Typically, when we see a microcontroller driving a MOSFET, it's not directly driving it; instead, a transistor is often used for driving.

However, in some cases, a microcontroller can directly drive a MOSFET.

MOSFETs are voltage-driven devices, and for them to be driven reliably, the driving voltage must reach the gate-source threshold voltage (Vgs). The operating voltage of a microcontroller is generally 3.3V or 5V, with some load-bearing capacity. However, the voltage swing and current drive capability of the I/O pins are limited. For some low-power MOSFETs, if the drive voltage from the microcontroller's I/O pins is suitable, direct driving is feasible.

In general, the drive voltage for MOSFETs is around 3V to 5V (varying with different MOSFET models). Microcontrollers can directly drive MOSFETs under light load conditions, but not for heavy loads. Due to the high internal resistance and power consumption, direct driving can easily lead to MOSFET damage. Therefore, it's advisable to use a transistor at the output of the I/O pin to drive the MOSFET.

Transistors are current-driven devices, and as long as a driving current is provided to the base of the transistor, it can conduct. The collector of the transistor then provides the driving voltage to the MOSFET.

For example, when the microcontroller outputs a high voltage, the transistor conducts, causing the gate (G) of the NMOS to be at a low voltage, turning off the NMOS. When the microcontroller outputs a low voltage, the transistor is off, causing the gate to be at a high voltage, turning on the NMOS. This effectively prevents situations where the microcontroller's output voltage is insufficient to meet the VTH.

Of course, besides using transistors, other devices such as optocouplers can also be used in similar applications.