Supply white/blue led with 3V3 at constant current
The following might work with the compensation cap and resistors set to zero (i.e., no C1, wires for R3 and R4), but only if you choose an op-amp that is designed to drive capacitive loads, and a FET that has a particularly low-capacitance gate.

In addition to gate capacitance, your FET also needs to be "logic level", and should probably be rated for a 3.3V gate voltage.

The component count is distressingly high, but you should be able to get away with cheap parts.







simulate this circuit &ndash; Schematic created using CircuitLab