I have seen in one of our design that +5V(VDD) and -5V(VSS) are connected to AD7226. Does it work?
You need to supply VDD within the range of 11.4V to 16.5V to properly operate the device.
VSS = -5V should be fine.
What's the reference voltage?
Reference voltage is ~1V
You will need at least 2V on the reference pin.
Attached the circuit what we implemented for Reference input. It is working fine.
My query is how does it work with -5V and +5V when the datasheet says the supply voltage should be within 11.4V to 16.5V?
The supply range in the spec table will guarantee that you will be able to achieve the specified performance.
Outside of that, there is no guarantee that the device will meet the specifications.