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Linear Technology Corporation logo.svg
Original author(s)Mike Engelhardt[1]
Developer(s) [2]
Initial releaseOctober 1999 (1999-10)[1]
Stable release
XVII / December 21, 2018; 19 days ago (2018-12-21)[3]
Operating system
PlatformIA-32, x86-64
Available inEnglish
TypeElectronic design automation

LTspice is freeware[4][5] computer software implementing a SPICE electronic circuit simulator, produced by semiconductor manufacturer Linear Technology (LTC), now part of Analog Devices.[2] It is used in-house at Linear Technology for IC design, and the most widely distributed and used SPICE program in the industry.[3]


LTspice provides a schematic capture and waveform viewer with enhancements and models to speed the simulation of switching regulators. Supplied with LTspice are macro models for most of LTC's switching regulators and operational amplifiers, transistors, MOSFETs, and passive components.

LTspice is node-unlimited and third-party models can be imported. Circuit simulations based on transient, AC, noise and DC analysis can be plotted as well as Fourier analysis. Heat dissipation of components can be calculated and efficiency reports can also be generated.

LTspice is used by many users in fields including radio frequency electronics, power electronics, digital electronics, and other disciplines. LTspice IV does not generate printed circuit board (PCB) layouts, but netlists can be imported into layout programs. While LTspice does support simple logic gate simulation, it is not designed specifically for simulating logic circuits.

The software was created by and currently maintained by Mike Engelhardt.[1]

LTspice/SwitcherCAD III

In 1999, LTspice III was released, the first public release.[1] It's designed to run on Windows 95, 98, 98SE, ME, NT4.0, 2K, XP. This version is no longer available for download from Analog Devices. Initially, LTspice III was internally released to Linear Technology's Field Application Engineers (FAE) in October 1999, who then gave it away during customer visits via CDROM media.[1] In June 2001, it was released for public downloading from the Linear Technology website.[1][6] Originally, LTspice/SwitcherCAD ran only on Microsoft Windows platforms, but since 2003 it is able to run under the Wine Windows compatibility layer on Linux.[7]

LTspice IV

In 2008, LTspice IV was released.[1][8][9] It's designed to run on Windows 2K, XP, Vista, 7 with a processor that that contains a minimum instruction set similar to a Pentium 4 processor.[10] Though IV is still available for download, it is no longer maintained. LTspice was originally called SwitcherCAD, but that name was removed when IV was released.[1] A native Apple macOS 10.7+ application was introduced in 2013.[11]

LTspice XVII

In 2016, LTspice XVII was released, and currently it's the latest version.[3] It's designed to run on 32-bit or 64-bit editions of Windows 7, 8, 8.1, 10, and macOS 10.7+.[2] Every month, minor updates are released for software fixes, device model updates, and new models added.

Summary of major changes from LTspice IV to LTspice XVII are:

Number conventions

In LTspice, numeric values can be expressed in four different ways: integer (i.e. 1000), real (i.e. 1000.0), scientific e-notation (i.e. 1e3, 1.0e3), scale factor notation (i.e. 1K, 1K0).[13]

If the first character after a number isn't the letter "e" for scientific e-notation or a scale factor suffix (left column of table), then trailing characters are ignored.[13] For example, 5 is treated the same as 5V / 5Volt / 5Volts / 5A / 5Amp / 5Amps / 5Hz / 5Hertz.

Scale factors

Integer and real numbers supports a scale factor (multiplier) suffix.[13] These are based mostly on metric conventions.

The suffix (left column) can be upper / lower / mixed case.[13] For example, 1MEG / 1meg / 1Meg represents 1000000; 1k / 1K represents 1000.

Any appended text after the suffix (left column) is ignored.[13] For example, 2MegHz / 2MegaOhm represents 2000000; 3mV / 3mOhm represents 0.003; 4uF / 4uHenry represents 0.000004.

In LTspice, any suffix (left column) can replace the decimal point of a real number, a common format for printed schematics.[13][12] For example, 4K7 represents 4700, 1u8 represents 0.0000018.

Notes and Common Mistakes
T tera 1012
G giga 109
MEG mega 106 "1M" & "1Mohm" are wrong use for "one megaohm", instead "1MEG" is correct[13]
K kilo 103
m milli 10-3 Wrong use of m / meg / mil are common mistakes in all SPICE programs
u or µ micro 10-6 Older SPICE software doesn't support the µ (Mu) character[12]
n nano 10-9
p pico 10-12
f femto 10-15 "1F" & "1Farad" are wrong use for "one farad, instead "1" is correct
mil thou 25.4 x 10-6 mil is a thousandth of an inch (0.001") which is 25.4 ?m[13]


Though LTspice is based on SPICE, it has some newer features that might allow users to create non-portable files. It should be noted that some competitor SPICE programs have non-portable features too.

