TI Driver for BLDC Motors

When simple motors were more frequently used, it was relatively easy to design products with them. Controlling such motors was simple, whether it was a brushed DC motor or a single-phase AC motor. There was no need for sophisticated hardware or software for designing a product with a motor.

However, sophisticated BLDC or brush-less DC motors are replacing most of the above motors because of several advantages like quiet operation and high efficiency. But these advantages come at the cost of design knowledge and effort, requiring both hardware and software development. Texas Instruments has developed a new integrated circuit that allows designers to achieve all the benefits easily from these motors.

The biggest benefit offered by BLDC motors over older designs is their improved power efficiency. Most government regulators today demand that electrical products meet strict efficiency standards. In most cases, meeting these requirements is possible only through the use of BLDC motors.

Motors are mechanical devices and therefore, they make noise when operating. Although the quiet operation is not usually a design goal for most products, using a BLDC motor offers a way to achieve low noise operation.

There are further advantages to using BLDC motors. One of them is low voltage operation, and the other is a longer life. Manufacturers of BLDC motors are now offering them in larger sizes for use in bigger products.

As stated earlier, BLDC motors are now replacing brushed DC motors and in some cases, AC motors as well. Some practical examples are robotic vacuum cleaners, pumps, fans, washing machines, humidifiers, and air purifiers. They are useful for multiple automotive devices as well.

Functionally, a BLDC motor works under the same principles that govern the operation of all motors—rotation is from the interaction of two magnetic fields, one fixed and the other movable. Frequently, the BLDC motor will have multiple stator coils embedded in the periphery of the motor assembly. With the stator coil wired into three groups, it performs as a three-phase motor does. The rotor on the BLDC motor consists of several permanent magnets rotating in the circle formed by the stator coils. The user only has to apply a sequence of pulses to the stator coils.

The timing of the pulses must match their interaction with the permanent magnets. The control circuitry that drives the stator coils gets the correct timing from multiple sensors indicating the orientation of the rotor. These sensors are mostly Hall-effect devices that produce signals that the controller requires for moving the magnetic fields on the stator coil.

There are numerous variations of the approach to control the BLDC motor. One of them is a sensor-less method using the back electromotive force the rotating rotor magnets induce into the stator coils. The sensor-less method typically reads the feedback voltages in the motor stator winding and processes them into control signals.

Many motor controllers are pre-programmed and packaged BLDC motor control modules. This is usually satisfactory for common applications. Others, however, require a custom design. The MCF8316A from TI is a single chip BLDC motor controller chip that only requires inputs for speed, direction, and torque. The IC takes care of the rest.