SNIS152E May   2009  – July 2015 LM57

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Device Comparison Table
  6. 6 Pin Configuration and Functions
  7. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics - Accuracy Characteristics - Trip Point Accuracy
    6. 7.6 Electrical Characteristics - Accuracy Characteristics - VTEMP Analog Temperature Sensor Output Accuracy
    7. 7.7 Electrical Characteristics
    8. 7.8 Switching Characteristics
    9. 7.9 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 LM57 VTEMP Temperature-to-Voltage Transfer Function
        1. 8.3.1.1 LM57 VTEMP Voltage-to-Temperature Equations
      2. 8.3.2 RSENSE
      3. 8.3.3 Resistor Selection
      4. 8.3.4 TOVER and TOVER Digital Outputs
        1. 8.3.4.1 TOVER and TOVER Noise Immunity
      5. 8.3.5 Trip Test Digital Input
      6. 8.3.6 VTEMP Analog Temperature Sensor Output
        1. 8.3.6.1 VTEMP Noise Considerations
        2. 8.3.6.2 VTEMP Capacitive Loads
        3. 8.3.6.3 VTEMP Voltage Shift
    4. 8.4 Device Functional Modes
  9. 9 Application and Implementation
    1. 9.1 Application Information
      1. 9.1.1 ADC Input Considerations
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
        1. 9.2.2.1 Selection of RSENSE Resistors
      3. 9.2.3 Application Curves
      4. 9.2.4 Grounding of the TRIP TEST Pin
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
    3. 11.3 Temperature Considerations
  12. 12Device and Documentation Support
    1. 12.1 Documentation Support
      1. 12.1.1 Related Documentation
    2. 12.2 Community Resources
    3. 12.3 Trademarks
    4. 12.4 Electrostatic Discharge Caution
    5. 12.5 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

Package Options

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

11 Layout

11.1 Layout Guidelines

The LM57 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 LM57 will also affect the temperature reading.

Alternatively, the LM57 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 LM57 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 VTEMP output to ground or VDD, the VTEMP output from the LM57 will not be correct. Printed-circuit coatings are often used to ensure that moisture cannot corrode the leads or circuit traces.

11.2 Layout Example

LM57 Layout01_SNIS152.gifFigure 25. PW (TSSOP) Package Layout Example
LM57 Layout02_SNIS152.gif
The best thermal conductivity to the junction of the LM57 is through the DAP. Make sure it is connected to the surface whose temperature that is being measured.
Figure 26. SD (WSON) Package Layout Example

11.3 Temperature Considerations

The junction temperature of the LM57 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 3 is used to calculate the rise in the die temperature of the LM57.

Equation 3. LM57 30080512.gif

where

  • TA is the ambient temperature.
  • IQ is the quiescent current.
  • IL is the load current on VTEMP.
  • RθJA can be found in Thermal Information

For example using an LM57 in the PW (TSSOP) package, in an application where TA = 30°C, VDD = 5.5 V, IDD = 28 μA, J5 gain, VTEMP = 2368 mV, and IL = 0 μA, the total temperature rise would be [183°C/W × 5.5 V × 28 μA] = 0.028°C. To minimize self-heating, the load current on VTEMP should be minimized.