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Microstepping Motor Driver with Built-In Translator
April 2006
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The A3979 is a complete microstepping motor driver with built-in translator for easy operation. It is designed to operate bipolar stepper motors in full-, half-, quarter-, and sixteenth-step modes, with output drive capability of 35 V and +/- 2.5 A, and is a drop-in replacement for the company’s A3977SLP with 16 microstep/step resolution.

The translator is key to the easy implementation of the A3979. By inputting one pulse on the Step input, the motor will take one microstep. There are no phase sequence tables, high-frequency control lines or complex interfaces to program. The simple, two-input Step and Direction interface of the A3979 makes it ideal for applications with multiple motors that would normally push the I/O capability of most µP controllers.

Internal synchronous rectification control circuitry is included in the A3979 to improve power dissipation during pulse width modulation operation. The power dissipation savings (typically greater than 20 percent) will result in lower temperature rise and eliminate the need for external Schottky diodes. The supplier says competitive devices with bipolar outputs cannot implement synchronous rectification.

The driver includes a fixed off-time current regulator that has the ability to operate in slow- or mixed-decay modes. This patented current decay scheme results in reduced audible noise, increased step accuracy and reduced power dissipation. Internal circuit protection includes thermal shutdown with hysteresis, undervoltage lockout and crossover-current protection. Special power-up sequencing is not required.

Targeted at the office automation and industrial markets, the A3979 is offered in an industry-standard low-profile (less than 1.2 mm), 28-lead TSSOP with an exposed thermal pad (suffix LP; PB-free suffix LP-T).

Allegro MicroSystems, Inc.


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