Tool/software:
Hi
I am using the ADS1234 component, with three channels connected differentially. I want to connect the fourth channel in a single-ended configuration to measure a temperature resistor. The gain I am using is 64. Should I connect the negative input of the channel to some reference voltage, and does the positive input also need to be connected to some reference voltage?
Hello Yakov,
There is a common mode requirement for the ADC inputs when using a gain of 64 or 128. Each of the inputs must be in the range of 1.5V up to 1.8V when using a 3.3V supply. You can meet this requirement on the negative input by using a voltage divider from 3.3V supply to mid-supply of 1.65V. However, you will need to ensure the positive input is also in this range for the expected temperature range that you want to measure.
Another option is to change the gain to 1 or 2, which bypasses the common mode limitation, allowing connection of the negative input to ground. If you want to keep the gain set at 64, you will need to adjust the resistor bias values to stay within the allowed input range. For example, using a bias network with 10k+Thermistor+10k, where the NTC thermistor is 100Ohm at 25C will allow temperature measurement in the range of about 15C up to 200C
Regards,
Keith Nicholas
Precision ADC Applications
