SLVS632K January   2006  – January 2024 TPS5430 , TPS5431

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 (DDA Package)
    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) and Internal Compensation
      7. 6.3.7  Voltage Feed-Forward
      8. 6.3.8  Pulse-Width-Modulation (PWM) Control
      9. 6.3.9  Overcurrent Limiting
      10. 6.3.10 Overvoltage Protection
      11. 6.3.11 Thermal Shutdown
    4. 6.4 Device Functional Modes
      1. 6.4.1 Operation near Minimum Input Voltage
      2. 6.4.2 Operation with ENA control
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Applications
      1. 7.2.1 12-V Input to 5.0-V Output
        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
          5. 7.2.1.2.5 Output Voltage Set-Point
          6. 7.2.1.2.6 BOOT Capacitor
          7. 7.2.1.2.7 Catch Diode
          8. 7.2.1.2.8 Advanced Information
            1. 7.2.1.2.8.1 Output Voltage Limitations
            2. 7.2.1.2.8.2 Internal Compensation Network
            3. 7.2.1.2.8.3 Thermal Calculations
        3. 7.2.1.3 Application Curves
      2. 7.2.2 Wide Input Voltage Ranges with TPS5430
        1. 7.2.2.1 Design Requirements
        2. 7.2.2.2 Detailed Design Procedure
        3. 7.2.2.3 Wide Input Voltage Ranges with TPS5431
          1. 7.2.2.3.1 Design Requirements
          2. 7.2.2.3.2 Detailed Design Procedure
      3. 7.2.3 Circuit Using Ceramic Output Filter Capacitors
        1. 7.2.3.1 Design Requirements
        2. 7.2.3.2 Detailed Design Procedure
          1. 7.2.3.2.1 Output Filter Component Selection
          2. 7.2.3.2.2 External Compensation Network
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Device Support
      1. 8.1.1 Third-Party Products Disclaimer
      2. 8.1.2 Development Support
        1. 8.1.2.1 Custom Design With WEBENCH® Tools
    2. 8.2 Receiving Notification of Documentation Updates
    3. 8.3 Support Resources
    4. 8.4 Trademarks
    5. 8.5 Electrostatic Discharge Caution
    6. 8.6 Glossary
  10. 9 Revision History
  11. 10Mechanical, Packaging, and Orderable Information
7.2.1.2.4.2 Capacitor Selection

The important design factors for the output capacitor are dc voltage rating, ripple current rating, and equivalent series resistance (ESR). The dc voltage and ripple current ratings cannot be exceeded. The ESR is important because along with the inductor ripple current it determines the amount of output ripple voltage. The actual value of the output capacitor is not critical, but some practical limits do exist. Consider the relationship between the desired closed loop crossover frequency of the design and LC corner frequency of the output filter. Due to the design of the internal compensation, it is desirable to keep the closed loop crossover frequency in the range 3 kHz to 30 kHz as this frequency range has adequate phase boost to allow for stable operation. For this design example, it is assumed that the intended closed loop crossover frequency will be between 2590 Hz and 24 kHz and also below the ESR zero of the output capacitor. Under these conditions the closed loop crossover frequency is related to the LC corner frequency by:

Equation 7. GUID-AAE6836D-23DF-4F1A-BBF6-F4BB2E2C7CED-low.gif

And the desired output capacitor value for the output filter to:

Equation 8. GUID-032D41D4-D6D9-4650-9350-714C4A1117AB-low.gif

For a desired crossover of 18 kHz and a 15 μH inductor, the calculated value for the output capacitor is 220 μF. The capacitor type must be chosen so that the ESR zero is above the loop crossover. The maximum ESR must be:

Equation 9. GUID-1CF891B0-06A6-415F-AC36-7274F43FF2AB-low.gif

The maximum ESR of the output capacitor also determines the amount of output ripple as specified in the initial design parameters. The output ripple voltage is the inductor ripple current times the ESR of the output filter. Check that the maximum specified ESR as listed in the capacitor data sheet results in an acceptable output ripple voltage:

Equation 10. GUID-D4BF420D-3956-46F1-A729-290EE79C1487-low.gif

where

  • ΔVPP is the desired peak-to-peak output ripple.
  • NC is the number of parallel output capacitors.
  • FSW is the switching frequency.

For this design example, a single 220 μF output capacitor is chosen for C3. The calculated RMS ripple current is 143 mA and the maximum ESR required is 40 mΩ. A capacitor that meets these requirements is a Sanyo Poscap 10TPB220M, rated at 10 V with a maximum ESR of 40 mΩ and a ripple current rating of 3 A. An additional small 0.1 μF ceramic bypass capacitor can also used, but is not included in this design.

The minimum ESR of the output capacitor must also be considered. For good phase margin, the ESR zero when the ESR is at a minimum must not be too far above the internal compensation poles at 24 kHz and 54 kHz.

The selected output capacitor must also be rated for a voltage greater than the desired output voltage plus one half the ripple voltage. Any derating amount must also be included. The maximum RMS ripple current in the output capacitor is given by Equation 11:

Equation 11. GUID-B2EF6D26-081D-43CD-8247-577A15E6CDEF-low.gif

where

  • NC is the number of output capacitors in parallel.
  • FSW is the switching frequency.

Other capacitor types can be used with the TPS5430, depending on the needs of the application.