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  • 3-Phase BLDC Sensorless Fan Controller

  • Created: Sep 20, 2016

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This reference design is an evaluation board for the demonstration of MTD6505 three-phase brushless DC (BLDC) sensorless fan controller. The MTD6505 device is a three-phase full-wave sensorless driver for brushless DC (BLDC) motors. It has adaptive features, parameters and wide range of power supply (2V to 5.5V) that are intended to cover a broad range of motor characteristics, while requiring minimum external components. It features 180° sinusoidal drive, high torque output and silent drive. Speed control can be achieved through either power supply modulation (PSM) or pulse-width modulation (PWM).

This evaluation board includes several components such as a microcontroller, an adjustable linear dropout regulator, digital potentiometer, and a delta-sigma analog-to-digital converter (ADC). A PIC24FJ256GB microcontroller is used for USB connection, PWM generation, FG frequency measurement, VDD measurement, other’s signal’s activations and component’s communication. The MCP1827 adjustable LDO, along with MCP42050 digital potentiometer, provides the VDD to the MTD6505 device. The LDO can be enabled or disabled by the microcontroller. The digital potentiometer is also used to set the MTD6505 RPROG external resistor value. The MCP3421 delta-sigma ADC is combined to a shunt resistor for sensing the MTD6505 current consumption on the VDD pin. The MTD6505 device has a thermal protection function which detects when the die temperature exceeds TJ=+170°C. When this temperature is reached, the circuit enters Thermal Shutdown mode, and outputs OUT1, OUT2 and OUT3 are disabled (high-impedance), avoiding IC destruction and allowing the circuit to cool down. When the junction temperature (TJ) drops below +145°C, normal operation resumes.

The MTD6505 is an ideal choice for cost-efficient fan applications. It can be used to control CPU cooling fans in notebook computers. It provides low acoustic noise, low mechanical vibration, and is highly efficient. The frequency generator (FG) output enables precision speed control in closed-loop applications. The MTD6505 device includes lockup protection mode to turn off the output current when the motor is in a lock condition, with an automatic recovery feature to restart the fan when the lock condition is removed. Motor overcurrent limitation and thermal shutdown protection are included for safety-enhanced operations.