Posted to News on 27th Mar 2008, 16:44
Automotive-grade controllers for 3-phase brushless DC motors
Allegro MicroSystems Europe is launching the new A3930 and A3931 automotive-grade motor controller integrated circuits that feature built-in commutation logic to lessen the burden on the system microprocessor, thereby simplifying system design and reducing cost.
The new devices are suitable for the control of Hall-commutated three-phase brushless DC motors driven by external N-Channel MOSFETs. If desired, 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 system.
On-chip commutation logic consists of a decoder and state machine that 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 bidirectional control of the motor. Output pins provide status and diagnostic information on speed and direction and provide signals to enable closed-loop speed control.
Other key features are a 5V supply for Hall sensors (used in conjunction with an external NPN transistor) and an integrated charge pump that allows operation at 100 per cnet PWM duty cycle. The driver ICs operate over a wide battery voltage range (5.5-50V) 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 operate over a temperature range from -40 to +150degC) and voltages from 5.5-45V, making them suitable for use in 14V or 24V automotive under-hood applications.
Both models are offered in a small thermally efficient 48L eLQFP package.
