SNIS187A March   2015  – July 2015 LMT70 , LMT70A

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Wide-Range Precision Active RTD or NTC Replacement (−55°C to 150°C)
  5. 5 Revision History
  6. 6 Device Comparison Table
  7. 7 Pin Configuration and Functions
  8. 8 Specifications
    1. 8.1 Absolute Maximum Ratings
    2. 8.2 ESD Ratings
    3. 8.3 Recommended Operating Conditions
    4. 8.4 Thermal Information
    5. 8.5 Electrical Characteristics
    6. 8.6 Electrical Characteristics Temperature Lookup Table (LUT)
    7. 8.7 Switching Characteristics
    8. 8.8 Typical Performance Characteristics
  9. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Temperature Analog Output (TAO)
        1. 9.3.1.1 LMT70 Output Transfer Function
          1. 9.3.1.1.1 First Order Transfer Function
          2. 9.3.1.1.2 Second Order Transfer Function
          3. 9.3.1.1.3 Third Order Transfer Function
        2. 9.3.1.2 LMT70A TAO Matching
        3. 9.3.1.3 TAO Noise Considerations
        4. 9.3.1.4 TAO Capacitive Loads
      2. 9.3.2 TON Digital Input
      3. 9.3.3 Light Sensitivity
    4. 9.4 Device Functional Modes
  10. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Design Requirements
      2. 10.2.2 Detailed Design Procedure
        1. 10.2.2.1 Temperature Algorithm Selection
        2. 10.2.2.2 ADC Requirements
      3. 10.2.3 Finer Resolution LUT
      4. 10.2.4 Application Curves
    3. 10.3 System Examples
  11. 11Power Supply Recommendations
  12. 12Layout
    1. 12.1 Layout Guidelines
      1. 12.1.1 Mounting and Temperature Conductivity
    2. 12.2 Layout Example
  13. 13Device and Documentation Support
    1. 13.1 Related Links
    2. 13.2 Documentation Support
      1. 13.2.1 Related Documentation
    3. 13.3 Community Resources
    4. 13.4 Trademarks
    5. 13.5 Electrostatic Discharge Caution
    6. 13.6 Glossary
  14. 14Mechanical, Packaging, and Orderable Information

12 Layout

12.1 Layout Guidelines

The LMT70 can be applied easily in the same way as other integrated-circuit temperature sensors. It can be glued or cemented to a surface. The temperatures of the lands and traces to the other leads of the LMT70 will also affect the temperature reading.

12.1.1 Mounting and Temperature Conductivity

Alternatively, the LMT70 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 LMT70 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. If moisture creates a short circuit from the TAO output to ground or VDD, the TAO output from the LMT70 will not be correct. Printed-circuit coatings are often used to ensure that moisture cannot corrode the leads or circuit traces.

The LMT70's junction temperature is the actual temperature being measured. The thermal resistance junction-to-ambient (RθJA) is the parameter (from Thermal Information) used to calculate the rise of a device junction temperature due to its power dissipation. Equation 1 is used to calculate the rise in the LMT70's die temperature.

Equation 1. LMT70 LMT70A 30080512.gif

where

  • TA is the ambient temperature.
  • IQ is the quiescent current.
  • IL is the load current on VTEMP.

For example, in an application where TA = 30°C, VDD = 3 V, IDD = 12µA, VTAO = 943.227 mV, and IL = 0 μA, the total temperature rise would be [187°C/W × 3 V × 12 μA] = 0.007°C. To minimize self-heating, the load current on TAO pin should be minimized.

12.2 Layout Example

LMT70 LMT70A Layout_SNIS187.gif