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TMP61-Q1: How to calculate ADC digital counts for TMP6131 thermistor with 8-bit ADC088S052

Nishant Gupta
Prodigy 40 points
Part Number: TMP61-Q1
Other Parts Discussed in Thread: ADC088S052, TMP61

I want the Digital value for the temperature having 19 degree and 23 degree celcius and 29 degree celcius and our ambient temperature is 22 degree celcius. what will be the we are using biasing voltage 3.3V and Rbias 10K and having 8 bit ADC ADC088S052 which is sensing analog voltage of thermistor. Please help in this regard. I want to map exact digital values and also tell is  there any error in adc or thermistor that needs to be cleared.? And how to check it . Can you please what and how we can make test setup to measure all this and get thermistor resistance vs temperature reading for every resistance. And is there way of approximating digital counts or exact one value . Thermistor we are using is TMP6131LPGM.And for mappping any Excel sheet available please provide for direct calculation 

Thanks & Regards

Nishant Gupta

 

  • 0
    TI__Intellectual 850 points

    Hi Mr. Gupta,

    To get the resistance of the TMP61 from the ADC value for voltage bias, you can use these formulas derived from the datasheet. I have assumed that your ADC supply voltage is 3.3V, same as the TMP61 bias voltage. 

    For the Resistance - Temperature relationship, you can use the thermistor design tool. I have also attached it below with the numbers you provided inputted. Refer to the "Device Resistance Tables" tab or the "Lookup Table" tab for the table. 

    There is maximum 1.5% resistance error in the thermistor. At the temperature extremes (close to 150°C or -40°C) it could be up to ~3°C of error for this configuration. This error would be closer to 1°C in the range closer to room temperature.

    On top of the thermistor error there will be error due to the ADC resolution. On the "Basic Formulas" tab of the thermistor design tool you can see the ADC resolution, which in this case is ~3°C for extreme temps. This could negate the error from the thermistor or add to it.

    It depends on your accuracy needs and operating temperature range, but an ADC with more bits might be needed. 

    Let me know if you have further questions or concerns. 

    Thanks,

    Hypatia

    Voltage_bias_3V3_10k_8bit.xlsm