SLVS752D November   2007  – April 2026 TPS5420-Q1

PRODUCTION DATA  

  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  Oscillator Frequency
      2. 6.3.2  Voltage Reference
      3. 6.3.3  Enable (ENA) and Internal Slow Start
      4. 6.3.4  Undervoltage Lockout (UVLO)
      5. 6.3.5  Boost Capacitor (BOOT)
      6. 6.3.6  Output Feedback (VSENSE)
      7. 6.3.7  Internal Compensation
      8. 6.3.8  Voltage Feed Forward
      9. 6.3.9  Pulse-Width-Modulation (PWM) Control
      10. 6.3.10 Overcurrent Limiting
      11. 6.3.11 Overvoltage Protection (OVP)
      12. 6.3.12 Thermal Shutdown
    4. 6.4 Device Functional Modes
      1. 6.4.1 Minimum Input Voltage
      2. 6.4.2 ENA Control
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Application Circuits
        1. 7.2.1.1 Design Requirements
        2. 7.2.1.2 Detailed Design Procedure
          1. 7.2.1.2.1  Custom Design With WEBENCH® Tools
          2. 7.2.1.2.2  Switching Frequency
          3. 7.2.1.2.3  Input Capacitors
          4. 7.2.1.2.4  Output Filter Components
            1. 7.2.1.2.4.1 Inductor Selection
            2. 7.2.1.2.4.2 Capacitor Selection
            3.         44
            4.         45
          5. 7.2.1.2.5  Output Voltage Setpoint
          6. 7.2.1.2.6  Boot Capacitor
          7. 7.2.1.2.7  Catch Diode
          8. 7.2.1.2.8  Output Filter Component Selection
          9. 7.2.1.2.9  External Compensation Network
          10. 7.2.1.2.10 Advanced Information
            1. 7.2.1.2.10.1 Output Voltage Limitations
            2. 7.2.1.2.10.2 Internal Compensation Network
            3. 7.2.1.2.10.3 Thermal Calculations
        3. 7.2.1.3 Application Curves
      2. 7.2.2 Additional Circuits
      3. 7.2.3 Circuit Using Ceramic Output Filter Capacitors
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 PCB Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Development Support
        1. 8.1.1.1 Custom Design With WEBENCH® Tools
    2. 8.2 Documentation Support
      1. 8.2.1 Related Documentation
    3. 8.3 Receiving Notification of Documentation Updates
    4. 8.4 Support Resources
    5. 8.5 Trademarks
    6. 8.6 Electrostatic Discharge Caution
    7. 8.7 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information
7.2.1.2.4.1 Inductor Selection

To calculate the minimum value of the output inductor, use Equation 4:

Equation 4. TPS5420-Q1

KIND is a coefficient that represents the amount of inductor ripple current relative to the maximum output current. Three things need to be considered when determining the amount of ripple current in the inductor: the peak-to-peak ripple current affects the output ripple voltage amplitude, the ripple current affects the peak switch current, and the amount of ripple current determines at what point the circuit becomes discontinuous. For designs using the TPS5420-Q1, KIND of 0.2 to 0.3 yields good results. Low output ripple voltages are obtained when paired with the proper output capacitor, the peak switch current is below the current limit set point, and low load currents can be sourced before discontinuous operation.

For this design example, use KIND = 0.2, and the minimum inductor value is 31μH. The next highest standard value used in this design is 33μH.

For the output filter inductor, it is important that the RMS current and saturation current ratings not be exceeded. The RMS inductor current is found from Equation 5:

Equation 5. TPS5420-Q1

and the peak inductor current is determined from Equation 6:

Equation 6. TPS5420-Q1

For this design, the RMS inductor current is 2.002A, and the peak inductor current is 2.16A. The chosen inductor is a Coilcraft MSS1260-333 type. The nominal inductance is 33μH. It has a saturation current rating of 2.2A and a RMS current rating of 2.7A, which meet the requirements. Inductor values for use with the TPS5420-Q1 are in the range of 10μH to 100μH.