The circuit I am currently working on has a common connector for 12V and up to 48V input - this is fixed due to retrofit of POE to a design.
The target board requires a 12V supply rail. With 12V in through a regulator, however, this voltage will drop and this cannot happen so, a solution would just be to put in a jumper across the input to regulator output (with the EN pin set so that Vin > 12V + Vregdrop). This is acceptable but in order to stop someone plugging in a 48V supply to a board with a jumper, an automatic switch would be ideal.
Now, the circuit I have designed here will do most of that for me. Vin is passed to 12V when it is 12V. If the input is above ~15V, the pass transistor M1 is turned off and the regulator is on. The issue comes with the startup of a power supply - there is a small peak at the start depending upon the input rise time. The power supplies can vary and that the current draw on the 12V rail is ~2A.
How can I delay this until it has reached a steady input voltage of ~12V or >15V?