Ok I looked at it again and I stand corrected, but the super caps are changed through the first buck, which as you say isn't very efficient (you're right, high voltage bucks aren't and are current limited, that one is 1A not 1.5A continuous).
Given my intention to use the PIC for the 2 minute shutoff and to gather stats for pushing to RS232 why not do the logic via the PIC?
Also note, your last buck will drain the supercaps to 4.3V which is below USB spec. This can cause many phones/powerbanks to lock up until the power is removed completely (I've experienced this before).
Running through the logic, if the supercaps began charging and "fought" with the 5V going to the device, the first buck would probably trigger it's PG causing the supercaps to discharge?
Given my intention to use the PIC for the 2 minute shutoff and to gather stats for pushing to RS232 why not do the logic via the PIC?
Also note, your last buck will drain the supercaps to 4.3V which is below USB spec. This can cause many phones/powerbanks to lock up until the power is removed completely (I've experienced this before).
Running through the logic, if the supercaps began charging and "fought" with the 5V going to the device, the first buck would probably trigger it's PG causing the supercaps to discharge?