用L297步进电机控制器与L298N双桥驱动器设计微处理器与概要.docx

用L297步进电机控制器与L298N双桥驱动器设计微处理器与概要.docx

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用L297步进电机控制器与L298N双桥驱动器设计微处理器与概要

APPLICATIONNOTE

AN470/0392THEL297STEPPERMOTORCONTROLLER

TheL297integratesallthecontrolcircuitryrequiredtocontrolbipolarandunipolarsteppermotors.UsedwithadualbridgedriversuchastheL298Nformsacompletemicroprocessor-to-bipolarsteppermotorinterface.UnipolarsteppermotorcanbedrivenwithanL297plusaquaddarlingtonarray.Thisnotede-scribestheoperationofthecircuitandshowshowitisused.

TheL297StepperMotorControllerisprimarilyin-tendedforusewithanL298NorL293Ebridgedriverinsteppermotordrivingapplications.

Itreceivescontrolsignalsfromthesystem’scontrol-ler,usuallyamicrocomputerchip,andprovidesallthenecessarydrivesignalsforthepowerstage.Ad-ditionally,itincludestwoPWMchoppercircuitstore-gulatethecurrentinthemotorwindings.

WithasuitablepoweractuatortheL297drivestwophasebipolarpermanentmagnetmotors,fourpha-seunipolarpermanentmagnetmotorsandfourpha-sevariablereluctancemotors.Moreover,ithandlesnormal,wavedriveandhalfstepdrivemodes.（Thisisallexplainedinthesection”StepperMotorBa-sics”.

Twoversionsofthedeviceareavailable:

theregularL297andaspecialversioncalledL297A.TheL297Aincorporatesasteppulsedoublerandisde-signedspecificallyforfloppy-diskheadpositioningapplications.

ADVANTAGES

TheL297+drivercombinationhasmanyadvanta-ges:

veryfewcomponentsarerequired（soassem-blycostsarelow,reliabilityhighandlittlespacerequired,softwaredevelopmentissimplifiedandtheburdenonthemicroisreduced.Further,thechoiceofatwo-chipapproachgivesahighdegreeofflexibility-theL298NcanbeusedonitsownforDCmotorsandtheL297canbeusedwithanypowerstage,includingdiscretepowerdevices（itprovides20mAdriveforthispurpose.

Figure1:

InthistypicalconfigurationanL297steppermotorcontrollerandL298dualbridgedrivercom-binetoformacompletemicroprocessortobipolarsteppermotorinterface.

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Forbipolarmotorswithwindingcurrentsupto2AtheL297shouldbeusedwiththeL298N;forwindingcurrentsupto1AtheL293Eisrecommended（theL293willalsobeusefulifthechopperisn’tneeded.HighercurrentsareobtainedwithpowertransistorsordarlingtonsandforunipolarmotorsadarlingtonarraysuchastheULN2075Bissuggested.Theblockdiagram,figure1,showsatypicalsystem.ApplicationsoftheL297canbefoundalmosteve-rywhere...printers（carriageposition,daisyposition,paperfeed,ribbonfeed,typewriters,plotters,nu-mericallycontrolledmachines,robots,floppydiskdrives,electronicsewingmachines,cashregisters,photocopiers,telexmachines,electroniccarbure-tos,telecopiers,photographicequipment,papertapereaders,opticalcharacterrecognisers,electricvalvesandsoon.

TheL297ismadewithSGS’analog/digitalcompa-tibleI2Ltechnology（likeZodiacandisassembledina20-pinplasticDIP.A5VsupplyisusedandallsignallinesareTTL/CMOScompatibleoropencol-lectortransistors.Highdensityisoneofthekeyfea-turesofthetechnologysotheL297dieisverycompact.THEL298NANDL293E

SincetheL297isnormallyusedwithanL298NorL293Ebridgedriverabriefreviewofthesedeviceswillmaketherestofthisnoteeasiertofollow.

TheL298NandL293Econtaintwobridgedriverstages,eachcontrolledbytwoTTL-levellogicinputsandaTTL-levelenableinput.Inaddition,theemitterconnectionsofthelowertransistorsarebroughtouttoexternalterminalstoallowtheconnectionofcur-rentsensingresistors（figure2.

FortheL298NSGS’innovativeion-implantedhighvoltage/highcurrenttechnologyisused,allowingittohandleeffectivepowersupto160W（46Vsupply,2Aperbridge.Aseparate5VlogicsupplyinputisprovidedtoreducedissipationandtoallowdirectconnectiontotheL297orothercontrollogic.

InthisnotethepinsoftheL298NarelabelledwiththepinnamesofthecorrespondingL297terminalstoavoidunnecessaryconfusion.

TheL298Nissuppliedina15-leadMultiwattplasticpowerpackage.It’ssmallerbrother,thefunctionallyidenticalL293E,ispackagedinaPowerdip–acop-perframeDIPthatusesthefourcenterpinstocon-ductheattothecircuitboardcopper.

Figure2:

TheL298Ncontainstwobridgedrivers（fourpushpullstageseachcontrolledbytwologicinputsandanenableinput.Externalemitterconnectionsareprovidedforcurrentsense

resistors.TheL293Ehasexternalconnectionsforallfouremitters.

APPLICATIONNOTE

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STEPPERMOTORBASICS

Therearetwobasictypesofsteppermotorincom-monuse:

permanentmagnetandvariablereluctan-ce.Permanentmagnetmotorsaredividedintobipolarandunipolartypes.

BIPOLARMOTORS

Simplifiedtothebareessentials,abipolarperma-nentmagnetmotorconsistsofarotatingpermanentmagnetsurroundedbystatorpolescarryingthewin-dings（figure3.Bidirectionaldrivecurrentisusedandthemotorissteppedbyswitchingthewindingsinsequence.

