NXP LPC1100 enables low-cost brushless DC motor control

Advanced motor control technologies such as brushless DC and brushless AC have been widely used in various industrial applications. Compared with general AC motor control technology, this technology has many advantages: higher efficiency, better durability and lower motor cost. On the other hand, the electronic components used to drive the motor have become increasingly complex, resulting in an increase in the total system cost.

As a market segment with obvious price-driven characteristics, the white goods market is particularly cautious in applying "new" motor control methods in home appliances such as washing machines and dishwashers. At present, the well-known traditional control is still the market's first choice, but in recent years, especially against the background of falling semiconductor prices year by year, the technology used in this market has quietly changed.

As a semiconductor supplier for industrial applications, NXP's products cover a wide range, including general application products (rectifiers, Zener diodes, etc.), logic and power products (bidirectional thyristors, power ICs), and interface and microcontroller products.

Today, brushless DC motors (BLDC) have replaced traditional brushed DC (BDC) motors and are widely used in various applications.

Brushless DC motors not only have excellent performance in efficiency and reliability, but also have lower noise, lighter weight and longer service life. They also eliminate commutator sparks and reduce overall electromagnetic radiation. Therefore, they are increasingly sought after in white appliances, HVAC and industrial applications.

Like most motor controls, a brushless DC motor controller consists of a control unit and a power supply unit, and NXP offers highly competitive solutions for both units. This article will focus on the demonstration board NXP has developed for 300W, 12-30V brushless DC motors. The rotor orientation feedback is determined using Hall sensors and connected to the outside world via a PC using CAN or UART.

Figure 1

The Cortex-M0 core is one of the latest cores released by ARM in 2009. It is also the smallest, lowest power and most energy-efficient ARM processor on the market. It can achieve the performance of 32-bit products at the price of 8-bit products, creating the possibility of skipping the 16-bit architecture and directly migrating from the 8-bit architecture to the 32-bit architecture.

The ARM Cortex-M0 core is based on the ARMv6-M architecture and uses the so-called Thumb instruction set including Thumb-2 technology.

The Thumb instruction set can implement 32-bit operations based on 16-bit instructions, thus making it possible to reduce code size.

The Thumb ISA (Instruction Set Architecture) includes only 56 instructions, each of which has a guaranteed execution time. From this perspective, the Cortex-M0 provides a completely deterministic response time. Since it uses a 32-bit architecture, even a 16-bit instruction can achieve 8-bit, 16-bit or 32-bit data transfer with one instruction.

As for the programming model, the Cortex-M0 uses a register set consisting of 13 general registers (r0-r7 low registers and r8-r12 high registers), 3 special registers (stack pointer, link register and program counter) and 1 device status indication register (xPSR, program status register), as shown in the figure below.

Figure 2

As mentioned above, all instructions are executed in a fixed time. For example, data processing instructions are completed in one cycle, data transfer instructions are completed in two cycles, and branch instructions are completed in three cycles.

In addition to the core, the Cortex-M0 integrates a nested vector interrupt controller (NVIC) that can handle interrupts and system exceptions. The Cortex-M0 core has a fully deterministic interrupt handling behavior with a default value of 16 cycles and no jitter. The NVIC can handle up to 32 priority vectors. Like the Cortex-M3 architecture, this architecture supports tail chaining and late arriving interrupts.

In 2009, NXP Semiconductors released the first product in the LPC1100 family, which was also the first microcontroller series based on the Cortex-M0 core.

According to Dhrystone's measurement results, the LPC1100 series can provide 0.9 DMIPS/MHz computing power.

According to the Coremark (http://www.coremark.org) benchmark based on the real performance of embedded devices, the NXP LPC1100 series achieved a high score of 1.4 Coremark/MHz, far exceeding similar products in the 8-bit and 16-bit product markets. At the same time, the reduced code size can also bring performance improvements to users. Thanks to the Cortex-M0 architecture, developers can save an average of about 40% of flash memory utilization space.

Due to the extremely low gate count, Cortex-M0-based devices can be used in low-power applications such as medical equipment, electronic metering instruments, motor control, battery-powered sensors, etc. The Cortex-M series processors produced by ARM support multiple power consumption modes: sleep mode, deep sleep mode and power saving mode.

The LPC1100 series supports a maximum clock rate of 50 MHz, has a zero-latency architecture, and integrates a simple AHB-Lite interface. The block diagram is shown below:

Figure 3

LPC111x integrates all the peripherals needed for embedded control systems in industrial, consumer, and white goods applications. Flash memory capacity is up to 32KB, and prices start at 65 cents per piece (for devices using 8K flash memory).

To meet the needs of brushless DC motor control, the LPC1100 series integrates 4 timers (2 each of 16-bit and 32-bit), with a total of 13 match outputs, each of which can be configured as PWM mode. Six PWM signals are used to drive the high and low ends of MOSFET in the demo board.

The general purpose input/output (GPIO) on the LPC1100 is highly configurable and can be used as external interrupts that activate on both the rising and falling edges or both edges simultaneously. The rotor orientation feedback is obtained through these GPIO interrupts.

Figure 4

The LPC1100 has an 8-channel 10-bit analog-to-digital converter (ADC), one of which is used for overcurrent protection by measuring the motor current through a shunt resistor.

The rotor position is detected without sensors by measuring the floating phase voltage during the commutation of the brushless DC motor. This requires precise timing when acquiring the floating phase voltage. In the LPC1100, the analog-to-digital conversion can be triggered by the matching events of two of the four timers. This reduces the CPU load and accurately captures the floating phase at the right moment.

To connect to the outside world, LPC1100 integrates UART and/or CAN interfaces.

To further support brushless DC motors, NXP Standard Products launched a new generation (sixth generation) of MOSFETs using Trench technology in 2009, providing support for a variety of applications such as motor control in the industrial sector.

Mosfet products have the following advantages: reducing the Rspec - mΩ / mm2 value of low on-resistance R DS(ON) devices, creating conditions for fast switching; reducing gate charge and switching losses; low Q G(tot) and low FOM, maximizing efficiency; increasing Tj(max) to 175C, providing strong support for high reliability and high performance applications. The expanding product portfolio will provide perfect support for motor control applications.

In the future, our Cortex-M product development will support the field-oriented control and U/f control of brushless DC motors. This is a continuation of our microcontroller series development concept. We have always provided similar peripheral IP, software compatibility support and easy porting capabilities based on ARM7, Cortex-M0, Cortex-M3, and the new Cortex-M4 architecture, demonstrating our inheritance of this concept.

This strategy not only allows us to achieve the best balance between CPU performance and necessary peripherals for different motor control methods, but also enables the recycling of tools and software in various projects (for example, software modules written for Cortex-M0 can be reused in Cortex-M3/M4 microcontrollers). This way, our customers can significantly shorten the time to market and minimize tool investments (same IDE, debugging and programming tools).