SNVS115E April   2000  – June 2019 LM2587

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Typical Applications
  3. 3 Description
    1.     Device Images
      1.      Flyback Regulator
  4. 4 Revision History
  5. 5 Pin Configurations
  6. 6 Specifications
    1. 6.1  Absolute Maximum Ratings
    2. 6.2  ESDRatings
    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  Electrical Characteristics: All Output Voltage Versions
    10. 6.10 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 Step-Up (Boost) Regulator Operation
  8. 8 Application And Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Typical Boost Regulator Applications
      2. 8.2.2 Typical Flyback Regulator Applications
        1. 8.2.2.1 Transformer Selection (T)
        2. 8.2.2.2 Transformer Footprints
          1. 8.2.2.2.0.1 T4
      3. 8.2.3 Design Requirements
      4. 8.2.4 Detailed Design Procedure
        1. 8.2.4.1 Custom Design With Webench® Tools
        2. 8.2.4.2 Programming Output Voltage (Selecting R1 And R2)
        3. 8.2.4.3 Short Circuit Condition
        4. 8.2.4.4 Flyback Regulator Input Capacitors
        5. 8.2.4.5 Switch Voltage Limits
        6. 8.2.4.6 Output Voltage Limitations
        7. 8.2.4.7 Noisy Input Line Condition)
        8. 8.2.4.8 Stability
    3. 8.3 Additional Application Examples
      1. 8.3.1 Test Circuits
  9. 9 Layout
    1. 9.1 Layout Guidelines
    2. 9.2 Layout Example
    3. 9.3 Heat Sink/Thermal Considerations
      1. 9.3.1 European Magnetic Vendor Contacts
      2. 9.3.2 Coilcraft
      3. 9.3.3 Pulse Engineering
  10. 10Device and Documentation Support
    1. 10.1 Device Support
      1. 10.1.1 Third-Party Products Disclaimer
      2. 10.1.2 Development Support
        1. 10.1.2.1 Custom Design With Webench® Tools
    2. 10.2 Receiving Notification Of Documentation Updates
    3. 10.3 Community Resources
    4. 10.4 Trademarks
    5. 10.5 Electrostatic Discharge Caution
    6. 10.6 Glossary
  11. 11Mechanical, Packaging, and Orderable Information

Package Options

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

9.3 Heat Sink/Thermal Considerations

In many cases, no heat sink is required to keep the LM2587 junction temperature within the allowed operating 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 LM2587). For a safe, conservative design, a temperature approximately 15°C cooler than the maximum junction temperature should be selected (110°C).

4) LM2587 package thermal resistances θJA and θJC (given in the Electrical Characteristics).

Total power dissipated (PD) by the LM2587 can be estimated as follows:

Boost:

Equation 7. LM2587 1231662.png

VIN is the minimum input voltage, VOUT is the output voltage, N is the transformer turns ratio, D is the duty cycle, and 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:

Boost:

Equation 8. LM2587 1231663.png

where

  • VF is the forward biased voltage of the diode and is typically 0.5V for Schottky diodes and 0.8V 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 temperatue 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, TI is making available computer design software. Switchers Made Simple software is available on a (3½″) diskette for IBM compatible computers from a TI sales office in your area or the TI WEBENCH Design Center team.

http://www.ti.com/ww/en/analog/webench/index.shtml?DCMP=hpa_sva_webench&HQS=webench-bb