3966

The A3966SA and A3966SLB are designed to drive both windings of a two-phase bipolar stepper motor.  Each 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-fre-quency, 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.  Except for package style and pinout, the two devices are identical.

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(TM) 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.

The A3966SA is supplied in a 16-pin dual in-line plastic package.  The A3966SLB is supplied in a 16-lead plastic SOIC with copper heat sink tabs. The power tab is at ground potential and needs no electrical isolation.