Addressing BLDC Controller Design Challenges with the Qorvo PAC5556

Brushless DC (BLDC) motors have become the default motor of choice for a wide variety of battery-powered and line-powered devices and appliances. Compared to brushed DC motors, brushless DC motors are more reliable, require less maintenance, and are widely understood by the application industry to be controlled using simple microcontroller algorithms. In today’s complex and advanced control applications, brushed motors generate too much electrical noise, which means that designers need to employ extensive electromagnetic immunity techniques.

Robert Huntley, Mouser Electronics

Addressing BLDC Controller Design Challenges with the Qorvo PAC5556

Brushless DC motors are commonly used in many consumer and industrial appliances. Building a controller for BLDC requires several key functions, all of which are incorporated into Qorvo’s single-package PAC5556 Power Application Controller® (PAC™).

Brushless motors gain favor

Brushless DC (BLDC) motors have become the default motor of choice for a wide variety of battery-powered and line-powered devices and appliances. Compared to brushed DC motors, brushless DC motors are more reliable, require less maintenance, and are widely understood by the application industry to be controlled using simple microcontroller algorithms. In today’s complex and advanced control applications, brushed motors generate too much electrical noise, which means that designers need to employ extensive electromagnetic immunity techniques. Audible noise from brushed motors is now a detriment, especially for portable battery-operated appliances such as vacuum cleaners and personal power tools, including jigsaws and drills/screwdrivers.

Manufacturers make brushless DC motors with fixed permanent magnets on the rotor drive shaft and a series of field windings (usually three) inside the motor housing. The current is switched through the three excitation windings in turn to make the drive shaft rotate. Controlling the pulse width and switching frequency of each field coil driver allows control of motor speed, acceleration and output torque. The operating state of the rotor needs to be closed-loop fed back to the three-phase motor control algorithm to closely monitor and control the current state of the drive shaft rotation. The two most common ways to provide this feedback are:

• Attach an encoder disk or other form of rotation sensor to the rotor shaft.
• Induction of the reverse electromagnetic field induced by the rotor permanent magnets in the field windings. Field Oriented Control (FOC) refers to the use of induced magnetic field voltages.

A sensorless approach can help improve overall motor reliability and reduce bill of materials (BOM) costs.

Architecture of a BLDC Motor Controller

As mentioned earlier, brushless motor controllers require three distinct circuit functions. These three different circuit functions are implemented by the following components:

• Microcontroller to run motor control algorithms
• Pulse Width Modulation (PWM) circuit providing switching signal
• Power output stage for the drive motor

The analog-to-digital function converts the shaft rotation sensor signal into the digital domain, which is processed by the microcontroller. There are several designs to consider when designing an embedded motor controller. Initial factors that contribute to the overall design of an embedded motor controller:

• Required power/torque
Power Supply
• Shaft speed

Today’s trend to move from prototype to production quickly keeps design engineers away from discrete components when developing custom controllers. The more common design approach is to use an off-the-shelf microcontroller to run the control algorithm. Most microcontrollers include various ADC/DAC conversion functions in addition to different peripheral interface options, clocks and timers. A properly equipped microcontroller may provide most of the required circuit functions. However, many microcontrollers tend not to be optimized for motor control applications or contain the necessary half/full H-bridge motor drive functionality. In addition, energy management is a necessary feature in most applications today, especially in motor control applications, where energy efficiency rating is often a key selection criterion for customers. There are also power management ICs, but this requires the engineering team to integrate additional ICs into the design, which increases BOM cost and board space requirements.

As more consumer and industrial motor-based appliances adopt brushless DC motor designs, there is a need for a Device that includes all the necessary functions, for which Qorvo has developed a full-featured Power Application Controller (PAC™). Qorvo’s PAC5556 Power Application Controller® (PAC™) integrates all necessary analog, power management and gate drive signal sources in a single compact package.

Brushless DC (BLDC) motors have become the default motor choice for a wide variety of battery-powered and line-powered devices and appliances.

