ZHCSQG8 October   2023 LP5811

PRODUCTION DATA  

  1.   1
  2. 1 特性
  3. 2 应用
  4. 3 说明
  5. 4 Revision History
  6. 5 Device Comparison
  7. 6 Pin Configuration and Functions
  8. 7 Specifications
    1. 7.1 Absolute Maximum Ratings
    2. 7.2 ESD Ratings
    3. 7.3 Recommended Operating Conditions
    4. 7.4 Thermal Information
    5. 7.5 Electrical Characteristics
    6. 7.6 Timing Requirements
  9. 8 Typical Characteristics
  10. 9 Detailed Description
    1. 9.1 Overview
    2. 9.2 Functional Block Diagram
    3. 9.3 Feature Description
      1. 9.3.1 Synchronous Boost Converter
        1. 9.3.1.1 Undervoltage Lockout
        2. 9.3.1.2 Enable and Soft Start
        3. 9.3.1.3 Switching Frequency
        4. 9.3.1.4 Current Limit Operation
        5. 9.3.1.5 Boost PWM Mode
        6. 9.3.1.6 Boost PFM Mode
      2. 9.3.2 Analog Dimming
      3. 9.3.3 PWM Dimming
      4. 9.3.4 Autonomous Animation Engine Control
        1. 9.3.4.1 Animation Engine Pattern
        2. 9.3.4.2 Sloper
        3. 9.3.4.3 Animation Engine Unit (AEU)
        4. 9.3.4.4 Animation Pause Unit (APU)
      5. 9.3.5 Protections and Diagnostics
        1. 9.3.5.1 Overvoltage Protection
        2. 9.3.5.2 Output Short-to-Ground Protection
        3. 9.3.5.3 LED Open Detections
        4. 9.3.5.4 LED Short Detections
        5. 9.3.5.5 Thermal Shutdown
    4. 9.4 Device Functional Modes
    5. 9.5 Programming
    6. 9.6 Register Maps
  11. 10Application and Implementation
    1. 10.1 Application Information
    2. 10.2 Typical Application
      1. 10.2.1 Application
      2. 10.2.2 Design Parameters
      3. 10.2.3 Detailed Design Procedure
        1. 10.2.3.1 Inductor Selection
        2. 10.2.3.2 Output Capacitor Selection
        3. 10.2.3.3 Input Capacitor Selection
        4. 10.2.3.4 Program Procedure
        5. 10.2.3.5 Programming Example
      4. 10.2.4 Application Performance Plots
    3. 10.3 Power Supply Recommendations
    4. 10.4 Layout
      1. 10.4.1 Layout Guidelines
      2. 10.4.2 Layout Example
  12. 11Device and Documentation Support
    1. 11.1 Documentation Support
    2. 11.2 接收文档更新通知
    3. 11.3 支持资源
    4. 11.4 Trademarks
    5. 11.5 静电放电警告
    6. 11.6 术语表

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9.3.1.6 Boost PFM Mode

The LP5811 works at PFM to improve efficiency at light load. When the load current decreases, the inductor valley current set by the output of the error amplifier no longer regulates the output voltage. When the inductor valley current hits the low limit, the output voltage exceeds the setting voltage as the load current decreases further. When the feedback voltage hits the PFM reference voltage (0.6 V typical), the LP5811 works at PFM. When the feedback voltage rises and hits the PFM reference voltage, the device continues switching for several cycles because of the delay time of the internal comparator — then it stops switching. The load is supplied by the output capacitor, and the output voltage declines. When the feedback voltage falls below the PFM reference voltage, after the delay time of the comparator, the device starts switching again to ramp up the output voltage. Figure 9-2 showes the waveform of voltage when the device works at PWM and PFM.

GUID-C435A6E0-00E4-4739-8822-AE2BE7016996-low.gif Figure 9-2 Output Voltage in PWM Mode and PFM