SNVS117E April   1998  – June 2019 LM2588

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 ESD Ratings
    3. 6.3 Recommended Operating Ratings
    4. 6.4 Electrical Characteristics: 3.3 V
    5. 6.5 Electrical Characteristics: 5 V
    6. 6.6 Electrical Characteristics: 12 V
    7. 6.7 Electrical Characteristics: Adjustable
    8. 6.8 Electrical Characteristics: All Output Voltage Versions
    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 Shutdown Control
      4. 7.3.4 Frequency Adjustment
      5. 7.3.5 Frequency Synchronization
      6. 7.3.6 Programming Output Voltage (Selecting R1 And R2)
      7. 7.3.7 Short-Circuit Condition
  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
    3. 9.3 Heat Sink/Thermal Considerations
  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

7.3.1 Flyback Regulator Operation

The operation of a flyback regulator is as follows (refer to Figure 16): when the switch is on, current flows through the primary winding of the transformer, T1, storing energy in the magnetic field of the transformer. Note that the primary and secondary windings are out of phase, so no current flows through the secondary when current flows through the primary. When the switch turns off, the magnetic field collapses, reversing the voltage polarity of the primary and secondary windings. Now rectifier D1 is forward biased and current flows through it, releasing the energy stored in the transformer. This produces voltage at the output.

The output voltage is controlled by modulating the peak switch current. This is done by feeding back a portion of the output voltage to the error amp, which amplifies the difference between the feedback voltage and a 1.23-V reference. The error amp output voltage is compared to a ramp voltage proportional to the switch current (in other words, inductor current during the switch on-time). The comparator terminates the switch on time when the two voltages are equal, thereby controlling the peak switch current to maintain a constant output voltage.

LM2588 01242024.png
As shown in Figure 16, the LM2588 can be used as a flyback regulator by using a minimum number of external components. The switching waveforms of this regulator are shown in Figure 18. Typical characteristics observed during the operation of this circuit are shown in Figure 19.
Figure 16. 12-V Flyback Regulator Design Example