Designing an adau1701 product. Hopefully an easy one here: Want to support 44.1, 48, and 96K sample rates (using an external MCLK source), with the same input sensitivity. The spec says to scale ADC_RES and ADCx resistor by frequency. But each scale by the same factor, therefore as frequency changes the input scaling should be the same? Can someone offer some wizdom here. Looks to me no change is needed. Design for 44.1K @ 100uA. Maybe lose of a couple dB's SNR @ 96K?

If you use the same resistors in series with the ADC inputs for different sampling rates, then your full-scale input value will differ for each different fs. For example, using the equation for the R_inputtotal calculation on page 18 of the ADAU1701 datasheet, to get a 1 Vrms full-scale input voltage, you will need the following resistor sizes (total resistance, including 2k internal resistor):

48 kHz 10 kohm

96 kHz 5 kohm

44.1 kHz 10.9 kohm

If you keep the input resistor value constant (assume 10k), then the full-scale input voltage at the different sampling rates will be:

48 kHz 1 Vrms

96 kHz 2 Vrms

44.1 kHz 0.919 Vrms

So, if you need to support different sampling rates in your design, then I would recommend that you have a way to support different input resistances. Otherwise, your design will end up with different full-scale voltage specs, depending on the sampling rate.