Can someone explain this constant current load circuit?
Basically A1 drives the gate of Q1 to maintain a voltage on \$R_{set}\$ that matches the command from the DAC. by maintaining a voltage there a current though the resistor is also maintained.

\$R_{FB}\$, \$C_F\$, and \$R_{ISO}\$ are there to stop various non-ideal behaviors like oscillation and wind-up.