LTspiceGettingStartedGuide

LTspice Getting Started Guide

Copyright 2007 Linear Technology. All rights reserved.

Why Use LTspice?Stable SPICE circuit simulation withUnlimited number of nodes Schematic/symbol editor Waveform viewer Library of passive devices Steady state detection Turn on transient Step response Efficiency / power computations Over 1100 macromodels of Over 1100 macromodels of Linear Technology products Linear Technology products 500+ SMPS 500+ SMPS

Fast simulation of switching mode power supplies

Advanced analysis and simulation optionsNot covered in this presentation

Outperforms pay-for optionsLTspice is also a great schematic capture LTspice is also a great schematic captureLTspice Getting Started Guide 2

How Do I Get LTspice?Go to http://www.linear.com Select Design Support and then Design Simulation Follow the instruction to install


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How Do I Get Started Using LTspice?

How Do I Get Started using LTspice?1. 2.

Use one of the 100s demo circuit available on linear.comDesigned and Reviewed by Factory Apps Group

Use a pre-drafted test fixture (JIG)Provides a good starting point Used in testing models during development

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Use the graphic editor to create your own design using the macro models providedLTspice contains models for most LTC power devices

You can also check out LTspice capabilities using the education examples You can also check out LTspice capabilities using the education examples available on C:\Program Files\LTC\SwCADIII\examples\Educational available on C:\Program Files\LTC\SwCADIII\examples\EducationalLTspice Getting Started Guide 5




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Demo Circuits on linear.com

Download LTspice Download Demo Circuit


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Demo CircuitDesigned and Reviewed by Factory Apps GroupIt remains the customer's responsibility to verify proper and reliable operation in the actual application Component substitution and printed circuit board layout may significantly affect circuit performance or reliability

What ififIIcannot find a demo circuit? What cannot find a demo circuit?LTspice Getting Started Guide 8




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Start with a New SchematicSelect File and New SchematicWill open up a black layout screen


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Add a ComponentUse Add a Component or F2

Take a moment to review all the components!LTspice Getting Started Guide 11

Selecting Model & Opening Test Fixture1.

Use the root part to search for the modeli.e. 3411

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Select Open this macromodels test fixture 2. Select

1. Enter 3411


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Pre-Drafted Test FixtureProvides a good starting pointUsed in testing models during development

It remains the customer's responsibility to verify proper It remains the customer's responsibility to verify proper and reliable operation in the actual application and reliable operation in the actual application Printed circuit board layout may significantly affect Printed circuit board layout may significantly affect circuit performance or reliability circuit performance or reliabilityLTspice Getting Started Guide 13




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Use the Graphic Editor to Create Your Own DesignSelect the Model Use the menu to design you circuit Also Great for drawing schematics for customers

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Additional Components Like Sources & LoadsLTspice Getting Started Guide 15

Custom Design

Schematic EditingPlace Circuit Element Place Diode Place Inductor Place Capacitor Place Resistor Label Node Place Ground Draw Wire

Zoom In Pan Zoom Out Autoscale Delete Duplicate Paste b/t Schematics

Find

Move Drag Undo Redo Rotate Mirror Place Comment Place SPICE directiveLTspice Getting Started Guide 16

Editing ComponentsComponents attributes can be edited by pointing at the component with the mouse and right clicking

You can also edit the visible attribute and label by pointing at the text You can also edit the visible attribute and label by pointing at the text with the mouse and then right clicking with the mouse and then right clicking Mouse cursor will turn into a text caret Mouse cursor will turn into a text caret


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Component DatabaseComponents such asResistors, capacitors, inductors, diodes, Bipolar transistors, MOSFET transistors, JFET transistors Independent voltage and current sources

can access a database of know devices


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Test Fixture Shortcut with LT MacromodelsPlace the mouse over the LT macromodels symbol Hold down the control key, and click the right mouse button A dialog box will appear that will allow you toOpen the test fixture Go to Linear website for the datasheet


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How Do You Run and Probe a Circuit in LTspice?

Running Demo CircuitRun Run

Select runRunning Man logo on menu


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Waveform ViewerLTspice has an integrated waveform viewer1. Plot the voltage on any wire by simply point and click Voltage probe cursor 2. Plot the current through any component with two connections by clicking on the body of the component R, C, L Current probe cursor Convention of positive current is in the direction into the pinLTspice Getting Started Guide 22

Probing a Demo CircuitClick Here Click Here for Input for Input Waveform Waveform Click Here Click Here for Output for Output Waveform Waveform

All Demo Circuits have INs and OUTs clearly labeled to help you quickly select them Select the waveform of a node by clicking on IN and OUT


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Zooming In and Out on a Waveform

Using the mouse to zoom in and outDrag a box about the region you wish to see drawn larger

Right click and select Zoom to Fit to zoom backLTspice Getting Started Guide 24

Measuring V, I and Time in the Waveform1. 2. 3.

Drag a box about the region you wish to measureHold the left click down

View the lower left hand side of the screen Shrink your box before you let go of the left mouse click or use the undo command on top to resize


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Voltage Differences Across NodesClick on one node and drag the mouse to another nodeRed voltage probe at the first node Black probe on the second

Will provide differentially plot of the voltages


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Average/RMS CalculationsAverage & RMS Current or VoltageControl - left click the I or V trace label in the waveform view


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Instantaneous & Average Power DissipationInstantaneous Power DissipationHold down the Alt key and left click on the symbol of the component Plotted in units of Watts

Average Power DissipationControl - left click the power Dissipation trace label in the waveform view


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Generating a BOM and Efficiency Report

BOMUnder View select Bill of MaterialDisplayed on Diagram Paste to Clipboard


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Computing EfficiencyTo compute efficiency of SMPS circuits:Check the "Stop simulating if steady state is detected" on the Edit Simulation Command editor Rerun simulation Use the menu command View=>Efficiency Report

Automatic detection of steady state may not always work Automatic detection of steady state may not always work criteria for steady state detection may be too strict or too lenient criteria for steady state detection may be too strict or too lenientLTspice Getting Started Guide 31

Viewing Efficiency Report


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Simulate a Transient Response?

Current Load and Pulse FunctionYour can simulate a load with a Resistor or Current load In particular the Pulse function in a current load is helpful in transient response analysisSteps a current load from one value to another


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Edit the Current Load to a Pulse FunctionRight click on the current load Select Pulse Modify the Attributes


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More Information and Support

Reminder to Periodically Sync Release

It is important to sync your release of LTspice once a month to get the latestSoftware update and bug fix Models Sample circuits and examples


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Built-in Help SystemSelect F1 for help menu


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Paper ManualDownload the pdf of the help pages from:http://LTspice.linear.com/software/scad3.pdf


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Emailing SupportMake sure youre using the current version with Field sync.


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LTspice Support GroupThe group has a Files section with additional tutorials, libraries, and examples Visit the user grouphttp://groups.yahoo.com/group/LTspice/

Join LTspice Yahoo GroupEmail [email protected] Subject=Subscribe


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LTspiceGettingStartedGuide

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