10.1 Layout Guidelines

The LM50 and LM50-Q1 can be applied easily 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 0.2°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 LM50 or LM50-Q1 die would be at an intermediate temperature between the surface temperature and the air temperature.

To ensure good thermal conductivity the backside of the LM50 and LM50-Q1 die is directly attached to the GND pin. The lands and traces to the device 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 LM50 or LM50-Q1's temperature to deviate from the desired temperature.

Alternatively, the LM50 and LM50-Q1 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 LM50 and LM50-Q1 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 ensure that moisture cannot corrode the device or its connections.

10.2 Layout Example

Figure 19. PCB Layout

1/2 in., square printed-circuit board with 2-oz foil or similar

Figure 20. Printed-Circuit Board Used for Heat Sink to Generate Thermal Response Curves

10.3 Thermal Considerations

Table 2 summarizes the thermal resistance of the LM50 and LM50-Q1 for different conditions.