SLVSHL9 November   2024 TPS922051

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  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 Receiving Notification of Documentation Updates
    2. 9.2 Support Resources
    3. 9.3 Trademarks
    4. 9.4 Electrostatic Discharge Caution
    5. 9.5 Glossary
  11. 10Revision History
  12. 11Mechanical, Packaging, and Orderable Information
    1. 11.1 Package Option Addendum
    2. 11.2 Tape and Reel Information
8.2.1.2.1 Inductor Selection

For this design, the input voltage is a 24V rail with 10% variation. The output is 4 white LEDs in series and the inductor current ripple by requirement is less than 30% of maximum inductor current. To choose a proper peak-to-peak inductor current ripple, the low-side FET current limit should 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 the equation below to calculate the recommended value of the output inductor L.

Equation 2. L = V O U T × V I N ( m a x ) - V O U T V I N ( m a x ) × K I N D × I L ( m a x ) × f S W

where

  • KIND is a coefficient that represents the amount of inductor ripple current relative to the maximum LED current.
  • IL(max) is the maximum inductor current.
  • fSW is the switching frequency.
  • VIN(max) is the maximum input voltage.
  • VOUT is the sum of the voltage across LED load and the voltage across sense resistor.

With the chosen inductor value, the user can calculate the actual inductor current ripple using the equation below.

Equation 3. I L ( r i p p l e ) = V O U T × V I N ( m a x ) - V O U T V I N ( m a x ) × L × f S W

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

Equation 4. I L ( p e a k ) = I L m a x + I L ( r i p p l e ) 2
Equation 5. I L ( r m s ) = I L m a x 2 + I L ( r i p p l e ) 2 12

In this design, VIN(max) = 24V, VOUT = 12V, ILED = 2A, fSW = 400kHz, choose KIND = 0.3, the calculated inductance is 25µH. A 33µH inductor is chosen. With this inductor, the ripple, peak, and rms currents of the inductor are 0.45A, 2.2A, and 2.01A, respectively.