The L297integratesa/l thecontrol circuitry required to control bipolar an d unipolar stepper motors.Used with
a
dualbridge driversuchas
the L298Nformsa
complete microprocessor-la-bipolarsteppermotor interface.Unipolarstepper motorcan be drivenwithan L297plusa
quad darlingtonarray.Thisnote de -scribesthe operation ofth e circuitandsho ws howit
is used.TheL297Steppe r Motor Controllerisprimarily in-tendedforusewith an L29BN or l293 E brdgedriver instepper motordrMngapplications.
It rece ives control signals fromthe syste m'scontrol-ler,usuall y amicrocomputer chip , and provid es all the necessarydriv esignals for the power staqe. Ad-ditionally,itinckJdes twoPWMcroooercscuits tore-gulate thecurrent inthe motor windings.
With
a
suitab le poweractuat or thel297 drivestwo phasebipolarpermanentmagnet motors,fou r pha -seunipolarpermanent magnetnotorsa ro tc ur pna-se variable reluctancemotors.Moreover,ithandles norma l,wavedriVeandhalfstep drivemodes.(This is all explainedin the section"StepperMotor Ba-sics").Too versionsofthedevice are available:the regular
Figure 1 : Inthistypical conf ig uratio n anL2 97 step per moto r controllerandL298dua l bridge driver com-bine to forma completemicroprocessorto bipolar ste ppermoto rintertace.
r r J: 0"
,~r
-Chapter 2 / Electronics
APPLICATION NOTE
I·
I-Forbipolarrnotorswithwindingcurrentsupto 2Athe L297 should be used with the L298N ; forwinding currents up to 1Athe L293E is recommended(the L293willalso be usefulif the chopperisn'tneeded).
Highercurrentsare obtainedwithpowertransistors ordarlingtonsandfor unipolar motors adarlington array such as theULN20758is suggested.The block diagram,figure1, showsa typical system.
Applicationsof theL297 canbe foundalmosteve-rywhere...printers(carriageposition,daisyposition, paperfeed,ribbon feed),typewriters, plotters, nu-mericallycontrolledmachines, robots, floppy disk drives,electronicsewing machines,cashregisters, photocop iers,telex machines,electronic carbure-tos, telecopiers,photographicequipment,paper tape readers,opticalcharacterrecognisers,electric valves andso on.
TheL297is made with SGS' analog/digitalcompa-tibler2Ltechnology(likeZodiac)and is assembled ina 20-pin plasticDIP.A 5V supply is usedand all signallines are TTUCMOS compatibleor open col-lectortransistors. High densityisone of the keyfea-turesof thetechnology so theL297 die is very compact.
THEL298NANDL293E
Since the L297is normallyused withanL29BN or L293E bridgedrivera briefreview of these devices willmake therest ofthisnote easierto follow.
TheL29BNandL293E contain two bridge driver stages,each controlledbytwo TIL-levellogic inputs andaTIL-levelenableinput.Inaddition,the emitter connectionsofthe lowertransistorsare broughtout to externalterminalsto allow the connectionof cur-rentsensingresistors(figure2).
For theL29BN SGS'innovativeion-implanted high voltage/highcurrenttechnologyis used,allowingit to handleeffectivepowersup to160W (46V supply, 2A per bridge).Aseparate 5V logic supplyinput is providedtoreduce dissipationandto allow direct connectionto the L297 or other controllogic.
Inthis note the pinsof theL29BN are labelledwith the pinnames of the correspondingL297terminals to avoid unnecessaryconfusion.
The L29BNissuppliedin a 15-leadMultiwattplastic powerpackage. It'ssmallerbrother,the functionally identicalL293E, is packagedina Powerdip-a cop-perframeDIP that uses the four centerpinsto con-duct heat tothe circuitboardcopper.
Figure 2:TheL29BNcontainstwobridge drivers(four pushpull stages) each controlledby two logic inputs and an enable input.Extemalemitterconnectionsare providedfor current sense resistors. The L293E hasexternalconnectionsfor all fouremitters.
2/18
CNC Robot ics
APPLICATION NOTE
The first isla energizethe windings in thesequence ABlCOtBNDC (SAmeans that the wiming AS is energizedbutintheoppositesense).Thissequence is known as"onephaseannfull steporwavedrive STEPPERMOTOR BASICS
There aretwobasic types of stepper motor in rom-moo use: permanentrnagnetand variable reluctan-ce. Permanent magnet motors are divided into bipolarandunipolartypes.
BIPOLAR MOTORS
Simplifiedtothe bare essentials, a bipolar perma-nentmagnetmotor consists ofa rotating pennanent magnetsurroundedbystator polescarrying the win-dings (figure 3).Bidirectional drive current is used and themotor is steppedby switching the windings insequence.
For a motoroft histypethere arethreepossibledrive sequences.
Figure3:Greatlysimplified,abipolarpermanent magnetsteppermotorconsist of a rota-ring magnetsurroundedbystator poles
as
shown.mode.Onlyonephase isenergizedat any givenrro-ment (figure4a).
Thesecondpossibiltyisto energizebothphasesto-gether,sothatthe rotoralwaysalignsitselt between two polepositions.Called"two-phase-en" fullstep, thisrrode is thenormaldrive sequenceforabipolar motor andgives the highesttorque (figure4b).
Thethird optionis to energizeonephase,thentwo, thenone,etc., sothat the motormoves in halfstep increments.This sequence,knownas half step mode,halvesthe effective stepangleof the motor butgives alessregulartorque(figure4c).
For rotationinthe opposfe directon(counter-c lock-wise) the same three sequencesareused,except ofcoursethat theorder is reserved.
As shownin these diagrams the motorwould have a stepangleof900.Real rrotors have multiplepoles to reduce the step angleto a fewdegrees but the numberof 'Nindingsandthedrivesequencesare un-changed.A typical bipolar stepper motorisshown in figure 5.
UNIPOLARMOTORS
A unipolarpermanentmagnet motoris identicalto thebipolar machinedescri:>edabove exceptthat bl-filar windingsare used to reversethe stator flux, ra-therthanbidirectional drive(figure6).
This motor isdriven inexaetly thesamewayasa bi-polarmotor except thatthe bri<:lge drivers are repla-cedby sirrp le unipolar stages-fourdarlingtonsor aquaddarlingtonarray.Clearly,unipolarmotorsare moreexpensivebecausethayhavetwiceasmany windings. Moreover, unipolar motors give less torque for a given motor size becausethewindings aremadewith thinner wire.In the pastunipolarmo-tors were attractivetodesignersbecausethey sim-plify the driverstage.Nowthat monolithic pushpull drivers like thel298N are availablebipolar motors are becoming morepopular.
All permanent magnetrrotorssufferfromthecoun -ter EMFgenerated by the rotor, which firrits the ro-tetonspeed.When very high slewing speeds are necessarya variablereluctance motor is used.
'Ir- + - c
Chapter 2 / El ectr onics
APPLICATION NOT E
Figure 4:The threedrivesequencesfor at\Wphasebipolarsleppermotor.Clockwise rotationisshown.
FiglJe4a :Wavedrive(onephaseon).
B-Figure4b :TY.Qphase on drive.
A_
o ~ ~ c
o
~ 0B.
/'
B- B. B. B_
,- ""
Figure 4c:HaKstepdrive.
A. A. AO
A-~<r0 0 ~~ ~.
D ~ C o • c o N e
B- B- BO B'
A- A- AO A'
~ $o 0 ~~ ~
o N e o 5 C
B. B. BO
B-4I1B