In applications such as industrial motor drives and safety power line communication digital output modules, N-Channel MOSFET based high side switch is very commonly used to disconnect the loads from supply line in case of faults such as overvoltage event . LM74502, LM74502H can be used to drive external MOSFET to realize simple high side switch with overvoltage protection. Figure 9-10 shows a typical application circuit where LM74502H is used to drive external MOSFET Q1 as a main power path connect and disconnect switch. A resistor divider from input to OV pin to ground can be used the set the overvoltage threshold.

If VOUT node (SRC pin) of the device is expected to drop in case of events such as overcurrent or short-circuit on load side then additional zener diode is required across gate and source pin of external MOSFET to protect it from exceeding it's maximum V_GS rating.

Many industrial safety applications require fast switching off of MOSFET to verify proper functioning of the high side disconnect switch for diagnostic purpose. LM74502H OV pin can be used as control input to realize fast turn-on and turn-off load switch functionality. with OV pin pulled above V_OVR threshold of (1.25-V typical), LM74502H turns off the external MOSFET (with Ciss = 4.7 nF) within 1 μs typically. When OV pin is pulled low, LM74502H with its peak gate drive strength of 11 mA turns on external MOSFET with turn on speed of 7-μs typical. Figure 9-11 shows LM74502H GATE to SRC response when OV pin is used as logic input for turning external MOSFET on and off.

Figure 9-11 Fast Turn-On and Turn-Off High Side Switch Driver Using LM74502H