The VCM pin provides a buffered output voltage at the mid-point of the AVDD1 – AVSS power supply. The VCM voltage is intended to drive the output common-mode control input of a fully differential amplifier (FDA) to establish the common-mode voltage for the ADC input signal. With many types of FDAs, the same common-mode voltage is provided when the common-mode control input of these devices are floated when using the same power supply. If VCM is not used, the pin can be left unconnected. The VCM output is enabled by the VCM bit of the CONFIG1 register.