LM135, LM135A, LM235, LM235A, LM335, LM335A

SNIS160E – MAY 1999 – REVISED FEBRUARY 2015

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8 Application and Implementation

NOTE

Information in the following applications sections is not part of the TI component

specification, and TI does not warrant its accuracy or completeness. TI’s customers are

responsible for determining suitability of components for their purposes. Customers should

validate and test their design implementation to confirm system functionality.

8.1 Application Information

To insure good sensing accuracy, several precautions must be taken. Like any temperature-sensing device, self-

heating can reduce accuracy. The LM135 should be operated at the lowest current suitable for the application.

Sufficient current, of course, must be available to drive both the sensor and the calibration pot at the maximum

operating temperature as well as any external loads.

If the sensor is used in an ambient where the thermal resistance is constant, self-heating errors can be calibrated

out. This is possible if the device is run with a temperature-stable current. Heating will then be proportional to

zener voltage and therefore temperature. This makes the self-heating error proportional to absolute temperature

the same as scale factor errors.

8.2 Typical Application

Figure 13. Basic Temperature Sensor

8.2.1 Design Requirements

Table 1. Design Parameters

PARAMETER

EXAMPLE VALUE

Accuracy at 25°C

±1°C

Accuracy from –55 °C to 150 °C

±2.7°C

Forward Current

1 mA

Temperature Slope

10m V/K

8.2.2 Detailed Design Procedure

For optimum accuracy, R1 is picked such that 1 mA flows through the sensor. Additional error can be introduced

by varying load currents or varying supply voltage. The influence of these currents on the minimum and

maximum reverse current flowing through the LM135 should be calculated and be maintained in the range of 0.4

mA to 5 mA. Minimizing the current variation through the LM135 will provide for the best accuracy. The

Operating Output Voltage Change with Current specification can be used to calculate the additional error which

could be up to 1 K maximum from the LM135A, for example.

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