Sinusoidal Three-Phase Gate Controller Goes Sensorless

Designed for the automotive market, the A4964 three-phase, sensorless, brushless DC (BLDC) motor controller operates with external N-channel power MOSFETs. The device provides motor control functions in a system where a small microcontroller provides the communication interface to a central ECU and intelligent fault and status handling. The A4964 provides the supply and watchdog for the microcontroller and the high-voltage interfaces between the microcontroller and the central ECU and ignition switch. It can also operate as an independent single chip remote motor controller.


Motor drive is developed using a three-phase sinusoidal current drive where phase commutation is determined, without the need for independent position sensors, by monitoring the motor back-EMF. The sensorless start-up scheme includes forward and reverse pre-rotation (windmill) detection and synchronization, and allows the device to operate over a wide range of motor and load combinations.


Three control modes are on tap: open loop (voltage) control, current (torque limit) control, and closed-loop speed control. The control mode, operating mode, and bridge parameters are programmed through an SPI-compatible serial interface. A single current sense amplifier provides peak current limiting and average current measurement through the serial interface. Also, integrated diagnostics provide indication of under-voltage, over-temperature, and power bridge faults and can protect the power switches under most short-circuit conditions.


The A4964 comes in both a 36-terminal QFN and a 32-lead QFP, both with an exposed thermal pad. Prices are $6.16 each/1,000 for the A4964KEVTR-J and $6.59 each/1,000 for the A4964KJPTR-T. For more spec, an A4964 datasheet is available. For more info, contact

Allegro MicroSystems, Worcester, MA. 508-853-5000