Hi Frank, Consider all current going through R79. There is a very tiny bias current going into the ADC, but this is so small in comparison to IDAC current, you can ignore this for the calculation. I'm not sure I fully follow your calculations. Essentially you want to make a ratiometric measurement where the code of the ADC relates to the ratio of the thermistor to the reference resistor. You can do this as the IDAC current is common to both. One code (LSB) relates to the full-scale range (FSR) of the ADC and the total available counts. FSR = +/-VREF/GAIN/(2^24 - 1) where VREF is Rref*IDAC. The voltage of the sensor is Rtherm*IDAC. Rtherm = Rref (ADC result)/(2^23)/GAIN. R79 is not a part of the conversion calculation. Its sole purpose is to lift (or bias) the sensor into the proper common-mode input range for the PGA if enabled. Best regards, Bob B
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