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TPS53515: About disorder of switching waveform

Tsukui Yusuke
Guru 21930 points
Part Number: TPS53515

Hi,

Could you tell me about
Please check the attached waveform.
When the input / output voltage ratio is small and the output current is high, the switching waveform is disturbed.
Mode pin setting is FCCM mode.
Please tell me the cause and the countermeasure method.
(Increasing the Cout capacity will improve the problem.)
Could you give me your advice?

TPS53515.pdf


Best Regards,
Yusuke



  • 0
    TI__Mastermind 22299 points
    Yusuke,
    Can you provide a schematic and operating conditions?
    This seems to be a subharmonic instability but we won't know with the schematic.
    Thanks,
    -Orlando
  • 0
    TI__Mastermind 29670 points
    Hi,

    Based on your pictures you shared it looks like your current design may be unstable under some of the test conditions shared (ie: VIN = 5V, IOUT = 5A).
    Do you have the ability to perform stability analysis (measure loop response) for your design?

    If you don't have measurement capabilities, a good starting point to verify if your component selection is appropriate for your given design parameters is to run your design with Webench Power Designer (link below).

    www.ti.com/.../webench-power-designer.html

    Webench will give you recommended component choice values and stability analysis plots (from the calculated component values) to verify if your design is stable. You could also change the design component choice values to the values that you currently have in your design. This will allow you to simulate if your design is stable and would be a good first step in debug process.

    Hopefully this answers your question!
  • 0
    TI__Intellectual 2460 points
    Hello Yusuke,
    From the waveforms, it looks double pulse due to small ramp amplitude. Please refer to Figure 4 on page 16 and table 4 on page 19. From table 4, you can change to larger RC time constant and re-check double pulses.
    We have the Excel design tool for this part. Please reach out to Ti local FAE or TSR and ask for my name (Huy(Kit) Nguyen) in the system. Then, I can forward the design tool.
    Kit