Protection circuit, blown FET. But weird low side FET circuit?

[sw_guy]

The circuit is a protection circuit for a device which is not a charger. One fet is blown and according to package pins I assume the order of Source and Drive pins.
The M1 FET looks like a standard low-side FET protection. However, the one that is blown, does not make sense to me. This kind of arrangement is often seen in battery protection circuits. Which this is not.
Based on the Gate circuit, this look like a N-type FET. If it is the same as M1, it does pretty much nothing since the internal diode lets current pass the fet (?)

[Kim Christensen]

M2 looks like a reverse polarity protection circuit. Instead of a diode, which has a 0.7V drop, they use a MOSFET which has a much lower voltage drop due to it's low RDS(on).

[sw_guy]

Right, thanks. Now when you say this, reverse protection it must be. And M2 "must" be the same as the M1.

[DavidAlfa]

Yep M2 is for reverse polarity protection, M1 does some sort of soft turn-on.

[inse]

But not with this voltage divider value…
and what’s the 50mR good for?

[sw_guy]

R3 is clearly higher than 8k2 which I measured in-circuit. >18VDC there is 14.7V over the D1. R1 is 124k and R4 is 3 x 124k
There are several unpopulated components on the board around 50mR resistor. I think there is an option to have over-current protection. I did not analyzed that further.