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.

Just wanted to ask whether my circuit configuration is correct? circuit

Primarily the questions I have are:

  1. MOSFET Q1 is there to act as reverse polarity protection; is this okay to use?

  2. 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?

  3. 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?

  4. 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?

  5. 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?

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    \$\begingroup\$ What is the batteryy voltage and please show the power pins of the op-amp connected to the relevant rails. \$\endgroup\$ – Andy aka Dec 10 '16 at 10:12
  • \$\begingroup\$ I've updated it @Andyaka. New image of the circuit. \$\endgroup\$ – deki Dec 11 '16 at 2:42
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    \$\begingroup\$ Are you including charging? Why not? \$\endgroup\$ – Ignacio Vazquez-Abrams Dec 11 '16 at 2:57
  • \$\begingroup\$ Charging for the LiPo battery? Yes I plan to include that. Just need to find a suitable controller. Right now my concern is to do with the input selection circuitry. \$\endgroup\$ – deki Dec 11 '16 at 4:01
  • \$\begingroup\$ Is anyone able to help out with my questions? There's gotta be people who know more about this. \$\endgroup\$ – deki Dec 12 '16 at 21:14

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