SNIS115S May   2001  – September 2015 LM26

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
    6. 7.6 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagrams
    3. 8.3 Feature Description
      1. 8.3.1 Hysteresis
      2. 8.3.2 VTEMP Output
    4. 8.4 Device Functional Modes
      1. 8.4.1 After Assembly PCB Testing
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 Design Requirements
      2. 9.2.2 Detailed Design Procedure
      3. 9.2.3 Application Curve
    3. 9.3 System Examples
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
    3. 11.3 Thermal Considerations
  12. 12Device and Documentation Support
    1. 12.1 Community Resources
    2. 12.2 Trademarks
    3. 12.3 Electrostatic Discharge Caution
    4. 12.4 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

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9 Application and Implementation

NOTE

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.

9.1 Application Information

The LM26 thermostat (temperature switch) can be used in applications such as microprocessor thermal management, appliances, fan control, industrial process control, power supplies for system protection, fan speed adjust or plain temperature monitoring.

9.2 Typical Application

LM26 10132303.gif Figure 8. Two-Speed Fan Speed Control

9.2.1 Design Requirements

The requirement is to change speed fo a fan to maximum at 45°C with an accuracy of

Table 2. Design Parameters

DESIGN PARAMETER EXAMPLE VALUE
Min Fan Speed 1900 RPM
Max Fan Speed 3800 RPM
Temperature Threshold To Switch From Min Speed to Max Speed 45°C
Threshold accuracy ±3°C

9.2.2 Detailed Design Procedure

The design procedure is simple. A fan was selected that has the capability to be controlled by an external NTC thermistor. The recommended NTC thermistor adjusts the fan speed to maximum at 40°C. The LM26 meets the threshold accuracy requirements for temperature control of the fan speed and allows setting the max speed temperature threshold higher as required to 45°C. The resistance of the thermistor for the min fan speed is 6.8 kΩ. Since thermistors have a negative temperature coefficient (NTC), 10 kΩ was chosen to ensure that the fan is at min speed when the LM26 OS is off. When the OS output goes low at 45°C it simulates the low thermistor resistance at higher temperatures thus setting fan to max speed.

9.2.3 Application Curve

LM26 TypAppCurve_SNIS115.gif Figure 9. Temperature Effect on Fan Speed

9.3 System Examples

LM26 10132320.gif Figure 10. Fan High-Side Drive
LM26 10132322.gif Figure 12. Audio Power Amplifier Thermal Protection
LM26 10132321.gif Figure 11. Fan Low-Side Drive
LM26 10132323.gif Figure 13. Simple Thermostat