SNVSB07C July   2018  – April 2019

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Typical Application
      2.      Typical Efficiency, VOUT = 5 V
  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 5 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  Zener 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
        3. 8.2.1.3 Application Curves
      2. 8.2.2 Design 2: PSR Flyback Converter With Dual Outputs of 15 V and –7.7 V at 200 mA
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1 Flyback Transformer – T1
          2. 8.2.2.2.2 Flyback Diodes – DFLY1 and DFLY2
          3. 8.2.2.2.3 Input Capacitor – CIN
          4. 8.2.2.2.4 Feedback Resistor – RFB
          5. 8.2.2.2.5 UVLO Resistors – RUV1, RUV2
        3. 8.2.2.3 Application Curves
      3. 8.2.3 Design 3: PSR Flyback Converter With Stacked Dual Outputs of 24 V and 5 V
        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 Feedback Resistor – RFB
          3. 8.2.3.2.3 UVLO Resistors – RUV1, RUV2
        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
      3. 11.1.3 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 Community Resources
    5. 11.5 Trademarks
    6. 11.6 Electrostatic Discharge Caution
    7. 11.7 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

8.2.3.2.1 Flyback Transformer – T1

The 24-V output is DC stacked on top of the 5-V output as they share a common return connection. This enables lower secondary-to-secondary leakage inductance for better cross regulation and also reduced rectifier diode reverse voltage stress. Choose a primary-secondary turns ratio for the effective 19-V secondary based on an approximate 60% max duty cycle at minimum input voltage using Equation 38.

Equation 38. LM5180-Q1 q_Nps_design3_nvsb06.gif

Set the turns ratio of the transformer secondary windings using Equation 39. The transformer turns ratio for both outputs is thus specified as 1 : 1.5 : 0.4.

Equation 39. LM5180-Q1 q_sec_turns_design3_nvsb06.gif

Select a magnetizing inductance based on the minimum off-time constraint using Equation 40. Choose a value of 30 µH with a saturation current of minimum 2 A for this application.

Equation 40. LM5180-Q1 q_Lmag_design3_nvsb06.gif