I am trying to select and ADC with single ended inputs which can input positive and negative voltages (around +500mV to -500mV). Due to the nature of the system I am selecting it for, the voltages cannot be DC biased and also cannot be amplified (in other words the exact DC level is the information). I was wondering if it would be possible to set the reference voltages to REF+ = 500mV and REF- = -500mV, while the power supply is 2.5V to -2.5 V (the ADC allows for true bipolar operation). For instance the ADC I am looking at is an Analog Devices AD7176-2. I noticed in the data sheet that the limits for the reference is that their total voltage difference can be 1V, but the tests they have are only for +5 V to Ground supply, not bipolar operation. Hopefully someone has experience with operating an ADC in this mode. Thanks
The datasheet of the AD7176-2 is pretty careful to always refer to specific pin names, like AVSS or AVDD, rather than just generically talking about "ground".
For example, when they talk about the input voltage range (p. 4), under the line "Absolute AIN voltage limits", they give the min limit as "AVSS - 0.050" and the max as "AVDD1 + 0.05". Similarly when they give the "Absolute Reference Input Voltage Limits" (p. 5), they give the same limits. As long as you obey these limits, the chip should work as advertised.
In particular, if your AVSS is -2.5 V, then REF- of -0.5 V is within the limits.
That said, if you can get the attention of an Analog applications engineer (like if you are doing this for a commercial project or at a university), it wouldn't hurt to show them your final design before sending it out for fab.