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
7.2.1.2.3 Input Capacitors

The TPS5420-Q1 requires an input decoupling capacitor and, depending on the application, a bulk input capacitor. The recommended value for the decoupling capacitor is 10μF. A high-quality ceramic type X5R or X7R is required. For some applications, a smaller-value decoupling capacitor can be used, if the input voltage and current ripple ratings are not exceeded. The voltage rating must be greater than the maximum input voltage, including ripple. For this design, two 4.7μF capacitors, C1 and C4 are used to allow for smaller 1812 case size to be used while maintaining a 50V rating.

This input ripple voltage can be approximated by Equation 2 :

Equation 2. TPS5420-Q1

Where IOUT(MAX) is the maximum load current, fSW is the switching frequency, CI is the input capacitor value, and ESRMAX is the maximum series resistance of the input capacitor.

The maximum RMS ripple current also needs to be checked. For worst-case conditions, this is approximated by Equation 3:

Equation 3. TPS5420-Q1

In this case, the calculated input ripple voltage is 118 mV, and the RMS ripple current is 1 A. The maximum voltage across the input capacitors would be VIN max plus delta VIN/2. The chosen input decoupling capacitors are rated for 50V, and the ripple current capacity for each is 3A at 500kHz, providing ample margin. The actual measured input ripple voltage can be larger than the calculated value, due to the output impedance of the input voltage source and parasitics associated with the layout.

CAUTION:

The maximum ratings for voltage and current are not to be exceeded under any circumstance.

Additionally, some bulk capacitance can be needed, especially if the TPS5420-Q1 circuit is not located within approximately two inches from the input voltage source. The value for this capacitor is not critical, but it must be rated to handle the maximum input voltage including ripple voltage and must filter the output so that input ripple voltage is acceptable.