LTC4366 at high voltage.

We have used an LTC4366 to protect a load from surges above 400VDC when driven from a PFC circuit.

Due to the slow response time needed for a PFC to operate correctly, there is a possibility of the nominal output voltage of 385VDC exceeding 400VDC when the load drops from 100% to 0%.

The 4366 is set to limit at about 395VDC and this it does well.

Our problem is that either at switch off, or the next switch on, the 4366 dies and does not produce the required gate drive to turn the pass MOSFET on.

Does anything look odd on the schematic below?