TC77 datasheet(12/22 Pages) MICROCHIP

12 / 22 page

TC77

DS20092A-page 12

 2002 Microchip Technology Inc.

5.0

APPLICATION INFORMATION

The TC77 does not require any additional components

in order to measure temperature. However, it is recom-

mended that a decoupling capacitor of 0.1 µF to 1 µF

be provided between the VDD and VSS (Ground) pins (a

high frequency ceramic capacitor should be used). It is

necessary for the capacitor to be located as close as

possible to the integrated circuit (IC) power pins in

order to provide effective noise protection to the TC77.

The TC77 measures temperature by monitoring the

voltage of a diode located on the IC die. A low-imped-

ance thermal path between the die and the printed cir-

cuit board (PCB) is provided by the IC pins of the TC77.

Therefore, the TC77 effectively monitors the tempera-

ture of the PCB board. The thermal path between the

ambient air is not as efficient because the plastic IC

housing package functions as a thermal insulator.

Thus, the ambient air temperature (assuming that a

large temperature gradient exists between the air and

PCB) has only a small effect on the temperature

measured by the TC77.

A potential for self-heating errors can exist if the TC77

SPI communication lines are heavily loaded. Typically,

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

tively small current consumption of the TC77. 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

TC77. Therefore, to maximize the temperature accu-

racy, the output loading of the SPI signals should be

minimized.

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