SLVS875C January   2009  – November 2014 TPS54332

PRODUCTION DATA.  

  1. Features
  2. Applications
  3. Description
    1.     Device Images
      1.      Simplified Schematic
      2.      Efficiency
  4. Revision History
  5. Pin Configuration and Functions
    1.     Pin Functions
  6. Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 Handling 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
  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 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
  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  Switching Frequency
        2. 8.2.2.2  Output Voltage Set Point
        3. 8.2.2.3  Input Capacitors
        4. 8.2.2.4  Output Filter Components
        5. 8.2.2.5  Inductor Selection
        6. 8.2.2.6  Capacitor Selection
        7. 8.2.2.7  Compensation Components
        8. 8.2.2.8  Bootstrap Capacitor
        9. 8.2.2.9  Catch Diode
        10. 8.2.2.10 Output Voltage Limitations
        11. 8.2.2.11 Power Dissipation Estimate
      3. 8.2.3 Application Curves
  9. Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
    3. 10.3 Estimated Circuit Area
    4. 10.4 Electromagnetic Interference (EMI) Considerations
  11. 11Device and Documentation Support
    1. 11.1 Device Support
      1. 11.1.1 Development Support
    2. 11.2 Trademarks
    3. 11.3 Electrostatic Discharge Caution
    4. 11.4 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

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订购信息

Inductor Selection

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

Equation 8. TPS54332 q_lmin_lvs875.gif

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 may be used. For designs using low-ESR output capacitors such as ceramics, a value as high as KIND = 0.4 may 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, it is important that the RMS current and saturation current ratings not be exceeded. The peak-to-peak inductor current is calculated using Equation 9.

Equation 9. TPS54332 q_ilpp1_lus851.gif

The RMS inductor current can be found from Equation 10.

Equation 10. TPS54332 q_ilrms_lvs875.gif

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

Equation 11. TPS54332 q_ilpk_lvs875.gif
Equation 12.

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. It 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 will have lower AC current and result in lower output voltage ripple, while smaller inductor values will 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.