What kind of reverse voltage protection methods should I use when the load can sometimes have greater voltage(5V) than the input(3.7~4.2V Li-po)? I'm not considering diodes, or even schottky diodes in order to minimize voltage drop. Using something like P-Channel MOSFET would be great, but with little math, when voltage is applied to load, it would turn on eventually be useless. What other methods would be present for this situation?

Any help would be greatly appreciated, Thanks!

 

Schematic?

You can use a MOSFET and turn it into an "ideal diode" (actually, that's a thing you can buy). You use a comparator to watch the voltage across the body diode and turn on the MOSFET when there is some ∆V there.

 

Here's an ideal-diode circuit using a P-MOSFET and a dual, matched PNP that should do what you want.
Q1a and Q1b sense the voltage drop across the MOSFET and when the Out voltage becomes positive with respect to the In voltage, the transistors raise the MOSFET gate voltage so Vgs is near zero, turning the MOSFET off and blocking any reverse current into V1.

 

Schematic?

You can use a MOSFET and turn it into an "ideal diode" (actually, that's a thing you can buy). You use a comparator to watch the voltage across the body diode and turn on the MOSFET when there is some ∆V there.

Thanks, MOSFET with comparator seems to be what I need. Would there be an IC which integrated both comparator and the MOSFET for convenience?

 

Would there be an IC which integrated both comparator and the MOSFET for convenience?

Here's one.