LTspice Getting Started Guide - Engrcs

SwitcherCAD III/LTspiceGetting Started GuideCopyright 2008 Linear Technology. All rights reserved.

2Benefits of Using SwitcherCAD III/LTspice Stable SPICE circuit simulation with Outperforms pay-for options LTspice is also a greatschematic captureFast simulation of switching mode power supplies (SMPS) Unlimited number of nodesSchematic/symbol editorWaveform viewerLibrary of passive devicesSteady state detection Over 1100 macromodels ofTurn on transientLinear Technology products 500 SMPSStep responseEfficiency / power computationsAdvanced analysis and simulation options Not covered in this presentation 2008 Linear Technology

3How Do You Get SwitcherCAD III/LTspice Go to http://www.linear.com/softwareLeft click on download SwitcherCAD III/LTspiceRegister for a new MyLinear account to receive updates if you have not done soalready 2008 Linear Technology

Getting StartedCopyright 2008 Linear Technology. All rights reserved.

5Getting Started using SwitcherCAD III/LTspice Use one of the 100s of demo circuits available on linear.com Use a pre-drafted test fixture (JIG) Reviewed by Linear Technology’s Factory Applications GroupProvides a good starting pointUse the schematic editor to create your own design LTspice contains macromodels for most LTC power devices 2008 Linear Technology

6Demo Circuits on linear.com Go to http://www.linear.com Enter root part number in the searchbox (e.g. 3411) Select Simulate Tab Follow the instructions providedIf you do not find a demo circuit ofinterest, use a pre-drafted testfixture – covered nextDownload LTspiceDownload Demo CircuitComplete list of demo circuits availableat www.linear.com/democircuits 2008 Linear Technology

7Demo Circuit9 Designed and Reviewed by Factory Apps GroupTo run a demo circuit jumpto the Run and Probe aCircuit in LTspice sectionWhat if I cannot finda demo circuit? It remains the customer's responsibility to verify proper and reliable operation in theactual application Printed circuit board layout may significantly affect circuit performance or reliability 2008 Linear Technology

8Getting Started using SwitcherCAD III/LTspice Use one of the 100s of demo circuits available on linear.com Use a pre-drafted test fixture (JIG) Reviewed by Linear Technology’s Factory Applications GroupProvides a good starting pointUse the schematic editor to create your own design LTspice contains macromodels for most LTC power devices 2008 Linear Technology

9Pre-Drafted Test Fixture (JIG) Used for testing models during developmentProvides a draft starting point Not reviewed by Linear Technology’s factory applications team It remains the customer's responsibility to verify proper and reliable operation in theactual application Printed circuit board layout may significantly affect circuit performance or reliability 2008 Linear Technology

10Start with a New SchematicNew Schematic Left click on the New Schematic symbol in the Schematic Editor Toolbar 2008 Linear Technology

11Add a Macromodel & Opening Test FixtureAdd Component Left click on the Component symbol inthe Schematic Editor ToolbarEnter “root” part to search for the model(e.g. 3411)Left click on Open this macromodel’stest fixtureTo run a test fixture, jump to the Run andProbe a Circuit in LTspice section 2008 Linear Technology

12Getting Started using SwitcherCAD III/LTspice Use one of the 100s of demo circuits available on linear.com Use a pre-drafted test fixture (JIG) Reviewed by Linear Technology’s Factory Applications GroupProvides a good starting pointUse the schematic editor to create your own design LTspice contains macromodels for most LTC power devices 2008 Linear Technology

Draft a Design Using theSchematic EditorCopyright 2008 Linear Technology. All rights reserved.

14Start with a New SchematicNew Schematic Left click on the New Schematic symbol in the Schematic Editor ToolbarLTspice is also a greatschematic capture 2008 Linear Technology

15Add a Linear Technology MacromodelAdd Component Left click on the Component symbol in the Schematic Editor ToolbarEnter “root” part to search for the model (e.g. 3411)Left click on OK 2008 Linear Technology

16Getting the Latest Datasheet Use the macromodel’s shortcuts to download the Datasheetas a reference for your design Hold Ctrl key and right click (Ctrl – right click) over the LTmacromodel’s symbolLeft click on Go to Linear website for datasheet on the dialogbox that appearsYou can also open the macromodel's test fixture as a draft starting point 2008 Linear Technology

17Adding Circuit ElementsPlace DiodePlace InductorPlace CapacitorPlace ResistorRotateMirror Left click on the desired component in the Schematic Editor Toolbar Left click on Rotate or Mirror to adjust orientation Alternate you can also use Ctrl – R and Ctrl – M key shortcutsMove the mouse to the position you want to place itLeft click to place itTo cancel or quit a component type,click the right mouse button 2008 Linear Technology

18Adding Sources, Loads & Additional Circuit Elements Left click on the Component symbol inthe Schematic Editor ToolbarSearch directory structure for desiredcircuit element (e.g. load and voltage)Left click on OKMove the mouse to the position youwant to place itLeft click to place itAdditional Circuit ElementsLike Sources and Loads 2008 Linear Technology

19Highlights of Additional Circuit Elements Left click on the Component symbol in the Schematic Editor Toolbar for adirectory of additional circuit elements: Lossy transmission line Arbitrary behavioral source Bipolar transistor Voltage dependent voltage Voltage controlled switch Current dependent current Lossless transmission line Voltage dependent current Uniform RC-line Current dependent voltage Independent voltage source Independent current source Current controlled switch JFET transistor Subcircuit Mutual inductance MESFET transistor MOSFET transistor many more 2008 Linear Technology

