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TPS5430 transient response issue

Jacky Chen29
Genius 4735 points
Other Parts Discussed in Thread: TPS5430

Hola,

I'm using TPS5430 for following input and output parameters：

Vin = 12V

Vout = 4.6V/1.5A(peak)

And the schematic were shown as below：

TPS5430 schematic：

Three buck regulator schematic：

According to the above conditions and we found the voltage drop as below figure：

Voltage dropped when three DC/DC regulators are turned on：

Blue color：Reset signal, High=reset off / three DC-DC regulator turned off、Low=reset on / three DC-DC regulator are turned on.

Yellow color：TPS5430 switching signal.

After analysis, the voltage drop will be disappeared when removed three buck regulator input 22uF capacitor：

But these three input capacitor are be needed for these regulators and we've changed TPS5430 output inductor value from 10uH to 18uH but it still cannot improve voltage drop, even we added a feedforward capacitor with 22pF to parallel with R207 and the result has no changed！

Have any body idea how I can overcome with is voltage drop？

  • 0
    TI__Guru**** 191445 points

    The bitmap of the 3 regulators is too blurry to make out.  can you get a high resolution screen shot?  I need to see what kind of regulators they are.  I do not see why

    removing the input capacitors would help.  They need to be there.  One thing I can suggest is to sequence them so they do not all start up at once.  Another thing is

    you can try a larger output capacitor for TPS5430.  Do the three down stream regulators have any internal slow start?

  • 0 in reply to Jacky Chen29
    TI__Guru**** 191445 points
    So have you tried sequencing the 3 buck converters to turn on one at a time?
  • 0 in reply to JohnTucker
    Genius 4735 points

    Hola John,

    Thank you. I summarize the test result as below：

    1. Yes you are right, the three DCDC regulator's input capacitors they need be there but the voltage drop still alive when regulators were be turned on.

    2. You mentioned that try to sequencing the 3 buck converters to turn on one at a time and I tried to remove these 3 converters output inductor and it means

    no output with these 3 converters but the voltage drop still alive！

    Is this caused by the reset circuit between TPS5430 and RT8097？because of the reset is our new circuit with this project. With old design we have no this

    reset circuit but for protection concerned and we have add this reset circuit between TPS5430 and RT8097. Do you have any suggestion that can improve this voltage drop？

    Thank you

  • 0 in reply to Jacky Chen29
    Genius 4735 points

    Hola,

    Anyone can help on this urgent issue？ Thanks ～

  • 0 in reply to Jacky Chen29
    TI__Guru**** 191445 points

    What is your reset circuit?  Generally if you are having issue, the best thing is to disconnect the load completely from the dc/dc converter.  Make sure it starts up properly and maintains regulation.  then ad some resistive load.  You cold then attach an electronic load to verify the load step transient.  Fter that you can add your on board loads one at a time to find out exactly where your issue is.