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Figure 2. Block diagram of a conceptual motor control for a drone application. (Source: STMicroelectronics) Figure 3. Power tool motor control system block diagram. (Source: STMicroelectronics) cycle results in higher applied voltage per motor phase, and thus higher current. Motor phase current sampling is usually synchronous with the PWM signal to reduce the effect of noise. During every PWM cycle, the motor phase current rises during the on-time, and decays (not ceasing immediately) during off-time. So the ADC sample timing is important. Typically, U, V, W PWM are central-aligned and ADC-sampling occurs around the center point of the PWM. Short ADC latency is always desirable. In FOC control, high-side and low-side PWM per phase is typically set as complementary. PWM frequency is usually above 20kHz (40kHz is ne also). Designers will not select a PWM frequency lower than 4MHz, as this is within the audible domain. It is usually more thermally efcient and cost effective to use external MOSFETs on the ESC board, as shown in (Figure 2). Power Tool Application Brushed DC motors have been used in power tools, such as drills, for decades. However, BLDC motors have started receiving greater attention due to better power efciency coupled with a reduction in the cost of the motors and associated control circuitry. Many high-end power drilling tools on the market today already use BLDC motors. The typical current rating of a power tool is much higher than that of a drone propeller, and power drills must be capable of adjusting to the various types of material it may encounter during operation. For example, when drilling a hole in a typical household wall, the drill bit rst meets the relatively soft drywall, then the much harder wooden stud. This means that the load torque can vary considerably during operation. A Hall sensor is thus needed to provide the rotor's position in real-time. Considering the high current rating, a discrete topology using external MOSFETs is required. Since motor current is very high, a small shunt resistor (about 1-5m) is recommended for current sensing, although the noise level can be quite high when such a small resistor is used. This is one of the key challenges in BLDC-based power tool design. While it's true that a dedicated current sensing IC can provide awless motor phase current feedback, this is usually not a cost-effective solution for power tools. A typical power tool BLDC motor control block diagram is shown in (Figure 3). 09