SNIS118G July   1999  – January 2017 LM50 , LM50-Q1


  1. Features
  2. Applications
  3. Description
  4. Revision History
  5. Pin Configuration and Functions
  6. Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics: LM50B
    6. 6.6 Electrical Characteristics: LM50C and LM50-Q1
    7. 6.7 Typical Characteristics
  7. Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 LM50 and LM50-Q1 Transfer Function
    4. 7.4 Device Functional Modes
  8. Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Full-Range Centigrade Temperature Sensor
        1. Design Requirements
        2. Detailed Design Procedure
          1. Capacitive Loads
        3. Application Curve
    3. 8.3 System Examples
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Thermal Considerations
  11. 11Device and Documentation Support
    1. 11.1 Related Links
    2. 11.2 Receiving Notification of Documentation Updates
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information


Layout Guidelines

The LM50 and LM50-Q1 can be applied easily in the same way as other integrated-circuit temperature sensors. The device can be glued or cemented to a surface and its temperature will be within about 0.2°C of the surface temperature.

This presumes that the ambient air temperature is almost the same as the surface temperature; if the air temperature were much higher or lower than the surface temperature, the actual temperature of the LM50 or LM50-Q1 die would be at an intermediate temperature between the surface temperature and the air temperature.

To ensure good thermal conductivity the backside of the LM50 and LM50-Q1 die is directly attached to the GND pin. The lands and traces to the device will, of course, be part of the printed-circuit board, which is the object whose temperature is being measured. These printed-circuit board lands and traces will not cause the LM50 or LM50-Q1's temperature to deviate from the desired temperature.

Alternatively, the LM50 and LM50-Q1 can be mounted inside a sealed-end metal tube, and can then be dipped into a bath or screwed into a threaded hole in a tank. As with any IC, the LM50 and LM50-Q1 and accompanying wiring and circuits must be kept insulated and dry, to avoid leakage and corrosion. This is especially true if the circuit may operate at cold temperatures where condensation can occur. Printed-circuit coatings and varnishes such as Humiseal and epoxy paints or dips are often used to ensure that moisture cannot corrode the device or its connections.

Layout Example

LM50 LM50-Q1 Layout_Config_SNIS177.gif Figure 19. PCB Layout
LM50 LM50-Q1 snis118_layout.gif
1/2 in., square printed-circuit board with 2-oz foil or similar
Figure 20. Printed-Circuit Board Used for Heat Sink to Generate Thermal Response Curves

Thermal Considerations

Table 2 summarizes the thermal resistance of the LM50 and LM50-Q1 for different conditions.

Table 2. Temperature Rise of LM50 and LM50-Q1 Due to Self-Heating

RθJA (°C/W)
SOT-23 No heat sink(1) Still air 450
Moving air
Small heat fin(2) Still air 260
Moving air 180
Part soldered to 30 gauge wire.
Heat sink used is 1/2-in., square printed-circuit board with 2-oz foil; part attached as shown in Figure 20.