SLVSJB8A July   2025  – September 2025 TPS543021

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  Fixed-Frequency PWM Control
      2. 6.3.2  Light Load Operation
      3. 6.3.3  Error Amplifier
      4. 6.3.4  Slope Compensation and Output Current
      5. 6.3.5  Enable and Adjusting Undervoltage Lockout
      6. 6.3.6  Safe Start-Up into Prebiased Outputs
      7. 6.3.7  Voltage Reference
      8. 6.3.8  Adjustable Output Voltage
      9. 6.3.9  Internal Soft Start
      10. 6.3.10 Bootstrap Voltage (BOOT)
      11. 6.3.11 Overcurrent Protection
        1. 6.3.11.1 High-Side MOSFET Overcurrent Protection
        2. 6.3.11.2 Low-Side MOSFET Overcurrent Protection
      12. 6.3.12 Spread Spectrum
      13. 6.3.13 Output Overvoltage Protection (OVP)
      14. 6.3.14 Thermal Shutdown
    4. 6.4 Device Functional Modes
      1. 6.4.1 Normal Operation
      2. 6.4.2 PFM Mode Operation
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 TPS543021 6V to 28V Input, 5V Output Converter
      2. 7.2.2 Design Requirements
      3. 7.2.3 Detailed Design Procedure
        1. 7.2.3.1 Custom Design With WEBENCH® Tools
        2. 7.2.3.2 Output Voltage Setpoint
        3. 7.2.3.3 Input Capacitor Selection
        4. 7.2.3.4 Bootstrap Capacitor Selection
        5. 7.2.3.5 Undervoltage Lockout Setpoint
        6. 7.2.3.6 Output Filter Components
          1. 7.2.3.6.1 Inductor Selection
          2. 7.2.3.6.2 Output Capacitor Selection
          3. 7.2.3.6.3 Feedforward Capacitor
      4. 7.2.4 Application Curves
    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 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

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information
7.2.3.6.2 Output Capacitor Selection

Consider three primary factors when selecting the value of the output capacitor. The output capacitor determines the modulator pole, the output voltage ripple, and how the regulator responds to a large change in load current. The output capacitance must be selected based on the more stringent of these three criteria.

The desired response to a large change in the load current is the first criterion. The output capacitor must supply the load with current when the regulator cannot. This situation occurs if the desired hold-up times are present for the regulator. In this case, the output capacitor must hold the output voltage above a certain level for a specified amount of time after the input power is removed. The regulator is also temporarily unable to supply sufficient output current if a large, fast increase occurs affecting the current requirements of the load, such as a transition from no load to full load. The regulator usually requires four or more clock cycles for the control loop to notice the change in load current and output voltage and to adjust the duty cycle to react to the change. The output capacitor must be sized to supply the extra current to the load until the control loop responds to the load change. The output capacitance must be large enough to supply the difference in current for four or more clock cycles while only allowing a tolerable amount of drop in the output voltage. Use the following equation to calculate the minimum required output capacitance.

Equation 11. CO=2×∆IOUTfSW×∆VOUT

where:

  • ∆IOUT is the change in output current
  • ƒSW is the switching frequency of the regulator
  • ∆V(OUT ) is the allowable change in the output voltage

For this example, the transient load response is specified as a 5% change in the output voltage, VOUT, for a load step of 1.5A. So the ΔIOUT = 1.5A and ΔVOUT = 0.25V. Using these values results in a minimum capacitance of 30μF. This value does not consider the ESR of the output capacitor in the output voltage change. For ceramic capacitors, the ESR is usually small enough to ignore in this calculation.

Equation 12 calculates the minimum output capacitance required to meet the output voltage ripple specification. In this case, the maximum output voltage ripple is 25mV. Under this requirement, Equation 12 yields 13.13μF.

Equation 12. CO=18×fSW×1VOUTrippleIripple

where:

  • ƒSW is the switching frequency
  • V(OUTripple) is the maximum allowable output voltage ripple
  • I(ripple) is the inductor ripple current

Use Equation 13 to calculate the maximum ESR an output capacitor can have to meet the output-voltage ripple specification. Equation 13 indicates the ESR must be less than 23.8mΩ. In this case, the ESR of the ceramic capacitor is much smaller than 23.8mΩ.

Equation 13. RESR<VOUTrippleIripple

Additional capacitance deratings for aging, temperature, and DC bias must be considered, which increases this minimum value. For this example, three 10uF 16V, X7R ceramic capacitors are used, two 22uF 10V, X7R ceramic capacitors also can used if the total effective capacitance larger than 30uF at 5VOUT bias. Capacitors generally have limits to the amount of ripple current the capacitors can handle without failing or producing excess heat. An output capacitor that can support the inductor ripple current must be specified. Some capacitor data sheets specify the RMS value of the maximum ripple current. Use Equation 14 to calculate the RMS ripple current that the output capacitor must support.

Equation 14. ICOUT(RMS)=112×VOUT×VIN(MAX)-VOUTVIN(MAX)×LO×fSW×NC