Highly integrated semiconductor products are not only the trend of consumer products, but also gradually penetrate into motor control applications. At the same time, brushless DC (BLDC) motors are also showing the same momentum in many markets, such as automotive and medical applications, and their market share is gradually surpassing that of other types of motors. With the growing demand for BLDC motors and the maturity of related motor technologies, the development strategy for BLDC motor control systems has evolved from discrete circuits to three different categories. These three main types of solutions are divided into system-on-a-chip (SoC), application-specific standard products (ASSP), and two-chip solutions.
These three main solutions are increasingly favored by motor system design engineers because they reduce the number of components required for the application and reduce the complexity of the design. However, each strategy has its own strengths and weaknesses. This article will discuss these three options and how they can be traded off between design integration and flexibility.
Figure 1: Block diagram of a typical discrete BLDC motor system
The basic motor system consists of three main modules: the power supply, the motor drive and the control unit. Figure 1 shows the design of a traditional discrete motor system. Motor systems typically include a simple RISC processor with integrated flash that drives the external MOSFET by controlling the gate driver. The processor can also drive the motor directly through an integrated MOSFET and voltage regulator that powers the processor and driver.
The SoC motor drive integrates all of the above modules and is programmable for a wide range of applications. In addition, it is ideal for applications that require space optimization due to space constraints. However, its low processing performance and limited internal memory space cannot be applied to motor systems that require advanced control. Another disadvantage of SoC motor driver ICs is the limited development tools, such as the lack of a firmware development environment. This is in stark contrast to the fact that most of the industry's leading microcontroller suppliers offer a wide range of easy-to-use tools.
ASSP motor drives are designed for a specific area and everything is optimized for a narrow application. It takes up very little space and requires no software adjustments. In addition, it is ideal for space-constrained applications. Figure 2 shows a block diagram of a 10-pin DFN fan motor driver. Because ASSP motor drives are often focused on high volume production applications, they often have excellent price/performance ratios. However, this does not mean that motors running on ASSP drives need to sacrifice performance. For example, most modern ASSP motor drives can drive BLDC motors with sensorless and sinusoidal algorithms, which in the past required high-performance microcontrollers. However, ASSP products lack programmability and do not adjust drive strength, which limits their ability to adapt to changing market demands.
Figure 2: Block diagram of a freestanding fan motor driver
Although high integration is a major trend in today's electronics, there is still a growing demand for dual-chip solutions with rich analog drivers and intelligent analog microcontrollers. The two-chip strategy allows designers to select from a variety of microcontrollers to support sensory commutation or sensorless commutation with trapezoidal or sinusoidal drive technology. When using this solution, the choice of the supporting driver chip is crucial. The ideal companion chip should contain at least the following features:
Efficient, adjustable regulator for reducing power consumption and powering all types of microcontrollers
Monitoring and background processing modules to ensure safe motor operation and allow two-way communication between the host and the drive
Optional parameters that optimize performance without the need for additional programming effort
Rated power driver for MOSFET or BLDC motors
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