I need to make a reverse polarity and over-voltage protection for a fairly powerful device (45W @ 12V input) and after some research I noticed a weird peculiarity. A typical reverse polarity protection circuit is shown below; it uses a p-channel MOSFET in a high-side configuration as a switch.
N-Channel MOSFETs tend to have lower Rdson, they are much more common and usually cheaper, so, as I guess, using a N-Channel MOSFET is preferable. The same schematic also exists with a N-Channel MOSFET, but to put the N-Channel MOSFET in a high-side switch configuration a charge pump or some other type of dc-dc inversion is required (second schematic).
But why not just put the N-channel MOSFET on the low side like on the third circuit? For some reason I've never seen in any device I've put my hands on a protection circuit with a low-side protection. So, my question is:
Why is it preferable to put the protection switch in the high-side configuration rather than the low-side?
*This peculiarity carries onto the over-voltage protection as well. The PMP10737 TI reference board, for example, uses a P-Channel MOSFET for the overvoltage protection; however, to prove my point that N-Channel MOSFET are better for this purpose, the same board uses a N-Channel MOSFET with a complex IC to drive it in the reverse polarity protection! *