Ignition cranking during startup and load dumps during shutdown are common sources of voltage transients on an automotive supply line. These undervoltage (UV) and overvoltage (OV) transients can have significant magnitudes and will damage circuits that are not designed to operate during these extremes.
Specialized UV and OV protection devices have been developed to disconnect sensitive electronics from power supply transients. For example, protection devices can monitor the input supply using a window comparator and then validate that it is within range. Similarly, the supply voltage can be monitored by a resistive divider network connected to the UV and OV monitor pins. The window comparator output can then drive the gates of two N-channel MOSFETs that make or break the connection between the supply and the load. The window comparator can be designed with hysteresis on its monitor pins to improve noise immunity. Hysteresis can prevent false MOSFET on/off switching