Unknown SMD Component

Question

I'm trying to find the components of the PCB I have. I have a problem with a 5 pin (SOT23-5) component. Can someone help me with this?

There are version1, version2 and version3 of the PCB and marking codes are AA43, AA44 and AACB respectively.

There is a reset button and an error switch on the board. I measured the voltage values ​​when I pressed any of them (see schematic.)

Answer 1

The usual search from s-manuals (https://www.s-manuals.com/smd/aa) didn't bring useful results.

The part looks like a low voltage op amp judging from the schematic. The right-hand side sub-circuit looks like a low-pass filtered non-inverting amplifier which converts the load current of the top-right NMOS to voltage. And the output goes to MCU (probably to ADC) through another RC low-pass filter. The other sub-circuit to the left is a buffer which gets its input from MCU/1.24V through a RC filter+divider and generates a reference/bias voltage for the amplifier stage for accurate/sensitive current measurement.

So what you can do is to search single low-voltage op amps with SOT-23-5 package from Digikey, Mouser, etc. and check their markings.

Answer 2

This is roughly how that circuit can be re-drawn:

^{simulate this circuit – Schematic created using CircuitLab}

And here is it re-drawn to be easier to follow:

^{simulate this circuit}