Customer demand continues to rise for motorized products that are more compact, simpler and easier to use. The combination of high-power motor control (up to 140W), USB PD functionality, and minimal need for external components has been a tough thing to achieve, but Infineon’s latest product does just that. In this article, learn how to use an Infineon EZ-PD™ PMG1-S3 motor controller to control brushless DC motors.
EZ-PD™ PMG1 introduction
Infineon’s EZ-PD™ PMG1 is a family of high-voltage USB-C Power Delivery (PD) MCUs. These chips include an Arm® Cortex®-M0/M0+ CPU and USB-C PD controller along with analog and digital peripherals. EZ-PD™ PMG1 is targeted at any embedded system that provides to or consumes power from a high-voltage USB-C PD port and leverages the MCU to provide additional control capability. The PMG1 MCU family is fully compliant with the USB PD and Type-C standards. Table 1 compares the features of different MCUs in the EZ-PD™ PMG1-Sx family.
Table 1: Comparison of features of different EZ-PD™ PMG1-Sx family MCUs
| Subsystem or range | Item | PMG1-S0 | PMG1-S1 | PMG1-S2 | PMG1-S3 |
|---|---|---|---|---|---|
| CPU and memory subsystem | Core | Arm® Cortex®-M0 | Arm® Cortex®-M0 | Arm® Cortex®-M0 | Arm® Cortex®-M0+ |
| Maximum frequency (MHz) | 48 | 48 | 48 | 48 | |
| Flash (KB) | 64 | 128 | 128 | 256 | |
| SRAM (KB) | 8 | 12 | 8 | 32 | |
| Power Delivery | PD ports | 1 | 1 | 1 | 1 port for 48-QFN 2 ports for 97-BGA |
| Role | Sink | DRP | DRP | DRP | |
| MOSFET gate drivers | 2× PFET | 2× PFET | 2× NFET | Flexible 2× NFET | |
| Fault protections | VBUS OVP and UVP | VBUS OVP, UVP and OCP SCP and RCP (for source configuration only) |
VBUS OVP, UVP and OCP | VBUS OVP, UVP and OCP SCP and RCP (for source configuration only) |
|
| USB | Integrated full-speed USB 2.0 device with billboard class support | No | No | Yes | Yes |
| Voltage range | Supply (V) | VDDD (2.7 to 5.5) VBUS (4 to 21.5) |
VSYS (2.75 to 5.5) VBUS(4 to 21.5) |
VSYS (2.7 to 5.5) VBUS (4 to 21.5) |
VSYS (2.8 to 5.5) VBUS (4 to 28) |
| I/O (V) | 1.71 to 5.5 | 1.71 to 5.5 | 1.71 to 5.5 | 1.71 to 5.5 | |
| SCB (configurable as I2C/UART/SPI) | 2 | 4 | 4 | 7 for 48-QFN (out of which 5 can be configured as SPI and UART) 8 for 97-BGA |
|
| TCPWM block (configurable as timer, counter or pulse width modulator) | 4 | 2 | 4 | 7 for 48-QFN 8 for 97-BGA |
|
| Hardware authentication block (Crypto) | No | No | Yes (AES- 128/192/256, SHA1, SHA2-224, SHA2-256, PRNG, CRC) | Yes (AES-128, SHA2- 256, TRNG, vector unit) | |
| Analog | ADC | 2× 8-bit SAR | 1× 8-bit SAR | 2× 8-bit SAR | 2× 8-bit SAR 1× 12-bit SAR |
| On-chip temperature sensor | Yes | Yes | Yes | Yes | |
| Direct memory access (DMA) | DMA | No | No | No | Yes |
| GPIO | Maximum number of I/Os | 12 (10+2 OVT) | 127 (15+2 OVT) | 20 (18+2 OVT) | 26 (24+2 OVT) for 48-QFN 50 (48+2 OVT) for 97-BGA |
| Charging standard | Charging source | - | BC 1.2, AC | BC 1.2, AC | BC 1.2, AC, AFC, and Quick Charge 3.0 |
| Charging sink | BC 1.2, Apple charging (AC) | BC 1.2, AC | BC 1.2, AC | BC 1.2, AC | |
| ESD protection | ESD protection | Yes (up to ±8kV contact discharge, up to ±15 kV air discharge, human body model and charged device model) | Yes (human body model and charged device model) | Yes (up to ±8kV contact discharge, up to ±15 kV air discharge, human body model and charged device model) | Yes (human body model and charged device model) |
| Packages | Package options | 24-QFN (4 × 4mm,0.5mm pitch) | 40-QFN (6 × 6mm,0.5mm pitch) 42-CSP (2.63 × 3.18 mm, 0.4 mm pitch) |
40-QFN (6 × 6mm,0.5mm pitch) | 48-QFN (6 × 6 mm, 0.5 mm pitch) 97-BGA (6 × 6 mm, 0.5 mm and 0.65 mm pitch) |
Introduction to Brushless DC motors
Brushless DC (BLDC) motors fall in the broad category of permanent magnet synchronous machines, which consist of a rotor made of permanent magnets and a stator housing three-phase windings made of copper coils. Unlike the brushed motors which are mechanically commutated using carbon contact brushes, brushless motors do not require any brush as commutation is handled electronically, using a microcontroller. Because of the absence of an electrical contact between the stator and the rotor, brushless motors offer several advantages over brushed counterparts. Some of them are higher efficiency, high torque and speed, less maintenance, low noise operation, and high torque-to-weight ratio.
