SNVS121E May   1996  – May 2019 LM2586

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Typical Applications
  3. 3 Description
    1.     Device Images
      1.      Block Diagram
  4. 4 Revision History
  5. 5 Pin Configurations
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Ratings
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics: 3.3 V
    6. 6.6 Electrical Characteristics: 5 V
    7. 6.7 Electrical Characteristics: 12 V
    8. 6.8 Electrical Characteristics: Adjustable
    9. 6.9 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 Flyback Regulator Operation
      2. 7.3.2 Step-Up (Boost) Regulator Operation
      3. 7.3.3 Programming Output Voltage (Selecting R1 And R2)
      4. 7.3.4 Shutdown Control
      5. 7.3.5 Frequency Adjustment
      6. 7.3.6 Frequency Synchronization
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Typical Flyback Regulator Applications
        1. 8.2.1.1 Design Requirements
          1. 8.2.1.1.1 Transformer Selection (T)
          2. 8.2.1.1.2 Transformer Footprints
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Custom Design With WEBENCH® Tools
          2. 8.2.1.2.2 Flyback Regulator Input Capacitors
          3. 8.2.1.2.3 Switch Voltage Limits
          4. 8.2.1.2.4 Output Voltage Limitations
          5. 8.2.1.2.5 Noisy Input Line Condition
          6. 8.2.1.2.6 Stability
      2. 8.2.2 Typical Boost Regulator Applications
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
    3. 8.3 System Examples
      1. 8.3.1 Test Circuits
  9. 9 Layout
    1. 9.1 Layout Guidelines
    2. 9.2 Layout Example
  10. 10Heat Sink/Thermal Considerations
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Third-Party Products Disclaimer
      2. 11.1.2 Development Support
        1. 11.1.2.1 Custom Design With WEBENCH® Tools
    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 Heat Sink/Thermal Considerations

In many cases, a heat sink is not required to keep the LM2586 junction temperature within the allowed operating temperature range. For each application, to determine whether or not a heat sink will be required, the following must be identified:

1) Maximum ambient temperature (in the application).

2) Maximum regulator power dissipation (in the application).

3) Maximum allowed junction temperature (125°C for the LM2586). For a safe, conservative design, a temperature approximately 15°C cooler than the maximum junction temperature should be selected (110°C).

4) LM2586 package thermal resistances θJA and θJC (given in the Electrical Characteristics).

Total power dissipated (PD) by the LM2586 can be estimated as follows:

Equation 7. LM2586 01251672.png

where

  • VIN is the minimum input voltage
  • VOUT is the output voltage
  • N is the transformer turns ratio, D is the duty cycle
  • ILOAD is the maximum load current (and ∑ILOAD is the sum of the maximum load currents for multiple-output flyback regulators)

The duty cycle is given by:

Equation 8. LM2586 01251673.png

where

  • VF is the forward biased voltage of the diode and is typically 0.5 V for Schottky diodes and 0.8 V for fast recovery diodes
  • VSAT is the switch saturation voltage and can be found in the Characteristic Curves

When no heat sink is used, the junction temperature rise is:

Equation 9. ΔTJ = PD • θJA.

Adding the junction temperature rise to the maximum ambient temperature gives the actual operating junction temperature:

Equation 10. TJ = ΔTJ + TA.

If the operating junction temperature exceeds the maximum junction temperature in item 3 above, then a heat sink is required. When using a heat sink, the junction temperature rise can be determined by the following:

Equation 11. ΔTJ = PD • (θJC + θInterface + θHeat Sink)

Again, the operating junction temperature will be:

Equation 12. TJ = ΔTJ + TA

As before, if the maximum junction temperature is exceeded, a larger heat sink is required (one that has a lower thermal resistance).

Included in the Switchers Made Simple® design software is a more precise (non-linear) thermal model that can be used to determine junction temperature with different input-output parameters or different component values. It can also calculate the heat sink thermal resistance required to maintain the regulator junction temperature below the maximum operating temperature.

To further simplify the flyback regulator design procedure, Texas Instruments is making available computer design software to be used with the Simple Switcher ® line of switching regulators.Switchers Made Simple is available on a 3½″ diskette for IBM compatible computers from a Texas Instruments sales office in your area or the Texas Instruments Customer Response Center ((800) 477-8924).