SNVS471H January   2007  – April 2026 LM5575

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 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 Shutdown / Standby
      2. 6.3.2 Soft Start
      3. 6.3.3 Thermal Protection
    4. 6.4 Device Functional Modes
      1. 6.4.1 High Voltage Start-Up Regulator
      2. 6.4.2 Oscillator and Sync Capability
      3. 6.4.3 Error Amplifier and PWM Comparator
      4. 6.4.4 Ramp Generator
      5. 6.4.5 Maximum Duty Cycle / Input Dropout Voltage
      6. 6.4.6 Boost Pin
      7. 6.4.7 Current Limit
  8. 7 Application and Implementation
    1. 7.1 Application Information
      1. 7.1.1 Bias Power Dissipation Reduction
    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  R3 (R)T
        3. 7.2.2.3  L1
        4. 7.2.2.4  C3 (C)RAMP
        5. 7.2.2.5  C9, C10
        6. 7.2.2.6  D1
        7. 7.2.2.7  C1, C2
        8. 7.2.2.8  C8
        9. 7.2.2.9  C7
        10. 7.2.2.10 C4
        11. 7.2.2.11 R5, R6
        12. 7.2.2.12 R1, R2, C12
        13. 7.2.2.13 R4, C5, C6
        14. 7.2.2.14 R7, C11
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Examples
        1. 7.4.2.1 Thermal Considerations
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Development Support
        1. 8.1.1.1 Custom Design With WEBENCH® Tools
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

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

6.4.5 Maximum Duty Cycle / Input Dropout Voltage

There is a forced off-time of 500 ns implemented each cycle to ensure sufficient time for the diode current to be sampled. This forced off-time limits the maximum duty cycle of the buck switch. The maximum duty cycle will vary with the operating frequency.

Equation 4. DMAX = 1 – Fs × 500 ns

where

  • Fs is the oscillator frequency

Limiting the maximum duty cycle will raise the input dropout voltage. The input dropout voltage is the lowest input voltage required to maintain regulation of the output voltage. Equation 5 calculates an approximation of the input dropout voltage.

Equation 5. LM5575

where

  • VD is the voltage drop across the re-circulatory diode

Operating at high switching frequency raises the minimum input voltage necessary to maintain regulation.