Interpretation of key parameters in MOSFET device manual

Write it at the front

I always thought , For electronic engineers , The best learning material is the data book of chips or electronic devices , It may be hard to read at first , But as long as you can hold on , And ask in a way that you don't understand , Will not check the attitude , believe me , It won't take long for you to see your progress .

So today I will take you to interpret a very common , But devices that seem to understand but not understand ——MOSFET, That's what we often say MOS Device manual of tube .

Interpretation object

Infineon NMOS：lRLML6346TRPbF.

The data manual can be downloaded at the following link ：https://www.semiee.com/file/Infineon/Infineon-IRLML6346.pdf

But one thing needs to be explained in advance , Different manufacturers , Manuals for the same device are different , Especially some unimportant parameters , Some will not even provide , Everyone must pay attention to observation .

Key parameters and shape

After opening the chip manual , The first thing that catches your eye is MOS Several key parameters and outline drawings of .

Here are several parameters that need your attention ：VDS Leakage source voltage 、VGS Maximum value of grid source voltage 、RDS The maximum value of the conduction internal resistance （ Under different voltage conditions ）. These parameters will be mentioned later , Later on .

On the right is the Internal schematic diagram and package model SOT-23.

Maximum value of key parameters

Further down you will see The maximum value of the six main parameters , This means that the device can operate at this value , But never exceed this value , Otherwise, the device will be damaged .

VDS Leakage source voltage 30V, This means that the maximum voltage you apply between the drain and the grid cannot exceed 30V;

ID Drain current value , The drain current values at the two backplane temperatures are given respectively , That is, the flow capacity of the drain , The maximum current that can flow , And the maximum flow capacity of the drain , It decreases with the increase of temperature ;

IDM Pulse peak , For power MOS Generally speaking, it has a strong peak flow capacity , The wiring between the connecting pin and the internal chip determines the size of this value ;

PD Maximum dissipation power , The dissipated power at two temperatures is given , The higher the temperature of the substrate , The lower the dissipated power ;

The following Linear derating factor , It means every degree of increase , Dissipated power decreases 0.01W;

VGS Voltage value between grid and source , No more than 12V;

TJ And TSTG The shell temperature and storage temperature that the device can withstand , Exceeding this temperature will make MOS The reliability of the tube decreases .

The extreme value of these key parameters is the limit that the device can withstand , Never exceed these values , At ordinary times, relevant allowance shall be reserved during type selection and design .

Thermal resistance parameters

Next you will see such a table , There are only two rows. , But it's very important .

This is the thermal resistance parameter from the device shell to the environment .

Of course, the premise is not to install radiators , When the device operates in the circulating air , How the shell temperature rises .

100 I mean , In the circulating air , The dissipation of power is 1W, There will be an ambient temperature that will make the shell temperature higher than the outside air 100 Centigrade .

Of course, the heat parameter should match the picture ~

chart 9 Is the relationship between shell temperature and drain current , With the increase of shell temperature , The flow capacity of the drain decreases .

Electrical characteristics

following , Electrical characteristics .

There are many parameters in this table , Let's choose some important parameters to understand .

VDSS Withstand voltage between drain and source ;

RDS(ON) The conduction internal resistance of the device ;

These three figures , They are the changes of internal resistance of conduction under different conditions ：

• The left one shows that the internal resistance of conduction is of positive temperature coefficient , As the temperature goes up , The greater the internal resistance of conduction ;
• In the middle is 2.5V And 4.5V Under driving voltage , The change of conduction internal resistance with drain current , Obviously, the driving voltage is high , The internal resistance of conduction is relatively small ;
• The right one indicates that under different shell temperatures , Increase the driving voltage , Change of conduction internal resistance , The lower the shell temperature is, the smaller the conduction internal resistance is .

VGS(th) Gate threshold voltage ,0.8V That is to say, the grid can only reach 0.8V, The leakage source will start to have current flow ;

 

These two pictures are MOSFET The variation curve of the grid characteristics under different conditions , The left one is different VDS Under the condition of ,Vgs and Qg Corresponding relationship .

Qg,Qgs,Qgd, What we are most concerned about is Qg This parameter , It is the total charge of the grid , It has a large relationship with drive loss ;

t Those parameters are the rising and falling time of the switch , But this value is measured under specific conditions , When the external environment changes , These parameters will also change ;

C These parameters are parasitic capacitance , Our longest concern is Coss Output capacitance , Especially in LLC In resonant power supply , This parameter is very important .

Body diode

Is Current is the current that the body diode can conduct continuously , Maximum 1.3A;

Ism Is the pulse current flowing through the lifting diode , The biggest is 17A;

Vsd Forward voltage drop of bulk diode , Maximum 1.2V;

trr And Qrr They are reverse recovery time and reverse recovery charge ;

The first on the left is flowing Isd The greater the current ,Vsd And the bigger .

The first on the right is the schematic diagram of reverse recovery of body diode .

At the end ：

Here, some common performance parameters are interpreted , This article is simply for everyone to know MOSFET What are the characteristic parameters , And have a simple understanding of these parameters , The specific and deeper ones are not stated .

The device manual is a little different from the chip data manual , There is no part involving circuit design , Next time I'll give you a manual to analyze a step-down chip , Focus on the construction of peripheral circuits .

by the way , I built a warehouse on YuQue , There are some hardware knowledge that I have recently sorted out and carried my personal notes , Students in need can have a look at . Embedded hardware knowledge · Language sparrow