INA819: Output not coming as expected

Hari,

• When I run your simulation in TINA-TI, I also see wrong behavior on the INA819. 
• For debug I added in current meters on the supplies of the INA819.  I see extremely high currents (e.g. 1.6A).  See PT100_INA_with_meters below.
• I built a simple version of the circuit that only has the INA819 with supplies.  I set the input voltage with DC volage sources.  In this case the simulation works as expected.
• I copied and pasted the entire schematic into a seporate file.  This version required a change in the analysis parameters ("DC Convergence of nonlinear circuits") but did eventually have a valid DC operating point.  In this version, the amplifier U2 is driven into the supply rail.  See copy RTD.
• I know this isn't a solution but I hope it helps you move in the right direction.  I will take a closer look at the overall circuit and function tomorrow and see if I can determine the issue.  I think I may need to gain a better understanding of the goal and purpose of each block.  For example, I don't really understand why T1 and T2 are being used.  Normally this would be included to allow for higher drive current.  However, in this case the circuit drives a 54.9k load.  This load does not require much current so why include T1 and T2.  I think this is a PID loop and the that is monitoring and adjusting the current drive.  Is there a reason you you don't just use a standard V-to-I converter?  Please help me better understand the goal of this circuit.

PT100_INA-with-meters.TSC

copy RTD.TSC

I hope we can help you solve this issue soon.  Best regards, Art

Hi Kay,

Thank you for your support.

This is a PI controller. I_PT100_SET is the signal coming from a DAC.

I_PT100_ACT is going to ADC STM32.

The load resistance is 54.9 Ohm sorry for my mistake.

Regards

HARI