AN2687 Freescale Semiconductor / Motorola, AN2687 Datasheet - Page 8

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

AN2687/D
Alarm Circuit
Motor-Lock Protection
In-Circuit-
Programming
8
In the evaluation demo, a piezoelectric buzzer is connected to the MCU pin-2.
In the reference demo, a surface-mount transducer is used (a PWM signal is
required to produce the audio tone). Since the operating voltage of the
transducer is 2.5V to 4.5V, a circuit is used to create the tones under a 12V
input supply. In the reference demo, difference tones are used to indicate
motor-lock and over-temperature alarms.
For the motor-lock alarm, a 350Hz, 15% duty cycle tone is used. This lets the
SMT transducer to turn on for around 15% of the time, and the current is under
5.3mA. We need to consider the rating in both the transducer and the SMT
transistor.
For the over-temperature alarm, a 770Hz, 13% duty cycle tone is used. This
lets the SMT transducer turn on for around 13% of the time, and the current is
under 2.6mA.
If the motor spindle is jammed, there will be no signal from the Hall effect
sensor. When the software detects a no Hall signal state for more than 100ms,
it assumes that the motor is jammed or locked. The MCU stops the motor
immediately to avoid over-current. The motor-lock alarm is then sounded.
An in-circuit programming feature is designed into the evaluation demo board.
The board provides two ICP interfaces: a standard 16-pin MON08 interface on
P5 and a 5-pin ICP interface.
For the standard 16-pin MON08 interface, it can be connected to a programmer
which provides the standard MON08 interface such as Cyclone, Multilink, or In-
Circuit Simulator (ICS).
Freescale Semiconductor, Inc.
Figure 8. BLDC Fan Evaluation Demo Board, ICP Connection with
BLDC Fan Control using the MC68HC908QT2
For More Information On This Product,
Go to: www.freescale.com
Cyclone (MON08 Interface)
MOTOROLA