SLVSI14 March   2026 TPS922152

ADVANCE INFORMATION  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Pin Configuration and Functions
  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 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 Adaptive Off-Time Mode
      2. 6.3.2 Setting LED Current
      3. 6.3.3 VIN UVLO & Clamping
      4. 6.3.4 Dimming Mode
        1. 6.3.4.1 PWM Dimming
        2. 6.3.4.2 Analog Dimming
        3. 6.3.4.3 External Shunt Dimming
      5. 6.3.5 Fault Protection
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 TPS922152 60V Input Bus, 5A Output, 16-piece WLED With Analog and PWM Dimming
        1. 7.2.1.1 Design Requirements
        2. 7.2.1.2 Detailed Design Procedure
          1. 7.2.1.2.1 Inductor Selection
          2. 7.2.1.2.2 Input Capacitor Selection
          3. 7.2.1.2.3 Output Capacitor Selection
          4. 7.2.1.2.4 Sense Resistor Selection
          5. 7.2.1.2.5 Other External Components Selection
        3. 7.2.1.3 Application Curves
    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 Receiving Notification of Documentation Updates
    2. 8.2 Support Resources
    3. 8.3 Trademarks
    4. 8.4 Electrostatic Discharge Caution
    5. 8.5 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information

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7.2.1.2.3 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 data sheet.

2. Calculate the required impedance of the output capacitor (ZCOUT) given the acceptable peak-to-peak ripple current through the LED string, ILED_RIP . IL_RIP is the peak-to-peak inductor ripple currentIL_MAX is the inductor maximum 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 13, Equation 14, and Equation 15.

Equation 13. RLED=∆VF∆IF×# of LEDs
Equation 14. Z C O U T = R L E D × I L E D _ R I P I L _ R I P - I L E D _ R I P
Equation 15. C O U T = 1 2 π × F S W × K D R × Z C O U T

Once the output capacitor is chosen, Equation 16 can be used to estimate the peak-to-peak ripple current through the LED string.

Equation 16. I L E D _ R I P = Z C O U T × I L _ R I P Z C O U T + R L E D

CREE WLED is used here. The dynamic resistance of the LED is 0.67Ω at 3A forward current. Ceramic capacitors with X5R or X7R dielectrics are highly recommended because of the low ESR and small temperature coefficients. In this design, a 3.3µF, 100V X7R ceramic capacitor and a 0.1µF, 100V X7R ceramic capacitor are chosen. The calculated ripple current of the LED is about 100mA.