MCP9700-ESLASHTO datasheet(8/18 Pages) MICROCHIP

8 / 18 page

MCP9700/9700A and MCP9701/9701A

DS21942C-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 MCP9700/9700A 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

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.

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

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:

MCP9700/9700A 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.

VOUT

TC TA V0°C

•

Where:

TA = Ambient Temperature

VOUT = Sensor Output Voltage

V0°C = Sensor Output Voltage at 0°C

TC = 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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