LM74-3EVAL National Semiconductor, LM74-3EVAL Datasheet - Page 12

• Manufacturer Part Number: LM74-3EVAL
• Manufacturer: National Semiconductor

Specifications of LM74-3EVAL

• Lead Free Status / Rohs Status: Not Compliant

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3.0 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 SO-8 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
4.0 Typical Applications
FIGURE 8. Temperature monitor using Intel 196 processor
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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.
3.1 micro SMD LIGHT SENSITIVITY
The LM74 in the micro SMD package should not be exposed
to ultraviolet light. The micro SMD package does not com-
pletely encapsulate the LM74 die in epoxy. Exposing the
LM74 micro SMD package to bright sunlight will not imme-
diatly cause a change in the output reading. Our experi-
ments show that directly exposing the circuit side (bump
side) of the die to high intensity (≥ 1mW/cm
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 coeffi-
cients, 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.
10090920
2
) ultraviolet light,