select the proper beta range, and Beta Compensation Configuration Register will be set the value with selected beta range automatically. is it right?

Thanks

Go

  • 0
    TI__Mastermind 44035 points
    Hi Go,

    1. No, nFactor and Beta Compensation have different purposes.
    2. Yes.
    3. Yes. You are observing a gain error over temperature (as opposed to an offset) and nFactor is a gain adjustment with regards to temperature.
    4. Yes. Which range is being chosen for your device? If the range is 1111b, your junction does not benefit from Beta Compensation feature.

    Thanks,
    Ren
  • 0 in reply to Ren Schackmann
    Genius 4220 points
    Hi, Ren

    Thank you for your comment.

    I'd like to ask you a follow-up question about nFactor register settings.

    If we try to compensate the gain error I described above,

    How do we calculate(or decide) the proper nfactor setting value for compensation?
    Do we need to know the non-ideality characteristic value of the internal thermal diode of target processor?

    Thanks,

    Go
  • 0 in reply to Go
    TI__Mastermind 44035 points
    Hi Go,

    Sorry for the delay; this week is US holiday.

    In your situation, you'll have to experiment with different settings. To increase by 3C at 120, you'll want to increase N by about 0.0076. However, this will also add about 2C error at 25C. Keep in mind your external reference may not accurately reflect internal temperature due to losses through the heatsink, and that thermocouples have +/-2C accuracy.

    It may be helpful to know N Factor as specified by processor manufacturer, but their characterization method may not match the way that TMP device operate. This can mean that N Factor from manufacturer is not appropriate for use with TMP.

    Thanks,
    Ren
  • 0 in reply to Ren Schackmann
    Genius 4220 points
    Hi, Ren

    Thank you for your comment.

    What do you mean by "external reference"?
    Does it mean the temperature value measured by thermocouple?

    Thanks,

    Go
  • 0 in reply to Go
    TI__Mastermind 44035 points
    Hi Go,

    Yes, I meant thermocouple when I said "external reference." We would normally use a higher precision reference for our work.

    Thanks,
    Ren
  • 0 in reply to Ren Schackmann
    Genius 4220 points
    Hi, Ren

    Really sorry for the late reply.

    I feel the result is unusual that internal temp of processor gets lower than surface temp.

    In this case, should we consider that the main cause of the gap was measurement error of external reference?

    Thanks

    Go
  • 0 in reply to Go
    TI__Mastermind 44035 points
    Hi Go,

    Yes, there is definitely a level of uncertainty that you won't easily overcome with the tools that you have.

    Thanks,
    Ren
  • 0 in reply to Ren Schackmann
    Genius 4220 points
    Hi Ren,

    Thank you for your prompt support.

    Out of curiosity, can I ask the specific method for "higher precision reference"?

    Is it constant-temperature oven or something?

    Thanks,

    Go
  • 0 in reply to Go
    TI__Mastermind 44035 points
    Hi Go,

    We use calibration baths with a special non-conductive thermal transfer fluid. The stirred fluid has temperature stability and uniformity better than 0.01­C.
    us.flukecal.com/.../calibration-baths

    Thanks,
    Ren