Printed Circuit Board

Applications

The LM45 can be applied easily in the same way as other

integrated-circuit temperature sensors. It can be glued or

cemented to a surface and its temperature will be within

about 0.2˚C of the surface temperature.

This presumes that the ambient air temperature is almost the

same as the surface temperature; if the air temperature were

much higher or lower than the surface temperature, the

actual temperature of the LM45 die would be at an interme-

diate temperature between the surface temperature and the

air temperature.

To ensure good thermal conductivity the backside of the

LM45 die is directly attached to the GND pin. The lands and

traces to the LM45 will, of course, be part of the printed

circuit board, which is the object whose temperature is being

measured. These printed circuit board lands and traces will

not cause the LM45s temperature to deviate from the de-

sired temperature.

Alternatively, the LM45 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 LM45 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 conden-

sation 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 LM45 or its connec-

tions.

Temperature Rise of LM45 Due to Self-Heating (Thermal

Resistance)

SOT-23

SOT-23

no heat sink*

small heat fin**

Still air

450˚C/W

260˚C/W

Moving air

180˚C/W

* Part soldered to 30 gauge wire.

attached as shown in Figure 3.

01175423

FIGURE 3. Printed Circuit Board Used for Heat Sink to Generate All Curves.

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