circuit board as shown in

Figure 2 was used to generate the following thermal curves. (Continued)

1.0 Mounting

The LM61 can be applied easily in the same way as other

integrated-circuit temperature sensors. It can be glued or ce-

mented to a surface. The temperature that the LM61 is sens-

ing will be within about +0.2˚C of the surface temperature

that LM61’s leads are attached to.

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 ac-

tual temperature measured would be at an intermediate tem-

perature between the surface temperature and the air tem-

perature.

To ensure good thermal conductivity the backside of the

LM61 die is directly attached to the GND pin. The lands and

traces to the LM61 will, of course, be part of the printed cir-

cuit board, which is the object whose temperature is being

measured.

Alternatively, the LM61 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 LM61 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 en-

sure that moisture cannot corrode the LM61 or its connec-

tions.

The thermal resistance junction to ambient (

θ

rameter used to calculate the rise of a device junction tem-

perature due to its power dissipation. For the LM61 the

equation used to calculate the rise in the die temperature is

as follows:

T

where I

the output. Since the LM61’s junction temperature is the ac-

tual temperature being measured care should be taken to

minimize the load current that the LM61 is required to drive.

The table shown in

Figure 3 summarizes the rise in die tem-

perature of the LM61 without any loading with a 3.3V supply,

and the thermal resistance for different conditions.

Supply Voltage

vs Supply Current

DS012897-12

Start-Up Response

DS012897-22

DS012897-14

FIGURE 2. Printed Circuit Board Used

for Heat Sink to Generate All Curves.

1

with 2 oz. Copper Foil or Similar.

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