LM50, LM50-Q1

SNIS118E – JULY 1999 – REVISED SEPTEMBER 2013

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Alternatively, the LM50/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/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 LM50/LM50-Q1 or

its connections.

Table 1. Temperature Rise of LM50/LM50-Q1 Due to Self-Heating

(Thermal Resistance,

SOT-23

SOT-23

Still air

450°C/W

260°C/W

Moving air

180°C/W

(1)

Part soldered to 30 gauge wire.

(2)

Heat sink used is ½

″ square printed circuit board with 2 oz. foil with part attached as shown in Figure 14.

Capacitive Loads

Figure 15. LM50/LM50-Q1 No Decoupling Required

for Capacitive Load

Figure 16. LM50C/LM50-Q1 with Filter for Noisy Environment

The LM50/LM50-Q1 handles capacitive loading very well. Without any special precautions, the LM50/LM50-Q1

can drive any capacitive load. The LM50/LM50-Q1 has a nominal 2 k

Ω output impedance (as can be seen in

Figure 17). The temperature coefficient of the output resistors is around 1300 ppm/°C. Taking into account this

temperature coefficient and the initial tolerance of the resistors the output impedance of the LM50/LM50-Q1 will

not exceed 4 k

Ω. In an extremely noisy environment it may be necessary to add some filtering to minimize noise

pickup. It is recommended that 0.1

in Figure 16. In a noisy environment it may be necessary to add a capacitor from the output to ground. A 1

μF

output capacitor with the 4 k

Ω output impedance will form a 40 Hz lowpass filter. Since the thermal time constant

of the LM50/LM50-Q1 is much slower than the 25 ms time constant formed by the RC, the overall response time

of the LM50/LM50-Q1 will not be significantly affected. For much larger capacitors this additional time lag will

increase the overall response time of the LM50/LM50-Q1.

6

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