Introduction to the Qorvo PAC5556

Qorvo PAC5556 Power Application Controller® (PAC™) in a thin QFN-52 package supports motor operation up to 600VDC and integrates a wide range of functions and features required for any BLDC or smart energy application (Figure 1). The highly integrated PAC architecture makes the Qorvo PAC5556 ideal for applications where PCB size is shrinking, such as white goods, compressors and power tools.

Addressing BLDC Controller Design Challenges with the Qorvo PAC5556
Figure 1: Diagram showing a simplified functional block diagram of the Qorvo PAC5556 power application controller.

At the heart of the device is a 150MHz 32-bit Arm with 128kB of user-programmable flash memory® Cortex®-M4F microcontroller core. The Nested Vectored Interrupt Controller (NVIC) can accommodate up to 25 external interrupts and provides wake-up functionality that enables the device to resume from different sleep modes. Clock gating of the 24-bit real-time clock allows low-power operation. The microcontroller unit (MCU) also integrates a high-speed 12-bit ADC. Arm PAC5556® Cortex®– The M4F microcontroller core is configured for little-endian operations, including hardware support for multiply and divide, DSP instructions, and an IEEE754 single-precision floating-point unit (FPU). The integrated FPU supports complex high-resolution control algorithms such as those used for FOC. The high-performance features of this MCU enable design engineers to easily implement complex real-time algorithms, safety software, and diagnostics in their applications.

A pulse width modulation (PWM) engine provides the drive signal to the motor gate driver. The PWM engine includes four 16-bit timers and 32 channels with precision motor control down to 10ns.

The PAC5556’s analog front end is highly configurable and offers differential and single-ended programmable gain amplifiers, 6 comparators, 10-bit DAC, programmable overcurrent protection, integrated VM ADC sampling, and sampling for interconnectable and programmable signals , feedback amplification and I/O for sensor monitoring of multiple analog input signals. These analog capabilities make the device suitable for field-oriented control or sensor-based BLDC control applications.

The Qorvo PAC5556 also includes a configurable power manager and application-specific power drivers. The configurable power manager contains a multi-mode switching power converter that allows the IC and motor driver circuits to be powered using a buck converter topology. An on-chip linear regulator provides the IC supply rails, and power management functions control the available sleep and hibernate modes. Designers can optimize the power manager’s runtime and standby modes. The standby current of the PAC is very low, so the battery-operated tool has a long battery life when not in use. In devices that are always connected to AC power, such as white goods, a power manager can help achieve Energy Star ratings. The power driver block provides all necessary high-side and low-side gate drivers for various motor drive configurations, including half-bridge and full H-bridge.

A simplified circuit diagram of the Qorvo PAC5556 for driving a BLDC motor is shown in Figure 2.

Brushless DC motors are commonly used in many consumer and industrial appliances.

Addressing BLDC Controller Design Challenges with the Qorvo PAC5556
Figure 2: Simplified circuit diagram of the Qorvo PAC5556 for controlling a BLDC motor.

To assist with prototyping and development efforts, a Qorvo PAC5556-based evaluation board is available. The Qorvo PAC5556EVK1 is a complete, full-featured evaluation and prototyping platform for the PAC5556 (Figure 3). The evaluation board supports up to three ratings up to 220VAC or 450VDC The gate drive of the half H-bridge Inverter. All applications running on the PAC5556EVK1 can be configured and controlled through a virtual COM port connection to a computer and a GUI-based software suite.

Addressing BLDC Controller Design Challenges with the Qorvo PAC5556
Figure 3: Qorvo PAC5556EVK1 evaluation board.

in conclusion

Brushless DC motors are commonly used in many consumer and industrial appliances. As brushless motors become more widely used, the ability to rapidly design, prototype and test motor controllers is key to speeding up the entire product design process. Therefore, design engineers need a device that integrates all the necessary analog, power management and gate drive signal sources in a single package. The highly integrated Qorvo PAC5556 power application controller addresses the need for compact power control solutions that reduce energy consumption, size and noise in consumer and industrial motor applications. The design also meets tighter board space requirements and keeps BOM costs to a minimum.

The Links:   SP14Q002-B1 LQ7BW556T

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