Motor controller ICs simplify system design

The Hall sensor inputs can be driven directly by a microprocessor, which makes the A3930 and A3931 key components in a robust sensorless back-EMF solution.

Allegro MicroSystems Europe's A3930 and A3931 automotive-grade motor controller integrated circuits have built-in commutation logic to lessen the burden on the system microprocessor, simplifying system design and reducing cost.

The new devices are suited to the control of Hall-commutated three-phase brushless DC motors driven by external N-Channel MOSFETs.

The Hall sensor inputs can be driven directly by a microprocessor, which makes the A3930 and A3931 key components in a robust sensorless back-EMF solution.

The on-chip commutation logic consists of a decoder and state machine which together read the inputs of three Hall sensor inputs (or I/O signals from a microprocessor).

The IC then outputs the correct gate drive signals to control six (three high-side, three low-side) external N-channel MOSFETs for driving the three-phase motor.

The highly flexible input logic provides a wide range of control possibilities including coast, brake and pulse-width modulation functions and the facility for single-pin bi-directional control of the motor.

Output pins provide status and diagnostic information on speed and direction and provide signals to enable closed-loop speed control.

The IC also includes a 5V supply for Hall sensors (used in conjunction with an external NPN transistor) and an integrated charge pump which allows operation at 100% PWM duty cycle.

The driver ICs operate over a battery voltage range of 5.5 to 50V and feature extensive diagnostics and a low-current quiescent mode.

The two devices are identical apart from the addition of an optional pre-positioning function on the A3931.

This operates by driving the three Hall inputs low to provide a known start-up position for the motor by forcing a position between two detent positions.

This start-up condition aids any algorithms that may be used with the IC (such as sensorless back EMF commutation schemes).

The A3930 and A3931 will operate over a temperature range from -40 to +150C) and voltages from 5.5 to 45V, making them suitable for use in 14 or 24V automotive under-bonnet applications.

Both the A3930 and A3931 are offered in a small, thermally efficient 48L eLQFP package.

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