Application information

LM135-LM235-LM335

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Application information

There is an easy method of calibrating the device for higher accuracies (see Typical

applications).

The single point calibration works because the output of the LM135, LM235, LM335 is

proportional to the absolute temperature with the extrapolated output of sensor going to 0V

at 0°K (-273.15°C). Errors in output voltage versus temperature are only slope. Thus a

calibration of the slope at one temperature corrects errors at all temperatures.

The circuit output (calibrated or not) is given by the equation:

where T is the unknown temperature and To is the reference temperature (in °K).

Nominally, the output is calibrated at 10mV/°K.

Precautions should be taken to ensure good sensing accuracy. As in the case of all

temperatures sensors, self-heating can decrease accuracy. The LM135, LM235, and LM335

should operate with a low current but sufficient to drive the sensor and its calibration circuit

to their maximum operating temperature.

If the sensor is used in surroundings where the thermal resistance is constant, the errors

due to self-heating can be externally calibrated. This is possible if the circuit is biased with a

temperature stable current. Heating will then be proportional to Zener voltage and therefore

temperature. In this way, the error due to self-heating is proportional to the absolute

temperature as scale factor errors.

Typical applications

T

To

-------

Figure 13.

Basic temperature sensor

Figure 14.

Wide operating supply