AN2687 Freescale Semiconductor / Motorola, AN2687 Datasheet - Page 10

• Manufacturer Part Number: AN2687
• Description: BLDC Fan Control using the MC68HC908QT2
• Manufacturer: Freescale Semiconductor / Motorola

AN2687/D
PART 3: SOFTWARE DESIGN
Commutation and
Position Detection
Motor Start-Up
Phase
Motor Running
Phase
Temperature-Speed
Mapping
10
The flow of the program is illustrated by the state diagram in
Details of the control blocks are explained in the following paragraphs.
The positional information comes from the Hall effect sensor that is mounted
on the BLDC motor. The signal from the Hall sensor provides the commutation
information that is required for driving the BLDC motor by Q1 and Q2. The
firmware uses the external interrupt (IRQ) to sense the falling edge of the Hall
sensor and uses the input capture interrupt to sense the rising edge of the Hall
sensor. The use of the interrupt sensing, as opposed to I/O port polling,
provides faster response time and better accuracy.
During the motor start-up period, a higher power is needed to start motor
rotation and to avoid motor lock-up. This is achieved by applying full-power
(i.e. off-time = 0) to the motor. Following this, the firmware needs to check for
the end of the start-up period and then jump into the running phase to adjust
the speed according to the input from the thermal sensor.
After the motor start-up period, the end of start-up flag will be set and then the
firmware will jump into the running mode. In the running mode the speed is set
according to the input of the thermal sensor.
Temperature vs. speed mapping is implemented to take into consideration of
variations in the following:
The firmware provides 256 steps thermal speed profile mapping. The profile
can easily be modified to suit user requirements.
relationship between the temperature and the speed (256 steps). The
characteristic can be modified by changing the value in the table at $FFD0 in
the firmware.
Freescale Semiconductor, Inc.
•
•
•
BLDC Fan Control using the MC68HC908QT2
For More Information On This Product,
Application cooling requirements
Thermal sensor characteristics
Motor characteristics
Go to: www.freescale.com
Figure 10
shows the
Figure
MOTOROLA
11.