7 V_DRAIN Switching Circuit

The V_DRAIN protection circuit uses NMOS and PMOS transistors to disable the voltage being applied to the PA drain. This PA_ON circuit functions as a high-voltage switch. The V_DRAIN needs to be disabled at key times during startup, shutdown, and alarm events. This is achieved in this design by an NMOS and PMOS circuit. When the PA_ON voltage is applied to the NMOS gate, the circuit turns on to allow V_DRAIN through the PMOS.