SLVSFJ9 September   2021 TPS25854-Q1 , TPS25855-Q1

PRODUCTION DATA  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
  4. 4 Revision History
  5. 5 Description (Continued)
  6. 6 Device Comparison Table
  7. 7 Pin Configuration and Functions
  8. 8 Specifications
    1. 8.1 Absolute Maximum Ratings
    2. 8.2 ESD Ratings
    3. 8.3 Recommended Operating Conditions
    4. 8.4 Thermal Information
    5. 8.5 Electrical Characteristics
    6. 8.6 Timing Requirements
    7. 8.7 Switching Characteristics
    8. 8.8 Typical Characteristics
  9. 9 Parameter Measurement Information
  10. 10Detailed Description
    1. 10.1 Overview
    2. 10.2 Functional Block Diagram
    3. 10.3 Feature Description
      1. 10.3.1  Power Down or Undervoltage Lockout
      2. 10.3.2  Input Overvoltage Protection (OVP) - Continuously Monitored
      3. 10.3.3  Buck Converter
      4. 10.3.4  FREQ/SYNC
      5. 10.3.5  Bootstrap Voltage (BOOT)
      6. 10.3.6  Minimum ON-time, Minimum OFF-time
      7. 10.3.7  Internal Compensation
      8. 10.3.8  Current Limit and Short Circuit Protection
        1. 10.3.8.1 USB Switch Programmable Current Limit (ILIM)
        2. 10.3.8.2 Cycle-by-Cycle Buck Current Limit
        3. 10.3.8.3 OUT Current Limit
      9. 10.3.9  Cable Compensation
      10. 10.3.10 Thermal Management With Temperature Sensing (TS) and OTSD
      11. 10.3.11 Thermal Shutdown
      12. 10.3.12 FAULT Indication
      13. 10.3.13 USB Specification Overview
      14. 10.3.14 USB Type-C® Basics
        1. 10.3.14.1 Configuration Channel
        2. 10.3.14.2 Detecting a Connection
        3. 10.3.14.3 Plug Polarity Detection
      15. 10.3.15 USB Port Operating Modes
        1. 10.3.15.1 USB Type-C® Mode
        2. 10.3.15.2 Dedicated Charging Port (DCP) Mode
          1. 10.3.15.2.1 DCP BC1.2 and YD/T 1591-2009
          2. 10.3.15.2.2 DCP Divider-Charging Scheme
          3. 10.3.15.2.3 DCP 1.2-V Charging Scheme
        3. 10.3.15.3 DCP Auto Mode
    4. 10.4 Device Functional Modes
      1. 10.4.1 Shutdown Mode
      2. 10.4.2 Active Mode
  11. 11Application and Implementation
    1. 11.1 Application Information
    2. 11.2 Typical Applications
      1. 11.2.1 Design Requirements
      2. 11.2.2 Detailed Design Procedure
        1. 11.2.2.1 Output Voltage Setting
        2. 11.2.2.2 Switching Frequency
        3. 11.2.2.3 Inductor Selection
        4. 11.2.2.4 Output Capacitor Selection
        5. 11.2.2.5 Input Capacitor Selection
        6. 11.2.2.6 Bootstrap Capacitor Selection
        7. 11.2.2.7 Undervoltage Lockout Set-Point
        8. 11.2.2.8 Cable Compensation Set-Point
        9. 11.2.2.9 FAULT, POL, and THERM_WARN Resistor Selection
      3. 11.2.3 Application Curves
  12. 12Power Supply Recommendations
  13. 13Layout
    1. 13.1 Layout Guidelines
    2. 13.2 Layout Example
    3. 13.3 Ground Plane and Thermal Considerations
  14. 14Device and Documentation Support
    1. 14.1 Receiving Notification of Documentation Updates
    2. 14.2 Support Resources
    3. 14.3 Trademarks
    4. 14.4 Electrostatic Discharge Caution
    5. 14.5 Glossary
  15. 15Mechanical, Packaging, and Orderable Information

10.3.8.2 Cycle-by-Cycle Buck Current Limit

The buck regulator cycle-by-cycle current limit on both the peak and valley of the inductor current.

High-side MOSFET overcurrent protection is implemented by the nature of the peak current mode control. The HS switch current is sensed when the HS is turned on after a set blanking time. The HS switch current is compared to the output of the Error Amplifier (EA) minus slope compensation every switching cycle. The peak current of HS switch is limited by a clamped maximum peak current threshold IHS_LIMIT which is constant. So the peak current limit of the high-side switch is not affected by the slope compensation and remains constant over the full duty cycle range.

The current going through LS MOSFET is also sensed and monitored. When the LS switch turns on, the inductor current begins to ramp down. The LS switch does not turn OFF at the end of a switching cycle if its current is above the LS current limit ILS_LIMIT. The LS switch is be kept ON so that inductor current keeps ramping down, until the inductor current ramps below the LS current limit ILS_LIMIT. Then the LS switch turns OFF and the HS switch turns on after a dead time. This action is somewhat different than the more typical peak current limit, and results in Equation 10 for the maximum load current.

Equation 10. GUID-894507D7-9E3C-4AED-99CF-0CDC13240446-low.gif