Why is AD8553 instrumental amplifier not working? It only outputs a 1V even after changing the input.

Hi shurp,

Thanks for reaching out to us regarding this.
I checked the AD8553 datasheet, and on the spec table at 5V source, your common-mode voltage should be at 2.5V.

I didn't see any input-common mode voltage vs output swing on the AD8533 datasheet though.
Instrumentation amplifiers normally have a diamond plot spec as explained in this article, so, I think it's worth a try to isolate the AD8553 from the LTC1968s and try it out with a 2.5Vcm to see if we can get our expected output.
Thanks shurp.

Best Regards,
Dann

DBautista Just want to verify, Common Mode Voltage should be 2.5V; is this the input voltage??? On the image that you have provided, if you look below, it tells you that the input voltage range is 0 to 3.3V. I think I am missing a concept here. How is Common Mode Voltage different from Input voltage range?

Hi shurp,

The input voltage range could be the differential input voltage you can input on the instrumentation amplifier.
It is also indicated at the top of the spec table Vin = Vinp - Vinn.

It also confuses me as the datasheet don't have a diamond plot on its TPC and I still find it odd that you get 1V at the output. That's why it would be good to test it out when isolated from the LTC1968s, out of curiosity, have you checked the actual output of these LTC1968 through the scope along with the AD8553's output?

I currently don't have an AD8553 but will try to work on getting a setup to test out the input characteristics myself. One more check shurp if you may, can you double check if your pin 6 is actually connected to Vs? because the datasheet explicitly say to not leave it floating.
Thanks shurp. Will surely work this out, thank you for your patience.

Stay Safe.

Best Regards,
Dann