The STSPIN32F0B from STMicroelectronics is a packaged system that includes a microcontroller, gate controller, DC / DC converter, linear regulator, and op amp.
DC motors can be divided into three general categories: brushed DC motors, stepper motors, and brushless DC motors. The simplest variety is the brushed DC motor. If you want to make it turn, all you need to do is supply a voltage – the polarity reversal necessary to keep the motor rotating is provided by brushes that create a sequence of physical connections and disconnections.
Stepper motors do not have brushes; rotation is accomplished by applying a specific sequence of control voltages. Steppers are ideal when you need precision rotation that occurs in discrete steps and are generally limited to low power applications.
Brushless DC (BLDC) motors combine the characteristics of brushed motors and stepper motors. Commutation is accomplished electrically, as is the case with stepper motors, but BLDC motors, such as brushed DC motors, are designed for continuous rotation of higher power. You can read more about brushless DC motors in this article on Sensorless BLDC Control.
This graphic, taken from an STMicro document titled “An introduction to electric motors“, Gives you a basic idea of the structure and operation of a 3-phase brushless DC motor.
Integrated circuits for BLDC systems
Controlling a BLDC motor is not a particularly simple task. The drive voltages should be carefully controlled according to information from the position sensors or from the back EMF of the motor. Not surprisingly, then, IC manufacturers have created devices that greatly simplify the task of BLDC control.
Advantages of BLDC motors
The availability of convenient controller ICs is a good thing, not only because it makes life easier for engineers, but also because it allows more systems to benefit from the superior performance that brushless motors offer. Compared to brushed DC motors, BLDC motors are more efficient, more compatible with high-precision control techniques, and more durable.
They also generate less electrical noise, because there are no brushes to create high-energy on / off transients. In some situations, using a brushed DC motor may be simply impossible: switching transients create sparks that would likely be dangerous in installations that might contain explosive fumes (I can’t say for sure, I’ve never worked in an explosive environment) .
If there is an upper limit to the amount of functionality that can be integrated into a single motor control IC, I think STMicro is getting close. I’m not saying this is necessarily fantastic, because extremely high integration levels are sometimes a bit overwhelming in my opinion, but if a packaged system is the type of BLDC motor controller you are looking for, the STSPIN32F0B is a good place. to start.
This device, which comes in a 7mm × 7mm VFQFPN48 package, includes
- three-phase gate drivers with integrated start diodes,
- a 32-bit microcontroller built around an Arm Cortex-M0 core,
- a DC / DC converter, generating a 3.3 V power supply that powers the microcontroller and is available for external components,
- a low-dropout linear regulator that powers the gate drivers,
- a rail-to-rail output op-amp that can be used for current sensing, and
- a comparator that can provide overcurrent protection by monitoring the load current and comparing it to a threshold set by the microcontroller.
Diagram taken from STSPIN32F0B Datasheet.
With an IC like this, it is important to point out the components that are no Integrated in the package. You’ll need a variety of external capacitors and resistors, as usual, but the most prominent external components are motor-drive transistors.
The STSPIN32F0B provides door drive outputs, not motor drive outputs. As shown in the application example on page 27 of the datasheet, the final system should include three half-bridge drivers (one per motor phase). Each half bridge uses two N-channel MOSFETs, as shown in the diagram below.
The gate drivers of the STSPIN32F0B, which have a current capacity of 600 mA, are also compatible with IGBTs. If you are interested in learning more about this type of transistor, which is more or less a hybrid of a MOSFET and a BJT, I recently wrote an article on an isolated IGBT gate driver from Analog Devices, and this article on high power transistors provides an full comparison of MOSFETs, BJTs and IGBTs.
Do you have any experience with brushless DC motor control? Feel free to share part recommendations in the comment section below.