Driver ICs Elevate Design of Stepper-Motor Control

Aug 1, 2007 12:00 PM
By Guido Remmerie, Director of Industrial ASSPs, and Peter Cox, Product Manager for Industrial ASSPs

In this case, the SLA output is internally connected to the integrated state machine, and its use is limited to the generation of stall detection. The on-chip position controller is configurable with one-time programmable (OTP) default settings and RAM to override the defaults through the I2C interface. These parameters have to be set to adapt the circuit for the specific motor type used, for the positioning ranges, and for setting the maximum speed, acceleration, deceleration, and stall detection.

The intelligent integrated stepper-motor driver/controller acts as a slave on an I2C bus or LIN bus, and the master (host) can fetch specific status information such as the actual rotor position, or error flags, from each individual slave node.

The key advantage of intelligent, integrated drivers and drivers/controllers is their ease of use. The designer can choose an embedded controller or use a simple low-cost controller. The designer can concentrate on designing the motion algorithm using a proven and reproducible translation of the motion to the driving of the coils. This translation depends on the specific mechanics of the application and involves the running of a characterization algorithm that returns the required parameter setting.

For designing the motion algorithm, the designer has a range of features available that are difficult if not impossible to achieve with a discrete solution or with simple standard products. The most important are micro-stepping for low acoustic noise, and the detection of rotor speed and load angle without external sensors. The latter can be used for stall detection, and to adapt the motor speed and drive current interactively with the feedback from the motion.

The communication is limited to a position command for the motor driver/controller or a next-step pulse for the intelligent motor driver. The low speed of the communications bus causes very little EMI. The high-speed PWM signals are limited to the short tracks between driver and motor coils, and those signals are slope controlled to further reduce any radiated emission.

The end solution is small and has a specific advantage for small-step positioning applications and mechatronics; it can even be built inside a small stepper motor or actuator. No sensors (and few other external component types) are needed. Even the current-sense resistor for the winding current is integrated. Fig. 5 shows an example of such an integrated module combining the motor with the controller/driver electronics.

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© 2007 Penton Media, Inc.