Full-bridge PWM motor driver IC from Allegro MicroSystems

The device has an internal fixed “off” time PWM current-control circuitry that can be used to regulate the maximum load current to a desired value. The peak load current limit is set by the user’s selection of an input reference voltage and external sensing resistor, while the fixed “off” time pulse duration is set by a user-selected external RC timing network.

Internal circuit protection includes thermal shutdown with hysteresis, transient suppression diodes, and crossover current protection. Special power-up sequencing is not required. The A4973 includes synchronous rectification which lowers IC power dissipation and reduces the need for external Schottky diodes.

With the “enable” input held low, the “phase” input controls load current polarity by selecting the appropriate source and sink driver pair. The “mode” input determines whether the PWM current-control circuitry operates in a slow current-decay mode (with only the selected source driver switching) or in a fast current-decay mode (with the selected source and sink both switching).

A user-selectable blanking window prevents false triggering of the PWM current-control circuitry. With the “enable” input held high, all output drivers are disabled. A “sleep” mode is provided to reduce power consumption.

When a logic “low” is applied to the “brake” input, the braking function is enabled. This overrides “enable” and “phase” to turn off both source drivers and turn on both sink drivers. The brake function can be used to dynamically brake brush DC motors.

Target markets include the office automation and industrial sectors, with particular emphasis on applications in printers, scanners and copiers.

The A4973 is supplied in a choice of two power packages; a 16-pin dual-inline plastic package with copper heat-sink tabs, and a 16-pin plastic SOIC with copper heat sink tabs. For both package styles, the power tab is at ground potential and needs no electrical isolation. Each package type is available in a lead (Pb) free version with 100% matt tin-plated lead frame.

Allegro MicroSystems

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