SLUSCV5 May   2022 TPS92643-Q1

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Revision History
  6. 5 Pin Configuration and Functions
  7. 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 Typical Characteristics
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Internal Regulator
      2. 7.3.2  Buck Converter Switching Operation
      3. 7.3.3  Bootstrap Supply
      4. 7.3.4  Switching Frequency and Adaptive On-Time Control
      5. 7.3.5  Minimum On-Time, Off-Time, and Inductor Ripple
      6. 7.3.6  LED Current Regulation and Error Amplifier
      7. 7.3.7  Start-Up Sequence
      8. 7.3.8  Analog Dimming and Forced Continuous Conduction Mode
      9. 7.3.9  External PWM Dimming and Input Undervoltage Lockout (UVLO)
      10. 7.3.10 Analog Pulse Width Modulator Circuit
      11. 7.3.11 Output Short and Open-Circuit Faults
      12. 7.3.12 Overcurrent Protection
      13. 7.3.13 Thermal Shutdown
      14. 7.3.14 Fault Indicator and Diagnostics Summary
    4. 7.4 Device Functional Modes
  9. 8 Application and Implementation
    1. 8.1 Application Information
      1. 8.1.1  Duty Cycle Considerations
      2. 8.1.2  Switching Frequency Selection
      3. 8.1.3  LED Current Programming
      4. 8.1.4  Inductor Selection
      5. 8.1.5  Output Capacitor Selection
      6. 8.1.6  Input Capacitor Selection
      7. 8.1.7  Bootstrap Capacitor Selection
      8. 8.1.8  Compensation Capacitor Selection
      9. 8.1.9  Input Dropout and Undervoltage Protection
      10. 8.1.10 APWM Input and Thermal Protection
      11. 8.1.11 Protection Diodes
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Calculating Duty Cycle
        2. 8.2.2.2 Calculating Minimum On-Time and Off-Time
        3. 8.2.2.3 Minimum Switching Frequency
        4. 8.2.2.4 LED Current Set Point
        5. 8.2.2.5 Inductor Selection
        6. 8.2.2.6 Output Capacitor Selection
        7. 8.2.2.7 Bootstrap Capacitor Selection
        8. 8.2.2.8 Compensation Capacitor Selection
        9. 8.2.2.9 VIN Dropout Protection and PWM Dimming
      3. 8.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
        1. 8.4.1.1 Compact Layout for EMI Reduction
          1. 8.4.1.1.1 Ground Plane
      2. 8.4.2 Layout Example
  10. 9 Power Supply Recommendations
  11. 10Layout
    1. 10.1 Layout Guidelines
      1. 10.1.1 Compact Layout for EMI Reduction
        1. 10.1.1.1 Ground Plane
    2. 10.2 Layout Example
  12. 11Device and Documentation Support
    1. 11.1 Receiving Notification of Documentation Updates
    2. 11.2 Support Resources
    3. 11.3 Trademarks
    4. 11.4 Electrostatic Discharge Caution
    5. 11.5 Glossary
  13. 12Mechanical, Packaging, and Orderable Information

Package Options

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

8.1.7 Bootstrap Capacitor Selection

The bootstrap capacitor biases the high-side gate driver during the high-side FET on-time. The required capacitance depends on the PWM dimming frequency, PWMFREQ, and is sized to avoid boot undervoltage and fault during PWM dimming operation. The bootstrap capacitance, CBST, is calculated using Equation 22:

Equation 22. C B S T = I Q B S T , M A X V C C + V B S T H Y S - V B S T U V × P W M F R E Q

Table 8-3 summarizes the TI recommended bootstrap capacitor value for different PWM dimming frequencies.

Table 8-2 Bootstrap Capacitor Value
PWM DIMMING FREQUENCY (Hz) BOOTSTRAP CAPACITOR (µF)
1500 0.1
1300 0.15
1000 0.22
800 0.22
600 0.33
400 0.47
200 1
100 2.2