PMOS is usually used in high-end switches, source connected to power supply, with a gate driving voltage that is relatively negative compared to the source, and operates in the off state with the highest voltage stress, which can easily lead to Vgs overvoltage (gate source breakdown) and Vds (drain source breakdown). The following are the reasons for the breakdown of both:

Core state: Closed state

When PMOS is used as a high-end switch and completely turned off:

Vgs ≈ 0V (assuming the gate is pulled to ground potential by the driving circuit)

Vds ≈ - VDD (drain is the input voltage, source is the output voltage/load terminal; For PMOS, Vds is negative when turned off, and its absolute value is equal to the power supply voltage.

Vgs overvoltage (gate source breakdown)

Direct cause: Pmos tube driving voltage directly exceeds the specification range (e.g. using 24V to drive 20V tube)

Indirect reasons:

The drive gate lead is too long, forming parasitic inductance with the ground plane. At the moment of shutdown, a back electromotive force is generated and superimposed on the original driving voltage, exceeding the withstand voltage value.

The "Miller coupling" effect caused by a sudden change in source potential: When the drain potential undergoes a drastic jump due to load or interference (dV/dt is very high), this change will couple to the gate through the gate drain parasitic capacitance Cgd, causing the gate voltage to be "levered" and may momentarily exceed the safe range. This is common in circuits with inductive loads.

Electrostatic discharge: Static electricity carried by the human body or tools is directly injected into the gate pin, with a voltage of several thousand volts, enough to immediately break through the gate oxygen.

Vds (leakage source breakdown)

Direct cause: The voltage difference between the drain and source stages directly exceeds VDD, even exceeding the specification range, and the current flowing through the drain and source stages exceeds the specification range.

Indirect reasons:

When applied to inductive load switches, the leakage source voltage is superimposed with the back electromotive force voltage, resulting in burnout. When in the off state, the reverse electromotive force is strengthened, and the polarity of the reverse electromotive force is positive at the bottom and negative at the top. There is a large negative overshoot voltage at the drain of the MOSFET, which greatly increases Vds and easily exceeds the Vds (max) of the PMOS transistor, causing the device to be instantly broken down and damaged.

When applied to inductive load switches, the inductor current changes sharply (di/dt is extremely large) in the off state, making it extremely easy to exceed the specification range.

Sudden changes in power supply voltage: surge voltage on power lines caused by hot swapping, grid fluctuations, and the start stop of other high-power devices.

Summary: When designing PMOS switch circuits, it is necessary to provide targeted protection for these two voltage stress paths separately.