LM34

SNIS161D – MARCH 2000 – REVISED JANUARY 2016

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9 Power Supply Recommendations

It may be necessary to add a bypass filter capacitor in noisy environments, as shown in as shown in Figure 13.

10 Layout

10.1 Layout Guidelines

The LM34 device can be easily applied in the same way as other integrated-circuit temperature sensors. The

device can be glued or cemented to a surface and its temperature will be within about 0.02°F 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 LM34

die would be at an intermediate temperature between the surface temperature and the air temperature. This is

especially true for the TO-92 plastic package, where the copper leads are the principal thermal path to carry heat

into the device, so its temperature might be closer to the air temperature than to the surface temperature.

To minimize this problem, be sure that the wiring to the LM34, as it leaves the device, is held at the same

temperature as the surface of interest. The easiest way to do this is to cover up these wires with a bead of

epoxy, which will insure that the leads and wires are all at the same temperature as the surface, and that the die

temperature of the LM34 device will not be affected by the air temperature.

The TO-46 metal package can be soldered to a metal surface or pipe without damage. In the case where

soldering is used, the V

− terminal of the circuit will be grounded to that metal. Alternatively, the LM34 device 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 LM34 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 a conformal coating and epoxy paints or

dips are often used to insure that moisture cannot corrode the LM34 or its connections.

These devices are sometimes soldered to a small, light-weight heat fin to decrease the thermal time constant

and speed up the response in slowly-moving air. On the other hand, a small thermal mass may be added to the

sensor to give the steadiest reading despite small deviations in the air temperature.

Table 2. Temperature Rise of LM34 Due to Self-Heating (Thermal Resistance)

TO-46,

TO-92,

TO-46

TO-92,

SO-8

SO-8

CONDITIONS

SMALL HEAT

SMALL HEAT

NO HEAT SINK

NO HEAT SINK

NO HEAT SINK

SMALL HEAT Fin

Fin(1)

Fin(2)

Still air

720°F/W

180°F/W

324°F/W

252°F/W

400°F/W

200°F/W

Moving air

180°F/W

72°F/W

162°F/W

126°F/W

190°F/W

160°F/W

Still oil

180°F/W

72°F/W

162°F/W

126°F/W

—

—

Stirred oil

90°F/W

54°F/W

81°F/W

72°F/W

—

—

(Clamped to metal,

(43°F/W )

—

—

(95°F/W )

infinite heart sink)

(1)

Wakefield type 201 or 1-inch disc of 0.020-inch sheet brass, soldered to case, or similar.

(2)

TO-92 and SO-8 packages glued and leads soldered to 1-inch square of 1/16 inches printed circuit board with 2 oz copper foil, or

similar.

16

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