Opamps usually have specs for Vos, Vos tempco, Theta-ja, and max power dissipation. But nobody seems to talk about input offset as a function of power dissipation.
The concern here is thermoelectrics driven by temperature gradients, both inside the chip and on the PC board.
We plan to use an ADA4638 opamp in a situation where we need to keep the max drift down around a few microvolts. The input drift spec is 80 nv/degC max, but I wonder how much offset we might make if we dissipate, say, 100 mW in the amp.
We could add a big ugly cheap follower amp after this good one, inside the loop, just to move the heat away. But space is scarce, so I'd rather not.
I guess we'll have to test it somehow.