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

1、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APPLICATION NOTEAN470/0392THE L297STEPPER MOTOR CONTROLLERThe L297integratesall the control circuitry required to control bipolar and unipolar stepper motors.Used with a dual bridge driver such as the L298N forms a complete microprocessor-to-bipolar stepper motor inte

2、rface.Unipolar stepper motor can be driven with an L297plus a quad darlington array.This note de-scribes the operation of the circuit and shows how it is used.The L297Stepper Motor Controller is primarily in-tendedfor use with anL298Nor L293Ebridge driver in stepper motor driving applications.It rec

3、eives control signals from the systems control-ler,usually a microcomputer chip,and provides all the necessarydrive signals for the power stage.Ad-ditionally,it includestwoPWM choppercircuits tore-gulate the current in the motor windings.With a suitable power actuator the L297drives two phase bipola

4、r permanent magnet motors,four pha-se unipolar permanentmagnet motorsandfour pha-se variable reluctance motors.Moreover,it handles normal,wave drive and half step drive modes.(This is all explained in the section”Stepper Motor Ba-sics”.Two versions of the device are available:the regular L297and a s

5、pecial version called L297A.The L297A incorporates a step pulse doubler and is de-signed specifically for floppy-disk head positioning applications.ADVANTAGESThe L297+driver combination has many advanta-ges:very few components are required(so assem-bly costs are low,reliability high and little space

6、 required,software development is simplified and the burden on the micro is reduced.Further,the choice of a two-chip approach gives a high degree of flexibility-the L298Ncan be usedon itsown for DC motors and the L297can be used with any power stage,including discrete power devices(it provides 20mA

7、drive for this purpose.Figure1:In this typical configuration an L297stepper motor controller and L298dual bridge driver com-bine to form a complete microprocessor to bipolar stepper motor interface.1/18Forbipolarmotors withwinding currents up to2Athe L297should be used with the L298N;for winding cur

8、rents up to1A the L293E is recommended(the L293will also be useful if the chopper isnt needed. Higher currents are obtained with power transistors or darlingtons and for unipolar motors a darlington array such as the ULN2075B is suggested.The block diagram,figure1,shows a typical system. Application

9、s of the L297can be found almost eve-rywhere.printers(carriage position,daisyposition, paper feed,ribbon feed,typewriters,plotters,nu-merically controlled machines,robots,floppy disk drives,electronic sewing machines,cash registers, photocopiers,telex machines,electronic carbure-tos,telecopiers,phot

10、ographic equipment,paper tape readers,optical character recognisers,electric valves and so on.The L297is made with SGSanalog/digitalcompa-tible I2L technology(like Zodiacand is assembled in a20-pin plastic DIP.A5V supply is used and all signal lines are TTL/CMOS compatible or open col-lector transis

11、tors.High density is one of the key fea-tures of the technology so the L297die is very compact.THE L298N AND L293ESince the L297is normally used with an L298N or L293E bridge driver a brief review of these devices will make the rest of this note easier to follow.The L298N and L293E contain two bridg

12、e driver stages,each controlled by two TTL-level logicinputs and a TTL-level enable input.In addition,the emitter connectionsof the lower transistors are brought out to external terminals to allow the connection of cur-rent sensing resistors(figure2.For the L298N SGSinnovative ion-implanted high vol

13、tage/high current technology is used,allowing it to handle effective powers up to160W(46V supply, 2A per bridge.A separate5V logic supply input is provided to reduce dissipation and to allow direct connection to the L297or other control logic.In this note the pins of the L298N are labelled with the

14、pin names of the corresponding L297terminals to avoid unnecessary confusion.The L298N is supplied in a15-lead Multiwatt plastic power package.Its smaller brother,the functionally identical L293E,is packaged in a Powerdipa cop-per frame DIP that uses the four center pins to con-duct heat to the circu

15、it board copper.Figure2:The L298N contains two bridge drivers(four push pull stageseach controlled by two logic inputs and an enable input.External emitter connections are provided for current senseresistors.The L293E has external connections for all four emitters.APPLICATION NOTE2/18STEPPER MOTOR B

16、ASICSThere are two basic types of stepper motor in com-mon use:permanentmagnet and variable reluctan-ce.Permanent magnet motors are divided into bipolar and unipolar types.BIPOLAR MOTORSSimplified to the bare essentials,a bipolar perma-nent magnet motor consists of a rotating permanent magnetsurroun

17、dedby stator poles carrying thewin-dings(figure3.Bidirectional drive current is used and the motor is stepped by switching the windings in sequence.For a motor ofthis type there are threepossibledrive sequences.The first is to energize the windings in the sequence AB/CD/BA/DC(BA means that the windi

