Valbulas Iac

APPLICATION NOTE

THE L297 STEPPER MOTOR CONTROLLER
The L297 integrates all 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 interface. Unipolar stepper motor can be driven with an L297 plus a quad darlington array. This note describes the operation of thecircuit and shows how it is used.
The L297 Stepper Motor Controller is primarily intendedfor use with anL298N or L293E bridge driver in stepper motor driving applications. It receives control signals from the system’s controller, usually a microcomputer chip, and provides all the necessary drive signals for the power stage. Additionally, it includes two PWM chopper circuits toregulate the current inthe motor windings. With a suitable power actuator the L297 drives two phase bipolar permanent magnet motors, four phase unipolar permanentmagnet motorsandfour phase variable reluctance motors. Moreover, it handles normal, wave drive and half step drive modes. (This is all explained in the section ”Stepper Motor Basics”). Two versions of the device are available : the regular L297 and a specialversion called L297A. The L297A incorporates a step pulse doubler and is designed specifically for floppy-disk head positioning applications. ADVANTAGES The L297 + driver combination has many advantages : very few components are required (so assembly costs are low, reliability high and little space required), software development is simplified and the burden on the micro is reduced. Further, thechoice of a two-chip approach gives a high degree of flexibility-the L298Ncan be usedon its own for DC motors and the L297 can be used with any power stage, including discrete power devices (it provides 20mA drive for this purpose).

Figure 1 : In this typical configuration an L297 stepper motor controller and L298 dual bridge driver combine to form a complete microprocessor to bipolar steppermotor interface.

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APPLICATION NOTE
For bipolar motors with winding currents up to 2A the L297 should be used with the L298N ; for winding currents up to 1A the L293E is recommended (the L293 will also be useful if the chopper isn’t needed). Higher currents are obtained with power transistors or darlingtons and for unipolar motors a darlington array such as the ULN2075B issuggested. The block diagram, figure 1, shows a typical system. Applications of the L297 can be found almost everywhere ... printers (carriage position,daisy position, paper feed, ribbon feed), typewriters, plotters, numerically controlled machines, robots, floppy disk drives, electronic sewing machines, cash registers, photocopiers, telex machines, electronic carburetos, telecopiers, photographicequipment, paper tape readers, optical character recognisers, electric valves and so on. The L297 is made with SGS’ analog/digital compatible I2L technology(like Zodiac) and is assembled in a 20-pin plastic DIP. A 5V supply is used and all signal lines are TTL/CMOS compatible or open collector transistors. High density is one of the key features of the technology so the L297 die is very compact.THE L298N AND L293E Since the L297 is 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 bridge 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 toallow the connection of current sensing resistors (figure 2). For the L298N SGS’ innovative ion-implanted high voltage/high current technology is used, allowing it to handle effective powers up to 160W (46V supply, 2A per bridge). A separate 5V logic supply input is provided to reduce dissipation and to allow direct connection to the L297 or other control logic. In this note the pins of the L298N...