I'm working on the design of the input stage for an application in which the nominal input voltage is 48 V but in some cases can goes up to 100 V.
This overvoltage condition can stand for several seconds. In this situation, I would like to clamp the output voltage at 90 V.
I'm thinking about using the LT4363 in the configuration reported below to extend the input voltage range above 80 V.
I've tried to simulate this circuit with LTSpice but it seems like the output voltage cannot be clamped at voltage higher then about VCC + 7.5 V (for example 85.5 V if I use a 78 V zener diode). What I get when I try to clamp the output voltage at a value higher than VCC + 7.5 V is that the output voltage is clamped at a voltage lower than the threshold value and the mosfet stays on, dissipating a large amount of power.
Is this the correct behaviour of the IC? (in the datasheet I can't find any relationship between the maximum voltage at Vout and the maximum voltage at VCC)