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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7.2.1.2.1 Inductor Selection

For this design, the input bus voltage is a 60V rail with 10% variation. The output is 16 white LEDs in series and the inductor current ripple by requirement is less than 60% of maximum inductor current. To select a proper peak-to-peak inductor current ripple, the low-side FET current limit must not be violated when the converter works in full-load condition. This requires half of the peak-to-peak inductor current ripple to be lower than that limit. Another consideration is to ensure reasonable inductor core loss and copper loss caused by the peak-to-peak current ripple. Once this peak-to-peak inductor current ripple is chosen, use Equation 8 to calculate the recommended value of the switching inductor LSW.

Equation 8. L S W = V L E D × V B U S _ M A X - V L E D K I N D × I L E D _ M A X × F S W × V B U S _ M A X

where

  • KIND is a coefficient that represents the amount of inductor ripple current relative to the maximum inductor current.
  • ILED_MAX is the maximum LED current.
  • FSW is the switching frequency.
  • VBUS_MAX is the maximum input bus voltage.
  • VLED is the sum of the voltage across LED load.

With the chosen inductor value, the user can calculate the actual inductor current ripple using Equation 9.

Equation 9. I L _ R I P = V L E D × V B U S _ M A X - V L E D L S W × F S W × V B U S _ M A X

The ratings of inductor RMS current and saturation current must be greater than those seen in the system requirement. This is to maintain no inductor overheat or saturation occurring. During power up, transient conditions or fault conditions, the inductor current can exceed the normal operating current and reach the current limit. Therefore, selecting a saturation current rating equal to or greater than the converter current limit is preferred. The peak-inductor-current and RMS current equations are shown in Equation 10 and Equation 11.

Equation 10. I L _ P E A K = I L _ M A X + I L _ R I P 2
Equation 11. I L _ R M S = I L _ M A X 2 + I L _ R I P 2 12

In this design, VBUS_MAX = 66V, VLED = 48V, ILED = 5A, FSW = 400kHz, select KIND = 0.6, the calculated switching inductance is 38µH. A 33µH inductor is chosen. With this inductor, the ripple, peak, and rms currents of the inductor are 0.7A, 1.35A, and 1.02A, respectively.