I'm revising a circuit for a client, and am looking for a 20 bit D/A. The present circuit uses the TI PCM1702, which is recently gone to "not recommended for new design" status. The DAC is used to produce a control voltage for a PWM circuit. It seems that most, if not all, of the 20+ bit DACs out there now are delta-sigma type. I've never used one of these in such a circuit, they all seem to be for digital audio. I'm not concerned about any DC errors, as the DAC is in a feedback loop and they will be taken care of. I am concerned about noise in the DAC output causing jitter in the PWM signal, though appropriate filtering should take care of that. The DAC output only needs to update at about a 1kHz rate.
That brings up the other problem - do these audio DACs need to be updated at a 44.1 kHz rate? Or can they just be updated at an arbitrary rate? Also, how critical is the clock used to drive the modulator? I'm not likely to have the necessary clock on the board already, although I could add it if necessary (I like to keep the number of clocks to an absolute minimum).
Thanks for any insights.