Freescale Semiconductor RS08 User manual

RS08
Microcontrollers
freescale.com
DRM079
Rev. 0
5/2006
Designer Reference Manual
Variable Speed DC Fan Control
using the MC9RS08KA2

Variable Speed DC Fan Control using the MC9RS08KA2, Rev. 0
Freescale Semiconductor 3
Variable Speed DC Fan Control using the MC9RS08KA2
Designer Reference Manual
by: Vincent Ko
Freescale Semiconductor, Inc.
Hong Kong
To provide the most up-to-date information, the revision of our documents on the World Wide Web will be
the most current. Your printed copy may be an earlier revision. To verify that you have the latest
information available, refer to http://www.freescale.com
The following revision history table summarizes changes contained in this document. For your
convenience, the page number designators have been linked to the appropriate location.
Revision History
Date Revision
Level Description Page Number(s)
05/2006 0 Initial release N/A

Revision History
Variable Speed DC Fan Control using the MC9RS08KA2, Rev. 0
4Freescale Semiconductor

Variable Speed DC Fan Control using the MC9RS08KA2, Rev. 0
Freescale Semiconductor 5
Table of Contents
Chapter 1
Introduction
1.1 Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 7
1.2 Freescale’s New Generation Ultra Low Cost MCU . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.3 DC Fan Reference Design Targets . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
1.4 Bi-Phase BLDC Motor . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
Chapter 2
Motor Control
2.1 Commutation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.2 Rotor Position Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
2.3 Commutation Waveforms . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.4 Speed Control . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 12
2.5 Motor Startup . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
2.6 Fault Detection. . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 13
Chapter 3
Implementation
3.1 Block Diagram . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.2 Hardware Resources . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15
3.3 Control Loop . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 16
3.4 Temperature Sensor Measurement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 18
3.4.1 Temperature Conversion . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 20
Appendix A.
Schematic
Appendix B.
Program Listing

Table of Contents
Variable Speed DC Fan Control using the MC9RS08KA2, Rev. 0
6Freescale Semiconductor

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)

Introduction
Variable Speed DC Fan Control using the MC9RS08KA2, Rev. 0
8Freescale Semiconductor
1.2 Freescale’s New Generation Ultra Low Cost MCU
The MC9RS08KA2 microcontroller unit (MCU) is an extremely low cost, small pin count device for home
appliances, toys, and small geometry applications, such as a DC fan controller. This device is composed
of standard on-chip modules including a very small and highly efficient RS08 CPU core, 62 bytes RAM,
2K bytes FLASH, an 8-bit modulo timer, keyboard interrupt, and analog comparator. The device is
available in small 6- and 8-pin packages.
Features of the MC9RS08KA2 include:
• 8-bit RS08 core
– Up to 10 MHz (bus frequency) at 1.8V for 100 ns minimum instruction time
– RS08 instruction set
– Supports tiny/short address mode
– 14-byte fast-access RAM
– Allows emulation of HC08/HCS08 zero-offset index addressing mode instructions
• Third-generation Flash and RAM (extremely fast, byte writable programming)
– 63 Byte RAM
– 2K Byte Flash
• Flexible clock options
• 4 Bidirectional I/O lines with software selectable pull-up (eliminates need for external resistors)
• Analog comparator
• Real time interrupt
• 8-bit timer with 8-bit prescale
• System protection
– Resets in instance of runaways or corrupted code
– Low voltage detection
– Illegal opcode and illegal address detection
– Flash security feature
• Single wire debugging and emulation interface; eliminates need for expensive emulation tools or
development hardware
1.3 DC Fan Reference Design Targets
Table 1-1. Design Targets
Item Requirement
Motor Type Bi-phase BLDC motor
Fan Dimensions 60mm x 60mm x 25mm
Operating Voltage 12V
Current Rating 0.18A (max.)
Speed 1000 to 4000 RPM
Temperature Feedback Yes
Fault Detection Air flow blocking (motor jam)
Fault Notification Buzzer alarm

Bi-Phase BLDC Motor
Variable Speed DC Fan Control using the MC9RS08KA2, Rev. 0
Freescale Semiconductor 9
1.4 Bi-Phase BLDC Motor
The brushless DC motor (BLDC) design for DC fan is commonly consist of a permanent magnet attached
on the rotor and the stator phase coil windings are mounted on the motor shaft as illustrated in Figure 1-2.
The BLDC has no brushes on the rotor and the commutation is performed electronically at certain rotor
positions.
Figure 1-2. Bi-Phase BLDC Motor Diagram
Fan Hub
Permanent
Magnets
Axle
Hall Effect
Sensor Stator
Coil

Introduction
Variable Speed DC Fan Control using the MC9RS08KA2, Rev. 0
10 Freescale Semiconductor