There are many relevant parameters in the MOS tube data sheet. Take the MOS tube 4C020 as an example. Let’s take a look at the parameters that are generally included in the MOS tube data sheet.
The limit parameters are also called the absolute maximum rated parameters. During the use of the MOS tube, these limit parameters in the figure below should not be exceeded under any circumstances, otherwise the MOS tube may be damaged.
VDS represents the maximum voltage value that can be applied between the drain and source. VGS represents the maximum voltage value that can be applied between the gate and the source. ID indicates the continuous current value that the drain can withstand. If the current flowing exceeds this value, it will cause the risk of breakdown. IDM represents the single pulse current intensity that can be tolerated between the drain and source. If it exceeds this value, it will cause the risk of breakdown.
EAS represents the single-pulse avalanche breakdown energy. If the voltage overshoot value (usually caused by leakage current and stray inductance) does not exceed the breakdown voltage, the device will not undergo avalanche breakdown, so there is no need to dissipate the energy of avalanche breakdown. ability. EAS calibrates the level at which a device can safely absorb reverse avalanche breakdown energy.
PD means the maximum power dissipation, which refers to the maximum drain-source dissipation power allowed when the MOS performance does not deteriorate. When using it, it should be noted that the actual power consumption of the MOS should be less than this parameter and leave a certain margin. derated with increasing junction temperature. (This parameter is unreliable)
TJ, Tstg , these two parameters calibrate the allowable junction temperature range of the device’s working and storage environment. It should avoid exceeding this temperature and leave a certain margin. If the device is guaranteed to work within this temperature range, its life span.
dV/dt reflects the ability of the device to withstand the rate of voltage change, the bigger the better. For the system, too high dv/dt will inevitably bring high voltage spikes and poor EMI characteristics, but the rate of change can be corrected through the system circuit.
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Thermal Resistance Indicates the difficulty of heat conduction. The thermal resistance 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
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△VDS /TJ represents the temperature coefficient of the drain-source breakdown voltage, the positive temperature coefficient, the smaller the value, the better the stability.
**VGS(th)** indicates the turn-on voltage (threshold voltage) of the MOS. For NMOS, when the applied gate control voltage VGS exceeds VGS(th), the NMOS will be turned on.
IGSS represents the gate drive leakage current, the smaller the better, it has a small impact on the system efficiency.
IDSS represents the drain-source leakage current, and the drain-source leakage current when the gate voltage VGS=0 and VDS is a certain value is generally in the microampere level.
**RDS(ON)** indicates the on-resistance of the MOS. Generally speaking, the smaller the on-resistance, the better. It determines the conduction loss of the MOS. The larger the on-resistance, the greater the loss, and the higher the temperature rise of the MOS. In a high-power power supply, the conduction loss will account for a large proportion of the total loss of the MOS.
gfs represents the forward transconductance, which reflects the ability of the gate voltage to control the drain-source current. If gfs is too small, the turn-off speed of the MOSFET will be reduced and the turn-off capability will be weakened. If it is too large, the turn-off will be too fast and the EMI characteristics will be poor. At the same time The drain-source produces a larger turn-off voltage spike during turn-off.
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Ciss represents the input capacitance, Ciss=Cgs+Cgd, this parameter will affect the switching time of the MOS, the larger the value, the slower the turn-on and turn-off time and the greater the switching loss under the same driving capability.
Coss represents the output capacitance, Coss=Cds+Cgd; Crss represents the reverse transmission capacitance, Crss=Cgd (Miller capacitance). These two parameters have a slight impact on the MOSFET turn-off time. Among them, Cgd will affect the amount of voltage energy transmitted to the gate of the MOSFET when the drain has an abnormally high voltage, and will have a certain impact on the lightning strike test item.
The parameters Qg, Qgs, Qgd, td(on), tr, td(off), and tf are all parameters related to time. The advantages of faster switching speed are smaller switching losses, high efficiency, and low temperature rise. The corresponding disadvantages are poor EMI characteristics and high MOSFET turn-off peaks.
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IS, If these parameters of ISM are too small, there will be a risk of current breakdown.
If VSD and trr are too large, it will cause excessive system loss and high temperature rise in bridge or LCC systems.
Qrr This parameter is proportional to the charging time, generally the smaller the better.
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Output Characteristics The curve is used to describe the relationship between the current and voltage of the MOS tube. The characteristic curve will be affected by the junction temperature. The general data sheet will list the characteristic curves at two temperatures.
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According to MOS The output characteristic curve of the tube, take one point of Uds, and then use it as a graph method to obtain the corresponding transfer characteristic curve. It can be seen from the transfer characteristic curve that when Uds is a certain value, the relationship between Id and Ugs.
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MOS The on-resistance and junction temperature show a positive temperature coefficient change, that is, the higher the junction temperature, the greater the on-resistance. The MOS data sheet generally draws a curve of on-resistance versus temperature when VGS=10V.
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Capacitor capacity The smaller the value, the smaller the total gate charge QG, the faster the switching speed, and the smaller the switching loss. Applications such as switching power supply DC/DC converters require a smaller QG value.
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MOS tube Generally, there will be a parasitic diode. The parasitic diode has a protective effect on the MOS tube. Its characteristics are the same as those of ordinary diodes, and it also has the characteristic of forward conduction.
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Maximum Safety The working area is a two-dimensional area formed by a series of (voltage, current) coordinate points. When the MOS tube is working, the voltage and current cannot exceed this area. If it exceeds this area, there is danger.
It can be seen that there are actually many related parameters of MOS tubes. In fact, in general applications, we mainly consider the drain-source breakdown voltage VDS, continuous drain current ID, on-resistance RDS(ON), maximum power dissipation PD, The parameters such as turn-on voltage VGS(th), switching time, and operating temperature range are enough.