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TMP64-Q1: Could I get the Thermistor Tool sheet password to change the top resistor value away from 47 kΩ?

Sebastian Dittmann
Prodigy 10 points
Part Number: TMP64-Q1
Other Parts Discussed in Thread: TMP63

Hi,

In the datasheet it is recommended to leave the top resistor at 47 kΩ, but it may make sense in some applications to do that anyway.

Could you provide the PW to change the value in your Excel tool?

Greetings, Sebastian

  • 0
    TI__Genius 9675 points

    Hi Sebastian,

    Unfortunately, the tool is locked and you will not be able to change the top resistor from 47kΩ. We recommend this because our validation data to generate the RT tables validates this configuration.

    If the 10kΩ variant, TMP6131Q1, can be of use in your application we have a PSPICE model on the product folder here that you can model with different bias resistance values.

    Jalen

  • +1
    TI__Genius 9310 points

    Hello Sebastian,

      The design tool does not allow changing the top resistor for several reasons. The main reason is because the TMP6 family of parts are not resistors. They are silicon. They don't behave like a standard thermistor in the sense that you can calculate the resistances in a divider using Ohms law. 

     Second the dynamic range is smaller than an NTC, so in almost all situations adjusting the top resister will move the divider slope but it will not provide much of a benefit because it is so linear. 

    Third we have locked the top resistor to provide the best performance for a temperature measurement. Although it is possible to change the top resistor, you will have to create the new profile yourself as the design tool will not be able to provide you with the new lookup tables, or the polynomials needed to get the temperature values.

    To create the new profile, you will need to sweep the temperature from -40C to 125C and collect the voltage from the divider at each temperature. Using this information you can create a new polynomial to provide the temperature from the ADC voltage directly without having to calculate a resistance value. This is the most accurate method to get a temperature. 

    If you stay with the fixed top resister value, the design tool already has this information in the temperature from voltage tab at the bottom.

  • 0 in reply to Gordon Varney
    Prodigy 10 points

    Thank you for the detailed answer!

  • 0 in reply to Jalen Tate89
    Prodigy 10 points

    Thank you, we will take it into account.

  • 0 in reply to Sebastian Dittmann
    TI__Genius 9310 points

    Sebastian,

      I think it's important to understand, That you simply can't replace a BJT transistor with a Mosfet. You have to understand the Mosfet and make a few changes. Why go through the effort. Because in most applications the Mosfet is better, more efficient and easier to us once you get use to it.

    The TMP63 parts are the same way. This part is not a direct replacement for an NTC. It is in fact a better, more accurate and easier to use replacement, you need to learn how to use it. We can help you with this. 

    There is a new technology available for temperature measurements and it is the TMP6 family of silicon thermistors.