Foramotorofthistypetherearethreepossibledrivesequences.

ThefirstistoenergizethewindingsinthesequenceAB/CD/BA/DC（BAmeansthatthewindingABisenergizedbutintheoppositesense.Thissequenceisknownas”onephaseon”fullsteporwavedrivemode.Onlyonephaseisenergizedatanygivenmo-ment（figure4a.

Thesecondpossibilityistoenergizebothphasesto-gether,sothattherotoralwaysalignsitselfbetweentwopolepositions.Called”two-phase-on”fullstep,thismodeisthenormaldrivesequenceforabipolarmotorandgivesthehighesttorque（figure4b.Thethirdoptionistoenergizeonephase,thentwo,thenone,etc.,sothatthemotormovesinhalfstepincrements.Thissequence,knownashalfstepmode,halvestheeffectivestepangleofthemotorbutgivesalessregulartorque（figure4c.

Forrotationintheoppositedirection（counter-clock-wisethesamethreesequencesareused,exceptofcoursethattheorderisreserved.

Asshowninthesediagramsthemotorwouldhaveastepangleof90°.Realmotorshavemultiplepolestoreducethestepangletoafewdegreesbutthenumberofwindingsandthedrivesequencesareun-changed.Atypicalbipolarsteppermotorisshowninfigure5.

UNIPOLARMOTORS

Aunipolarpermanentmagnetmotorisidenticaltothebipolarmachinedescribedaboveexceptthatbi-filarwindingsareusedtoreversethestatorflux,ra-therthanbidirectionaldrive（figure6.

Thismotorisdriveninexactlythesamewayasabi-polarmotorexceptthatthebridgedriversarerepla-cedbysimpleunipolarstages-fourdarlingtonsoraquaddarlingtonarray.Clearly,unipolarmotorsaremoreexpensivebecausethayhavetwiceasmanywindings.Moreover,unipolarmotorsgivelesstorqueforagivenmotorsizebecausethewindingsaremadewiththinnerwire.Inthepastunipolarmo-torswereattractivetodesignersbecausetheysim-plifythedriverstage.NowthatmonolithicpushpulldriversliketheL298Nareavailablebipolarmotorsarebecomingmorepopular.

Allpermanentmagnetmotorssufferfromthecoun-terEMFgeneratedbytherotor,whichlimitsthero-tationspeed.Whenveryhighslewingspeedsarenecessaryavariablereluctancemotorisused.

Figure3:

Greatlysimplified,abipolarpermanent

magnetsteppermotorconsistofarota-

ringmagnetsurroundedbystatorpoles

asshown.

APPLICATIONNOTE

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APPLICATIONNOTE

Figure4:

Thethreedrivesequencesforatwophasebipolarsteppermotor.Clockwiserotationisshown.Figure4a:

Wavedrive（onephaseon.

Figure4b:

Twophaseondrive.

Figure4c:

Halfstepdrive.

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VARIABLERELUCTANCEMOTORS

Avariablereluctancemotorhasanon-magnetizedsoftironrotorwithfewerpolesthanthestator（fig-ure7.Unipolardriveisusedandthemotorisstep-pedbyenergizingstatorpolepairstoaligntherotorwiththepolepiecesoftheenergizedwinding.Onceagainthreedifferentphasesequencescanbeused.ThewavedrivesequenceisA/C/B/D;two-phase-onisAC/CB/BD/DAandthehalfstepse-quenceisA/AC/C/BC/B/BD/D/DA.Notethatthestepangleforthemotorshownaboveis15°,not45°.Asbefore,praticalmotorsnormallyemploymultiplepolestogiveamuchsmallerstepangle.Thisdoesnot,however,affecttheprincipleofoperationofthedrivesequences.

GENERATINGTHEPHASESEQUENCESTheheartoftheL297blockdiagram,figure8,isablockcalledthetranslatorwhichgeneratessuitablephasesequencesforhalfstep,one-phase-onfullstepandtwo-phase-onfullstepoperation.Thisblockiscontrolledbytwomodeinputs–direction（CW/CCWandHALF/FULL–andastepclockwhichadvancesthetranslatorfromonesteptothenext.

Fouroutputsareprovidedbythetranslatorforsub-sequentprocessingbytheoutputlogicblockwhichimplementstheinhibitandchopperfunctions.Internallythetranslatorconsistsofa3-bitcounterplussomecombinationallogicwhichgeneratesabasiceight-stepgraycodesequenceasshowninfigure9.Allthreedrivesequencescanbegeneratedeasilyfromthismastersequence.Thisstatese-quencecorrespondsdirectlytohalfstepmode,se-lectedbyahighlevelontheHALF/FULLinput.

Figure6:

AunipolarPMmotorusesbifilarwin-

dingstoreversethefluxineachphase.Figure7:

Avariablereluctancemotorhasasoftironrotorwithfewerpolesthanthesta-

tor.Thestepangleis15°forthismotor.

Figure5:

Arealmotor.Multiplepolesarenorma-

llyemployedtoreducethestepangleto

apracticalvalue.Theprincipleofopera-

tionanddrivesequencesremainthe

same.

APPLICATIONNOTE

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Theoutputwaveformsforthissequenceareshowninfigure10.

Notethattwoothersignals,INH1andINH2arege-neratedinthissequence.Thepurposeofthesesi-gnalsisexplainedalittlefurtheron.

Thefullstepmodesarebothobtainedbyskippingalternatestatesintheeight-stepsequence.Whathappensisthatthestepclockbypassesthefirststa-geofthe3-bitcounterinthetranslator.Theleastsi-gnificantbitotthiscounterisnotaffect