Power Limiting circuit for very low powers

[snoozy]

Hi guys,

I'm need to create a circuit, that limits the power to a CAN transceiver on the data lines.

It is a protection cirucit only and should not be active under normal operation.

The power needs to be less than 25 mW on the primary side of this isolating tranceiver in total. That means on the lines CANH, CANL and VCC.

My first try was a current limiter followed by a Zener, but I cannot reach such low power levels without a huge shunt, that will effect the function.
 
I was thinking, there might be a way to adjust the reference voltage that is parallel to the shunt to a lower voltage.

Thanks for any ideas or pushs in the right direction.