SLUAA69 July   2020  – MONTH  TPS548D22

 

  1.   Trademarks
  2. 1Introduction
    1. 1.1 LED Driver Methods
    2. 1.2 Power Supply Solutions for Common-Cathode LED Display
  3. 2Principle of Synchronous Buck with Sinking Current Application
  4. 3 Design Considerations and Analysis
    1. 3.1 Choose an IC with Sufficient Current Sinking
    2. 3.2 Choose IC Supporting Negative OCP
    3. 3.3 Choose an IC Supporting Pre-Bias Startup
    4. 3.4 Analysis of System Startup
  5. 4 TI Devices and Functionalities
    1. 4.1 Negative OCP Functionality
    2. 4.2 Hiccup Mode and Latch-off Mode
    3. 4.3 UVP and OVP Functionality
  6. 5 TI Solution
  7. 6 Bench Test and Result
    1. 6.1 Bench Test Configuration
    2. 6.2 Startup Waveforms and Behaviors Analysis Overview
    3. 6.3 Startup Waveforms and Behaviors Analysis at the First OVP
    4. 6.4 Startup Waveforms and Behaviors Analysis after the First OVP
    5. 6.5 Waveforms and Behaviors Analysis of Startup Solution with Lazy Loading
  8. 7 Conclusion
  9. 8References

3.1 Choose an IC with Sufficient Current Sinking

Synchronous buck allows for FPWM operation. Normally it is desired to have FPWM only in light load mode - not in full load mode. Hence, most synchronous buck converters have a much smaller negative inductor current limit than a positive inductor current limit. If an IC is chosen without sufficiently large negative inductor current limit for a sinking current application, the output power will be limited by the small negative inductor current limit.

Fortunately, some TI devices such as TPS548B22 and TPS548D22 perform both positive and negative inductor current limits with the same magnitudes, allowing the sinking current application the same large output current as the sourcing current application.