.125 R2

+

R2

A2

A1

nR1

i

8.8 mV/°C

nR1

Q1

Q2

10E

E

LM35

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SNIS159F – AUGUST 1999 – REVISED JANUARY 2016

7 Detailed Description

7.1 Overview

The LM35-series devices are precision integrated-circuit temperature sensors, with an output voltage linearly

proportional to the Centigrade temperature. The LM35 device has an advantage over linear temperature sensors

calibrated in Kelvin, as the user is not required to subtract a large constant voltage from the output to obtain

convenient Centigrade scaling. The LM35 device does not require any external calibration or trimming to provide

typical accuracies of ± ¼ °C at room temperature and ± ¾ °C over a full

−55°C to 150°C temperature range.

Lower cost is assured by trimming and calibration at the wafer level. The low output impedance, linear output,

and precise inherent calibration of the LM35 device makes interfacing to readout or control circuitry especially

easy. The device is used with single power supplies, or with plus and minus supplies. As the LM35 device draws

only 60

μA from the supply, it has very low self-heating of less than 0.1°C in still air. The LM35 device is rated to

operate over a

−55°C to 150°C temperature range, while the LM35C device is rated for a −40°C to 110°C range

(

−10° with improved accuracy). The temperature-sensing element is comprised of a delta-V BE architecture.

The temperature-sensing element is then buffered by an amplifier and provided to the VOUT pin. The amplifier

has a simple class A output stage with typical 0.5-

Ω output impedance as shown in the Functional Block

Diagram. Therefore the LM35 can only source current and it's sinking capability is limited to 1

μA.

7.2 Functional Block Diagram

7.3 Feature Description

7.3.1 LM35 Transfer Function

The accuracy specifications of the LM35 are given with respect to a simple linear transfer function:

where

•

•

T is the temperature in °C

(1)

7.4 Device Functional Modes

The only functional mode of the LM35 is that it has an analog output directly proportional to temperature.

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