Hi,

For your general understanding: A delta-sigma modulator is a feed-back system. For input signal larger than the max. feedback (reference voltage), the modulator can't be stable. This is your full-scale input, which depends directly on the reference voltage. Depending on the loop filter, the modulator turn instable already for smaller input signals (e.g. 0.5*vref).

The dynamic range is therefore given by a lower value (SNR=0dB) and full-scale (or where SNR becomes 0dB again due to instability).

Hope this helps!