INA849: Issues with output balancing the output using a DC servo feedback

Part Number: INA849
Other Parts Discussed in Thread: PGA2320, OPA192, OPA140


I am using the INA849 in a differential microphone setup as described in the INA849 datasheet on page 24 using a gain setting of 40dB.

For a flexible gain setting of the microphone amplifier the INA849 is followed by a PGA2320 allowing a maximum gain of 40+32=76dB.

In order to keep the DC offset at the output of the PGA2320 at a minimum I incorporated a DC servo over the INA849 using an OPA140 or OPA192, feeding back the output of the INA849 via the OPA192

(setup as integrator with a 100K/1uF integration constant) and its output directly connected to the REF input.

Tina simulations showed this should work fine.

Building the design according to the Tina schematic the output of the INA849 slams to the positive or negative rail and no DC balancing is achieved as I expected from simulations.

I can send the Tina schematic if needed.

Is there a difference in behaviour (internal working) between the Tina model and the actual device that causes this behaviour or do you have suggestions why this happens?