Although, several other types of motors are brushless, including AC synchronous motor, AC induction (asynchronous) motor, stepper motor, permanent magnet synchronous motor (PMSM), the main feature which characterizes the BLDC motor is the trapezoidal shape of the back EMF generated when the motor rotates. This is mainly due to the winding fashion of the stator. The current flow through each of the three phases is switched according to a certain sequence using a microcontroller, which generates a rotating magnetic field in the stator. The rotor containing permanent magnets try to chase this rotating magnetic field by the magnetic flux linkage between them and thus rotates behind the stator magnetic field, which forms the main principle of operation of the brushless motors.
Brushless motor structure
Brushless motors are physically made up of two parts, a rotor steel core containing permanent magnetic poles and a stator steel core housing three-phase windings as shown in Figure 1. The rotor can be situated either within the stator (in-runner) or outside the stator (out-runner). In either case, there is no electrical contact between the rotor and the stator. The three-phase windings on the stator may be connected either in star (wye) or delta fashion as shown in Figure 1. This decides the characteristics such as torque and speed of the motor but hardly impacts the control strategy, which will be discussed in section 4. Similarly, the number of magnetic pole-pairs on the rotor and the number of slots on the stator also have an impact on the torque produced. In general, more the number of magnetic poles on the rotor, higher the torque produced. Figure 1 shows a BLDC motor with 8 rotor poles (4 pole-pairs) and 9 stator slots.
Brushless motor drive schemes
Brushless motors derive power from a three-phase inverter circuit which generates three phases (A, B, and C) that supplies current in the three terminals such as A, B, and C of the brushless motor winding as shown in Figure 1. In an AC-powered drive, the three-phase AC voltage is fed directly to the terminals of the motor. However, in case of brushless DC (BLDC) motors which are driven by a DC power source, the three-phase inverter circuit performs the task of converting the direct current into three-phase voltages, which are continuously switched in a particular sequence by a microcontroller. This switching sequence, in turn, depends on the changing position of the rotor with respect to the stator. Therefore, often BLDC motors are operated in closed-loop with a position feedback signal to determine the current position of the rotor. This leads to divide the control scheme into the following two categories, sensored control and sensorless control.
Sensored BLDC motor control
In the sensored control technique, a suitable type of position sensors, often hall-effect sensors are placed along the circumference of the rotor. The magnetic field interaction caused by the permanent magnetic poles placed on the rotor creates a corresponding voltage at the output terminals of the hall sensor, which is then read by the microcontroller to determine the transition (N to S or S to N) of a rotor pole about the hall sensor. Based on this transition point, the phases are commutated. Three hall sensors are to be placed at either 60 or 120 electrical degrees apart to read the complete information of the rotor movement around the stator. The major advantage of sensored control is that the rotor position is known even when the rotor is at rest. However, the sensored control method is not recommended for use in harsh environments since it may affect the system's robustness.
Sensorless BLDC motor control
Sensorless control, as the name suggests, does not use any sensor interface to determine the position of the rotor. The information regarding the rotor position is known solely based on the back EMF signal generated on each of the three-phase windings when the rotor is in motion. The nature of the phase windings in the stator will determine the shape of the back EMF profile. Usually, a trapezoidal back EMF waveform characterizes a BLDC motor. The main advantage of using a sensorless control is the robustness feature obtained by the absence of delicate sensors for the control strategy. However, the instantaneous magnitude of the back EMF depends on the rotor speed and also on the type of commutation technique used and is given by the following equation:
𝑣𝐵𝐸𝑀𝐹 = E x F(𝜃𝑒)
𝐸 = 𝜔𝐾𝑒
Where
E is the maximum value of the back EMF
F(Θe) is the function dependent on the commutation technique used
Ke is the back EMF constant of the motor expressed in mV-s/rad
ω is the angular velocity of the rotor in rad/s
Θe is the instantaneous electrical angular position of the rotor in rad
But since the amplitude of the back EMF is either zero or very low to be sensed when the rotor is at rest or at very low RPM, this technique suffers from a major problem as the rotor position cannot be known in these cases. Therefore, the control has to drive the motor in open loop until a threshold RPM is reached where the back EMF signal level is readable.
Application overview
BLDC motor applications are gaining popularity in the electronic market due to their numerous advantages in comparison to conventional AC induction and brushed DC motors. Many of the low-power consumer electronic goods that are currently operated by BLDC motors rely on a fixed AC to DC power adapter as the input power source. Few other solutions use either a brushed AC motor or an AC induction motor to receive AC power directly from a wall-plug. But, considering the energy efficiency factor in BLDC motors, controllability and the rapid growth in the field of electronics, there is a market tendency to shift to the usage of BLDC motors.
In addition to this, the present growth trend of USB Power Delivery (PD) market has created a demand for a USB PD integrated solution for motor control as this is an ideal choice for many of the consumer electronic devices. Infineon’s EZ-PD™ PMG1 devices are a family of high-voltage microcontrollers with USB Power Delivery, ideally designed for developing such integrated solutions. This application note, therefore, demonstrates such an integrated single-chip solution using the EZ-PD™ PMG1-S3 device, to control up to 140-W USB PD driven sensorless BLDC motors.
Solution examples
The block diagram in Figure 2 shows an integrated solution developed on the EZ-PD™ PMG1-S3 device to support a USB PD driven sensorless BLDC motor control. This solution targets to use a USB PD source as a universal DC power source to provide up to 140 watts of power through a standard USB Type-C cable to run various motorized devices. This solution uses minimal external components for motor control, other than the EZ-PD™ PMG1-S3 MCU. Here, PMG1-S3 acts as both a USB PD controller and a BLDC motor controller. External interfaces for BLDC motor control include the three-phase MOSFET inverter circuit and gate driver ASICs, which form the power circuits for driving the BLDC motor. Additionally, the passive electronic components form an integral part of filters and voltage divider circuits.
To read the rest of this article and get an in-depth understanding of the process of setting up a USB PD sensorless brushless DC (BLDC) motor controller using Infineon solutions, click below to download.