SNVSBJ6A March   2020  – August 2020 LM25184-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin 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  Integrated Power MOSFET
      2. 7.3.2  PSR Flyback Modes of Operation
      3. 7.3.3  Setting the Output Voltage
        1. 7.3.3.1 Diode Thermal Compensation
      4. 7.3.4  Control Loop Error Amplifier
      5. 7.3.5  Precision Enable
      6. 7.3.6  Configurable Soft Start
      7. 7.3.7  External Bias Supply
      8. 7.3.8  Minimum On-Time and Off-Time
      9. 7.3.9  Overcurrent Protection
      10. 7.3.10 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Standby Mode
      3. 7.4.3 Active Mode
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Applications
      1. 8.2.1 Design 1: Wide VIN, Low IQ PSR Flyback Converter Rated at 12 V, 1 A
        1. 8.2.1.1 Design Requirements
        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  Custom Design With Excel Quickstart Tool
          3. 8.2.1.2.3  Flyback Transformer – T1
          4. 8.2.1.2.4  Flyback Diode – DFLY
          5. 8.2.1.2.5  Leakgae Inductance Clamp Circuit – DF, DCLAMP
          6. 8.2.1.2.6  Output Capacitor – COUT
          7. 8.2.1.2.7  Input Capacitor – CIN
          8. 8.2.1.2.8  Feedback Resistor – RFB
          9. 8.2.1.2.9  Thermal Compensation Resistor – RTC
          10. 8.2.1.2.10 UVLO Resistors – RUV1, RUV2
          11. 8.2.1.2.11 Soft-Start Capacitor – CSS
          12.        50
      2. 8.2.2 Application Curves
      3. 8.2.3 Design 2: PSR Flyback Converter With Dual Outputs of 15 V and –8 V at 0.5 A
        1. 8.2.3.1 Design Requirements
        2. 8.2.3.2 Detailed Design Procedure
          1. 8.2.3.2.1 Flyback Transformer – T1
          2. 8.2.3.2.2 Flyback Diodes – DFLY1 and DFLY2
          3. 8.2.3.2.3 Input Capacitor – CIN
          4. 8.2.3.2.4 Output Capacitors – COUT1, COUT2
          5. 8.2.3.2.5 Feedback Resistor – RFB
          6. 8.2.3.2.6 Thermal Compensation Resistor – RTC
          7. 8.2.3.2.7 Output Voltage Clamp Zeners – DOUT1 and DOUT2
        3. 8.2.3.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Examples
  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 Documentation Support
      1. 11.2.1 Related Documentation
    3. 11.3 Receiving Notification of Documentation Updates
    4. 11.4 Support Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information
8.2.3.2.2 Flyback Diodes – DFLY1 and DFLY2

The flyback diode reverse voltages for the positive and negative outputs are given respectively by Equation 37 and Equation 38.

Equation 37. GUID-D761A524-365F-4305-8689-2D75136B69DF-low.gif
Equation 38. GUID-9C6D8137-5656-4A5E-A7EE-FF7A99696C33-low.gif

Choose 100-V, 1-A and 60-V, 3-A Schottky diodes for the positive and negative outputs, respectively, to allow some margin for inevitable voltage overshoot and ringing related to leakage inductance and diode capacitance. Use an RC snubber circuit across each diode, for example, 100 Ω and 22 pF, to mitigate such overshoot and ringing, particularly if the transformer leakage inductance is high.