SNIS159G August 1999  – August 2016 LM35

PRODUCTION DATA. 

  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1Absolute Maximum Ratings
    2. 6.2ESD Ratings
    3. 6.3Recommended Operating Conditions
    4. 6.4Thermal Information
    5. 6.5Electrical Characteristics: LM35A, LM35CA Limits
    6. 6.6Electrical Characteristics: LM35A, LM35CA
    7. 6.7Electrical Characteristics: LM35, LM35C, LM35D Limits
    8. 6.8Electrical Characteristics: LM35, LM35C, LM35D
    9. 6.9Typical Characteristics
  7. Detailed Description
    1. 7.1Overview
    2. 7.2Functional Block Diagram
    3. 7.3Feature Description
      1. 7.3.1LM35 Transfer Function
    4. 7.4Device Functional Modes
  8. Application and Implementation
    1. 8.1Application Information
      1. 8.1.1Capacitive Drive Capability
    2. 8.2Typical Application
      1. 8.2.1Basic Centigrade Temperature Sensor
        1. 8.2.1.1Design Requirements
        2. 8.2.1.2Detailed Design Procedure
        3. 8.2.1.3Application Curve
    3. 8.3System Examples
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1Layout Guidelines
    2. 10.2Layout Example
  11. 11Device and Documentation Support
    1. 11.1Receiving Notification of Documentation Updates
    2. 11.2Community Resources
    3. 11.3Trademarks
    4. 11.4Electrostatic Discharge Caution
    5. 11.5Glossary
  12. 12Mechanical, Packaging, and Orderable Information

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

LM35 fbd_snis159.gif

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:

Equation 1. VOUT = 10 mv/°C × T

where

  • VOUT is the LM35 output voltage
  • T is the temperature in °C

7.4 Device Functional Modes

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