JAJSVO8 November   2024 TPS922051

PRODUCTION DATA  

  1.   1
  2. 1 特長
  3. 2 アプリケーション
  4. 3 概要
  5. 4 Device Comparison Table
  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 Adaptive Off-Time Current Mode Control
      2. 7.3.2 Setting LED Current
      3. 7.3.3 Internal Soft Start
      4. 7.3.4 Dimming Mode
        1. 7.3.4.1 PWM Dimming
        2. 7.3.4.2 Analog Dimming
      5. 7.3.5 Fault Protection
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 TPS922051D2 24V Input, 2A Output, 4-piece WLED Driver With Analog Dimming
        1. 8.2.1.1 Design Requirements
        2. 8.2.1.2 Detailed Design Procedure
          1. 8.2.1.2.1 Inductor Selection
          2. 8.2.1.2.2 Input Capacitor Selection
          3. 8.2.1.2.3 Output Capacitor Selection
          4. 8.2.1.2.4 Sense Resistor Selection
          5. 8.2.1.2.5 Other External Components Selection
        3. 8.2.1.3 Application Curves
      2. 8.2.2 TPS922050D1 48V Input, 1A Output, 12-piece WLED Driver with PWM Dimming
        1. 8.2.2.1 Design Requirements
        2. 8.2.2.2 Detailed Design Procedure
          1. 8.2.2.2.1 Inductor Selection
          2. 8.2.2.2.2 Input Capacitor Selection
          3. 8.2.2.2.3 Output Capacitor Selection
          4. 8.2.2.2.4 Sense Resistor Selection
          5. 8.2.2.2.5 Other External Components Selection
        3. 8.2.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
  10. 9 Device and Documentation Support
    1. 9.1 ドキュメントの更新通知を受け取る方法
    2. 9.2 サポート・リソース
    3. 9.3 Trademarks
    4. 9.4 静電気放電に関する注意事項
    5. 9.5 用語集
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information
    1. 11.1 Package Option Addendum
    2. 11.2 Tape and Reel Information
8.2.2.2.3 Output Capacitor Selection

The output capacitor reduces the high-frequency current ripple through the LED string. Excessive current ripple increases the RMS current in the LED string, therefore increasing the LED temperature.

1. Calculate the total dynamic resistance of the LED string (RLED) using the LED manufacturer's datasheet.

2. Calculate the required impedance of the output capacitor (ZOUT) given the acceptable peak-to-peak ripple current through the LED string, ILED(ripple) . IL(ripple) is the peak-to-peak inductor ripple current as calculated with the selected inductor.

3. Calculate the minimum effective output capacitance required.

4. Increase the output capacitance appropriately due to the derating effect of applied DC voltage.

See the equations below.

Equation 16. R L E D = ∆ V F ∆ I F × #   o f   L E D s
Equation 17. Z C O U T = R L E D × I L E D ( r i p p l e ) I L ( r i p p l e ) - I L E D ( r i p p l e )
Equation 18. C C O U T = 1 2 π × f S W × Z C O U T

Once the output capacitor is chosen, the equation below can be used to estimate the peak-to-peak ripple current through the LED string.

Equation 19. I L E D ( r i p p l e ) = Z C O U T × I L ( r i p p l e ) Z C O U T + R L E D

Osram WLED is used here. The dynamic resistance of the LED is 0.67Ω at 1A forward current. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of their low ESR and small temperature coefficients. In this design, a 1µF, 100V X7R ceramic capacitor and a 0.1µF, 100V X7R ceramic capacitor are chosen. The calculated ripple current of the LED is about 6mA.