Managing reverse currents using MOSFETs
If you are going to use a mechanical switch anyway,then this one is simple and cheap.　Both your supplies will be mechanically isolated.



If you want electric circuit, and if you are sure that 5.3V supply will always be greater than (Pin1 - Vf(diode) - Vf(schottky)) and Pin1 &amp; Pin2 supply won't be less than (5.3V - Vf(diode) - Vf(schottky)), then you can use this diode based circuit.You just need to used diode with high forward votlage drop. And schottky aren't that useful in that case. 







simulate this circuit &ndash; Schematic created using CircuitLab

Else the @next-hack's Answer is the solution.