SNVS397E September   2005  – November 2016 LM5005

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Pin Configuration and 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 Switching Characteristics
    7. 6.7 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 High-Voltage Start-Up Regulator
      2. 7.3.2 Shutdown and Standby
      3. 7.3.3 Oscillator and Synchronization Capability
      4. 7.3.4 Error Amplifier and PWM Comparator
      5. 7.3.5 RAMP Generator
      6. 7.3.6 Current Limit
      7. 7.3.7 Soft-Start Capability
      8. 7.3.8 MOSFET Gate Driver
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Standby Mode
      3. 7.4.3 Light-Load Operation
      4. 7.4.4 Thermal Shutdown Protection
  8. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1 Reducing Bias Power Dissipation
      2. 8.1.2 Input Voltage UVLO Protection
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1  Frequency Set Resistor (RT)
        2. 8.2.2.2  Inductor (LF)
        3. 8.2.2.3  Ramp Capacitor (CRAMP)
        4. 8.2.2.4  Output Capacitors (COUT)
        5. 8.2.2.5  Schottky Diode (DF)
        6. 8.2.2.6  Input Capacitors (CIN)
        7. 8.2.2.7  VCC Capacitor (CVCC)
        8. 8.2.2.8  Bootstrap Capacitor (CBST)
        9. 8.2.2.9  Soft Start Capacitor (CSS)
        10. 8.2.2.10 Feedback Resistors (RFB1 and RFB2)
        11. 8.2.2.11 RC Snubber (RS and CS)
        12. 8.2.2.12 Compensation Components (RC1, CC1, CC2)
        13. 8.2.2.13 Bill of Materials
      3. 8.2.3 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 PCB Layout for EMI Reduction
      2. 10.1.2 Thermal Design
      3. 10.1.3 Ground Plane Design
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Third-Party Products Disclaimer
    2. 11.2 Device Support
      1. 11.2.1 Development Support
    3. 11.3 Documentation Support
      1. 11.3.1 Related Documentation
        1. 11.3.1.1 PCB Layout Resources
        2. 11.3.1.2 Thermal Design Resources
    4. 11.4 Receiving Notification of Documentation Updates
    5. 11.5 Community Resources
    6. 11.6 Trademarks
    7. 11.7 Electrostatic Discharge Caution
    8. 11.8 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

Package Options

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

9 Power Supply Recommendations

The LM5005 converter is designed to operate from a wide input voltage range from 7 V to 75 V. The characteristics of the input supply must be compatible with the Absolute Maximum Ratings and Recommended Operating Conditions. In addition, the input supply must be capable of delivering the required input current to the fully-loaded regulator. Estimate the average input current with Equation 20.

Equation 20. LM5005 Iin_max1.gif

where

  • η is the efficiency

If the converter is connected to an input supply through long wires or PCB traces with large impedance, special care is required to achieve stable performance. The parasitic inductance and resistance of the input cables may have an adverse affect on converter operation. The parasitic inductance in combination with the low ESR ceramic input capacitors form an underdamped resonant circuit. This circuit can cause overvoltage transients at VIN each time the input supply is cycled ON and OFF. The parasitic resistance causes the input voltage to dip during a load transient. If the regulator is operating close to the minimum input voltage, this dip can cause false UVLO fault triggering and a system reset. The best way to solve such issues is to reduce the distance from the input supply to the regulator and use an aluminum or tantalum input capacitor in parallel with the ceramics. The moderate ESR of the electrolytic capacitors helps to damp the input resonant circuit and reduce any voltage overshoots. A capacitance in the range of 10 µF to 47 µF is usually sufficient to provide input damping and helps to hold the input voltage steady during large load transients.

An EMI input filter is often used in front of the regulator that, unless carefully designed, can lead to instability as well as some of the effects mentioned above. The user's guide Simple Success with Conducted EMI for DC-DC Converters (SNVA489) provides helpful suggestions when designing an input filter for any switching regulator.