SLVS875D January   2009  – September 2023 TPS54332

PRODUCTION DATA  

  1.   1
  2. 1 Features
  3. 2 Applications
  4. 3 Description
  5. 4 Revision History
  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 Switching Characteristics
    7. 6.7 Typical Characteristics: Characterization Curves
    8. 6.8 Typical Characteristics: Supplemental Application Curves
  8. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1  Fixed Frequency PWM Control
      2. 7.3.2  Voltage Reference (Vref)
      3. 7.3.3  Bootstrap Voltage (BOOT)
      4. 7.3.4  Enable and Adjustable Input Undervoltage Lockout (VIN UVLO)
      5. 7.3.5  Programmable Slow Start Using the SS Pin
      6. 7.3.6  Error Amplifier
      7. 7.3.7  Slope Compensation
      8. 7.3.8  Current Mode Compensation Design
      9. 7.3.9  Overcurrent Protection and Frequency Shift
      10. 7.3.10 Overvoltage Transient Protection
      11. 7.3.11 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Operation With VIN < 3.5 V
      2. 7.4.2 Operation With EN Control
      3. 7.4.3 Eco-mode
  9. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1  Custom Design with WEBENCH® Tools
        2. 8.2.2.2  Switching Frequency
        3. 8.2.2.3  Output Voltage Set Point
        4. 8.2.2.4  Input Capacitors
        5. 8.2.2.5  Output Filter Components
        6. 8.2.2.6  Inductor Selection
        7. 8.2.2.7  Capacitor Selection
        8. 8.2.2.8  Compensation Components
        9. 8.2.2.9  Bootstrap Capacitor
        10. 8.2.2.10 Catch Diode
        11. 8.2.2.11 Output Voltage Limitations
        12. 8.2.2.12 Power Dissipation Estimate
      3. 8.2.3 Application Curves
    3. 8.3 Power Supply Recommendations
    4. 8.4 Layout
      1. 8.4.1 Layout Guidelines
      2. 8.4.2 Layout Example
      3. 8.4.3 Estimated Circuit Area
      4. 8.4.4 Electromagnetic Interference (EMI) Considerations
  10. 9 Device and Documentation Support
    1. 9.1 Device Support
      1. 9.1.1 Development Support
        1. 9.1.1.1 Custom Design with WEBENCH® Tools
    2. 9.2 Support Resources
    3. 9.3 Receiving Notification of Documentation Updates
    4. 9.4 Trademarks
    5. 9.5 Electrostatic Discharge Caution
    6. 9.6 Glossary
  11. 10Mechanical, Packaging, and Orderable Information

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

8.2.2.6 Inductor Selection

To calculate the minimum value of the output inductor, use Equation 8.

Equation 8. L M I N = V O U T M A X × V I N M A X - V O U T V I N M A X × K I N D × I O U T × F S W × 0.8

KIND is a coefficient that represents the amount of inductor ripple current relative to the maximum output current. In general, this value is at the discretion of the designer; however, the following guidelines can be used. For designs using low-ESR output capacitors such as ceramics, a value as high as KIND = 0.4 can be used. When using higher ESR output capacitors, KIND = 0.2 yields better results.

For this design example, use KIND = 0.3 and the minimum inductor value is calculated to be 2.48 μH. For this design, a l 2.5-μH inductor is chosen.

For the output filter inductor, make sure that the RMS current and saturation current ratings not be exceeded. The peak-to-peak inductor current is calculated using Equation 9.

Equation 9. ILPP=VOUT×VINMAX-VOUTVINMAX×LOUT×FSW×0.8

The RMS inductor current can be found from Equation 10.

Equation 10. ILRMS=IOUTMAX2+112×VOUT×VINMAX-VOUTVINMAX×LOUT×FSW×0.82

And the peak inductor current can be determined with Equation 11.

Equation 11. ILPK=IOUTMAX+VOUT×VINMAX-VOUT1.6×VINMAX×LOUT×FSW

For this design, the RMS inductor current is 3.51 A and the peak inductor current is 4.15 A. The chosen inductor is a Coilcraft MSS1038-252NX_ 2.5 μH. The inductor has a saturation current rating of 7.62 A and an RMS current rating of 6.55 A, meeting these requirements. Smaller or larger inductor values can be used depending on the amount of ripple current the designer wishes to allow so long as the other design requirements are met. Larger value inductors have lower AC current and result in lower output voltage ripple, while smaller inductor values increase ac current and output voltage ripple. In general, inductor values for use with the TPS54332 are in the range of 1 μH to 47 μH.