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High-efficiency motor driver IC offers high current rating from very small package

5th July 2007

ES Admin

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The new A3989 from Allegro MicroSystems Europe is a high-efficiency motor driver IC designed to drive one bipolar stepper motor at up to 1.2 A and one DC motor at up to 2.4 A. The A3989 is designed for applications, typically found in office automation, automated handling equipment and gaming machines, that incorporate one DC motor and one stepper motor. The integration of two motor drivers in one compact package makes the A3989 more cost effective than most combinations of discrete IC motor drivers, while the small footprint is important in applications where PC board space is limited.

The new DMOS device can generate drive voltages of up to 36 V, and includes three full-bridge circuits, each with an independent fixed off-time pulse width modulation (PWM) current regulator.

The two stepper-motor full-bridge circuits feature Allegro's patented mixed decay mode: a current decay control scheme which results in reduced audible motor noise, increased step accuracy, and reduced power dissipation. The DC motor full-bridge current regulator operates in either fast or slow decay mode, determined by the signal on the mode input pin.

High and low side internal synchronous rectification control circuitry is provided to improve power dissipation during PWM operation, eliminating the need for external Schottky diodes. Low-resistance DMOS outputs further reduce the power dissipation, and allow higher average output currents because of the lower die temperature rise.

Phase, enable and mode inputs are provided for use in controlling the speed, torque, direction and brake or coast functions of a DC motor. The stepper motor driver features dual 2-bit nonlinear DACs (digital-to-analogue
convertors) that enable control in full, half, and quarter steps.

Protection features include thermal shutdown with hysteresis, undervoltage lockout and crossover current protection. Special power-up sequencing is not required.

The A3989 is supplied in a 6 x 6 x 0.9 mm, 36-pin QFN package with an exposed power tab for enhanced thermal performance. The package is lead (Pb) free, with 100% matte tin leadframe plating.