LM35 Precision Temperature Sensor

Overview

The LM35 series is a precision integrated-circuit temperature sensor that provides an output voltage linearly proportional to the Celsius (Centigrade) temperature. Unlike sensors calibrated in Kelvin, the LM35 eliminates the need for subtracting a large constant voltage from its output, offering direct Centigrade scaling. This device is factory-calibrated during wafer-level trimming, ensuring typical accuracies of ±¼°C at room temperature and ±¾°C over the full -55°C to +150°C temperature range without requiring additional calibration or trimming.

The LM35 features low output impedance, excellent linearity, and inherent calibration precision, making it exceptionally easy to interface with readout or control circuitry. It operates from single power supplies (4V to 30V) or dual supplies with minimal current draw (60 µA), resulting in negligible self-heating (less than 0.1°C in still air). These characteristics make the LM35 ideal for a wide range of temperature measurement applications.

Features

• Calibrated directly in Celsius (Centigrade)
• Linear +10.0 mV/°C scale factor
• 0.5°C accuracy guaranteed (at +25°C)
• Rated for full -55°C to +150°C range
• Suitable for remote applications
• Low cost due to wafer-level trimming
• Operates from 4V to 30V
• Less than 60 µA current drain
• Low self-heating: 0.08°C in still air
• Nonlinearity only ±¼°C typical
• Low impedance output: 0.1 Ω for 1 mA load

Applications

The LM35's precision, linear output, and wide operating range make it suitable for numerous temperature sensing applications, including:

• Environmental monitoring systems
• HVAC control systems
• Industrial process control
• Battery management systems
• Medical equipment
• Automotive temperature monitoring
• Consumer electronics thermal protection
• Laboratory instrumentation
• Food processing and storage

Electrical Characteristics

Absolute Maximum Ratings

• Supply Voltage: +35V to -0.2V
• Output Voltage: +6V to -1.0V
• Output Current: 10 mA
• Operating Temperature Range:
  • LM35/LM35A: -55°C to +150°C
  • LM35C/LM35CA: -40°C to +110°C
  • LM35D: 0°C to +100°C
• Storage Temperature Range: -60°C to +180°C

Key Electrical Parameters (TA = +25°C, VS = +5V)

• Scale Factor: +10.0 mV/°C (nominal)
• Accuracy:
  • LM35A: ±0.25°C (at +25°C)
  • LM35: ±0.5°C (at +25°C)
• Nonlinearity: ±0.25°C (typical)
• Output Impedance: 0.1 Ω (for 1 mA load)
• Supply Current: 60 µA (typical)
• Thermal Time Constant: 10s (in still air)

Package Information

The LM35 is available in multiple package options to suit various application requirements:

TO-46 Metal Can Package

• Case connected to negative pin (GND)
• Order Numbers: LM35H, LM35AH, LM35CH, LM35CAH, LM35DH
• NS Package Number: H03H

TO-92 Plastic Package

• Order Numbers: LM35CZ, LM35CAZ, LM35DZ
• NS Package Number: Z03A

SO-8 Small Outline Molded Package

• Top View N.C. (No Connection)
• Order Number: LM35DM
• NS Package Number: M08A

TO-202 Plastic Package

• Order Number: LM35DP
• NS Package Number: P03A

Typical Applications

Basic Centigrade Temperature Sensor (2°C to 150°C)

The simplest application circuit requires only power supply connections and provides a direct voltage output proportional to temperature. For full-range operation, choose R1 = -VS/50 µA. The output voltage will be +1,500 mV at +150°C.

Remote Temperature Sensing

The LM35's low output impedance makes it suitable for remote sensing applications where the sensor may be located some distance from the measuring circuitry. Twisted pair cables can be used for noise immunity.

Negative Temperature Measurement

When measuring temperatures below 0°C, the LM35 can be powered from a dual supply or a single supply with a pull-down resistor to allow the output to go below ground potential.