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Original question:

TPS56221: Variable switching frequency?

TPS56221: output power up waveform with many steps

Jerry Chen
Expert 5110 points
Part Number: TPS56221

Hi there,

I knew,during startup, tps56221 may trigger the current limit. But in one of my customer desgin with no load startup test, there are many steps in the power up waveform.  I tried to increase the inductance and soft start time, no improvement. I also reduce the output capacitance.

Is there any other measure I could have a try?

I attach the schematic here.

3v3.pdf

Thanks.

  • 0
    TI__Mastermind 23965 points

    When you increased your soft start time, what value of C579 did you use?

    Can you get a scope plot of output voltage, the soft start voltage and input voltage on same screen

    The 1000pF capacitor for C579 only gives a 60 microsecond soft start time.  Use a 0.1uF on EN/SS pin