TC72 datasheet(13/24 Pages) MICROCHIP

13 / 24 page

 2002 Microchip Technology Inc.

DS21743A-page 13

TC72

5.0

APPLICATIONS INFORMATION

The TC72 does not require any additional components

in order to measure temperature; however, it is recom-

mended that a decoupling capacitor of 0.1mF to 1mF

be provided between the VDD and GND pins. Although

the current consumption of the TC72 is modest

(250 mA, typical), the TC72 contains an on chip data

acquisition with internal digital switching circuitry. Thus,

it is considered good design practice to use an external

decoupling capacitor with the sensor. A high frequency

ceramic capacitor should be used and be located as

close as possible to the IC power pins in order to

provide effective noise protection to the TC72.

The TC72 measures temperature by monitoring the

voltage of a diode located on the IC die. The IC pins of

the TC72 provide a low impedance thermal path

between the die and the PCB, allowing the TC72 to

effectively monitor the temperature of the PCB board.

The thermal path between the ambient air is not as effi-

cient because the plastic IC housing package functions

as a thermal insulator. Thus the ambient air tempera-

ture (assuming that a large temperature gradient exists

between the air and PCB) has only a small effect on the

temperature measured by the TC72.

Note that the exposed metal center pad on the bottom

of the DFN package is connected to the silicon sub-

strate. The center pad should be connected to either

the PCB ground plane or treated as a “No Connect” pin.

The mechanical dimensions of the center pad are given

in Section 6.0, “Packaging Information”, of this

datasheet.

A potential for self-heating errors can exist if the TC72

SPI communication lines are heavily loaded. Typically,

the self-heating error is negligible because of the rela-

tively small current consumption of the TC72. A tem-

perature accuracy error of approximately 0.5°C will

result from self-heating if the SPI communication pins

sink/source the maximum current specified for the

TC72. Thus to maximize the temperature accuracy, the

output loading of the SPI signals should be minimized.

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