SNVSCC4A October   2023  – September 2024 LP5811

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Device Comparison
  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 Timing Requirements
    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 Synchronous Boost Converter
        1. 6.3.1.1 Undervoltage Lockout
        2. 6.3.1.2 Enable and Soft Start
        3. 6.3.1.3 Switching Frequency
        4. 6.3.1.4 Current Limit Operation
        5. 6.3.1.5 Boost PWM Mode
        6. 6.3.1.6 Boost PFM Mode
      2. 6.3.2 Analog Dimming
      3. 6.3.3 PWM Dimming
      4. 6.3.4 Autonomous Animation Engine Control
        1. 6.3.4.1 Animation Engine Pattern
        2. 6.3.4.2 Sloper
        3. 6.3.4.3 Animation Engine Unit (AEU)
        4. 6.3.4.4 Animation Pause Unit (APU)
      5. 6.3.5 Protections and Diagnostics
        1. 6.3.5.1 Overvoltage Protection
        2. 6.3.5.2 Output Short-to-Ground Protection
        3. 6.3.5.3 LED Open Detections
        4. 6.3.5.4 LED Short Detections
        5. 6.3.5.5 Thermal Shutdown
    4. 6.4 Device Functional Modes
    5. 6.5 Programming
    6. 6.6 Register Maps
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Application
      2. 7.2.2 Design Parameters
      3. 7.2.3 Detailed Design Procedure
        1. 7.2.3.1 Inductor Selection
        2. 7.2.3.2 Output Capacitor Selection
        3. 7.2.3.3 Input Capacitor Selection
        4. 7.2.3.4 Program Procedure
        5. 7.2.3.5 Programming Example
      4. 7.2.4 Application Performance Plots
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Documentation Support
    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

6.3.1.4 Current Limit Operation

The LP5811 uses a valley current limit sensing scheme. The inductor current is detected during the switching off-time, by sensing the voltage across the synchronous rectifier.

When the load current increases, such that the inductor current is above the current limit within the whole switching cycle , the off-time increases to discharge the inductor current. The current decreases below the limit before the next on-time. When the current limit is reached, the output voltage decreases if the load current continually increases.

The maximum continuous output current (IOUT(CL)), before entering current limit (CL) operation, can be defined by Equation 1.

Equation 1. I O U T ( C L ) = 1 - D × I L I M + 1 2 ∆ I L P - P

where

  • D is the duty cycle
  • ΔIL(P-P) is the inductor ripple current

The duty cycle can be estimated by Equation 2.

Equation 2. D = 1 - V I N × η V O U T

where

  • VOUT is the output voltage of the boost converter
  • VIN is the input voltage of the boost converter
  • η is the efficiency of the converter, use 90% for most applications

The peak-to-peak inductor ripple current is calculated by Equation 3.

Equation 3. ∆ILP-P=VIN×DL×fSW

where

  • L is the inductance value of the inductor
  • fSW is the switching frequency
  • D is the duty cycle
  • VIN is the input voltage of the boost converter