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TMP61: TMP6131LPGM

Souheil Slim
Prodigy 80 points
Part Number: TMP61
Other Parts Discussed in Thread: TMP6-THERMISTOR-DESIGN

Tool/software:

I downloaded the latest version of the TMP6-THERMISTOR-DESIGN tool from TI’s website. (Date: May 30th 2025)

I’m trying to generate a resistance vs. temperature table for the TMP6131LPGM with:

RBias = 14 kΩ (1%)

VBias = 5.1 V

Step = 1 °C

However, the RBias value seems fixed at 10 kΩ and I can't change it.

Question:

Could you please advise how to set a custom RBias or help generate the table with these parameters?

  • 0
    TI__Genius 12185 points

    Souheil,

    You are correct that the RBias value is locked at 10KOhms, and that it cannot be changed. The characterization data embedded int the tool was done for a 10Kohm bias resistor, so the tool is only valid for that configuration.

    I strongly recommend switching your RBias from 14KOhm to 10KOhm so that you can use the thermistor design tool. With the 10KOhm bias resistor, we guarantee the temperature accuracy and you will have access to the polynomial coefficients & LUT in the design tool.

    Is there a reason you want to use a 14KOhm bias resistor?

    Thanks

    -Alex Thompson

  • 0 in reply to Alex Thompson
    Prodigy 80 points

    The TMP6131LPGM is connected in series with a 14 kΩ resistor (RBias) to a fixed 5.1 V bias rail (VBias) to generate a voltage output VTemp. This voltage is fed to a voltage follower and non-inverting amplifier with a negative offset, which translates the VTemp to a 0–5 V signal for a control system.

    Design targets:

    VTemp ~ 1.947 V at +1 °C --> VOUT= 0 V

    VTemp ~ 2.868 V at +125 °C --> VOUT= = 5 V

    Due to existing PCB constraints:

    VBias = 5.1 V (cannot be modified).

    The Vref=2.5 V used in the conditioning circuit is fixed  (cannot be modified).

    Consequently, the only adjustable parameter is the RBias resistor, which has been set to 14 kΩ to satisfy the required transfer characteristics.

    Question: Given that RBias is fixed at 14 kΩ, how can we derive the TMP6131LPGM resistance table versus temperature ?

  • 0 in reply to Souheil Slim
    TI__Genius 12185 points

    Souheil,

    It would take a lot of testing to create a new resistance table for a different bias resistor vs temperature. You would need a repeatable and accurate temperature testing system, like an oil bath since ovens have too much temperature volatility. Then you would need to characterize many TMP61s (ideally at least 30 for a robust sample size) over temperature to measure VTemp. Then you would use that value to calculate the resistance, and once you have all the resistances over temp, you could create your own 4th order polynomial fit or a look up table like we have in the design tool for 10KOhm. I don't recommend you take this approach since it will be a very significant time and likely cost investment. 

    Can you elaborate on why the existing transfer characteristics require a 14Kohm bias resistor? I think the better path here is modifying things to get a 10Kohm bias resistor.

    Thanks

    -Alex Thompson