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TMP61-Q1: explain max and min resistor

Elec Cheng
Expert 7055 points
Part Number: TMP61-Q1
Other Parts Discussed in Thread: TMP61

Hi Expert,

In calculation excel tool, I see bel0w tables. Could you please help explain what Min and Max resistor mean? I also see line1 and line2 have some resistor rang overlapping? Do you consider Vbias and Rbias error/tolerance in below table? Thanks a lot for help!

BR,

Elec Cheng

  • 0
    TI__Genius 9675 points

    Hi Elec,

    The min and max resistance columns factor in the TMP61 tolerance spec from the datasheet shown below:

    From the table you've shown the typical resistance is multiplied by the tolerance % and then both added and subtracted to determine the min and max values.

    6603Ω * .015 (1.5% tol spec at -40°C) = 99Ω

    Min resistance = 6603Ω - 99Ω = 6504Ω

    Max resistance = 6603Ω + 99Ω = 6702Ω

    This does not account for the Vbias and Rbias error/tolerance.

    We recommend using the 4th order polynomial rather than the Look Up Table as a preferred temperature conversion calculation method. You can find more information on the 4th order polynomial tab of the Thermistor Design Tool.

    Jalen

  • 0 in reply to Jalen Tate89
    TI__Expert 7055 points

    Hi Jalen,

    Thanks for your quick reply!

    I have two more questions:

    1. Elec Cheng said:
      I also see line1 and line2 have some resistor rang overlapping?

    Will this be a problem if I use this lookup table? 

    2.

    Jalen Tate89 said:
    4th order polynomial tab

    Which one do you mean? Does the "interpolation from lookup table" come from "4th order polynomial"?

    Thanks!

    BR,

    Elec Cheng

  • 0 in reply to Elec Cheng
    TI__Expert 7055 points

    Hi Jalen,

    Add the screen shot for question 2.

    BR,

    Elec Cheng

  • 0 in reply to Elec Cheng
    TI__Genius 9675 points

    Elec,

    1. Yes, that is something you will have to consider if you use the Look Up Table method. This is one reason why we recommend the polynomial approach.

    2. Either the "4th Order Polynomial TMP vs Res" or "4th Order Polynomial TMP vs Vdc". The difference between the two is that the formula will result in a temperature value based on either measured resistance or measured voltage respectively.

    Jalen

  • 0 in reply to Jalen Tate89
    TI__Expert 7055 points

    Hi Jalen,

    What about this one?

    Elec Cheng said:
    interpolation from lookup table

    BR,

    Elec Cheng

  • 0 in reply to Elec Cheng
    TI__Genius 9675 points

    Elec,

    The "Interpolation from Lookup Table" tab determines the temperature by resistance value. You can use a 1°C look up table or the 5°C and based on the resistance value a temperature between the stored values in the look up will be determined. The 5°C method uses less memory than required for a 1°C lookup table. It is a linear approximation between the lookup table points and does not apply a 4th order polynomial. 

    The 1°C Lookup Table is provided on the "Lookup Table" tab. The 5°C Lookup table is provided in the "Interpolation from Lookup Table" tab. 

    Jalen