MCP9808 datasheet(35/52 Pages) MICROCHIP

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DS25095A-page 35

MCP9808

6.0

APPLICATIONS INFORMATION

6.1

Layout Considerations

The MCP9808 does not require any additional

components besides the master controller in order to

measure temperature. However, it is recommended

that a decoupling capacitor of 0.1 µF to 1 µF be used

between the VDD and GND pins. A high-frequency

ceramic capacitor is recommended. It is necessary for

the capacitor to be located as close as possible to the

power and ground pins of the device in order to provide

effective noise protection.

In addition, good PCB layout is key for better thermal

conduction from the PCB temperature to the sensor

die. For good temperature sensitivity, add a ground

layer under the device pins, as shown in Figure 6-1.

6.2

Thermal Considerations

A potential for self-heating errors can exist if the

MCP9808 SDA, SCL and Event lines are heavily

loaded with pull-ups (high current). Typically, the

self-heating error is negligible because of the relatively

small current consumption of the MCP9808. A temper-

ature accuracy error of approximately +0.5°C could

result from self-heating if the communication pins

sink/source the maximum current specified.

For example, if the event output is loaded to maximum

IOL, Equation 6-1 can be used to determine the effect

of self-heating.

EQUATION 6-1:

EFFECT OF

SELF-HEATING

At room temperature (TA =+25°C) with maximum

IDD = 500 µA and VDD = 3.6V, the self-heating due to

power dissipation TΔ is +0.2°C for the DFN-8 package

and +0.5°C for the TSSOP-8 package.

FIGURE 6-1:

DFN Package Layout (Top View).

TΔ

OL_Alert

OL_SDA

•

()

Where:

TΔ =TJ – TA

TJ = Junction Temperature

TA = Ambient Temperature

JA = Package Thermal Resistance

VOL_Alert, SDA = Alert and SDA Output VOL

(0.4 Vmax)

IOL_Alert, SDA = Alert and SDA Output IOL

(3 mAmax)

SDA

SCL

Alert

GND

VDD

EP9

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