LM74

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SNIS107K – MAY 2000 – REVISED MARCH 2013

Serial Bus Timing Diagrams

Figure 14. a) Reading Continuous Conversion - Single Eight-Bit Frame

Figure 15. b) Reading Continuous Conversion - Two Eight-Bit Frames

Figure 16. c) Writing Shutdown Control

Application Hints

To get the expected results when measuring temperature with an integrated circuit temperature sensor like the

LM74, it is important to understand that the sensor measures its own die temperature. For the LM74, the best

thermal path between the die and the outside world is through the LM74's pins. In the SOIC package all the pins

on the LM74 will have an equal effect on the die temperature. Because the pins represent a good thermal path to

the LM74 die, the LM74 will provide an accurate measurement of the temperature of the printed circuit board on

which it is mounted. There is a less efficient thermal path between the plastic package and the LM74 die. If the

ambient air temperature is significantly different from the printed circuit board temperature, it will have a small

effect on the measured temperature.

In probe-type applications, the LM74 can be mounted inside a sealed-end metal tube, and can then be dipped

into a bath or screwed into a threaded hole in a tank. As with any IC, the LM74 and accompanying wiring and

circuits must be kept insulated and dry, to avoid leakage and corrosion. This is especially true if the circuit may

operate at cold temperatures where condensation can occur. Printed-circuit coatings and varnishes such as

Humiseal and epoxy paints or dips are often used to insure that moisture cannot corrode the LM74 or its

connections.

DSBGA Light Sensitivity

The LM74 in the DSBGA package should not be exposed to ultraviolet light. The DSBGA package does not

completely encapsulate the LM74 die in epoxy. Exposing the LM74 DSBGA package to bright sunlight will not

immediatly cause a change in the output reading. Our experiments show that directly exposing the circuit side

(bump side) of the die to high intensity (

≥ 1mW/cm2) ultraviolet light, centered at a wavelength of 254nm, for

greater than 20 minutes will deprogram the EEPROM cells in the LM74. Since the EEPROM is used for storing

calibration coefficients, the LM74 will function but the temperature accuracy will no longer be as specified. Light

can penetrate through the side of the package as well, so exposure to ultra violet radiation is not recommended

even after mounting.

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