BLDC motor control without the need for an MCU

BLDC motor control without the need for an MCU

Brushless DC (BLDC) motors offer many advantages over brushed DC motors including their ability to deliver more torque in the same form factor, generate less electrical and audible noise, and demand significantly less maintenance.

However, commutation must be achieved with electronics which increases design complexity including the need to know the angle of the rotor. Physical sensors are available, but they add to bulk and cost so, generally this approach is non-preferred. Other approaches exist although often they require a microcontroller and the development of code which lengthens the development time.

Fortunately, there are highly integrated motor controllers available that will operate without a microcontroller unit (MCU).

There are multiple types of BLDC motor available, those generating a trapezoidal back-EMF are typically termed BLDC motors, while those generating a sine wave are known as permanent magnet synchronous motors (PMSM). The type can be determined by looking at the output waveform when the rotor is turned by hand.

PMSM motors are preferred in applications where lower torque ripple is needed, along with quieter operation, and higher efficiency. However, while driving a BLDC motor faster simply requires applying more current to the coils but, for a PMSM, faster rotational speeds require application of a higher frequency sine wave to the coils. As the sine wave shape is calculated - computationally complex process - a high-performance processor, field-programmable gate array (FPGA), or a device with hardware acceleration is typically required.

Today, highly integrated MCU-less solutions deliver simple configurability for PMSM motor control without requiring rotor sensors. One such device is Toshiba’s TC78B011FTG sine wave pre-driver for sensorless three-phase brushless motor control. Operating from 5.5V to 27V, (30V absolute max.), the device is ideal for driving Delta or Wye configured motors in fans, pumps, and portable vacuum applications.

Operation is configured via an I2C interface, with settings stored in non-volatile memory (NVM) allowing programming during manufacture. Motor speed can be set via I2C, or via a PWM or analogue input. Braking and direction control is set via input pins or I2C.

To speed up evaluation and development, the TC78B011FTG is available from MIKROE on the Brushless 23 Click board that is suitable for the efficient operation of blowers, pumps, and high-velocity fans for servers.

Toshiba has just published a white paper on MCU-less BLDC control. It is available to download here:

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