SNIS121J June   1999  – November 2016 LM61

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
  6. 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
    6. 6.6 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 LM61 Transfer Function
    4. 7.4 Device Functional Modes
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Typical Temperature Sensing Circuit
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Capacitive Loads
        3. 8.2.1.3 Application Curve
      2. 8.2.2 Other Application Circuits
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Mounting
    2. 10.2 Layout Examples
    3. 10.3 Thermal Considerations
  11. 11Device and Documentation Support
    1. 11.1 Related Documentation
    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

10 Layout

10.1 Layout Guidelines

10.1.1 Mounting

The LM61 can be applied easily in the same way as other integrated-circuit temperature sensors. It can be glued or cemented to a surface. The temperature that the LM61 senses is within about 0.2°C of the surface temperature that LM61's leads are attached to.

This presumes that the ambient air temperature is almost the same as the surface temperature; if the air temperature is much higher or lower than the surface temperature, the actual temperature measured would be at an intermediate temperature between the surface temperature and the air temperatures.

To ensure good thermal conductivity the backside of the LM61 die is directly attached to the GND pin. The lands and traces to the LM61 are part of the printed-circuit board, which is the object whose temperature is being measured.

Alternatively, the LM61 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 LM61 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 connections.

10.2 Layout Examples

LM61 1289720.png Figure 17. Recommended Solder Pads for SOT-23 Package
LM61 1289714.png
A. 1/2 in.2 printed-circuit board with 2 oz copper foil or similar.
Figure 18. Printed-Circuit Board Used for Heat Sink to Generate All Curves
LM61 Layout_Config_SNIS177.gif Figure 19. PCB Layout

10.3 Thermal Considerations

The junction-to-ambient thermal resistance is the parameter used to calculate the rise of a device junction temperature due to its power dissipation. For the LM61, Equation 2 is used to calculate the rise in the die temperature.

Equation 2.

where

  • IQ is the quiescent current
  • ILis the load current on the output

Table 2 summarizes the rise in die temperature of the LM61 without any loading with a 3.3-V supply, and the thermal resistance for different conditions.

Table 2. Temperature Rise of LM61 Due to Self-Heating and Thermal Resistance (RθJA)

RθJA (°C/W) TJ – TA (°C)
SOT-23 No heat sink(1) Still air 450 0.26
Moving air — —
Small heat fin(2) Still air 260 0.13
Moving air 180 0.09
TO-92 No heat sink(1) Still air 180 0.09
Moving air 90 0.05
Small heat fin(3) Still air 140 0.07
Moving air 70 0.03
(1) Part soldered to 30 gauge wire.
(2) Heat sink used is 1/2 in.2 printed -circuit board with 2-oz foil with part attached as shown in Figure 18.
(3) Part glued and leads soldered to 1 in.2 of 1/16 in. printed circuit board with 2-oz foil or similar.

Table 3. Temperature and Typical VO Values

TEMPERATURE VO(TYPICAL)
100°C 1600 mV
85°C 1450 mV
25°C 850 mV
0°C 600 mV
–25°C 350 mV
–30°C 300 mV