SNIS159G August 1999  – August 2016 LM35


  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. Requirements
        2. Design Procedure
        3. 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

8 Application and Implementation


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

The features of the LM35 make it suitable for many general temperature sensing applications. Multiple package options expand on it's flexibility.

8.1.1 Capacitive Drive Capability

Like most micropower circuits, the LM35 device has a limited ability to drive heavy capacitive loads. Alone, the LM35 device is able to drive 50 pF without special precautions. If heavier loads are anticipated, isolating or decoupling the load with a resistor is easy (see Figure 12). The tolerance of capacitance can be improved with a series R-C damper from output to ground (see Figure 13).

When the LM35 device is applied with a 200-Ω load resistor as shown in Figure 16, Figure 17, or Figure 19, the device is relatively immune to wiring capacitance because the capacitance forms a bypass from ground to input and not on the output. However, as with any linear circuit connected to wires in a hostile environment, performance is affected adversely by intense electromagnetic sources (such as relays, radio transmitters, motors with arcing brushes, and SCR transients), because the wiring acts as a receiving antenna and the internal junctions act as rectifiers. For best results in such cases, a bypass capacitor from VIN to ground and a series R-C damper, such as 75 Ω in series with 0.2 or 1 μF from output to ground, are often useful. Examples are shown in Figure 13, Figure 24, and Figure 25.

LM35 ta_decoupling_snis159.gif Figure 12. LM35 with Decoupling from Capacitive Load
LM35 ta_rc_damper_snis159.gif Figure 13. LM35 with R-C Damper

8.2 Typical Application

8.2.1 Basic Centigrade Temperature Sensor

LM35 basic_sensor_snis159.gif Figure 14. Basic Centigrade Temperature Sensor (2 °C to 150 °C) Design Requirements

Table 1. Design Parameters

Accuracy at 25°C ±0.5°C
Accuracy from –55 °C to 150°C±1°C
Temperature Slope 10 mV/°C Detailed Design Procedure

Because the LM35 device is a simple temperature sensor that provides an analog output, design requirements related to layout are more important than electrical requirements. For a detailed description, refer to the Layout. Application Curve

LM35 C008_SNIS159.png Figure 15. Accuracy vs Temperature (Ensured)

8.3 System Examples

LM35 ta_grounded_sensor_snis159.gif Figure 16. Two-Wire Remote Temperature Sensor
(Grounded Sensor)
LM35 ta_single_supply_snis159.gif Figure 18. Temperature Sensor, Single Supply
(−55° to +150°C)
LM35 ta_current_source_snis159.gif Figure 20. 4-To-20 mA Current Source
(0°C to 100°C)
LM35 ta_C_thermometer_snis159.gif Figure 22. Centigrade Thermometer
(Analog Meter)
LM35 ta_temp_DC_snis159.gif Figure 24. Temperature to Digital Converter
(Serial Output)
(128°C Full Scale)
LM35 ta_bar_graph_snis159.gif
*=1% or 2% film resistor
Trim RB for VB = 3.075 V
Trim RC for VC = 1.955 V
Trim RA for VA = 0.075 V + 100 mV/°C ×Tambient
Example, VA = 2.275 V at 22°C
Figure 26. Bar-Graph Temperature Display
(Dot Mode)
LM35 ta_ouput_ground_snis159.gif Figure 17. Two-Wire Remote Temperature Sensor
(Output Referred to Ground)
LM35 ta_ouput_ground_2_snis159.gif Figure 19. Two-Wire Remote Temperature Sensor
(Output Referred to Ground)
LM35 ta_F_thermometer_snis159.gif Figure 21. Fahrenheit Thermometer
LM35 ta_F_expanded_snis159.gif Figure 23. Fahrenheit Thermometer, Expanded Scale Thermometer
(50°F to 80°F, for Example Shown)
LM35 ta_temp_DC_parallel_snis159.gif Figure 25. Temperature to Digital Converter
(Parallel TRI-STATE Outputs for Standard Data Bus to μP Interface)
(128°C Full Scale)
LM35 ta_voltage_freq_snis159.gif Figure 27. LM35 With Voltage-To-Frequency Converter and Isolated Output
(2°C to 150°C; 20 to 1500 Hz)