MCP9700 datasheet(8/18 Pages) MICROCHIP

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MCP9700/01

DS21942B-page 8

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

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.

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

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).

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 200

Ω 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.

OUT

°C

•

Where:

TA = Ambient Temperature

VOUT = Sensor Output Voltage

V0°C = Sensor Output Voltage at 0°C

TC1 = Temperature Coefficient

-3.0

-2.0

-1.0

0.0

1.0

2.0

3.0

-50

-25

100

125

TA (°C)

VDD= 3.3V

10 Samples

-4.0

-2.0

0.0

2.0

4.0

6.0

-50

-25

100

125

Temperature (°C)

Average

Spec. Limits

100 Samples

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