SLVSEI2A November   2018  – May 2019 TPS56339

PRODUCTION DATA.  

  1. 1 Features
  2. 2 Applications
  3. 3 Description
    1.     Device Images
      1.      Simplified Schematic
      2.      TPS56339 Efficiency
  4. 4 Revision History
  5. 5 Pin Configuration and Functions
    1.     Pin Functions
  6. 6 Specifications
    1. 6.1 Absolute Maximum Ratings
    2. 6.2 ESD Ratings
    3. 6.3 Recommended Operating Conditions
    4. 6.4 Thermal Information
    5. 6.5 Electrical Characteristics
    6. 6.6 Timing Requirements
    7. 6.7 Typical Characteristics
  7. 7 Detailed Description
    1. 7.1 Overview
    2. 7.2 Functional Block Diagram
    3. 7.3 Feature Description
      1. 7.3.1 Advanced Emulated Current Mode Control
      2. 7.3.2 Enable and Adjusting Undervoltage Lockout
      3. 7.3.3 Soft Start and Pre-Biased Soft Start
      4. 7.3.4 Voltage Reference
      5. 7.3.5 Minimum ON-time, Minimum OFF-time and Frequency Foldback at Dropout Conditions
      6. 7.3.6 Overcurrent and Undervoltage Protection
      7. 7.3.7 Thermal Shutdown
    4. 7.4 Device Functional Modes
      1. 7.4.1 Shutdown Mode
      2. 7.4.2 Active Mode
      3. 7.4.3 CCM Operation
    5. 7.5 Light-Load Operation
  8. 8 Application and Implementation
    1. 8.1 Application Information
    2. 8.2 Typical Application
      1. 8.2.1 Design Requirements
      2. 8.2.2 Detailed Design Procedure
        1. 8.2.2.1 Custom Design With WEBENCH® Tools
        2. 8.2.2.2 Output Voltage Resistors Selection
        3. 8.2.2.3 Output Inductor Selection
        4. 8.2.2.4 Output Capacitor Selection
        5. 8.2.2.5 Input Capacitor Selection
        6. 8.2.2.6 Bootstrap Capacitor Selection
      3. 8.2.3 Undervoltage Lockout Set Point
      4. 8.2.4 Application Curves
  9. 9 Power Supply Recommendations
  10. 10Layout
    1. 10.1 Layout Guidelines
    2. 10.2 Layout Example
  11. 11Device and Documentation Support
    1. 11.1 Receiving Notification of Documentation Updates
    2. 11.2 Related Links
    3. 11.3 Community Resources
    4. 11.4 Trademarks
    5. 11.5 Electrostatic Discharge Caution
    6. 11.6 Glossary
  12. 12Mechanical, Packaging, and Orderable Information

7.5 Light-Load Operation

The light load running includes Discontinuous Conduction Mode (DCM) and Pulse Frequency Modulation Mode (PFM).

As the output current decreases from heavy load condition, the inductor current is also reduced and eventually comes to point that its rippled valley touches zero level, which is the boundary between CCM and DCM. The low-side MOSFET is turned off when the zero inductor current is detected. As the load current further decreases, the converter runs into DCM.

At even lighter current loads, PFM is activated to maintain high efficiency operation. The On-time is kept almost the same as it was in the CCM so that it takes longer time to discharge the output capacitor with smaller load current to the level of the reference voltage. This makes the switching frequency lower, proportional to the load current, and keeps the light load efficiency high. The transition point to the light load operation IOUT(LL) current can be calculated in Equation 8.

Equation 8. TPS56339 eq-01-SLVSEI2.gif