Author: Kristian Saxrud Bekken, Microchip Technology Inc.

As package dimensions reduce and power consumption figures increase, thermal management becomes an increasingly important factor in modern-day electronics design. Perhaps the simplest form of thermal management is forced convection, i.e. increasing the dissipation of heat by moving the air inside and around the heat source. This is most conveniently done using fans, which are powered by BLDC motors. BLDC motors are commutated electronically, eliminating problems such as mechanical wear of brushes, but also reducing EMI (Electromagnetic Interference). The most straightforward fan designs simply spin the fan rotor at full speed, but as the number of fans tends to increase, so does the noise and power consumption. In many cases, it would be desirable to keep noise and power consumption at a minimum. This, in turn, could create a demand for adjusting the speed of the fan according to environmental conditions and/or other external factors.

This application note describes a core independent method of using an AVR® device to control a simple BLDC fan. Many peripherals are configured to work together, enabling the Configurable Custom Logic (CCL) module to achieve BLDC motor commutation and dead-time insertion while feeding a PWM signal to a dual driver BLDC motor circuit, independent of CPU operation. After initialization, no CPU cycles are needed to operate the motor at the set PWM duty cycle, achieving minimal process delay compared to an interrupt based configuration.

The device configuration described in this application note could serve as starting point for an intelligent BLDC motor control application with features such as automatic speed control and external monitoring. A typical application could be monitoring and control of a cooling fan.