Hi Damien,
Apologies for the delay.
When the analog input buffers are enabled, AINCOM needs to be biased to some voltage above 0.25 V. The analog input voltage will be AIN1-AINCOM. So, AINCOM could be tied to 2.5 V and with bipolar mode selected, the voltage on AINCOM can swing from 0.25 V to AVDD - 0.25V at a gain of 1.
The reference inputs can tolerate the same RC values as the analog inputs in unbuffered mode. So, the reference inputs can tolerate a resistance of 1.4 KOhms and 50 pF capacitance. If resistor/capacitor values larger than this are used, then an external buffer for the reference is recommended as larger RC values will introduce gain errors.
Regards,
Johnny