LM74CIMX-3 National Semiconductor, LM74CIMX-3 Datasheet - Page 12

• Manufacturer Part Number: LM74CIMX-3
• Description: IC TEMP SENSOR DGTL 8-SOIC
• Manufacturer: National Semiconductor

Specifications of LM74CIMX-3

• Function: Temp Monitoring System (Sensor)
• Topology: ADC (Sigma Delta), Register Bank
• Sensor Type: Internal
• Sensing Temperature: -55°C ~ 150°C
• Output Type: MICROWIRE™, SPI™
• Output Alarm: No
• Output Fan: No
• Voltage - Supply: 3 V ~ 5.5 V
• Operating Temperature: -55°C ~ 150°C
• Mounting Type: Surface Mount
• Package / Case: 8-SOIC (0.154", 3.90mm Width)
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Other names: LM74CIMX-3TR

www.national.com
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 cir-
cuit 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 in-
sulated and dry, to avoid leakage and corrosion. This is
4.0 Typical Applications
FIGURE 8. Temperature monitor using Intel 196 processor
12
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 of-
ten 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 immedi-
atly cause a change in the output reading. Our experiments
show that directly exposing the circuit side (bump side) of the
die to high intensity (
a wavelength of 254nm, for greater than 20 minutes will de-
program the EEPROM cells in the LM74. Since the EEPROM
is used for storing calibration coefficients, the LM74 will func-
tion but the temperature accuracy will no longer be as speci-
fied. Light can penetrate through the side of the package as
well, so exposure to ultra violet radiation is not recommended
even after mounting.
≥
1mW/cm
2
10090920
) ultraviolet light, centered at