LM45

SNIS117C – AUGUST 1999 – REVISED FEBRUARY 2013

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PRINTED CIRCUIT BOARD

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

Figure 15. ½

″ Square Printed Circuit Board with 2 oz. Foil or Similar

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 intermediate 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 desired 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 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 LM45 or its connections.

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

Typical Applications

CAPACITIVE LOADS

Like most micropower circuits, the LM45 has a limited ability to drive heavy capacitive loads. The LM45 by itself

is able to drive 500 pF without special precautions. If heavier loads are anticipated, it is easy to isolate or

decouple the load with a resistor; see Figure 16. Or you can improve the tolerance of capacitance with a series

R-C damper from output to ground; see Figure 17.

Any linear circuit connected to wires in a hostile environment can have its performance affected adversely by

intense electromagnetic sources such as relays, radio transmitters, motors with arcing brushes, SCR transients,

etc, as its wiring can act as a receiving antenna and its internal junctions can act as rectifiers. For best results in

μF from output to ground, as shown in Figure 17, are often useful.

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