MCP9700-E/LT(2005) 查看數據表（PDF） - Microchip Technology
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MCP9700-E/LT Datasheet PDF : 18 Pages
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MCP9700/01
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 125°C. The change
in voltage is scaled to a temperature coefficient of
10.0 mV/°C (typ.) for the MCP9700 and 19.5 mV/°C
(typ.) for the MCP9701. The output voltage at 0°C is
also scaled to 500 mV (typ.) and 400 mV (typ.) for the
MCP9700 and MCP9701, respectively. This linear
scale is described in the first-order transfer function
shown in Equation 4-1.
EQUATION 4-1: SENSOR TRANSFER
FUNCTION
VOUT = TC1 • TA + V0°C
Where:
TA = Ambient Temperature
VOUT = Sensor Output Voltage
V0°C = Sensor Output Voltage at 0°C
TC1 = Temperature Coefficient
4.1 Improving Accuracy
The MCP9700/01 accuracy can be improved by
performing a system calibration at a specific tempera-
ture. For example, calibrating the system at +25°C
ambient improves the measurement accuracy to a
±0.5°C (typ.) from 0°C to +70°C, as shown in
Figure 4-1. 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 4-1:
Relative Accuracy to +25°C
vs. Temperature.
The change in accuracy from the calibration tempera-
ture 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 (typ.) accuracy over the
operating temperature (Figure 4-2).
6.0
4.0
Spec. Limits
2.0
100 Samples
0.0
-2.0
-4.0
-50 -25
+ V
Average
- V
0 25 50 75 100 125
Temperature (°C)
FIGURE 4-2:
MCP9700 Calibrated
Sensor Accuracy.
The compensation technique provides a linear temper-
ature reading. A firmware look-up table can be
generated to compensate for the sensor error.
4.2 Shutdown Using Microcontroller
I/O Pin
The MCP9700/01 low operating current of 6 µA (typ.)
makes it ideal for battery-powered applications.
However, for applications that require tighter current
budget, this device can be powered using a microcon-
troller Input/Output (I/O) pin. The I/O pin can be toggled
to shut down the device. In such applications, the
microcontroller internal digital switching noise is
emitted to the MCP9700/01 as power supply noise.
This switching noise compromises measurement
accuracy. Therefore, a decoupling capacitor and series
resistor will be necessary to filter out the system noise.
4.3 Layout Considerations
The MCP9700/01 does not require any additional
components to operate. However, it is recommended
that a decoupling capacitor of 0.1 µF to 1 µF be used
between the VDD and GND pins. In high-noise applica-
tions, connect the power supply voltage to the VDD pin
using a 200Ω resistor with a 1 µF decoupling capacitor.
A high-frequency ceramic capacitor is recommended. It
is necessary for the capacitor to be located as close as
possible to the VDD and GND pins in order to provide
effective noise protection. In addition, avoid tracing
digital lines in close proximity to the sensor.
DS21942B-page 8
© 2005 Microchip Technology Inc.
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