I am reposting a post from last year that I think is important for users to get an answer for. I personally have also been very curious about this (for a CubeSat PCB I’m making derived from the ATSAM3X8E) and hope there is someone out there that understands the use of an op-amp and P-channel transistor for the circuitry in these two concepts. Here is the post:
In the DUE schematics, there are two things that I do not understand. First is the working principle of erase button (see: erase_button.png). I have my own idea how does it work, but would like to clarify the working principle from someone that know exactly what is the purpose of all the elements that are connected to erase button. Second thing is switching of power supply between external power and both usbs (see: usb_switch.png). Again, would someone please just briefly describe working principle? Here I really do not understand why is there op amp added?
Thank you for your time!