20Drawing Lines and Labeling NodesDraw WirePlace GroundLabel Node Do not forget to place aground in your design, it isrequired for simulation!Lines Left click on the Draw Wire in the Schematic Editor Toolbar Left click a blue box (terminal) Define the line’s path with a left click over intermediate points Left click on another blue box (terminal) 2008 Linear Technology

21Editing Circuit ElementsDeleteDuplicateMoveDragUndoRedo Left click on the desired editing optionLeft click on the circuit elementTo organize your layout, use the Drag option to move circuitelements around and to adjust lines between terminals 2008 Linear Technology

22Editing Circuit Elements Attributes Right click on the component symbol to modify attributes Right click on the text next to the component to edit thevisible attribute and label Pointer will turn into a text caret 2008 Linear Technology

23Use Labels to Specify Units in Circuit Elements Attributes K k kilo 103MEG meg 106G g giga 109T t terra 1012 M m milli 10-3U u micro 10-6N n nano 10-9P p pico 10-12F f femto 10-15Hints Use MEG to specify 106, not M Enter 1 for 1 Farad, not 1F 2008 Linear Technology

24Circuit Elements Database Some components have an available database ofmanufacturers’ attributes Resistors, capacitors, inductors, diodes, Bipolar transistors, MOSFET transistors, JFETtransistors Independent voltage and current sourcesTo configure a component to a manufacture’sattributes Right click on the component symbol Left click on Select or Pick New Left click on a selected device Left click on OK 2008 Linear Technology

25Editing Voltage Sources and Loads Voltage Source Right click the voltagesymbol Enter DC voltage value and(optional) Series Resistance Left click on OKLoad (current) Right click on the loadsymbol Enter DC current value Left click on OK 2008 Linear Technology

26Summary of Schematic Editor ToolbarPlace Circuit ElementPlace DiodePlace InductorPlace CapacitorPlace ResistorLabel NodePlace GroundDraw WireDeleteDuplicatePaste b/t Schematics 2008 Linear TechnologyFindMoveDragUndoRedoRotateMirrorPlace CommentPlace SPICE directive

Run and Probe a CircuitCopyright 2008 Linear Technology. All rights reserved.

28Simulation Commands To run a simulation, specify the type of analysis to beperformedThere are six different types of analyses: Transient analysisSmall signal ACDC sweepNoiseDC transfer functionDC operating pointMore information on simulation and dotcommands are available inSwitcherCAD III/LTspice User GuideSimulation commands are placed on the schematic as text Called dot commands 2008 Linear Technology

29Editing Simulation Commands Left click on Simulation menu Left click on Edit Simulation Cmd As a starting point in a simulation Left click on Transient tab Enter a Stop Time You may need to adjust thisagain laterSelect OK 2008 Linear TechnologyDemo Circuits and Test Fixtureshave predefined SimulationsCommands

30Running a CircuitRunIf model is not found please Sync Releaseunder Help menu to update LTspice 2008 Linear Technology

31Probing a Circuit & Waveform Viewer Left click on any wire to plot the voltageon the waveform viewerVoltage probe cursor Left click on the body of the componentto plot the current on the waveformviewer Convention of positive current is inthe direction into the pinCurrent probe cursor 2008 Linear Technology

32Probing a Demo Circuit and Test Fixture Demo Circuits and Test Fixtures have INs and OUTs clearlylabeled to help you quickly select themTo view the waveform left click on IN and OUTLeft ClickHere forInputWaveform 2008 Linear TechnologyLeft ClickHere forOutputWaveform

33Voltage Differences Across Nodes Left click and hold on onenode and drag the mouseto another node Red voltage probe at the firstnodeBlack probe on the secondDifferential voltages aredisplayed in the waveformviewer 2008 Linear Technology

34Plot Planes Multiple plot panes can be displayed on one window to allow betterseparation between traces permitting different traces to beindependently autoscaled Right click in the waveform pane Select Add Plot Pane Left click and hold to drag a label to a new plot pane 2008 Linear Technology

35Zooming In and Out in the Waveform Viewer To zoom in Left click and hold as youdrag a box about the regionyou wish to zoom in thenreleaseTo zoom out Right click and select Zoomto Fit or Zoom BackZoom InPanZoom OutAutoscale 2008 Linear Technology

36Measuring VRipple, IRipple and Time (Frequency) Drag a box about the region you wish to measure (peak to peakover a period) Left click and hold to drag a box over the portion of interestView the lower left hand side of the screen To avoid resizing, shrink your box before you let go of the left mouseclick or use the Undo command in the Edit menuTo view SMPS voltage ripple you willneed to zoom into a narrow sectionsince waveform is initiallycompressed to full range 2008 Linear Technology

37Average/RMS Current or Voltage Calculations Hold down Ctrl and left click on the I or V trace label in thewaveform viewer 2008 Linear Technology

38Instantaneous & Average Power Dissipation Instantaneous Power Dissipation Hold down the ALT key andleft click on the symbol of thecomponent Pointer will change to athermometer Plotted in units of Watts Average Power Dissipation Hold down the Ctrl key andleft click on the trace labelpower dissipation waveform 2008 Linear Technology

Generating a BOM andEfficiency ReportCopyright 2008 Linear Technology. All rights reserved.

40Bill of Materials (BOM) Left click on View menuLeft click on Bill of Materials 2008 Linear Technology

41Computing Efficiency of SMPS Circuits Left click on Simulate menuLeft click on Edit Simulation CmdLeft click on Stop simulating if steady state is detected Automatically detect the steady state by checking the internalstate of the macromodelsRerun simulation 2008 Linear TechnologyAutomatic detection of steady statemay not work – steady state detectionmay be too strict or lenient

42Viewing Efficiency Report Left click on Simulate menuLeft click on Efficiency Report 2008 Linear Technology