ltspice getting started guide - university of florida · ltspice getting started guide 13...

Copyright © 2007 Linear Technology. All rights reserved.

LTspice Getting Started Guide

2LTspice Getting Started Guide

Why Use LTspice?Stable SPICE circuit simulation with

Unlimited number of nodesSchematic/symbol editorWaveform viewerLibrary of passive devices

Fast simulation of switching mode power suppliesSteady state detectionTurn on transientStep responseEfficiency / power computations

Advanced analysis and simulation optionsNot covered in this presentation

Outperforms pay-for options

Over 1100 macromodels ofLinear Technology products500+ SMPS

Over 1100 macromodels ofLinear Technology products500+ SMPS

LTspice is also a great schematic captureLTspice is also a great schematic capture


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

How Do I Get Started Using LTspice?


How Do I Get Started using LTspice?1. Use one of the 100’s demo circuit available on linear.com

Designed and Reviewed by Factory Apps Group

2. Use a pre-drafted test fixture (JIG)Provides a good starting pointUsed in testing models during development

3. Use the graphic editor to create your own design using the macro models provided

LTspice contains models for most LTC power devices

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

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


Demo Circuits on linear.com

Download LTspice

Download Demo Circuit


Demo CircuitDesigned and Reviewed by Factory Apps Group

It remains the customer's responsibility to verify proper and reliable operation in the actual applicationComponent substitution and printed circuit board layout may significantly affect circuit performance or reliability

What if I cannot find a demo circuit?What if I cannot find a demo circuit?


Start with a New SchematicSelect File and New Schematic

Will open up a black layout screen


Add a ComponentUse Add a Component or F2

Take a moment to review all the components!


Selecting Model & Opening Test Fixture1. Use the “root” part to search for the model

i.e. 34112. Select “Open this macromodel’s test fixture

1. Enter 3411

2. Select


Pre-Drafted Test FixtureProvides a good starting point

Used in testing models during development

It remains the customer's responsibility to verify proper and reliable operation in the actual application

Printed circuit board layout may significantly affect circuit performance or reliability

It remains the customer's responsibility to verify proper and reliable operation in the actual application

Printed circuit board layout may significantly affect circuit performance or reliability


Use the Graphic Editor to Create Your Own DesignSelect the ModelUse the menu to design you circuit

=

Cus

tom

Des

ign

Also Great for drawing schematics

for customers

Additional ComponentsLike Sources

& Loads


Schematic EditingPlace Circuit Element

Place DiodePlace Inductor

Place CapacitorPlace Resistor

Label NodePlace Ground

Draw Wire

MoveDragUndo

RedoRotate

MirrorPlace Comment

Place SPICE directive

DeleteDuplicate

Paste b/t SchematicsFind

Zoom InPan

Zoom OutAutoscale


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 with the mouse and then right clicking

Mouse cursor will turn into a text caret

You can also edit the visible attribute and label by pointing at the text with the mouse and then right clicking

Mouse cursor will turn into a text caret


Component DatabaseComponents such as

Resistors, capacitors, inductors, diodes, Bipolar transistors, MOSFET transistors, JFET transistorsIndependent voltage and current sources

can access a database of know devices


Test Fixture Shortcut with LT MacromodelsPlace the mouse over the LT macromodel’s symbolHold down the control key, and click the right mouse buttonA dialog box will appear that will allow you to

Open the test fixtureGo to Linear website for the datasheet

How Do You Run and Probe a Circuit in LTspice?


Running Demo Circuit

Select run“Running Man” logo on menu

RunRun


Current probe cursor

Waveform ViewerLTspice has an integrated waveform viewer 1. Plot the voltage on any wire by

simply point and click

2. Plot the current through any component with two connections by clicking on the body of the component

R, C, L

Convention of positive current is in the direction into the pin

Voltage probe cursor


Probing a Demo Circuit

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

Click Here for Output Waveform

Click Here for Output Waveform

Click Here for Input

Waveform

Click Here for Input

Waveform


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 back


Measuring V, I and Time in the Waveform1. Drag a box about the region you wish to measure

Hold the left click down

2. View the lower left hand side of the screen 3. Shrink your box before you let go of the left mouse click or

use the undo command on top to resize


Voltage Differences Across NodesClick on one node and drag the mouse to another node

Red voltage probe at the first nodeBlack probe on the second

Will provide differentially plot of the voltages


Average/RMS Calculations

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


Instantaneous & Average Power Dissipation

Instantaneous Power Dissipation Hold down the Alt key and left clickon the symbol of the componentPlotted in units of Watts

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

Generating a BOM and Efficiency Report


BOMUnder View select Bill of Material

Displayed on DiagramPaste to Clipboard


Computing EfficiencyTo compute efficiency of SMPS circuits:

Check the "Stop simulating if steady state is detected" on the Edit Simulation Command editorRerun simulationUse the menu command View=>Efficiency Report

Automatic detection of steady state may not always work –criteria for steady state detection may be too strict or too lenient

Automatic detection of steady state may not always work –criteria for steady state detection may be too strict or too lenient


Viewing Efficiency Report

Simulate a Transient Response?


Current Load and Pulse FunctionYour can simulate a load with a Resistor or Current loadIn particular the Pulse function in a current load is helpful intransient response analysis

Steps a current load from one value to another


Edit the Current Load to a Pulse FunctionRight click on the current loadSelect PulseModify the Attributes

More Information and Support


Reminder to Periodically Sync Release

It is important to sync your release of LTspice once a month to get the latest

Software update and bug fixModelsSample circuits and examples


Built-in Help SystemSelect F1 for help menu


Paper ManualDownload the pdf of the help pages from:

http://LTspice.linear.com/software/scad3.pdf


Emailing SupportMake sure you’re using the current version with Field sync.


LTspice Support GroupThe group has a Files section with additional tutorials, libraries, and examplesVisit the user group

http://groups.yahoo.com/group/LTspice/

Join LTspice Yahoo GroupEmail [email protected]=Subscribe

ltspice getting started guide - university of florida · ltspice getting started guide 13...

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