MCP9700-ESLASHTO datasheet(8/22 Pages) MICROCHIP

8 / 22 page

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

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

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:

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)

OUT



0°C

VDD

GND

ANI

VDD

GND

VOUT

MCP9700

PIC®

MCU

-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)

+ s

Average

- s

Spec. Limits

100 Samples

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