Hi,

For over current protection, one simple and effective method is to use a sens resistor and a switch in series with the current you want to control and a comparator. That comparator would be looking at the voltage drop accross the sense resistor and would switch when a certain threshold is reached. When this happens, you could do several things. One option is to use negative feedback: the comparator would remain in the linear region and should control the switch in series with the sense resistor. In this way, by means of the feedback the switch would have its on resistance modulated in order to keep the voltage drop accross the resistor constant.

Hope this helps
Tosei.

The reference voltage is usually not the problem. An (untrimmed)
bandgap should be accurate enought for an over-current protection
(...and usually a bandgap-voltage is available on every IC).
But the process variation of the sense resistor (normal resistor) can
cause large variation. But there you can find many publications dealing
with that problem.

Cheers