What SMD is "A40" and "SB"?
The bottom of the two is a SOT23-6 package (3 x 1.5mm, 6-pin).
With the marking code, that could indicate something like an OPA363 Operational Amplifier for TI. Does seem odd, but the pinout matches fairly well. Not entirely sure what it's doing in the circuit though.


From the update of a second board, AAUW is again as SOT23-6 package, this time a Maxim Integrated MAX4237EUT device. This is also a single channel op-amp with the same pinout, so that suggests that the TI part is correct.