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In my last post, 'Capacitor DC Bias Modeling - SPICE', I was asked about modeling MOSFET parasitic capacitance and their non-linearities. Could my capacitor DC bias model be used to simulate the effects of MOSFET capacitance versus Vds?
I'm sure it could, but I wanted to do a little research to make sure I wasn't reinventing the wheel. You'll want to read this one to the end. I got amazing results when simulating MOSFETs and comparing to datasheets.
Has This Been Done?
- Adding additional component models to the ltspice library LTspice comes with an extensive library of electrical component models for resistors, capacitors, inductors, diodes, and transistors. You will not have to add any more of these types of component models to its library to perform the simulations described on this website.
- In this tutorial video I look at the various ways in which simulation libraries and component models can be imported to the LTspice simulator, one of which i.
The websites of manufacturers are often great resources for additional SPICE models that can be used in Micro-Cap. For importing models into Micro-Cap, the Component Editor provides two wizards, the Import Wizard and the Add Part Wizard, or the user may also add the model manually. Sound like the symbol is missing parameters needed with the CD4000.lib library file. Open the symbol and: 1. Add this to the 'Spiceline' field: VDD=5 SPEED=1.0 TRIPDT=5e-9 VDD sets the supply voltage. Change 5 to whatever voltage your circuit uses. Add this to the 'Spicemodel' field: VDD 0 This is for internal use by the library.
It turns out this has been done and the LTSpice simulator has an intrinsic model for this (other ways exist outside LTSpice), so not quite a 'new' model, but maybe it is to a few of you reading this. On the LTSpice MOSFET documentation, there are three MOSFET types listed:
NMOS
PMOS
VDMOS
The NMOS and PMOS are for monolithic FETs whereas the VDMOS is a model unique to LTSpice that models discrete MOSFETs and has a parameter for specifying NMOS or PMOS. VDMOS is what I'll cover in this post.
One thing I was surprised about is that ALL of the MOSFETs in LTSpice's standard.mos library are modeled using the VDMOS type. The picture below shows one way the capacitance is described using this model.
In my last post, 'Capacitor DC Bias Modeling - SPICE', I was asked about modeling MOSFET parasitic capacitance and their non-linearities. Could my capacitor DC bias model be used to simulate the effects of MOSFET capacitance versus Vds?
I'm sure it could, but I wanted to do a little research to make sure I wasn't reinventing the wheel. You'll want to read this one to the end. I got amazing results when simulating MOSFETs and comparing to datasheets.
Has This Been Done?
- Adding additional component models to the ltspice library LTspice comes with an extensive library of electrical component models for resistors, capacitors, inductors, diodes, and transistors. You will not have to add any more of these types of component models to its library to perform the simulations described on this website.
- In this tutorial video I look at the various ways in which simulation libraries and component models can be imported to the LTspice simulator, one of which i.
The websites of manufacturers are often great resources for additional SPICE models that can be used in Micro-Cap. For importing models into Micro-Cap, the Component Editor provides two wizards, the Import Wizard and the Add Part Wizard, or the user may also add the model manually. Sound like the symbol is missing parameters needed with the CD4000.lib library file. Open the symbol and: 1. Add this to the 'Spiceline' field: VDD=5 SPEED=1.0 TRIPDT=5e-9 VDD sets the supply voltage. Change 5 to whatever voltage your circuit uses. Add this to the 'Spicemodel' field: VDD 0 This is for internal use by the library.
It turns out this has been done and the LTSpice simulator has an intrinsic model for this (other ways exist outside LTSpice), so not quite a 'new' model, but maybe it is to a few of you reading this. On the LTSpice MOSFET documentation, there are three MOSFET types listed:
NMOS
PMOS
VDMOS
The NMOS and PMOS are for monolithic FETs whereas the VDMOS is a model unique to LTSpice that models discrete MOSFETs and has a parameter for specifying NMOS or PMOS. VDMOS is what I'll cover in this post.
One thing I was surprised about is that ALL of the MOSFETs in LTSpice's standard.mos library are modeled using the VDMOS type. The picture below shows one way the capacitance is described using this model.
