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Variable Speed DC Fan Control using the MC9RS08KA2, Rev. 0
Freescale Semiconductor 7
Chapter 1
Introduction
1.1 Introduction
This document describes the implementation of a DC brushless fan controller using the Freescale ultra
low cost MC9RS08KA2 8-bit microcontroller (MCU). The design contains a temperature sensor the MCU
reads with control on fan speed against the ambient temperature. Complete coding and schematic are
included.
Figure 1-1. The MC9RS08KA2 DC Fan Reference Design
The DC fan used is a brushless DC motor fan. It is widely used in chip cooling or system ventilation
applications. In the market, most of the DC fans are of the constant air flow design. As the high
performance electronic products continue to increase, cooling requirement becomes more and more
sophisticated. MCU approach provides a cost effective solution to this application. There are several
advantages of a MCU based design over traditional solutions.
1. Instead of having a constant air flow the MCU provides enough processing power to modify the fan
speed according to environment changes such as the temperature of the target system.
2. Fault detection can easily be implemented by the MCU. For example, the MCU can detect for the
air flow blocking or motor jam, the motor driver can be stopped completely to avoid further damage.
3. Buzzer alarm or digital output acknowledgement can be generated under the faulty situation.
The MCU chosen for this purpose must be low cost and it must provide small geometry package to
integrate into the fan controller printed circuit board (PCB). The MC9RS08KA2 is ideal for this application.
MC9RS08KA2
MCU IN 8-PIN NARROW BODY
SOIC PACKAGE
BUZZER
VARIABLE RESISTOR
(TO EMULATE A TEMPERATURE SENSOR)