AD822 issue

[ircrashed]

Hello Fellow Electronics Enthusiasts,
I have a couple of AD822 single supply op amps. I wanted to clear one thing that is if i connect both the inputs of the op amp to the ground i still get a voltage of 5mV at the output. Is this normal or is there a problem with my ICs. Should the voltage be very close to zero if both the inputs are connected together and grounded.

 

[gophert]

I think you need a 5k load on the the output (to ground) - otherwise you can expect some mV of offset (and some feedback is needed (even unity gain feedback. That is, connect (-j input to the output and connect (+) input to ground.

 

[Diver300]

If both the inputs are the same, the output voltage is difficult to predict. The input offset is +/- 0.1 mV typical, and the gain is typically 1000. That would give the output voltage as being +/- 100 mV typically with the inputs connected together.

Also, the output saturation voltage with minimal load is about 5 mV so I don't think that you will get a lower voltage than that, even if the -ve input is larger than the +ve input.

The data comes from here:- https://www.analog.com/media/en/technical-documentation/data-sheets/AD822.pdf

 

[danadak]

Both inputs to ground then Opmp is acting as a comparator, so Vout = Aol x Voffset,
Aol for this part is 500,000 min with no load on output. So 500, 000 x Voffset = the
output V you will get. If sign of offset is - then it drives output to ground. Also keep in
mind that Aol is min, it can vary as much as 100's of % so output very unpredictable as
pointed out Diver300.


Regards, Dana.