1. Drain-Source Voltage Rating (V₍DSS₎)

VDS is the maximum sustainable voltage between drain and source when the MOSFET is off.

Rule of thumb: Select a VDS with at least 30% voltage margin above the circuit’s maximum operating drain voltage. Voltage spikes from inductive loads (BLDC motors, transformers) will easily break down the device without sufficient margin.

2. Continuous Drain Current (I₍D₎)

Represents the rated continuous current under specified thermal conditions.

Do not only reference the datasheet nominal value: this parameter drops significantly as junction temperature rises. For motor drive and high-power switching applications, reserve a current safety margin of 50% or higher. Pay attention to both DC current and pulsed drain current I₍DM₎ for surge loads.

3. On-Resistance R₍DS(on)₎

RDS(on) determines conduction loss when the MOSFET turns on. Lower RDS(on) brings less heat generation.

Key note: R₍DS(on)₎ rises with increasing junction temperature. For low-voltage high-current BLDC driver solutions, low RDS(on) MOSFETs (Winsok series) effectively reduce thermal stress. Also check test conditions: VGS and current level specified in datasheet.

4. Gate Threshold Voltage V₍GS(th)₎

The minimum gate-source voltage required to turn the MOSFET on.

Logic-level MOSFET: VGS(th) ~1–2V, suitable for direct driving by MCU IO ports
Standard power MOSFET: VGS(th) 2–4V, needs dedicated gate driver

Avoid mismatch: If your controller only outputs 3.3V, regular power MOSFETs may not fully turn on.

5. Gate Charge (Qg, Qgs, Qgd)

Gate charge directly decides switching speed and driver current requirements.

High Qg demands stronger gate drive current; switching loss increases at high frequency. For high-frequency BLDC, DC-DC converters, balance R₍DS(on)₎ and total gate charge to optimize overall power loss. Qgd (Miller charge) is critical for preventing shoot-through in half-bridge circuits.

6. Body Diode Characteristics

All silicon power MOSFETs integrate an intrinsic body diode.

Focus on: Reverse recovery charge Qrr. Large Qrr causes severe switching loss and noise in hard-switching topologies. In BLDC three-phase inverters, body diode reverse recovery is a common root cause of device failure. Select fast recovery MOSFETs if external freewheeling diodes are not added.

7. Thermal Parameters

Maximum junction temperature Tj(max)
Thermal resistance RθJA / RθJC

These parameters define heat dissipation capability. For SMD MOSFETs, PCB copper area acts as the main heatsink. If the design lacks sufficient copper layout, even devices with high current ratings will overheat.

8. Switching Parameters (tr, tf, td(on), td(off))

Rise time, fall time and delay times affect EMI noise and switching losses.

Fast switching reduces power loss but generates larger electromagnetic interference. Slow switching lowers noise but increases heat. Match switching speed to your application frequency.