LTspice features that may not be supported by other SPICE programs:

  • Unicode characters. A new feature in LTspice XVII. Older LTspice and some SPICE programs don't support Unicode.[3]
  • µ (Mu) character conversion, alternate symbol for "micro" scale factor. Option setting at LTspice -> Tools -> Control Panel -> Netlist Options -> Convert 'µ' to 'u'.[12]
  • Suffix replacing decimal point. Option setting at LTspice -> Tools -> Control Panel -> SPICE -> Accept 3K4 as 3.4K.[12]

LTspice doesn't support the following features from some other simulation programs:

  • Scale factors of "atto" 10-18, "peta" 1015, "exa" 1018.

Node name conventions

In LTspice, a node/net (connection point) on the schematic can be labeled by using the Label Net tool button or F4 key. The "Label Net" wizard has three choices for a label, two predefined graphical symbols (GND, COM), or a user-defined node/net name.[14]

The two graphical symbols represent:

  • GND - The ground symbol assigns a node with a special global net name of "0".[14]
  • COM - The COM symbol assigns a mode with a net name of "COM", which doesn't have any special significance.[14]

Historically, SPICE and older version of LTspice software only supported printable ASCII characters for node/net names, then LTspice XVII added support for Unicode characters.[3]

A user-defined name supports two optional features that can be prepended to the text name:

  • _ - An underscore causes an overbar to be placed above the entire name, which commonly means an active low signal. For example, "_RESET" is shown on the schematic as "RESET".[15]
  • $G_ - This means a node is global, no matter where the name occurs in the circuit hierarchy. For example, "$G_ENABLE" / "$G_ERROR". It should be noted the ground symbol is treated in a similar way, but it doesn't have "$G_" prepended to it.[14]

When a node/net name is placed on a schematic, it will have one of five different visual representations. Two are automatically determined, while three others are chosen by the "Port Type" field in the "Label Net" wizard.[14]

  • None - Bare text. This is the default.[16]
  • Global - "Rectangle" around the text. This is automatically shown for a global net name that starts with "$G_".[16]
  • Input - "Rectangle with triangle end" around the text. This is chosen by the "Port Type" field in the "Label Net" wizard.[16]
  • Output - "Rectangle with triangle on other end" around the text. This is chosen by the "Port Type" field in the "Label Net" wizard.[16]
  • Bidirectional - "Rectangle with triangle on two ends" around the text. This is chosen by the "Port Type" field in the "Label Net" wizard.[16]

File format

Many of the LTspice files are stored as an ASCII text file, which can be viewed or edited with any ASCII text editor programs. One of the side benefits of an ASCII file format is that a schematic can be listed in a printed document / book / magazine / datasheet / research paper / homework assignment, which allows the reader to recreate LTspice files without electronic file distribution.

LTspice filename extensions:[17]

  • asc - schematic. It consists of a netlist based on SPICE text-based commands.[17]
  • asy - electronic symbol shown in a schematic.[17]
  • cir - external netlist input.[17]
  • fft - FFT binary output.[17]
  • lib - model library subcircuits.[18]
  • plt - waveform viewer plot settings.[17]
  • raw - binary output, optional ASCII output.[17]
  • sub - subcircuit.[18]
  • lib / sub / mod / model - device model. While any file extension is allowed, users tend to gravitate towards common ones.[17]


The following example can be viewed by copying each into two different text files. For each, copy the text in the gray box from this article, paste into an ASCII text editor, saving as a text file. Both files must have the same "base name" and sit in the same directory. To see it, opening the "asc" file with LTspice then click the "Run" button inside LTspice software.

  • LTspice_RC.asc
  • LTspice_RC.plt

Schematic file

LTspice schematics are stored as an ASCII text file with a filename extension of "asc".[17]

The following example shows the contents from a small LTspice schematic file for a simple RC circuit with four schematic symbols: V1 is 10 volt DC voltage source, R1 is 1K ohm resistor, C1 is 1 uF capacitor, ground. The bottom three TEXT lines are: 1) a transient simulation directive with a stop time parameter of 10 ms (.tran 10mS), 2) a SPICE directive to set the initial condition of RC "out" net to zero volts (.ic v(OUT)=0V), and 3) a text comment (title).

