Comprehensive analysis of MOS transistor performance parameters

As an important component widely used in modern electronic technology, the performance parameters of MOS transistors have a crucial impact on circuit design and system performance. The following will provide a detailed interpretation of the main performance parameters of MOS transistors.

1、 Limit parameter

VDS: represents the maximum voltage value that can be applied between the drain and source. In practical applications, it is necessary to ensure that the applied voltage does not exceed this limit, otherwise it may cause damage to the MOS transistor.

VGS: The maximum voltage value that can be applied between the gate and source. Similarly, exceeding this value poses a risk of damage.

ID: The sustained current value that the drain can withstand. Exceeding this value can cause breakdown, so special attention should be paid when designing circuits.

IDM: The single pulse current intensity that can be sustained between the leakage source. Exceeding this value may result in breakdown.

EAS: Single pulse avalanche breakdown energy. If the voltage overshoot does not exceed the breakdown voltage, the device will not experience avalanche breakdown, but EAS has calibrated the device's ability to safely absorb reverse avalanche breakdown energy.

PD: Maximum dissipated power. When using, it should be noted that the actual power consumption of MOS should be less than this parameter and leave a certain margin, and this parameter will decrease with the increase of junction temperature.

TJ, Tstg: These two parameters calibrate the allowed junction temperature range for device operation and storage environment, which should be avoided to extend the working life.

DV/dt: reflects the ability of the device to withstand the rate of voltage change, the larger the better. However, for the system, excessively high dV/dt can cause high voltage spikes and poor EMI characteristics, but can be corrected through the system circuit.

Thermal resistance: Thermal resistance indicates the difficulty of heat conduction, which is divided into the thermal resistance between the channel and the environment, and the thermal resistance between the channel and the package. The smaller the thermal resistance, the better the heat dissipation performance.

2、 Technical parameters

For MOSFETs, the on resistance per unit area and the coefficient of merit (FOM) are key indicators that represent their performance. Generally, the lower the unit area on resistance value and the coefficient of merit value, the better the performance.

For ultra-low voltage MOSFETs, the on resistance per unit area and the drain breakdown voltage are comparative indicators. The lower the unit area on resistance (Ronsp), the lower the unit area power consumption, and the higher the current density; The higher the drain breakdown voltage (BVDSS), the better, but increasing this value will result in an increase in the on resistance per unit area.

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3、 Static parameters

△ VDS/TJ: Temperature coefficient of the breakdown voltage of the drain source, positive temperature coefficient. The smaller the value, the better the stability.

VGS (th): The turn-on voltage (threshold voltage) of MOS. When the applied gate control voltage VGS exceeds VGS (th), NMOS conducts.

IGSS: Gate driven leakage current, the smaller the better, the less impact it has on system efficiency.

IDSS: Leakage source leakage current, the leakage source leakage current when the gate voltage VGS=0 and VDS is a certain value, generally at the microampere level.

4、 Other important parameters

Threshold Voltage (Vth): determines the turn-on characteristics of MOSFETs, with typical values ranging from a few volts to several tens of volts.

On Resistance (Rds (on)): The equivalent resistance between the drain and source in a conducting state, typically ranging from a few milliohms to several ohms, with lower conduction losses.

Maximum Drain Source Voltage (Vds (max)): The maximum drain source voltage that can be sustained, typically ranging from tens to hundreds of volts, which determines the voltage tolerance.

Maximum Gate Source Voltage (Vgs (max)): The maximum gate source voltage that can be sustained, typically ± 20V, which determines the range of gate driving voltage.

Maximum Drain Current (Id (max)): The maximum drain current that can be sustained, typically ranging from a few amps to several hundred amps, which determines the current carrying capacity.

Maximum Power Dissipation (Pd): The maximum power loss that can be sustained, typically ranging from a few watts to several hundred watts, which determines the thermal management capability.

Input Capacity (Ciss): The equivalent capacitance between the gate and source, with typical values ranging from a few picofarads to several thousand picofarads, which affects the switching speed.

Output Capacity (Coss): The equivalent capacitance between the drain and source, typically ranging from a few picofarads to several thousand picofarads, which affects the switching speed.

Reverse Transfer Capacity (Crss): The equivalent capacitance between the drain and gate, typically ranging from a few picofarads to several hundred picofarads, which affects the switching speed.

Switching Time: including Turn On Time (Ton) and Turn Off Time (Toff), with typical values ranging from a few nanoseconds to several hundred nanoseconds, affecting switching speed and efficiency.

Gate Charge (Qg): The amount of charge required for gate charging, typically ranging from a few nanocombs to several hundred nanocombs, which affects the design of driving circuits.

Thermal Resistance (Rth): Refers to the heat dissipation capacity, with typical values ranging from a few degrees per watt to several tens of degrees per watt, which affects temperature rise and reliability.

Operating Temperature Range: The temperature range within which normal operation can occur, typically ranging from -55 ℃ to+150 ℃, determining environmental adaptability.

Package Type: such as TO-220, TO-247, SOT-23, etc., which affects installation and heat dissipation.

Body diode characteristics: including forward voltage drop (Vf) and reverse recovery time (Trr), which affect performance in applications such as synchronous rectification.

In high-speed applications, switch speed indicators are particularly important, such as conduction delay time, rise time, shutdown delay time, descent time, etc. Meanwhile, in high-speed H-bridge applications, the response speed index Trr of the reverse parallel parasitic diode inside the MOS transistor is also crucial, otherwise it is prone to explosion.

In short, a deep understanding of the various performance parameters of MOS transistors is of great significance for correctly selecting and applying MOS transistors, optimizing circuit design, and improving system performance.