I understand VREF=REF(+)-REF(-)
But, I'm NOT sure how REF(-) is used.
So, would you teach if my setting works correctly for AD7177-2 below.
ADD1=AVDD2=IOVDD=REF(+)=2.5V, AVSS=REF(-)=-2.5V and analog input range: ±2.5V/gain
I would recommend to use our Virtual Eval online tool to help you understand the allowable configurations for the part such as Analog input, supplies, timing, etc.
But what you have provided above is correct and within the AD7177-2 specs. The absolute input voltage per pin is +/-2.5V but the differential input can go +/-5V as VREF= 2.5 - (-2.5V) = 5V.