How is the MOS tube driven?

The left side is NMOS and the right side is PMOS. We distinguish them by their driving circuits.

For NMOS, when Ctrl In outputs a low level, NMOS is not turned on, and when it outputs a high level, NMOS is turned on.

For PMOS, when the output is low level, PMOS is turned on, and when the output is high level, PMOS is turned off.

The difference between the two is that the enable voltage of NMOS is referenced to GND, while that of PMOS is referenced to VDD.

 R1 here can be added or not, it mainly plays a biasing role.

For NMOS, when the output changes from high level to low level, R1 is pulled down to GND, and the gate can be pulled down faster and fixed to GND for reliable shutdown.

Similarly, for PMOS, when the output goes from low level to high level, R1 is pulled up to VDD, the gate can be pulled up faster, then fixed at VDD, and finally turned off.

Now that we understand the most basic driving circuit, we can upgrade this circuit.

The gate and source of the MOS tube can act as a capacitor. When the MOS tube is in a steady state, when the capacitor is charged, the current flowing through it will be more at the beginning, and then less and less. When the capacitor is fully charged, no current flows through it.

However, if the MOS tube is in a passive opening state, a large amount of current will flow in the gate during the short period of time when the current charges the gate source. To ensure this process, a resistor needs to be added. The higher the resistance, the slower the opening and closing speed of the MOS tube. Conversely, the faster it is.

 In addition, there is another situation where the gate resistor is placed on the left side of the pull-down resistor, which is a voltage divider circuit. However, if their values are close, the gate voltage will be lower than the Ctrl in voltage, affecting the opening of the MOS tube, so it is best to place it on the left side of R1.