SLVSGH1A April   2023  – September 2023 TPS923652 , TPS923653 , TPS923654 , TPS923655

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Revision History
  6. 5 Device Comparison Table
  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 Typical Characteristics
  9. 8 Detailed Description
    1. 8.1 Overview
    2. 8.2 Functional Block Diagram
    3. 8.3 Feature Description
      1. 8.3.1 Adaptive Off-Time Current Mode Control
        1. 8.3.1.1 Switching Frequency Settings
        2. 8.3.1.2 Spread Spectrum
      2. 8.3.2 Setting LED Current
      3. 8.3.3 Undervoltage Lockout
      4. 8.3.4 Internal Soft Start
      5. 8.3.5 Dimming Mode
        1. 8.3.5.1 PWM Dimming
        2. 8.3.5.2 Analog Dimming
        3. 8.3.5.3 Hybrid Dimming
        4. 8.3.5.4 Flexible Dimming
      6. 8.3.6 CC/CV Charging Mode
      7. 8.3.7 Fault Protection
      8. 8.3.8 Thermal Foldback
  10. 9 Application and Implementation
    1. 9.1 Application Information
    2. 9.2 Typical Application
      1. 9.2.1 TPS923654 Boost, 12-V Input, 1-A Output, 12-piece WLED 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 Sense Resistor Selection
          5. 9.2.1.2.5 Other External Components Selection
        3. 9.2.1.3 Application Curves
      2. 9.2.2 TPS923654 Buck-Boost, 24-V Input, 2-A Output, 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 Sense Resistor Selection
          5. 9.2.2.2.5 Other External Components Selection
        3. 9.2.2.3 Application Curves
    3. 9.3 Power Supply Recommendations
    4. 9.4 Layout
      1. 9.4.1 Layout Guidelines
      2. 9.4.2 Layout Example
  11. 10Device and Documentation Support
    1. 10.1 Receiving Notification of Documentation Updates
    2. 10.2 Support Resources
    3. 10.3 Trademarks
    4. 10.4 Electrostatic Discharge Caution
    5. 10.5 Glossary
  12. 11Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information
9.2.1.2.3 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 Equation 7, Equation 8, and Equation 9.

Equation 7. R L E D = ∆ V F ∆ I F × #   o f   L E D s
Equation 8. ZCOUT=RLED×ILED(ripple)IL(max)-ILED(ripple)
Equation 9. C C O U T = 1 2 π × f S W × Z C O U T

Once the output capacitor is chosen, Equation 21 can be used to estimate the peak-to-peak ripple current through the LED string.

Equation 10. ILED(ripple)=ZCOUT×IL(max)ZCOUT+RLED

CREE WLED is used here. The dynamic resistance of the LED is 0.67 ohm at 3-A 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 22-µF, 100-V X7R ceramic capacitor and a 0.1-µF, 100-V X7R ceramic capacitor are chosen. The calculated ripple current of the LED is about 65 mA.