18、ng AB is energizedbut in theopposite sense.This sequence is known as”one phase on”full step or wave drive mode.Only onephaseisenergized atany given mo-ment(figure4a.The second possibility is to energizebothphasesto-gether,sothat the rotor always aligns itself between two pole positions.Called”two-ph

19、ase-on”full step, this mode is the normal drive sequence for a bipolar motor and gives the highest torque(figure4b. The third option is to energize one phase,then two, then one,etc.,so that the motor moves in half step increments.This sequence,known as half step mode,halves the effective step angle

20、of the motor but gives a less regular torque(figure4c.For rotation in the opposite direction(counter-clock-wisethe same three sequences are used,except of course that the order is reserved.As shown in these diagrams the motor would have a stepangleof90.Real motors havemultiple poles to reduce the st

21、ep angle to a few degrees but the numberof windingsand thedrive sequencesare un-changed.A typical bipolar stepper motor is shown in figure5.UNIPOLAR MOTORSA unipolar permanent magnet motor is identical to the bipolar machine described above except that bi-filar windings are used to reverse the stato

22、r flux,ra-ther than bidirectional drive(figure6.This motor is driven in exactly the same way as a bi-polar motor except that the bridge drivers are repla-ced by simple unipolar stages-four darlingtons or a quaddarlington array.Clearly,unipolarmotors are more expensivebecause thay have twice as many

23、windings.Moreover,unipolar motors give less torque for a given motor size because the windings are made with thinner wire.In the past unipolar mo-tors were attractive to designers because they sim-plify the driver stage.Now that monolithic push pull drivers like the L298N are available bipolar motor

24、s are becoming more popular.All permanent magnet motors suffer from the coun-ter EMF generated by the rotor,which limits the ro-tation speed.When very high slewing speeds are necessary a variable reluctance motor is used.Figure3:Greatly simplified,a bipolar permanentmagnet stepper motor consist of a

25、 rota-ring magnet surrounded by stator polesas shown.APPLICATION NOTE3/18APPLICATION NOTEFigure4:The three drive sequences for a two phase bipolar stepper motor.Clockwise rotation is shown. Figure4a:Wave drive(one phase on.Figure4b:Two phase on drive.Figure4c:Half step drive.4/18VARIABLE RELUCTANCE

26、MOTORSA variable reluctance motor has a non-magnetized soft iron rotor with fewer poles than the stator(fig-ure7.Unipolar drive is used and the motor is step-ped by energizing stator pole pairs to align the rotor with the pole pieces of the energized winding. Once again three different phase sequenc

27、escan be used.The wave drive sequence is A/C/B/D;two-phase-on is AC/CB/BD/DA and the half step se-quence is A/AC/C/BC/B/BD/D/DA.Note that the step angle for the motor shown above is15,not45. As before,pratical motors normally employ multiple poles to give a much smaller step angle.This does not,howe

28、ver,affect the principle of operation of the drive sequences.GENERATING THE PHASE SEQUENCES The heart of the L297block diagram,figure8,is a block called the translator which generatessuitable phase sequences for half step,one-phase-on full step and two-phase-on full step operation.This block is cont

29、rolled by two mode inputsdirection (CW/CCWand HALF/FULLand a step clock which advances the translator from one step to the next.Four outputs are provided by the translator for sub-sequent processing by the output logic block which implements the inhibit and chopper functions. Internally the translat

30、or consists of a3-bit counter plus some combinational logic which generates a basic eight-step gray code sequence as shown in figure9.All three drive sequencescan be generated easily from this master sequence.This state se-quence corresponds directly to half step mode,se-lected by a high level on th

31、e HALF/FULL input.Figure6:A unipolar PM motor uses bifilar win-dings to reverse the flux in each phase.Figure7:A variable reluctance motor has a soft iron rotor with fewer poles than the sta-tor.The step angle is15for this motor.Figure5:A real motor.Multiple poles are norma-lly employed to reduce th

32、e step angle toa practical value.The principle of opera-tion and drive sequences remain thesame.APPLICATION NOTE5/18The output waveforms for this sequence are shown in figure10.Note that two other signals,INH1and INH2are ge-nerated in this sequence.The purpose of these si-gnals is explained a little further on.The full step modes are both obtained by skipping alternate states in the eight-step sequence.What happensis that the step clock bypassesthe first sta-ge of the3-bit counter in the translator.The least si-gnificant bit ot this counter is not affect