Is it possible to replace the ref pin of AD620A with a fixed voltage?
Is it possible to replace the ref pin of AD620A with a fixed voltage?


Probably not is the simple answer. 

The DAC output (under software control) will examine the ADC digital output and make an estimate of whether the signal it is receiving needs slightly lowering or slightly raising in its DC offset level. It does this to avoid signal clipping. Clipping the signal means that the top or bottom section of the signal is "out of range" and causing the ADC to end-stop.

This needs to be avoided to achieve maximum dynamic range and so, the DAC will constantly tweak the offset to centralize the signal fed to the ADC.

If your proposed MCU doesn't have a DAC output, you should be able to make an effective DAC output using PWM and a low pass filter. This can then be used to feed pin 6 of the AD620.