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 02 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 inter-

mediate 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 be-

ing 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 var-

nishes 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 CW

260 CW

Moving air

180 CW

Heat sink used is

square printed circuit board with 2 oz foil with part

attached as shown in

Figure 3

Part soldered to 30 gauge wire

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 4 Or you can improve the tolerance of

capacitance with a series R-C damper from output to

ground see

Figure 5

Any linear circuit connected to wires in a hostile environ-

ment can have its performance affected adversely by in-

tense electromagnetic sources such as relays radio trans-

mitters 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 such cas-

damper such as 75X in series with 02 or 1 mF from output

to ground as shown in

Figure 5 are often useful

TLH11754 – 8

FIGURE 4 LM45 with Decoupling from Capacitive Load

TLH11754 – 9

FIGURE 5 LM45 with R-C Damper

TLH11754 – 12

FIGURE 6 Temperature Sensor

4