The example model below shows the model parameters. Parameters enabling the VDMOS model non-linear capacitances is Cgdmax, Cgdmin, and a. The other arguments (C, D, B, etc) in the graph above are computed from these parameters.
There are about 1000 VDMOS models in the standard.mos file, so it isn't exhaustive by any means. However, there is a way to make a VDMOS model in a matter of minutes based off the datasheet information.
MOSFET Model Generation
Gathering all of this information took quite a bit of research, but eventually, I found information describing how the model parameters can be extracted from the MOSFET datasheet and all the equations used to do so.
Even better, the person explaining this developed an application that does this for you. The software also generates test circuits which allow you to verify the model against the datasheet with the following tests:
Parasitic capacitance vs Vds
Vds vs Ids output characteristics
Vgs vs Ids transfer characteristics
Gate charge
The software is buried in a Groups.io LTSpice page and can be downloaded.
This was a little involved for me because the application was written in VB6 and the installer didn't run. I had to manually 'register' the DLL and OCX files in the OS system directories with 'regsvr32.exe' so the executable would run.
The following link is to the LTspice Groups.io page where the software lives: https://groups.io/g/LTspice
You must be a member of the group to download the files:
https://groups.io/g/LTspice/files/z_yahoo/1_LTspiceFiles/Util.zip in the 'Model ToolsBoard Level MOSFET (VDmos)Software' subdirectory.
Add To Library Lt Spices
Testing The Model
The following is he MOSFET I used in this example: SQ7414CENW
All the necessary information from the datasheet was entered into the application.
In the software, a simple File -> Save Test Circuits generates a good amount of tests to validate the model against the datasheet inputs.
The following is an example of the schematics automatically generated for datasheet validation (parasitic capacitance schematic):
For example, here are the outputs of the four test circuits (datasheet plot on the left, simulation output on the right):
Temperature Dependence
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Another thing I've seen done with the VDMOS models is where temperature dependence is added by placing inline equations in the model. Here's an example related to the MOSFET's body diode:
Follow Up
Ltspice Add Library
These models above aren't perfect, but they can be tweaked for better performance. For those that don't use LTSpice, but want to do similar modeling, this seems to be possible with standard models using the MOSFET Meyer parameters.
With that said, I haven't spend too much time investigating this since I went down the rabbit hole with the LTSpice VDMOS model. Maybe another post on this in the future? I may also go over how to model temperature dependence in future posts, so stay tuned.
Sources
I wanted to give credit to the hard work that has gone into this by other individuals. I merely found this information buried in the Internet and attempted to understand it. Notably, the names Mike Engelhardt and Ian Hegglun came up quite a bit.
Add To Library Lt Spicewood
Just last day I was searching all over the net to find out how this is done. In order for you to not have the trouble I went through, I am posting it here.
TRYING TO CREATE IRF540N from IRF540N.SPI
This is the process I have used to add .LIB files from ONsemi and .SPI files from IRF into my LTSPICE program.
In case of SPI file just rename it to a LIB file. Then place the LIB file in /SPICE/LIB/sub directory
Select a component file (with extension .asy) that looks like your new one from libsym
Lets say nmos.asy
(If you want to place the new component under a new category, create a new Directory here as CATEGORYNAME) and copy the file libsymnmos.asy to libsimCATEGORYNAMEIRF540N.asy
Open 1N5338B.asy in a text editor, and make the following changes:
* change SYMATTR Prefix D to SYMATTR Prefix X
(This says that the model we're using is a .subckt.)
* change SYMATTR Value D to SYMATTR Value IRF540N
(This says that the name that will show up on the schematic is IRF540N.)
* add a line SYMATTR ModelFile IRF540N.LIB
(This says that the name of the file containing the subcircuit we're using is 1N5338B.LIB.)
* add a line SYMATTR SpiceModel IRF540N
Restart LTSpice and you will have the component there.
DERIVED from what was found on this page : https://denethor.wlu.ca/ltspice/