Overview
This article explains common MOSFET datasheet parameters and the abbreviations used to describe their characteristics.
Key Parameters
Rated voltage (VR): The maximum allowable voltage for the MOSFET.
Rated current (IR): The maximum current the MOSFET can carry under normal operating conditions.
On-resistance (RON): The resistance between source and drain when the MOSFET is on. On-resistance directly affects device power loss and heating.
Switching time (TON, TOFF): The MOSFET turn-on and turn-off transition times. Switching speed is critical for high-frequency applications.
Threshold voltage (VTH): The minimum gate voltage at which the MOSFET starts to conduct. A lower threshold voltage generally leads to faster switching.
Surge tolerance (SURG): The MOSFET's ability to withstand avalanche or surge conditions in current and voltage. Higher surge tolerance improves device robustness.
Junction temperature (TJ): The maximum operating temperature of the MOSFET die. Excessive junction temperature can degrade performance or cause failure.
Input capacitance (Ciss, Cgs): Capacitance between gate and source. Input capacitance affects switching speed and drive requirements.
Output capacitance (Coss, Cds): Capacitance between drain and source. Output capacitance affects switching behavior and drive characteristics.
Reverse transfer capacitance (Crss, Cgd): Capacitance between gate and drain. Reverse transfer capacitance affects switching speed and signal integrity.
Common Electrical Terms
Drain-source voltage (VDS): The voltage between the drain and source. VDS is the maximum voltage the MOSFET can withstand; exceeding it may damage the device.
Drain-source current (IDS): The current flowing between drain and source. IDS directly affects MOSFET power dissipation and heating.
Gate-source voltage (VGS): The voltage applied between gate and source. VGS controls the MOSFET switching state and thus influences IDS conduction.
Drive voltage (VDRV): The voltage provided by the gate driver circuit to control the MOSFET gate-source voltage. The magnitude and stability of the drive voltage affect switching performance and reliability.
Dynamic resistance (Ron): The drain-source resistance of the MOSFET during conduction, which may vary with drain-source current. Lower dynamic resistance indicates better conduction performance.
Reverse transfer capacitance (Cgd): Capacitance between gate and drain that affects switching speed and signal quality.
On-resistance (Ron): The resistance from source to drain when the MOSFET is on. Lower on-resistance enables higher current flow and lower power loss.
Leakage current (Igss): The leakage current when the MOSFET is in the off state. Leakage should be minimized to avoid power loss when off.
Threshold voltage (Vth): The gate voltage at which the MOSFET begins to conduct.
Limits and Ratings
Maximum drain current (ID): The maximum allowable continuous current between drain and source during normal operation. The operating current should not exceed ID. This parameter may be derated at elevated junction temperatures.
Maximum pulsed drain current (IDM): The maximum allowable pulsed drain current. This parameter may be derated at elevated junction temperatures.
Maximum gate-source voltage (VGS): The maximum allowable voltage between gate and source under normal operation.
Drain-source breakdown voltage (V(BR)DSS): The maximum drain-source voltage the device can withstand when VGS is 0. This is a limit parameter; operating voltage must be below V(BR)DSS. It has a positive temperature coefficient, so consider its low-temperature value for safety margins.
Turn-on voltage (VGS(th)): The gate voltage at which a conductive channel forms between drain and source. In practice, the gate voltage measured when ID equals 1 mA with the drain shorted is often used as the threshold. This parameter typically decreases as junction temperature rises.
Power dissipation (PD): The maximum allowed drain-source dissipation power without damaging the device. Actual device power should be kept below PD with an appropriate safety margin. This rating is normally derated at elevated junction temperatures.
Maximum operating junction temperature (Tj): Typical values are 150°C or 175°C. Device operation should avoid exceeding this temperature and include a safety margin.
