RTFM:
Third-party Models
This section explains the basics to adding a third-party model to
LTspice XVII.
Basically there are two types of third party SPICE models, those
described with a .MODEL statement and those defined with a .SUBCKT.
Models given as .MODEL statements are for intrinsic SPICE devices like
diodes and transistors. The .MODEL statement gives the parameters for
the specific component. The behavior of the device is already known by
SPICE, only the parameters need to be given to finish specifying the
component's electrical characteristics.
On the other hand, models given by .SUBCKT statements define the modeled
component by a collection of circuitry of intrinsic SPICE devices. For
example, the SPICE model of an opamp would be given as a subcircuit.
The way how to include the model in LTspice depends on whether the model
is given as a .MODEL statement or a .SUBCKT.
Example for an NPN transistor defined with a .MODEL statement:
1. Add an instance of the symbol NPN to your schematic.
2. Edit the value "NPN" to be "BC547C" to coincide with the name used in
the target .MODEL statement.
3. Now either
3a) Add the .MODEL BC547C... statement as a SPICE directive on your
schematic.
or
3b) If you have a file bipol.lib containing your .MODEL BC547C... (other
models may be too in this file), then add the SPICE directive ".INCLUDE
bipol.lib" on your schematic. Note that "bipol.lib" must be the complete
name with any file extensions and that Windows Explorer defaults to not
showing the file extension. So you if you have a file called
"bipol.lib.txt", which you can edit/view in notepad, and Windows
Explorer shows you the file exits as "bipol.lib" The SPICE directive to
include this file is ".inc bipol.lib.txt" If you used, ".inc bipol.lib"
you will get an error message that that file can't be found.
or
3c) You can alternatively add the .MODEL BC547C... statement to the file
typically installed at
%HOMEPATH%\Documents\LTspiceXVII\lib\cmp\standard.bjt. If you do that
you will automatically see the model as a choice was editing the NPN
transistor. If you edit this standard.bjt file outside of LTspice, you
will have to restart LTspice for it to notice that the file has changed.
Example for a 5-pin opamp. This will be defined with a .SUBCKT
statement:
1. Add an instance of symbol opamp2 to your schematic.
2. Edit the value "opamp2" to "TL072" on the schematic to coincide with
the name of the .SUBCKT.
3. Either
3a) Paste the ".SUBCKT TL072 ..... .ENDS" definition as one multi-line
SPICE directive to your schematic.
or
3b) If you have a file called "TI.lib" containing the definition of
subcircuit TL072(It will look like a line that starts out as ".SUBCKT
TL072...") add the SPICE directive ".INCLUDE TI.lib" to the schematic.
It is possible to create a new symbol and program it to automatically
include the necessary model for the simulation whenever it is used on a
schematic. See help section Schematic Capture=>Creating New Symbols.
It is possible to create an automatically generated symbol that netlists
correctly against an arbitrary third party model and have it programmed
so that it includes the necessary model for the simulation whenever it
appears on a schematic. See help section Schematic Capture=>Creating New
Symbols. For most users, this is the only method you should consider for
adding new models defined as subcircuits since all the details are
handled for you.
Example for a 3-pin NPN transistor but defined with a .SUBCKT statement:
1. Add an instance of symbol NPN to your schematic.
2. Move the cursor over the body of the newly-placed NPN symbol
instance. Press <Ctrl>RightMouseButton. A dialog box will appear. Change
Prefix: QN to Prefix: X. This causes this instance of the symbol to
netlist as a subcircuit instead of an intrinsic bipolar transistor.
3. Edit the value "NPN" to be "BFG135" to coincide with the name given
on the .SUBCKT line.
4. Then either
4a) Add the .SUBCKT BFG135 lines to your schematic
or
4b) If you have a file Phil.lib containing your .SUBCKT BFG135 ....
(others may be too in this file) then you have to add a SPICE directive
.INCLUDE Phil.lib
One aspect of adding a .SUBCKT model to LTspice is that you need have
the symbol used to call the subcircuit and the model agree on the same
pin/port netlist order. The above examples assume the 3rd party model
you're adding follows popular pin order conventions.
Further related information is in the help sections Schematic Capture
and LTspice. The basic idea is that the schematic capture program
generates a netlist that the simulator, LTspice reads. Any aspect of
importing 3rd party models can be resolved by understanding SPICE
netlist syntax and how the schematic capture program generates that
syntax. There are also tutorials prepared on this topic archived at the
independent users' group at http://groups.yahoo.com/group/LTspice.
