As per data sheet page 18 which state Direct out 6 Vrms = 16.9V p-p .
Max = 0x7FFFFF
0 = 0x000000
Min = 0x800000
1H = 16.9 / 1677215 = 1 uVp-p
Is this right .
Your math looks good -- 24 bits (1 in 1677215) at 16.9V works out to 1uV per bit. The lowest bits are affected, however, by the part's noise floor. The AD1955's rated S/N is about 120 dB. You get roughly one useful bit for each 6dB of S/N -- in this case, about 20 bits. So in that sense your useful resolution could be pegged at about 16uV. Still very good -- 16x better than standard CDs, for example.
I agree with Bob that your math looks correct. Remember that the AD1955 is an I-out DAC and the I/V stage is critical for maintaining linearity, low distortion and noise. The gain of the I/V stage can be scaled to provide whatever full scale voltage swing is appropriate for the gain staging of your system, thereby optimizing the performance of the DAC and the system. If you are interested in higher performance, this part can be used in mono mode, requiring two AD1955 for stereo; mono mode improves the SNR and THD+N by 3 dB.
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