AN1857 Freescale Semiconductor / Motorola, AN1857 Datasheet - Page 24

• Manufacturer Part Number: AN1857
• Description: A 3-Phase ac Induction Motor Control System Based on the MC68HC908MR32
• Manufacturer: Freescale Semiconductor / Motorola

Application Note
Temperature
Sensing
24
It is a good idea to keep track of the temperature of the power module.
The circuit shown in
used to monitor temperature. A silicon diode has a temperature
coefficient of approximately –2.2 mV /degree Centigrade. The forward
bias voltage of a silicon diode is approximately 0.6 volts. Therefore, the
circuit shown in
and decrease at a slope of approximately –8.8 mV/degree Centigrade.
Using this information, it is apparent that the temperature of the power
module can be monitored easily for over- temperature conditions. The
output of this temperature sensing circuit is connected to an analog
optoisolation circuit. From the analog optoisolation circuit’s output, it is
connected to the control board’s Temp_sense input and routed to the
MR32’s A/D (analog-to-digital) converter input.
Freescale Semiconductor, Inc.
For More Information On This Product,
Figure 15. Temperature Sensing Circuit Schematic
Go to: www.freescale.com
BAV99LT1
D13
Figure 15
TEMPERATURE SENSING
Figure 15
will output approximately 2.4 volts at 25 C
BAV99LT1
D14
is a schematic of the temperature circuit
2.21 k – 1%
100 nF
C301
R302
GNDA
+3.3V_A
Temp_sense
MOTOROLA
AN1857