MCP9700-ESLASHTO datasheet(11/24 Pages) MICROCHIP

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DS21942E-page 11

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 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 out-

put 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 measures

temperature with higher accuracy.

FIGURE 4-2:

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

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 (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. A firmware look-up table can be

generated to compensate for the sensor error.

VOUT

TC TA V0°C

•

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)

VDD

VSS

GND

ANI

VDD

VSS

VOUT

MCP9700

PICmicro®

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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