I'm making a development board, and trying to sort out the input selection circuitry, where if a battery (3.7V lipo) and USB is connected at the same time, it doesn't damage the circuitry, by stopping current flowing back into the USB.
So the design I followed was taken from the Arduino schematic: https://www.arduino.cc/en/uploads/Main/arduino-uno-schematic.pdf and I chose the linear regulators + op-amp based on their properties.
Primarily the questions I have are:
MOSFET Q1 is there to act as reverse polarity protection; is this okay to use?
MOSFET Q2 acts as an ideal diode by permitting either the op-amp to drive the regulator, or the USB, depending on whether the battery is connected. Is this correct?
Is the 5V regulator correct? Other configurations have a capacitor on the output, but the reference schematic for this didn't have one; is it necessary?
The 5V regulator output also goes into the input of the 3.3V buck converter, so it can be supplied by a stable 5V, and thus guarantee a 3.3V output; is this correct?
Is it okay to have my Vbat connection pin where it's at, just after Q1? And to have that connected to the input of the 5V regulator?