Over current protection

I'm measuring current for a project using a shunt monitor. I'm switching an N channel MOSFET and the load is resistance wire. Load can draw up to 80a normally. I'm wondering about what the best way would be to handle an over current situation. There's potential of a direct short and I'm not sure how fast the MCU/other components would fry.

I know one way is to use a comparator and compare the voltage drop across the shunt resistor to a reference. When the drop is above the reference, we can trigger a hardware interrupt. I'm not sure if this is fast enough. Project is using an Atmega328p and the internal comparator says 1-2 clock cycles at 16mhz. I found a dedicated comparator that has a propagation delay of 7ns. Do you think that's fast enough?

I would really like a way to stop the short before it occurs with hardware. Any idea about this?

For fast over-current events (shorts) you generally use a fast comparator to shutdown the gate drive signals as fast as possible. Some MOSFETs/IGBTs have ratings for high current overloads, and they are measured in a few microseconds...

You also need a latch to prevent the circuit immediately re-enabling itself.

Hi, thanks for the reply. The voltage drop across the shunt resistor will be <100mV. What do you think the best option would be to use as a reference for a voltage that low?

A resistor divider from a known voltage is fine. Protect the sensitive analog sensing from the high current wiring, high current wiring induces voltages in nearby circuits, so take the sense leads from the shunt out sideways for some distance to the comparator, away from the magnetic fields of the 80A wiring.

Use one of the shunt connections as analog ground for the comparator, and remember a shunt is a 4-terminal device.

I'll keep that in mind, thanks. ;D