Datasheet

MCP9700/9700A and MCP9701/9701A
DS20001942G-page 8  2005-2016 Microchip Technology Inc.
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
output 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
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 of devices
measures temperature with higher accuracy.
FIGURE 4-2: Relative Accuracy to +25°C
vs. Temperature.
The change in accuracy from the calibration tempera-
ture is due to the output nonlinearity from the first-order
equation, as specified in Equation 4-2. The accuracy
can be further improved by compensating for the output
nonlinearity.
For higher accuracy using a sensor compensation
technique, refer to Application Note AN1001,
“IC Temperature Sensor Accuracy Compensation with
a PIC
®
Microcontroller” (DS00001001). The application
note shows that if the device 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).
FIGURE 4-3: MCP9700/9700A Calibrated
Sensor Accuracy.
The compensation technique provides a linear
temperature reading. The application note includes
compensation firmware so that a look-up table can be
generated to compensate for the sensor error.
Where:
T
A
= Ambient Temperature
V
OUT
= Sensor Output Voltage
V
0°C
= Sensor Output Voltage at 0°C
(see DC Electrical Characteristics
table)
T
C
= Temperature Coefficient
(see DC Electrical Characteristics
table)
V
OUT
T
C
T
A
 V
0°C
+=
V
DD
GND
GND
ANI
V
DD
GND
V
OUT
MCP9700
PIC
®
MCU
-3.0
-2.0
-1.0
0.0
1.0
2.0
3.0
-50 -25 0 25 50 75 100 125
T
A
(°C)
Accuracy (°C)
V
DD
= 3.3V
10 Samples
-4.0
-2.0
0.0
2.0
4.0
6.0
-50 -25 0 25 50 75 100 125
Temperature (°C)
Accuracy (°C)
+ s
Average
- s
Spec. Limits
100 Samples