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

Furthermore, several parameters can be controlled via the SPI bus, including current amplitude (5-bit DAC), step mode, PWM frequency, EMC slope control, enabling and disabling of the driver, and sleep-mode entry. The intelligent-driver device also provides information to the external controller through the SPI bus, such as thermal warning and shutdown status flags, detection of winding coil open circuits, detection of shorts and overcurrents, and rotor position data generated by the internal translator table.

The most interesting feature, however, is the speed-and-load-angle (SLA) output signal. This signal measures and interprets the back electromagnetic force (EMF) induced in the motor. The SLA output signal enables the running of stall-detection algorithms on the external microcontroller, which offers silent, yet accurate position calibrations during the referencing run, without an external sensor.

In addition, the microcontroller can be programmed with control loops based on the load-angle information provided by the SLA output to adjust torque and speed accordingly. This feature can be used to avoid step loss or to temporarily boost the motor current and torque.

The AMIS-30522 has an on-chip voltage regulator able to deliver power to externals, a reset output, and a watchdog circuit reset to supply and monitor the external microcontroller. When interfaced to a simple microcontroller, the intelligent, integrated stepper-motor driver completes it to a fully integrated stepper-motor driver/controller circuit without need for either external current or position sensors, or external drivers. The designer can fully concentrate on the driver algorithm on his preferred platform and use the SLA feature to design even better algorithms.

Integration can go a step further. The AMIS-30624 stepper-motor driver/controller is similar to the AMIS-30522 but also contains an integrated programmable state machine. The state machine translates a target position into the required sequence of microsteps to get to the target rotor position with desired acceleration, speed and deceleration.

The target position and other high-level positioning information is dictated by a remote host, which communicates with the intelligent stepper-motor driver/controller through an I2C bus (used in the AMIS-30624) or LIN bus (used in the AMIS-30623). The high abstraction level of the product's command set reduces the load of the processor on the master side. Scaling of the application toward the number of axes is straightforward. Hardware and software designs are extended in a modular way, without severely affecting the demands on the master microcontroller. The bus structure simplifies pc-board layout and wiring architectures.

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© 2007 Penton Media, Inc.