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Figure 1. Block diagram of a conceptual motor control for a fan application. (Source: STMicroelectronics) preferred. Positioning applications, on the other hand, are more suited to the use of Hall sensor outputs, which provide the rotor's electrical position at a 60-degree resolution, or position encoders/sensors, which provide rotor positioning data at a much higher resolution (e.g. less than 1 degree). Fan Application In low-power applications, a cooling fan for a computer laptop, desktop, or server provides a good example. Since the load torque of the fan changes little while spinning and low noise levels are required, an all-in-one, integrated motor control IC is usually the best option. Generally, no external microcontroller is used in this type of motor control system due to cost considerations. There is typically 4-wire communication (voltage supply (Vs), ground (GND), PWM-in, and tech-output) between the host and fan-control system. PWM-in and tech- output can be replaced by an inter-integrated circuit (I2C) clock and data in some applications. The host commands and monitors the fan RPM as the baseline. Increasingly in emerging designs, fan fault conditions in areas such as motor phase current are monitored. In addition to spinning the motor, a full-featured protection system is also required to protect the fan and complete the design. Indeed, protection against overcurrent, undervoltage lockout, overtemperature, and short-circuits are all widely supported in today's motor driver ICs. Using a server fan as an example, the supply voltage of this type of fan is typically 12VDC, although 24V is sometimes used. Since the fan load (blades + air resistance) does not vary signicantly at a given speed/RPM, a sensorless control scheme can achieve the target level of performance. However, sinusoidal control schemes are increasingly chosen by fan manufacturers because they offer better power efciency and lower noise levels. In a typical fan, a sensorless sinusoidal motor control scheme is far simpler than a full-featured eld- orientation control (FOC) design. The motor phase current of the fan is usually less than 3A. Therefore, an integrated fan motor control IC has become an industrial trend. A conceptual server fan motor control block diagram is shown in (Figure 1). Since sensorless control algorithms can present some design challenges at low speeds due to BEMF waveform distortion, the host will usually not allow them to maintain very low speeds (e.g. less than 10% of full motor speed). Drone Propeller Application Although radio-controlled (RC), xed-wing model airplanes have been available in hobby stores for decades, they have never gained the popularity already enjoyed by their modern successor: the drone (commercially-available, non-military). Most commercial drones are powered by a 2-6 cell Li-ion battery. This means that the propeller motor's rated supply voltage ranges from about 6 to18V. Although there has been recent talk about parcel delivery using drones, the most common drone payload today is a camera used for aerial photography. For a typical 6-cell drone carrying a camera, the propeller's motor current is usually below 20A. A drone is expected to y with the load swiftly in outdoor conditions. Its 3D movement is enabled by 4 to 6 propellers spinning precisely, and in parallel. Typically, a drone propeller motor has 6 to 7 pole pairs, although it can have more. Since the propeller must be capable of reaching 10,000 RPM, it can be challenging to reliably employ a Hall sensor in the motor due to the effects of vibration. Therefore, the propeller motor is frequently controlled using a sensorless, full-featured FOC scheme, with sinusoidal control and both speed and current/ torque loop enabled. 1 to 3 shunt resistors are required on the propeller electrical speed controller (ESC) board to sense and provide a motor phase current value to the control algorithm every PWM cycle. The integrity of the motor phase current sensing feedback signal is essential to the performance of the motor. To avoid excessive heat dissipation, a very-low resistance shunt resistor (e.g. 10m) can be used. An op-amp is usually employed to amplify the current sensing voltage enough (0-3.3V typ.) for the analog-to-digital converter (ADC) to pick up. It is critical then to properly balance the shunt resistor value and the amplication factor so as to t within the ADC operating range. When the motor is loaded lightly and spinning slowly, the current-sensing voltage must still be sufcient for the ADC to sample; when the motor is fully loaded and spinning at full speed, the ADC input is not saturated. An op-amp amplies both the signal and the noise together. In other words, a high amplication factor increases the noise level undesirably. Certain low-pass lters may be used to remove noise from the IQ and ID in the control scheme. As motor phase current is alternating current (AC), not DC, and motor control is enabled by the PWM, a higher PWM duty- 08

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