The LT4320 datasheet summary says it is good for 72V AC, yet the absolute maximum rating table of the input pins says a minimum of -3V. I am confused?
LT4320 absolute maximum ratings are all referenced to OUTN = 0V, see Note 2 in the datasheet. With OUTN as the reference, IN1 and IN2 will be clamped by the body diode of each bottom MOSFET to 0.7V below OUTN, typical. During normal operation this voltage is much lower as the MOSFETs are turned on. This is why IN1 and IN2 are rated to 3V below OUTN. LTSpice is very useful for visualizing this circuit.