This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TMP61-Q1: how to get proper formula when Rbias is not 10k?

Part Number: TMP61-Q1

Hi Epxert,

I see in calculation sheet that for 4th order polynomial the Rbias is fixed at 10k. Can we change Rbias to another value? What would it affect? If then, how can I get proper calculation formula? Thanks.


Elec Cheng 

  • Hi Elec,

    The Rbias value in the Thermistor Design Tool is fixed at 10kΩ and cannot be changed if using the TMP61-Q1. Due to the intrinsic nature of the TMP61-Q1 changing the bias resistor will change the current through the device. This will result in a different resistance to temperature table for the device. Since the resistance to temperature will change due to any Rbias change, there are too many permutations that we would need to validate. If you plan on using a Rbias value different than 10kΩ you will need to validate the new Resistance to Temperature table and then generate a new 4th order polynomial.

    We have the following note in the Thermistor Design Tool:

    "TI thermistors are silicon-based linear PTCs and are affected by the total current and voltage applied to the divider circuit. Changing the top resistance or bias voltage will affect the resistance to temperature relationship and may cause temperature errors outside of the specified tolerances in the datasheet."

    Additionally, you can use the PSPICE model of the TMP61 to help with validation of a new RT table with configurable Rbias value.