operational-amplifier
I want to use section A of an LM358 OpAmp to limit the current and section B to convert Arduino PWM to analog, and then connect output B to non-inverting input of input A as reference voltage.
The LM358 VCC is not going to be lower than 12V or higher than 16V.
Is there something like "leakage" of current/voltage or anything else between two sections that can damage the Arduino or two sections are isolated from each other?
They are regulators as you thought.
To properly control the MOSFET on each regulator, the gate needs to rise several volts above the source, probably over 6 volts greater than the source. If the source voltage is 3.3 volts the gate might need to rise as high as 9 or 10 volts when the MOSFET is driving a heavy load current. This means the op-amp MUST be powered from a supply greater than 10 volts.
The non-inverting input is the demand voltage for the regulator - for the 3V3 supply the non-inverting input will be 3.3 volts and ditto the 2V5 supply.
The MOSFET is rated at 20 amps and this means the supply current to the circuit might be in the realm of 5 to 8 amps - try and find a linear voltage regulator that would fit the bill an be a low drop-out type - realistically with a drain voltage of fractionally above 3.3 volts the output would still be in regulation. This is of course due to the op-amp being powered from 12 volts.
As to whether it is a bad design, I'd say not BUT I don't know the full spec of the circuit.
It's not in either of those modes, but it's being used as a differential amplifier:
It doesn't amplify a single signal, either inverting or non-inverting - it amplifies the difference between two signals - in this case the difference in voltage between the two sides of R8.
Best Answer
There is a very slight interaction between the two amplifiers at low frequencies that is likely equivalent to a few uV of Vos shift.
That is in part due to the shared bias network. Changing dissipation from the output section of one amplifier can cause temperature gradients across the die as well has heating, as @analogsystemsrf mentions in a comment, which will cause Vos changes in the other amplifier.
If both amplifiers are working with signals measured in volts it won’t likely be noticeable, let alone problematic.