SNVS397F September   2005  – December 2025 LM5005

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  6. 5 Specifications
    1. 5.1 Absolute Maximum Ratings
    2. 5.2 ESD Ratings
    3. 5.3 Recommended Operating Conditions
    4. 5.4 Thermal Information
    5. 5.5 Electrical Characteristics
    6. 5.6 Switching Characteristics
    7. 5.7 Typical Characteristics
  7. 6 Detailed Description
    1. 6.1 Overview
    2. 6.2 Functional Block Diagram
    3. 6.3 Feature Description
      1. 6.3.1 High-Voltage Start-Up Regulator
      2. 6.3.2 Shutdown and Standby
      3. 6.3.3 Oscillator and Synchronization Capability
      4. 6.3.4 Error Amplifier and PWM Comparator
      5. 6.3.5 RAMP Generator
      6. 6.3.6 Current Limit
      7. 6.3.7 Soft-Start Capability
      8. 6.3.8 MOSFET Gate Driver
    4. 6.4 Device Functional Modes
      1. 6.4.1 Shutdown Mode
      2. 6.4.2 Standby Mode
      3. 6.4.3 Light-Load Operation
      4. 6.4.4 Thermal Shutdown Protection
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Reducing Bias Power Dissipation
      2. 7.1.2 Input Voltage UVLO Protection
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1  Custom Design With WEBENCH® Tools
        2. 7.2.2.2  Frequency Set Resistor (RT)
        3. 7.2.2.3  Inductor (LF)
        4. 7.2.2.4  Ramp Capacitor (CRAMP)
        5. 7.2.2.5  Output Capacitors (COUT)
        6. 7.2.2.6  Schottky Diode (DF)
        7. 7.2.2.7  Input Capacitors (CIN)
        8. 7.2.2.8  VCC Capacitor (CVCC)
        9. 7.2.2.9  Bootstrap Capacitor (CBST)
        10. 7.2.2.10 Soft Start Capacitor (CSS)
        11. 7.2.2.11 Feedback Resistors (RFB1 and RFB2)
        12. 7.2.2.12 RC Snubber (RS and CS)
        13. 7.2.2.13 Compensation Components (RC1, CC1, CC2)
        14. 7.2.2.14 Bill of Materials
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
        1. 7.4.1.1 PCB Layout for EMI Reduction
        2. 7.4.1.2 Thermal Design
        3. 7.4.1.3 Ground Plane Design
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Third-Party Products Disclaimer
    2. 8.2 Device Support
      1. 8.2.1 Development Support
        1. 8.2.1.1 Custom Design With WEBENCH® Tools
    3. 8.3 Documentation Support
      1. 8.3.1 Related Documentation
        1. 8.3.1.1 PCB Layout Resources
        2. 8.3.1.2 Thermal Design Resources
    4. 8.4 Receiving Notification of Documentation Updates
    5. 8.5 Support Resources
    6. 8.6 Trademarks
    7. 8.7 Electrostatic Discharge Caution
    8. 8.8 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

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7.2.2.6 Schottky Diode (DF)

A Schottky-type freewheeling diode is required for all LM5005 applications. Select the reverse breakdown of the diode rating for the maximum VIN plus some safety margin. Ultra-fast diodes are not recommended and can result in damage to the regulator due to reverse recovery current transients. The near ideal reverse recovery characteristics and low forward voltage drop of a Schottky diode are particularly important diode characteristics for high input voltage and low output voltage applications common to the LM5005.

The reverse recovery characteristic determines how long the current surge lasts each cycle when the buck switch is turned on. The benign reverse recovery characteristics of a Schottky diode minimizes the peak instantaneous power in the buck switch occurring during turnon each cycle, and the resulting switching losses of the buck switch are significantly reduced.

The forward voltage drop of the diode has a significant impact on the conversion efficiency, especially for applications with a low output voltage. Rated current for diodes vary widely from various manufactures. The worst case is to assume a short-circuit load condition. In this case the diode conducts the output current almost continuously. For the LM5005 this current can be as high as 3.5A. Assuming a worst-case 1V drop across the diode, the maximum diode power dissipation can be as high as 3.5W. For this design example, a 100V, 6A Schottky in a DPAK package is selected.