SLVSHH9 February   2024 TPS54KC23

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  Internal VCC LDO and Using External Bias On the VCC Pin
      2. 6.3.2  Enable
      3. 6.3.3  Adjustable Soft Start
      4. 6.3.4  Power Good
      5. 6.3.5  Output Voltage Setting
      6. 6.3.6  Remote Sense
      7. 6.3.7  D-CAP4 Control
      8. 6.3.8  Multifunction Select (MSEL) Pin
      9. 6.3.9  Low-side MOSFET Zero-Crossing
      10. 6.3.10 Current Sense and Positive Overcurrent Protection
      11. 6.3.11 Low-side MOSFET Negative Current Limit
      12. 6.3.12 Overvoltage and Undervoltage Protection
      13. 6.3.13 Output Voltage Discharge
      14. 6.3.14 UVLO Protection
      15. 6.3.15 Thermal Shutdown
    4. 6.4 Device Functional Modes
      1. 6.4.1 Auto-Skip Eco-mode Light Load Operation
      2. 6.4.2 Forced Continuous-Conduction Mode
      3. 6.4.3 Powering the Device From a Single Bus
      4. 6.4.4 Powering the Device From a Split-rail Configuration
  8. 7 Application and Implementation
    1. 7.1 Application Information
    2. 7.2 Typical Application
      1. 7.2.1 Design Requirements
      2. 7.2.2 Detailed Design Procedure
        1. 7.2.2.1  Output Voltage Setting Point
        2. 7.2.2.2  Choose the Switching Frequency and the Operation Mode
        3. 7.2.2.3  Choose the Inductor
        4. 7.2.2.4  Set the Current Limit (ILIM)
        5. 7.2.2.5  Choose the Output Capacitor
        6. 7.2.2.6  RAMP Selection
        7. 7.2.2.7  Choose the Input Capacitors (CIN)
        8. 7.2.2.8  Soft-Start Capacitor (SS Pin)
        9. 7.2.2.9  EN Pin Resistor Divider
        10. 7.2.2.10 VCC Bypass Capacitor
        11. 7.2.2.11 BOOT Capacitor
        12. 7.2.2.12 RC Snubber
        13. 7.2.2.13 PG Pullup Resistor
      3. 7.2.3 Application Curves
    3. 7.3 Power Supply Recommendations
    4. 7.4 Layout
      1. 7.4.1 Layout Guidelines
      2. 7.4.2 Layout Example
  9. 8 Device and Documentation Support
    1. 8.1 Documentation Support
      1. 8.1.1 Related Documentation
    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

Package Options

Mechanical Data (Package|Pins)
Thermal pad, mechanical data (Package|Pins)
Orderable Information

6.3.3 Adjustable Soft Start

The device implements an externally adjustable soft start set by the external soft-start capacitor (CSS) connected between the SS and AGND pins. The SS pin has a 36µA internal pullup current source (ISS) that charges CSS. The FB voltage follows the SS pin voltage with a small offset. When the SS pin voltage is near the internal reference voltage, a smooth transition occurs to FB being regulated to the internal reference. The device soft-start period is complete when the SS pin voltage reaches VSS(DONE) given in the Electrical Characteristics table.

The CSS value can be determined by Equation 1. The soft-start capacitor must be in the range of 10nF to 1µF. TI does not recommend leaving the SS pin open. The soft-start time is typically selected to either satisfy timing requirements in the system or to minimize inrush current to charge the output capacitors during start-up.

Equation 1. C S S = t S S × I S S V F B _ R E G

If during normal operation VIN goes below the UVLO, VCC goes below the UVLO, the EN pin is pulled below the VEN(F) threshold, the output turns off due to under voltage protection or a thermal shutdown event occurs, the device stops switching and an internal discharge path is enabled to discharge the SS pin capacitance. This internal discharge path remains active as long as there is sufficient VCC to enable the path, typically 1.5V. The internal discharge path is disabled when the device enters the soft-start period during power up.

CSS also sets the hiccup wait-time before a restart attempt. After a fault triggers the hiccup response the soft-start capacitor is discharged through the internal discharge path, then recharged with the internal pullup current source to VSS(DONE) seven times. This response sets the hiccup wait time to 7×tSS. Figure 6-1 shows the device entering hiccup due to an output short circuit and Figure 6-2 shows the device exiting hiccup after the output short has been removed.

GUID-20240124-SS0I-56H4-ZTVD-WRXXPTGK54GB-low.svgFigure 6-1 Entering Hiccup
GUID-20240124-SS0I-C9Q0-SLKC-CCGLW6BVNZZK-low.svgFigure 6-2 Exiting Hiccup