MCP9700 datasheet(9/18 Pages) MICROCHIP

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DS21942A-page 9

MCP9700/01

4.0

APPLICATIONS INFORMATION

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 relative change in accuracy from the calibration

temperature is due to the output non-linearity from the

first-order equation, specified in Equation 3-1. The

accuracy can be further improved by compensating for

the output non-linearity.

For higher accuracy, the sensor output transfer function

is also derived using a second-order equation as

shown in Equation 4-1. The equation describes the

output non-linearity. This equation is not used to

characterize the part as specified in the DC Electrical

Characteristics table; however, it provides better

accuracy.

EQUATION 4-1:

SECOND-ORDER

TRANSFER FUNCTION

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 shutdown 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 will be

necessary.

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 dig-

ital lines in close proximity to the sensor.

-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

Where:

= Ambient Temperature

VOUT = Sensor Output Voltage

V0°C = Sensor Output Voltage at 0°C

(refer to Figure 2-7 and 2-10)

TC1

= Temperature Coefficient

(refer to Figure 2-8 and 2-11)

TC2

= Temperature Coefficient

MCP9700 1.4 µV/°C2 (typ.)

MCP9701 2.7 µV/°C2 (typ.)

(refer to Figure 2-9 and 2-12)

VOUT = TC2 (TA + 10°C)(125°C – TA) + TC1 TA + V0°C

= -TC2 TA

2 + (T

C1 + 115 TC2)TA + 1250 TC2 + V0°C

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