Rats. Just remembered RPi GPIO is not 5V tolerant, so will need a few extras to interface between it and my circuit...

The PGOOD line should just need a pair of resistors. The nSHDN line might be a bit trickier...

I've chosen to use GPIO17 and GPIO27 which are both pins with pull-downs by default, with a value of about 50k-60k ohms if the internet is to be believed. That means I only need another 30k-50k or so in parallel (i.e. external pull-down) in combination with the 10k series already in the circuit to ensure the voltage on these pins doesn't exceed 3v3.