Full-bridge PWM microstepping motor driver IC from Allegro

Internal pulse-width-modulated (PWM) current control combined with an internal three-bit nonlinear digital-to-analogue converter allows the motor current to be controlled in full-, half-, quarter- or eighth-step (microstepping) modes, while nonlinear increments minimise the number of control lines necessary for microstepping. The benefits of microstepping include increased step resolution and reduced torque variations and resonance problems at low speed.

The outputs of the A4975 are rated for continuous output currents up to ±1.5 A and operating voltages up to 50 V. The device includes synchronous rectification control circuitry which lowers IC power dissipation during PWM operation and reduces the need for external Schottky diodes.

Internal circuitry determines whether the PWM current-control circuitry operates in a slow (recirculating) current-decay mode, fast (regenerative) current-decay mode, or mixed current-decay mode in which the “off” time is divided into a period of fast and slow current decay.

The combination of user-selectable current-sensing resistor and reference voltage, digitally selected output current ratio; and slow, fast, or mixed current-decay modes provides users with a broad, variable range of motor current control.

Internal circuit protection includes thermal shutdown with hysteresis, an undervoltage monitor, and crossover-current protection. Special power-up sequencing is not required.

This new device is targeted at the office automation and industrial markets – in particular, applications including printers, scanners and copiers.

The A4975 is supplied in a choice of two power packages; a 16-pin dual-in-line plastic package with copper heat-sink tabs (suffix B), and a 16-lead plastic SOIC with internally fused pins (suffix LB). For both package styles, the thermally enhanced pins are at ground potential and need no electrical isolation. Both packages are lead (Pb) free, with 100% matt tin lead-frame plating.

Allegro Microsystems

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