AN2687 Freescale Semiconductor / Motorola, AN2687 Datasheet - Page 11

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

Over-Temperature
and Motor-Lock
Alarms
(Evaluation Demo)
Over-Temperature
and Motor-Lock
Alarms
(Reference Demo)
MOTOROLA
Figure 10.
If there are no interrupts for more than 100ms, the firmware will assume that
the motor spindle has locked. When this occurs, the firmware will stop the
motor by turning off Q1 and Q2. Further interrupts are masked to avoid mis-
triggering from external noise. Q3 is turned on to alarm the buzzer. The
firmware then jumps into an idle loop until the system is reset by a power off
and on sequence (power-on reset).
The over-temperature value is set to around 60°C in the firmware. The alarm
will sound when this temperature is reached, but the motor keeps running, with
the speed defined by the mapping table. The over-temperature value can be
changed by the Thermal_Limit variable in the firmware.
On the reference demo, a surface-mount transducer (SMT) is used for
sounding the alarms. The SMT needs special tone generation method to let the
transducer sound and under the operating specification in both Q3 and BUZ1.
The tone generation is done by the output compare and overflow features in
timer module. It generates two different tones to indicate the over-temperature
and motor-lock alarms. The tone frequencies can be changed by
PWM_Period_H:L. Because of the SMT rating, the driving PWM duty cycle
must be less than 15%.
Freescale Semiconductor, Inc.
BLDC Fan Control using the MC68HC908QT2
For More Information On This Product,
Temperature and Speed Mapping (Thermal Speed Profile)
Go to: www.freescale.com
PART 3: SOFTWARE DESIGN
AN2687/D
11