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

Waveforms and Behaviors Analysis of Startup Solution with Lazy Loading

Figure 6-16, Figure 6-17, and Figure 6-18 show the startup waveforms of the lazy loading solution. The inductor current gradually increases in the negative direction and then goes into steady state. The shape of the inductor waveform looks like the normal startup of buck with sourcing current but is horizontally symmetrical. The output voltage before the startup of buck with sourcing current application is 0 V ground. Similarly, for buck with sinking current application, the output needs to be pre-biased to the target level before startup since the output is regarded as the floating ground for the load.

GUID-20200604-SS0I-3W4G-KP80-SCBH5J9XJ376-low.pngFigure 6-16 Startup Waveforms with Lazy Loading: 1
GUID-20200604-SS0I-DMSR-CJ2S-22TVVWR9ZX2H-low.pngFigure 6-17 Startup Waveforms with Lazy Loading: 2
GUID-20200604-SS0I-D0L8-QDZH-4XFCLN4TZMSL-low.pngFigure 6-18 Startup Waveforms with Lazy Loading: 3

Figure 6-19, Figure 6-20, Figure 6-21, and Figure 6-22 show steady state, output ripple, transient response, and shutdown waveforms.

GUID-20200604-SS0I-4GFD-LFMH-C8TFPRZNJPTT-low.pngFigure 6-19 Steady State Waveforms of 4.2-V Input, 1-V 9.3-A Output

GUID-20200604-SS0I-VXCW-FCS2-JDCXXXBWZBPQ-low.pngFigure 6-20 Output Ripple Waveforms of 4.2-V Input, 1-V 9.3-A Output

GUID-20200604-SS0I-TTGL-D45M-21NVJRBDGRPQ-low.pngFigure 6-21 Transient Response of 4.2-V Input, 1-V Output, 0 A to 9.3 A, 2.5 A/μs Transient
GUID-20200604-SS0I-6PJW-Z2FQ-FSQC8GDSKBMG-low.pngFigure 6-22 Shutdown Waveforms