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INA2321 REF Question

Other Parts Discussed in Thread: INA2321


I am trying to use the INA2321 to amplify signals from two strain gauges - each configured in a quarter bridge circuit. Each circuit is identical to the one in Figure 2 of the datasheet (page 10 and copied below), except that I'm running +3.3V and I'm using both of the provided amplifiers in the dual package.

My gain on both circuits is set to 395X with R1 = 2.05k and R2 = 160k, my bridge circuits (330ohm over 120ohm) both output at around 0.88V (Vin+ and Vin-), and both circuits are provided a 1.25V reference (from the same source).

My question is this: When I disconnect one of my gauges (lower left corner of the above bridge), I see a rise in the shared reference voltage (up as far as 1.58V), an increase in the output voltage of the second circuit, and a change in the resulting gain of the second circuit. I've tried a few different 1.25V references... and though some display better behavior than others, I still see these issues.

I realize that when I do this I'm now operating the first circuit outside of the input common-mode range. Is this what is causing this problem? If so, is there any way to maintain this shared reference and to allow for the disconnect of one of these gauges?

Any insight into this problem would be greatly appreciated!