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Allegro's new motor driver gets a step on ?C-based systems

Posted: 16 Sep 2005 ?? ?Print Version ?Bookmark and Share

Keywords:allegro Microsystems? a3979? motor driver?

Allegro MicroSystems' A3979 is a complete microstepping motor driver with built-in translator targeted at the office automation and industrial markets. A drop-in replacement for the company's A3977SLP with 16 microstep/step resolution, it is designed to operate bipolar stepper motors in full-, half-, quarter- and sixteenth-step modes, with output drive capability of 35 volts and 2.5A.

The chip's "step" and "direction" inputs makes the device suited for applications with multiple motors; in these cases, its performance will be superior to most microcontroller-based systems, according to the company, given their limited I/O. In operation, each pulse on the device's "step" input advances the motor one microstep. As with the company's A3982 microstepper motor IC, there are no phase sequence tables, high-frequency control lines or complex interfaces to program.

Internal synchronous rectification control circuitry is included to improve power dissipation during PWM operation. The power dissipation savings (typically greater than 20 percent) results in better thermal performance and eliminates the need for external Schottky diodes. Competitive devices with bipolar outputs cannot implement synchronous rectification, according to the company.

The A3979 includes a fixed off-time current regulator that can operate in slow- or mixed-decay modes. This current decay scheme is designed to reduce audible noise, increase step accuracy and reduce power dissipation. Internal circuit protection includes thermal shutdown with hysteresis, undervoltage lockout and crossover-current protection. Special power-up sequencing is not required.

The product datasheet is available at The A3979 is offered in an industry-standard 28-lead TSSOP with an exposed thermal pad (suffix LP; PB-free suffix LP-T). Pricing is $3.01 each in quantities of 10k.

- Vince Biancomano


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