MCP9700 查看數據表（PDF） - Microchip Technology
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MCP9700 Datasheet PDF : 22 Pages
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MCP9700/9700A and MCP9701/9701A
4.0 APPLICATIONS INFORMATION
The Linear Active Thermistor™ IC uses an internal
diode to measure temperature. The diode electrical
characteristics have a temperature coefficient that
provides a change in voltage based on the relative
ambient temperature from -40°C to 150°C. The change
in voltage is scaled to a temperature coefficient of
10.0 mV/°C (typical) for the MCP9700/9700A and
19.5 mV/°C (typical) for the MCP9701/9701A. The out-
put voltage at 0°C is also scaled to 500 mV (typical)
and 400 mV (typical) for the MCP9700/9700A and
MCP9701/9701A, respectively. This linear scale is
described in the first-order transfer function shown in
Equation 4-1 and Figure 2-16.
EQUATION 4-1: SENSOR TRANSFER
FUNCTION
VOUT = TC • TA + V0°C
Where:
TA = Ambient Temperature
VOUT = Sensor Output Voltage
V0°C = Sensor Output Voltage at 0°C
(See DC Electrical Characteristics
table)
TC = Temperature Coefficient
(See DC Electrical Characteristics
table)
VDD
VDD
MCP9700
VOUT
GND
VSS
ANI PICmicro®
MCU
VSS
FIGURE 4-1:
Typical Application Circuit.
4.1 Improving Accuracy
The MCP9700/9700A and MCP9701/9701A accuracy
can be improved by performing a system calibration at
a specific temperature. For example, calibrating the
system at +25°C ambient improves the measurement
accuracy to a ±0.5°C (typical) from 0°C to +70°C, as
shown in Figure 4-2. Therefore, when measuring
relative temperature change, this family measures
temperature with higher accuracy.
3.0
2.0
1.0
0.0
-1.0
-2.0
-3.0
VDD= 3.3V
10 Samples
-50 -25 0
25 50
TA (°C)
75 100 125
FIGURE 4-2:
Relative Accuracy to +25°C
vs. Temperature.
The change in accuracy from the calibration
temperature is due to the output non-linearity from the
first-order equation, as specified in Equation 4-2. The
accuracy can be further improved by compensating for
the output non-linearity.
For higher accuracy using a sensor compensation
technique, refer to AN1001 “IC Temperature Sensor
Accuracy Compensation with a PICmicro®
Microcontroller” (DS01001). The application note
shows that if the MCP9700 is compensated in addition
to room temperature calibration, the sensor accuracy
can be improved to ±0.5°C (typical) accuracy over the
operating temperature (Figure 4-3).
6.0
4.0
2.0 Spec. Limits
100 Samples
0.0
-2.0
-4.0
-50 -25
+s
Average
-s
0 25 50 75 100 125
Temperature (°C)
FIGURE 4-3:
MCP9700/9700A Calibrated
Sensor Accuracy.
The compensation technique provides a linear
temperature reading. A firmware look-up table can be
generated to compensate for the sensor error.
© 2009 Microchip Technology Inc.
DS21942E-page 11
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