Hello,

 

I am attempting to stand up a low-side current sense amplifier circuit using the OPAx197. I selected the OPAx197 simply because it is already in the larger design. I have tired to "dumb down" the circuity significantly; meaning that in this simulation I am not showing the half bridge circuits or FET drivers. I am not sure if I have dumbed down too far, and that's what's causing issues. My intent was to pass +/- 2A through the sense resistor.

 

Anyway, when I simulate with the OPAx197 opamp, I see the output of the opamp rail and there appears to be a phase inversion. I am totally stumped here and I've been staring at this for so long that I am sure I could be missing something obvious.

 

Here are my files:

 

Thank you and Happy Friday!!

-May

May wrote, "OPAx197 simulation gone wrong"

 

I would say there is a pretty good chance that the simulation is right.  It is your expectations that were wrong.

 

Did you really expect the amplifier to have an input voltage range from -28 V to +28 V, with only +5 V and Ground for supplies?

 

Check the amplifier's Absolute Maximum ratings.  You have greatly exceeded them.  You might have let out the "magic smoke".  You cannot expect that the amplifier works normally when the transistors inside it have fried.  This amp has rail-to-rail inputs, but that does not include beyond-rail-to-rail operation.

 

Where the simulation is wrong, is by not showing the smoke.

 

Andy

 

 

Wow. What an idiot I have been. You're absolutely right. My "approximation" of the source is completely wrong. Thank you SO much.

You're not an idiot.  Watch out for those unexpected details that can get you.

 

If you reduce the input amplitude to +/- 0.28 V, it looks OK.  Technically even that goes too much below ground, but it still works, in simulation.

 

Andy