we would like to use the ADC5940 respectively the ADUCM355 for voltage measurements (OCP, open circuit voltage) on an electrochemical sensor. Concerning this issue, two questions occurred. I guess ADC5940 and ADUCM355 are somehow similar.
1)We want to make a shortcut between the pins CE0 and RE0 and then measuring the voltage between CE0/RE0 and WE0 (OCP). Is it possible to measure that voltage by setting the MUXSELP-bits of the ADCCON-register to 01110 (page 70, ADuCM355 Hardware Reference Manual, https://www.analog.com/media/en/technical-documentation/user-guides/ADuCM355-Hardware-Reference-Manual-UG-1262.pdf respectivley page 61, AD5940 datasheet, https://www.analog.com/media/en/technical-documentation/data-sheets/AD5940-5941.pdf)
2) Which magnitude would be the referring input impedance?
AD5940 is similar with ADuCM355, the difference is ADuCM355 has a cortex-m3 MCU inside.
1. You need to set MUXP and MUXN to the differential voltage you want to measure. For example, set MUXP to pin CE0 and MUXN to SE0 to measure the voltage between CE0 and SE0.
2. There is no input impedance parameter in datasheet, but has a input current. Please check Table 1, ADC INPUT section.