SLUSCO8B November   2016  – June 2018 TPS54200 , TPS54201

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
      2.      Excellent Deep Dimming in ADIM
  4. 4 Revision History
  5. 5 Description (continued)
  6. 6 Pin Configuration and Functions
    1.     Pin Functions
  7. 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
    7. 7.7 Switching Characteristics
    8. 7.8 Typical Characteristics
  8. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1  Fixed-Frequency PWM Control
      2. 8.3.2  Error Amplifier
      3. 8.3.3  Slope Compensation and Output Current
      4. 8.3.4  Input Undervoltage Lockout
      5. 8.3.5  Voltage Reference
      6. 8.3.6  Setting LED Current
      7. 8.3.7  Internal Soft Start
      8. 8.3.8  Bootstrap Voltage (BOOT)
      9. 8.3.9  Overcurrent Protection
        1. 8.3.9.1 High-Side MOSFET Overcurrent Protection
        2. 8.3.9.2 Low-Side MOSFET Overcurrent Protection
        3. 8.3.9.3 Low-Side MOSFET Reverse Overcurrent Protection
      10. 8.3.10 Fault Protection
        1. 8.3.10.1 LED-Open Protection
        2. 8.3.10.2 LED Short Protection
        3. 8.3.10.3 Sense-Resistor Short Protection
        4. 8.3.10.4 Sense-Resistor Open Protection
        5. 8.3.10.5 Overvoltage Protection
        6. 8.3.10.6 Thermal Shutdown
    4. 8.4 Device Functional Modes
      1. 8.4.1 Enable and Disable Device
      2. 8.4.2 Mode Detection
      3. 8.4.3 Analog Dimming Mode Operation
      4. 8.4.4 PWM Dimming-Mode Operation
  9. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 TPS5420x 12-V Input, 1.5-A, 3-Piece IR LED Driver With Analog Dimming
        1. 9.2.1.1 Design Requirements
        2. 9.2.1.2 Detailed Design Procedure
          1. 9.2.1.2.1 Inductor Selection
          2. 9.2.1.2.2 Input Capacitor Selection
          3. 9.2.1.2.3 Output Capacitor Selection
          4. 9.2.1.2.4 FB Pin RC Filter Selection
          5. 9.2.1.2.5 Sense Resistor Selection
        3. 9.2.1.3 Application Curves
      2. 9.2.2 TPS5420x 24-V Input, 1-A, 4-Piece WLED Driver With PWM Dimming
        1. 9.2.2.1 Design Requirements
        2. 9.2.2.2 Detailed Design Procedure
          1. 9.2.2.2.1 Inductor Selection
          2. 9.2.2.2.2 Input Capacitor Selection
          3. 9.2.2.2.3 Output Capacitor Selection
          4. 9.2.2.2.4 FB Pin RC Filter Selection
          5. 9.2.2.2.5 Sense Resistor Selection
        3. 9.2.2.3 Application Curves
  10. 10Power Supply Recommendations
  11. 11Layout
    1. 11.1 Layout Guidelines
    2. 11.2 Layout Example
  12. 12Device and Documentation Support
    1. 12.1 Device Support
      1. 12.1.1 Third-Party Products Disclaimer
    2. 12.2 Documentation Support
      1. 12.2.1 Related Links
    3. 12.3 Receiving Notification of Documentation Updates
    4. 12.4 Community Resources
    5. 12.5 Trademarks
    6. 12.6 Electrostatic Discharge Caution
    7. 12.7 Glossary
  13. 13Mechanical, Packaging, and Orderable Information

9.2.2.2.1 Inductor Selection

A Cree white LED XLampXML is used. According to the LED manufacturer’s data sheet, this LED has 2.9-V forward voltage at 1-A current, so VOUT = 2.9 V × 4 + 0.1 V = 11.7 V. Choose KIND = 0.3, which gives a 36-µH inductance. With this inductance, the ripple current on the inductor is only 0.3-A peak-to-peak, which is too conservative and increases total system cost and size.

For this application, with concerns about system cost and size taken into account, decide the inductance by choosing a larger peak-to-peak inductor ripple current. To choose a proper peak-to-peak inductor ripple, the low-side FET sink current limit should not be exceeded when the converter works in a no-load condition. To meet this requirement, half of the peak-to-peak inductor ripple must be lower than that limit. Another consideration with this larger peak-to-peak ripple current is the increased core loss and copper loss in the inductor, which is also acceptable. Once this peak-to-peak inductor ripple current is chosen, Equation 14 can be used to calculate the required inductance.

Equation 14. TPS54200 TPS54201 qu14_lusco8.gif

where

  • IL(RIPPLE) is the peak-to-peak inductor ripple current.

Choose 1-A peak-to-peak inductor ripple current, and half of the current is 0.5 A, much lower than the minimum low-side sink current limit of 1.25 A. The calculated inductance is 10.9 µH. Choose a 10-µH inductor with part number 744066100 from Wurth. The ripple, peak, and rms currents of the inductor are 1.09 A, 1.54 A, and 1.05 A, respectively. The chosen inductor has ample margin in this design.