Analysis

Dual full-bridge PWM motor driver IC

7th December 2006
ES Admin
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The new A3969 from Allegro MicroSystems Europe is a compact dual full-bridge pulse-width modulated (PWM) motor driver integrated circuit which is ideally suited to applications in portable equipment or where board space is limited.
The new device is designed to drive both windings of a two-phase bipolar stepper motor, and 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 optimised for low saturation voltages. The sink drivers feature Allegro's patented Satlington( output structure, which combine the low voltage drop of a saturated transistor and the high peak current capability of a Darlington device.

For each bridge, a 'phase' input controls load-current polarity by selecting the appropriate source and sink driver pair, while 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.

The A3969 is supplied in a 28-pin quad MLP/QFN lead (Pb) free plastic package with exposed thermal pad and 100% matt tin leadframe plating. It has a 5 x 5 mm footprint and 0.90 mm nominal height.

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