SLVSEM3D May   2020  – September 2021 TPS25850-Q1 , TPS25851-Q1 , TPS25852-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  Selectable Output Voltage (VSET)
      9. 10.3.9  Current Limit and Short Circuit Protection
        1. 10.3.9.1 USB Switch Programmable Current Limit (ILIM)
        2. 10.3.9.2 Interlocking for Two-Level USB Switch Current Limit
        3. 10.3.9.3 Cycle-by-Cycle Buck Current Limit
        4. 10.3.9.4 OUT Current Limit
      10. 10.3.10 Cable Compensation
      11. 10.3.11 Thermal Management With Temperature Sensing (TS) and OTSD
      12. 10.3.12 Thermal Shutdown
      13. 10.3.13 USB Enable On/Off Control (TPS25852-Q1)
      14. 10.3.14 FAULT Indication (TPS25851-Q1 and TPS25852-Q1)
      15. 10.3.15 USB Specification Overview
      16. 10.3.16 USB Type-C® Basics
        1. 10.3.16.1 Configuration Channel
        2. 10.3.16.2 Detecting a Connection
        3. 10.3.16.3 Plug Polarity Detection (TPS25851-Q1)
      17. 10.3.17 USB Port Operating Modes
        1. 10.3.17.1 USB Type-C® Mode
        2. 10.3.17.2 Dedicated Charging Port (DCP) Mode (TPS25850-Q1 Only)
          1. 10.3.17.2.1 DCP BC1.2 and YD/T 1591-2009
          2. 10.3.17.2.2 DCP Divider-Charging Scheme
          3. 10.3.17.2.3 DCP 1.2-V Charging Scheme
        3. 10.3.17.3 DCP Auto Mode (TPS25850-Q1)
    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
      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

10.3.6 Minimum ON-Time, Minimum OFF-Time

Minimum ON-time, TON_MIN, is the smallest duration of time that the HS switch can be on. TON_MIN is typically 84 ns in the TPS2585x-Q1. Minimum OFF-time, TOFF_MIN, is the smallest duration that the HS switch can be off. TOFF_MIN is typically 81 ns in the TPS2585x-Q1. In CCM (FPWM) operation, TON_MIN and TOFF_MIN limit the voltage conversion range given in a selected switching frequency.

The minimum duty cycle allowed is:

Equation 5. DMIN = TON_MIN × fSW

And the maximum duty cycle allowed is:

Equation 6. DMAX = 1 – TOFF_MIN × fSW

Given fixed TON_MIN and TOFF_MIN, the higher the switching frequency, the narrower the range of the allowed duty cycle.

Given an output voltage, the choice of the switching frequency affects the allowed input voltage range, solution size, and efficiency. The maximum operation supply voltage can be found by:

Equation 7. GUID-3922E2DB-A0A2-46C1-85E4-348841D22BB8-low.gif

At lower supply voltage, the switching frequency is limited by TOFF_MIN. The minimum VIN can be approximated by:

Equation 8. GUID-54852D19-1A6B-4D15-BBA9-BA919C4A0DF4-low.gif

Considering power losses in the system with heavy load operation, VIN_MAX is higher than the result calculated in Equation 7.

If minimum ON-time or minimum OFF-time do not support the desired conversion ratio, frequency is reduced, automatically allowing regulation to be maintained during load dump and with very low dropout during cold crank even with high operating-frequency setting.