LM20

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SNIS106Q – DECEMBER 1999 – REVISED JANUARY 2015

Figure 4. LM20 With Filter for Noisy Environment and Capacitive Loading Greater Than 300 pF

NOTE

Either placement of resistor, as shown in Figure 3 and Figure 4, is just as effective.

8.1.2 LM20 DSBGA Light Sensitivity

Exposing the LM20 DSBGA package to bright sunlight may cause the output reading of the LM20 to drop by

1.5 V. In a normal office environment of fluorescent lighting the output voltage is minimally affected (less than a

millivolt drop). In either case, TI recommends that the LM20 DSBGA be placed inside an enclosure of some type

that minimizes its light exposure. Most chassis provide more than ample protection. The LM20 does not sustain

permanent damage from light exposure. Removing the light source will cause the output voltage of the LM20 to

recover to the proper value.

8.2 Typical Applications

8.2.1 Full-Range Celsius (Centigrade) Temperature Sensor (

−55°C to 130°C) Operating from a Single Li-

Ion Battery Cell

The LM20 has a very low supply current and a wide supply range; therefore, it can easily be driven by a battery

as shown in Figure 5.

Figure 5. Full-Range Celsius (Centigrade) Temperature Sensor (

−55°C To 130°C) Operating from a Single

Li-Ion Battery Cell

8.2.1.1 Design Requirements

Because the LM20 is a simple temperature sensor that provides an analog output, design requirements related

to layout are more important than electrical requirements. Refer to the Layout section for a detailed description.

8.2.1.2 Detailed Design Procedure

The LM20 transfer function can be described in different ways with varying levels of precision. A simple linear

transfer function with good accuracy near 25°C is:

(4)

Over the full operating temperature range of

−55°C to 130°C, best accuracy can be obtained by using the

parabolic transfer function.

(5)

Solving Equation 5 for T:

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