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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7.2.2.5 Output Capacitors (COUT)

The output capacitor filters the inductor ripple current and provides a source of charge for transient load conditions. Use a wide range of output capacitors with the LM5005 to provide various advantages. The best performance is typically obtained using ceramic or polymer electrolytic type components. Typical trade-offs are that the ceramic capacitor provides extremely low ESR to reduce the output ripple voltage and noise spikes, while electrolytic capacitors provide a large bulk capacitance in a small volume for transient loading conditions.

When selecting an output capacitor, the two performance characteristics to consider are the output voltage ripple and load transient response. Approximate the output voltage ripple using Equation 11.

Equation 11. ∆ V O U T = ∆ I L R E S R 2 + 1 8 × F S W × C O U T 2

where

  • ΔVOUT = peak-to-peak output voltage ripple
  • RESR = effective series resistance (ESR) of the output capacitor
  • FSW = switching frequency
  • COUT = effective output capacitance

The amount of output voltage ripple is application specific. A general recommendation is to keep the output ripple less than 1% of the rated output voltage.

Sometimes capacitors are preferred because capacitors have low ESR. However, depending on package and voltage rating of the capacitor, the effective in-circuit capacitance can drop significantly with applied voltage. The output capacitor selection also affects the output voltage droop during a load transient. The peak deviation of the output voltage during a load transient is dependent on many factors. Equation 12 calculates an approximation of the transient dip ignoring loop bandwidth.

Equation 12. V D R O O P = ∆ I O U T - S T E P × R E S R + L F × Δ I O U T - S T E P 2 C O U T × V I N - V O U T

where

  • COUT = minimum required output capacitance
  • LF = buck filter inductance
  • VDROOP = output voltage deviation ignoring loop bandwidth considerations
  • ΔIOUT-STEP = load step change
  • RESR = output capacitor ESR
  • VIN = input voltage
  • VOUT = output voltage setpoint

A 22µF, 16V ceramic capacitor with X7R dielectric and 1210 footprint and a 150µF, 6.3V polymer electrolytic capacitor are selected here based on a review of the tolerance and voltage coefficient of each capacitor to meet output ripple specification. The ceramic capacitor provides ultra-low ESR to reduce the output ripple voltage and noise spikes, while the electrolytic capacitor provides a large bulk capacitance in a small volume for transient loading conditions.