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Why Use LTspice? Stable SPICE circuit simulation with Unlimited number of nodes Schematic/symbol editor Waveform viewer Library of passive devices Fast simulation of switching mode power supplies Steady state detection Turn on transient Step response Efficiency / power computations Advanced analysis and simulation options Not covered in this presentation Outperforms pay-for options Over 1100 macromodels of of Linear Technology products 500+ SMPS LTspice is is also also a great schematic capture 2
How Do I Get LTspice? Go to http://www.linear.com Select Design Support and then Design Simulation Follow the instruction to install 3
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 point Used 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 You can can also also check out out LTspice capabilities using the the education examples available on on C:\Program Files\LTC\SwCADIII\examples\Educational 5
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 point Used 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 6
Demo Circuits on linear.com Download LTspice Download Demo Circuit 7
Demo Circuit Designed and Reviewed by Factory Apps Group It 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 if if I I cannot find find a demo circuit? 8
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 point Used 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 9
Start with a New Schematic Select File and New Schematic Will open up a black layout screen 10
Add a Component Use Add a Component or F2 Take a moment to review all the components! 11
Selecting Model & Opening Test Fixture 1. Use the root part to search for the model i.e. 3411 2. Select Open this macromodel s test fixture 2. Select 1. Enter 3411 12
Pre-Drafted Test Fixture Provides a good starting point Used in testing models during development It It remains the the customer's responsibility to to verify proper and and reliable operation in in the the actual application Printed circuit board layout may may significantly affect circuit performance or or reliability 13
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 point Used 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 14
Use the Graphic Editor to Create Your Own Design Select the Model Use the menu to design you circuit Also Great for drawing schematics for customers = Custom Design Additional Components Like Sources & Loads 15
Schematic Editing Place 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 directive 16
Editing Components Components attributes can be edited by pointing at the component with the mouse and right clicking You You can can also also edit edit the the visible attribute and and label by by pointing at atthe the text text with with the the mouse and and then then right right clicking Mouse cursor will will turn turn into into a text text caret 17
Component Database Components such as Resistors, capacitors, inductors, diodes, Bipolar transistors, MOSFET transistors, JFET transistors Independent voltage and current sources can access a database of know devices 18
Test Fixture Shortcut with LT Macromodels Place the mouse over the LT macromodel s symbol Hold down the control key, and click the right mouse button A dialog box will appear that will allow you to Open the test fixture Go to Linear website for the datasheet 19
How Do You Run and Probe a Circuit in LTspice?
Running Demo Circuit Run Run Select run Running Man logo on menu 21
Waveform Viewer LTspice has an integrated waveform viewer 1. 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 pin 22
Probing a Demo Circuit Click Here for for Input Waveform Click Here for for Output 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 23
Zooming In and Out on a Waveform Using the mouse to zoom in and out Drag a box about the region you wish to see drawn larger Right click and select Zoom to Fit to zoom back 24
Measuring V, I and Time in the Waveform 1. 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 25
Voltage Differences Across Nodes Click on one node and drag the mouse to another node Red voltage probe at the first node Black probe on the second Will provide differentially plot of the voltages 26
Average/RMS Calculations Average & RMS Current or Voltage Control - left click the I or V trace label in the waveform view 27
Instantaneous & Average Power Dissipation Instantaneous Power Dissipation Hold down the Alt key and left click on the symbol of the component Plotted in units of Watts Average Power Dissipation Control - left click the power Dissipation trace label in the waveform view 28
Generating a BOM and Efficiency Report
BOM Under View select Bill of Material Displayed on Diagram Paste to Clipboard 30
Computing Efficiency To 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 of steady state may may not not always work criteria for for steady state detection may may be be too too strict strict or or too too lenient 31
Viewing Efficiency Report 32
Simulate a Transient Response?
Current Load and Pulse Function Your can simulate a load with a Resistor or Current load In particular the Pulse function in a current load is helpful in transient response analysis Steps a current load from one value to another 34
Edit the Current Load to a Pulse Function Right click on the current load Select Pulse Modify the Attributes 35
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 fix Models Sample circuits and examples 37
Built-in Help System Select F1 for help menu 38
Paper Manual Download the pdf of the help pages from: http://ltspice.linear.com/software/scad3.pdf 39
Emailing Support Make sure you re using the current version with Field sync. 40
LTspice Support Group The group has a Files section with additional tutorials, libraries, and examples Visit the user group http://groups.yahoo.com/group/ltspice/ Join LTspice Yahoo Group Email LTspice-subscribe@yahoogroups.com Subject=Subscribe 41