Allegro MicroSystems, Inc. announces a new dual full-bridge pulse-width modulated (PWM) motor driver designed to drive both windings of a two-phase bipolar stepper motor. The device includes two H-bridges capable of continuous output currents of ±650 mA and operating voltages to 30 V. Motor winding current can be controlled by the internal fixed-frequency, pulse-width modulated (PWM), current-control circuitry. The peak load current limit is set by the user’s selection of a reference voltage and current-sensing resistors. The fixed-frequency pulse duration is set by a user-selected external RC timing network. The capacitor in the RC timing network also determines a user selectable blanking window that prevents false triggering of the PWM current control circuitry during switching transitions. To reduce on-chip power dissipation, the H-bridge power outputs have been optimized for low saturation voltages. The sink drivers feature Allegro’s patented Satlington™ output structure. The Satlington™ outputs combine the low voltage drop of a saturated transistor and the high peak current capability of a Darlington. For each bridge, a PHASE input controls load-current polarity by selecting the appropriate source and sink driver pair. For each bridge, an ENABLE input, when held high, disables the output drivers. Special power-up sequencing is not required. Internal circuit protection includes thermal shutdown with hysteresis, ground-clamp and flyback diodes, and crossover-current protection. Allegro’s A3969 is supplied in a 28-pin quad MLP/QFN lead (Pb) free plastic package with exposed thermal pad and 100% matte tin leadframe plating. It has a 5 x 5 mm footprint and 0.90 mm nominal height.
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