This weekend I was looking into how to (cheaply) power esp32. in my throw away designs I usually use 1117 which is not good but dirt cheap. but one board now has a major update, and i run out of space on the board so i was looking for a good, small and cheap replacement for it.
i never paid much attention but esp32 has requirement for power source to deliver 500mA at least as wifi can result in power bursts. previously i thought that i can use lp5907 but it's rated up to 250 mA only. i did check what all cheap boards use and quite a lot of them use me6211 that looks like a good fit: small, can use ceramic capacitors, deliver up to 500mA. good.
another thing that i need now is to use power from usb and from ext source. so i need to connect two 5v rails somehow. considering everything, i can use schottky on usb, it won't be perfect but good enough with 4.5-4.7 volts on 5v, enough for ldo to work.
but reverse current into dcdc (that converts from 9-24v to 5v) should be blocked as it can damage ic. as dcdc has one fet inside, we can add one more after dcdc to block current in both directions - so i've added pfet in dcdc output. then i need to somehow control that fet. while i was looking for ldo in boards, i found one neat solution in lolin d32 board: usb power is used to control the gate. they use it for battery but i think it can be used for my case too, and it's only schottky and pfet, very cheap! will see how it work.
now the only thing remaining is to fit everything together on the board but I'm pretty happy with solution.