MOSFET as a Switch

Choose a logic-level MOSFET whose $R_{DS(on)}$ is specified at your gate voltage (e.g. at $V_{GS}$ = 2.5 V or 4.5 V). Note that $V_{th}$ is only where it starts to conduct — a "2 V threshold" part may be far from fully on at 3.3 V.

Typical low-side circuit:

• a gate resistor (~100 Ω) to limit ringing,
• a 10–100 kΩ pull-down so the load stays off while the MCU boots,
• a flyback diode across inductive loads.

For fast PWM, the gate capacitance must be charged quickly — use a gate driver IC when switching amps at tens of kHz.