Version 4
SHEET 1 880 680
WIRE 224 96 128 96
WIRE 128 160 128 96
WIRE 224 192 224 176
WIRE 288 192 224 192
WIRE 224 208 224 192
WIRE 128 288 128 240
WIRE 224 288 224 272
WIRE 224 288 128 288
WIRE 224 304 224 288
FLAG 224 304 0
FLAG 288 192 OUT
IOPIN 288 192 Out
SYMBOL res 208 80 R0
SYMBOL cap 208 208 R0
SYMATTR SpiceLine V=50
SYMBOL voltage 128 144 R0
WINDOW 123 0 0 Left 0
WINDOW 39 0 0 Left 0
TEXT 120 344 Left 2 !.tran 10mS
TEXT 120 376 Left 2 !.ic v(OUT)=0V
TEXT 8 72 Left 2 ;RC Circuit - LTspice - Wikipedia

Plot file

LTspice waveform viewer plot settings are stored as an ASCII text file with a filename extension of "plt".[17] If this optional plot file is present, then all plot planes will automatically be displayed after the "Run" button is pressed, otherwise the user will need to click on each net to see the waveform(s). To create a plot file on Windows, after a plot graph is displayed, right-click on it and choose "File", then choose "Save Plot Settings".[19]

The following example shows settings for a "transient analysis" simulation with one plot plane that consists of a voltage waveform of the "out" net from the above schematic.

[Transient Analysis]
   Npanes: 1
      traces: 1 {524290,0,"V(out)"}
      X: ('m',0,0,0.001,0.01)
      Y[0]: (' ',0,0,1,10)
      Y[1]: ('_',0,1e+308,0,-1e+308)
      Volts: (' ',0,0,0,0,1,10)
      Log: 0 0 0
      GridStyle: 1

See also


  1. ^ a b c d e f g h "LTspice Genealogy - The Heritage of Simulation Ubiquity". LTwiki. Archived from the original on December 2, 2018.
  2. ^ a b c "LTspice". Analog Devices. Archived from the original on December 3, 2018.
  3. ^ a b c d e f g h i j k "LTspice XVII Introduction". LTwiki. Archived from the original on December 2, 2018.
  4. ^ a b Mike Engelhardt: LTspice IV Help -> F.A.Q. -> License and Distribution. (Help of software version 4.19u of 4 September 2013)
  5. ^ a b Mike Engelhardt: LTspice IV Help -> Introduction -> License Agreement/Disclaimer. (Help of software version 4.19u of 4 September 2013)
  6. ^ "Linear Technology announces SwitcherCAD III a fully functional Spice Simulator for switcher applications". May 16, 2001. Archived from the original on December 4, 2018.
  7. ^ news:sci.electronics.cad: LTspice/SwitcherCAD III now runs on Linux accessdate=September 27, 2013
  8. ^ "Linear released LTspice IV for multicore processors". EE Herald. February 13, 2009. Archived from the original on December 2, 2018.
  9. ^ Pell, Rich (January 13, 2009). "Free SPICE software exploits multicore processors". EE Times. Retrieved 2011.
  10. ^ news:sci.electronics.cad: Announce: Multi-threaded LTspice accessdate=September 27, 2013
  11. ^ "LTspice IV Is Now Native on Mac OS X". Evaluation Engineering. November 9, 2013.
  12. ^ a b c d e "LTspice - Control Panel". LTwiki. Archived from the original on December 4, 2018.
  13. ^ a b c d e f g h i "LTspice - General Conventions". LTwiki. Archived from the original on December 4, 2018.
  14. ^ a b c d e "Label a node name". LTwiki. Archived from the original on December 8, 2018.
  15. ^ "LTspice: Undocumented Shortcuts". Analog Devices. Archived from the original on December 8, 2018.
  16. ^ a b c d e "Port Type drawing". LTwiki. Retrieved 2018.
  17. ^ a b c d e f g h i j What are the different LTspice file types; LTwiki.
  18. ^ a b Subcircuit structure guide; Audio perfection.
  19. ^ Save Plot Configurations; LTwiki.

Further readings

  • SPICE Differentiation; Mike Engelhardt; Linear Technology; LT Journal of Analog Innovation; 7 pages; January 2015. (link)
  • The LTspice IV Simulator: Manual, Methods and Applications; Gilles Brocard; Würth Elektronik; 744 pages; 2013; ISBN 978-3899292589.
  • Switch-Mode Power Supplies - SPICE Simulations and Practical Designs; 2nd Ed; Christophe Basso; McGraw-Hill; 992 pages; 2014; ISBN 978-0071823463.
  • SPICE; 2nd Ed; Gordon Roberts and Adel Sedra; Oxford University Press; 464 pages; 1996; ISBN 978-0195108422.
  • SPICE - A Guide to Circuit Simulation and Analysis Using PSpice; 3rd Ed; Paul Tuinenga; Prentice Hall; 288 pages; 1995; ISBN 978-0131587755.
  • Semiconductor Device Modeling with SPICE; 2nd Ed; Giuseppe Massobrio and Paolo Antognetti; McGraw Hill; 479 pages; 1993; ISBN 978-0070024694.

External links

  This article uses material from the Wikipedia page available here. It is released under the Creative Commons Attribution-Share-Alike License 3.0.



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