Low Side Overcurrent Detection with Adjustable Maximum - Difference amplifier or non-inverting amplifier?
As a first-look/first-try, I would make a comparator circuit on the power ground side, make it trimable however you like, then output a digital output into Itrip. That way you've got 0.5V to play with and don't have to worry about minuscule ground differentials creating noise in your trip point.