MCP9844 datasheet(33/44 Pages) MICROCHIP

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 2013 Microchip Technology Inc.

DS20005192A-page 33

MCP9844

6.0

APPLICATIONS INFORMATION

6.1

Layout Considerations

The MCP9844 device 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

MCP9844 SDA, SCLK 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 MCP9844. A

temperature 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 T is 0.58°C for the TDFN-8

package.

FIGURE 6-1:

TDFN Package Layout.

T



OL_Event

OL_SDA





Where:

T =TJ - TA

TJ = Junction Temperature

TA = Ambient Temperature

JA = Package Thermal Resistance

VOL_Event, SDA = Event and SDA Output VOL

(0.4 Vmax)

IOL_Event, SDA = Event and SDA Output IOL

(3 mAmax and 20 mAmax,

respectively)

GND

VDD

Event

SCL

SDA

EP9

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