Highly integrated semiconductor products are not only a trend in consumer products but are also gradually penetrating motor control applications. Simultaneously, brushless DC (BLDC) motors are showing a similar trend in numerous markets, including automotive and medical applications, with their market share gradually surpassing that of other types of motors. With the increasing demand for BLDC motors and the growing maturity of related motor technologies, the development strategy for BLDC motor control systems has gradually evolved from discrete circuits into three distinct categories. These three main solutions are categorized as System-on-Chip (SoC), Application-Specific Standard Products (ASSP), and dual-chip solutions.
These three main approaches all reduce the number of components required for an application and lower design complexity, thus gaining increasing popularity among motor system design engineers. However, each strategy has its own advantages and disadvantages. This article will discuss these three approaches and how to strike a balance between design integration and flexibility.
Figure 1: Block diagram of a typical discrete BLDC motor system
A basic motor system comprises three main modules: a power supply, a motor driver, and a control unit. Figure 1 illustrates a traditional discrete motor system design. The motor system typically includes a simple RISC processor with integrated flash memory, which drives external MOSFETs by controlling the gate drivers. Alternatively, the processor can directly drive the motor via integrated MOSFETs and a voltage regulator (powering both the processor and the driver).
SoC motor driver integrates all the above modules and is programmable, making it suitable for a variety of applications. Furthermore, it is ideal for applications requiring optimization due to space constraints. However, its lower processing performance and limited internal storage make it unsuitable for motor systems requiring advanced control. Another drawback of SoC motor driver ICs is the limited development tools, such as the lack of firmware development environments. This contrasts sharply with the wide range of easy-to-use tools offered by most leading microcontroller vendors.
ASSP motor drivers are designed for a specific domain, with everything optimized for a narrow application. They have a very small footprint and require no software adjustment. Furthermore, they are ideal for space-constrained applications. Figure 2 shows a block diagram of a 10-pin DFN fan motor driver. Because ASSP motor drivers are typically focused on high-volume production applications, they often offer excellent cost-effectiveness. However, this does not mean that motors running on ASSP drivers need to sacrifice performance. For example, most modern ASSP motor drivers can drive BLDC motors using sensorless and sinusoidal algorithms, whereas in the past, this required high-performance microcontrollers. However, ASSP products lack programmability and cannot adjust drive strength, which limits their ability to adapt to ever-changing market demands.
Figure 2: Block diagram of independent fan motor driver
Despite the high integration trend in today's electronics, there remains a growing demand for dual-chip solutions with abundant analog drivers and intelligent analog microcontrollers. The dual-chip strategy allows designers to select from a variety of microcontrollers, supporting sensor-based or sensorless commutation using trapezoidal or sinusoidal drive technology. When employing this approach, the selection of the matching driver chip is crucial. An ideal matching chip should at least possess the following characteristics:
High-efficiency adjustable voltage regulators are used to reduce power consumption and power various microcontrollers.
The monitoring and background processing module ensures safe motor operation and allows bidirectional communication between the host and the drive.
Optional parameters that can optimize performance without requiring additional programming effort.
Rated power drivers for MOSFET or BLDC motors
Figure 3 illustrates an example of a dual-chip solution, which uses a feature-rich three-phase motor driver and a high-performance digital signal controller (DSC) to drive six N-channel MOSFETs, achieving field-oriented control of a permanent magnet synchronous motor (PMSM, a type of brushless motor). If a simple six-step control architecture is sufficient, a low-cost, low-end 8-bit microcontroller can be used to replace the DSC. When selecting a BLDC motor with approximately its rated power, the above control can be achieved without changing the drive circuitry.
Figure 3: Dual-chip BLDC solution with external MOSFET
In general, using SoC and ASSP motor drivers allows motor system designers to use a minimal number of components and achieve a moderate level of flexibility. However, these highly integrated solutions each have their own limitations, such as fixed functionality, limited storage capacity, and processing power. Table 1 compares the three main BLDC motor control strategies mentioned above.
Table 1: Comparison of BLDC Motor Control Strategies
Compared to discrete designs, modern motor control and drive solutions not only reduce material costs but also shorten system development time, without impacting the construction of systems optimized for the selected BLDC motor. Hardware and firmware reference designs and libraries provided by semiconductor vendors can significantly reduce development time, thereby accelerating the pace of bringing advanced motor control and drive concepts to market.
