SLVSH68B June   2023  – June 2024 TPS543B25T

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  VIN Pins and VIN UVLO
      2. 6.3.2  Internal Linear Regulator and Bypassing
      3. 6.3.3  Enable and Adjustable UVLO
        1. 6.3.3.1 Internal Sequence of Events During Start-Up
      4. 6.3.4  Switching Frequency Selection
      5. 6.3.5  Switching Frequency Synchronization to an External Clock
        1. 6.3.5.1 Internal PWM Oscillator Frequency
        2. 6.3.5.2 Loss of Synchronization
        3. 6.3.5.3 Interfacing the SYNC/FSEL Pin
      6. 6.3.6  Remote Sense Amplifier and Adjusting the Output Voltage
      7. 6.3.7  Loop Compensation Guidelines
        1. 6.3.7.1 Output Filter Inductor Tradeoffs
        2. 6.3.7.2 Ramp Capacitor Selection
        3. 6.3.7.3 Output Capacitor Selection
        4. 6.3.7.4 Design Method for Good Transient Response
      8. 6.3.8  Soft Start and Prebiased Output Start-Up
      9. 6.3.9  MSEL Pin
      10. 6.3.10 Power Good (PG)
      11. 6.3.11 Output Overload Protection
        1. 6.3.11.1 Positive Inductor Current Protection
        2. 6.3.11.2 Negative Inductor Current Protection
      12. 6.3.12 Output Overvoltage and Undervoltage Protection
      13. 6.3.13 Overtemperature Protection
      14. 6.3.14 Output Voltage Discharge
    4. 6.4 Device Functional Modes
      1. 6.4.1 Forced Continuous-Conduction Mode
      2. 6.4.2 Discontinuous Conduction Mode During Soft Start
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Applications
      1. 7.2.1 1.0V Output, 1MHz Application
        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  Output Inductor Selection
          4. 7.2.1.2.4  Output Capacitor
          5. 7.2.1.2.5  Input Capacitor
          6. 7.2.1.2.6  Adjustable Undervoltage Lockout
          7. 7.2.1.2.7  Output Voltage Resistors Selection
          8. 7.2.1.2.8  Bootstrap Capacitor Selection
          9. 7.2.1.2.9  VDRV and VCC Capacitor Selection
          10. 7.2.1.2.10 PGOOD Pullup Resistor
          11. 7.2.1.2.11 Current Limit Selection
          12. 7.2.1.2.12 Soft-Start Time Selection
          13. 7.2.1.2.13 Ramp Selection and Control Loop Stability
          14. 7.2.1.2.14 MODE Pin
        3. 7.2.1.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
      3. 7.4.3 Thermal Performance
  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 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
7.2.1.2.2 Switching Frequency

The first step is to decide on a switching frequency. The TPS543B25T can operate at five different frequencies from 500kHz to 2.2MHz. fSW is set by the resistor value from the FSEL pin to ground. Typically, the highest switching frequency possible is desired because the highest switching frequency produces the smallest design size. A high switching frequency allows for smaller inductors and output capacitors compared to a power supply that switches at a lower frequency. The main tradeoff made with selecting a higher switching frequency is extra switching power loss, which hurts the efficiency of the regulator.

The maximum switching frequency for a given application can be limited by the minimum on time of the regulator and the maximum fSW can be estimated with Equation 15. Using the maximum minimum on time of 40ns and 18.0V maximum input voltage for this application, the maximum switching frequency is 1389kHz. The selected switching frequency must also consider the tolerance of the switching frequency. A switching frequency of 1000kHz was selected for a good balance of design size and efficiency. To set the frequency to 1000kHz the selected FSEL resistor is 11.8kΩ per Table 6-1.

Equation 15. TPS543B25T

Figure 7-2 shows the maximum recommended input voltage versus output voltage for each FSEL frequency. This graph uses the maximum minimum on time of 40ns and includes 10% tolerance on the switching frequency.

TPS543B25T Maximum Input Voltage vs Output VoltageFigure 7-2 Maximum Input Voltage vs Output Voltage