LM135, LM135A, LM235, LM235A, LM335, LM335A

SNIS160E – MAY 1999 – REVISED FEBRUARY 2015

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7 Detailed Description

7.1 Overview

Applications for the LM135 include almost any type of temperature sensing over a

−55°C to 150°C temperature

range. The low impedance and linear output make interfacing to readout or control circuitry especially easy.

The LM135 operates over a

−55°C to 150°C temperature range while the LM235 operates over a −40°C to

125°C temperature range. The LM335 operates from

−40°C to 100°C.

Operating as a 2-terminal zener, the LM135 has a breakdown voltage directly proportional to absolute

temperature at 10 mV/°K. With less than 1-

Ω dynamic impedance, the device operates over a current range of

400

μA to 5 mA with virtually no change in performance. When calibrated at 25°C, the LM135 has typically less

than 1°C error over a 100°C temperature range. Unlike other sensors, the LM135 has a linear output.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 Temperature Calibration Using ADJ Pin

Included on the LM135 chip is an easy method of calibrating the device for higher accuracies. A pot connected

across the LM135 with the arm tied to the adjustment terminal (as shown in Figure 12) allows a 1-point

calibration of the sensor that corrects for inaccuracy over the full temperature range.

This single point calibration works because the output of the LM135 is proportional to absolute temperature with

the extrapolated output of sensor going to 0-V output at 0 K (

−273.15°C). Errors in output voltage versus

temperature are only slope (or scale factor) errors so a slope calibration at one temperature corrects at all

temperatures.

The output of the device (calibrated or uncalibrated) can be expressed as:

where

8

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