MCP9700A(2006) 查看數據表（PDF） - Microchip Technology
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MCP9700A Datasheet PDF : 18 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 125°C. The change
in voltage is scaled to a temperature coefficient of
10.0 mV/°C (typ.) for the MCP9700/9700A and
19.5 mV/°C (typ.) for the MCP9701/9701A. The output
voltage at 0°C is also scaled to 500 mV (typ.) and
400 mV (typ.) for the MCP9700/9700A and
MCP9701/9701A, respectively. This linear scale is
described in the first-order transfer function shown in
Equation 4-1.
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
TC = Temperature Coefficient
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 (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
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 (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:
MCP9700/9700A 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.
4.2 Shutdown Using Microcontroller
I/O Pin
The MCP9700/9700A and MCP9701/9701A family of
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 microcontroller
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 MCP9700/9700A and MCP9701/9701A
as power supply noise. This switching noise compro-
mises measurement accuracy. Therefore, a decoupling
capacitor and series resistor will be necessary to filter
out the system noise.
4.3 Layout Considerations
The MCP9700/9700A and MCP9701/9701A family
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 applications, 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.
DS21942C-page 8
© 2006 Microchip Technology Inc.
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