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TPS54331 Output Noise

Sameera Fonseka
Prodigy 20 points
Other Parts Discussed in Thread: TPS54331

Hi,

I am using TPS54331,for DC-DC conversion from 24V to 5V.

Here is the typical circuit which i am using.

I got following Output oscillation,at the Connection of inductor(L9) & Resistor(R343) :

My Design Considerations are,

Output Current Max : 1.25A

Output Voltage : 5V

Any help is highly appreciated.

BR

Sameera

  • 0
    TI__Guru**** 191445 points

    It's not really clear what your concern is.  Can you post a shot of your output waveform that is ac coupled and a lower V/div scale?  Then annotate clearly your concern with the waveform.

  • 0 in reply to JohnTucker
    Prodigy 20 points

    Hi,

    I have attached 500mv/Div scale Screen shot.

    This Shows the Spikes and small oscillation at the Output.

         I am using ES3A as the Catchup Diode.It's switching time is 20ns.

    Is that a Problem?(Becasue for 570KHz Timing is 1.75us).

    Thanks for your Support.                                                              

       

  • 0 in reply to Sameera Fonseka
    TI__Guru**** 191445 points

    At 500 usec/div it is hard to tell what is happening.  Since one switching cycle is 1,75 usec, it would be best to measure at 2 usec/div or so.  Otherwise the waveform is highly aliased.  If you are referring to the high frequency spikes, that is probably switching noise which is inherent in SMPS.  How are you measuring this?  It is best to use the "tip and ring" method, directly across the output capacitor.  Any type of long ground lead will cause you to see extra noise.  If it is still a problem you may want to consider an RC snubber from PH to GND.  Also it may be layout dependent.  It is critical to keep the circulating current loops as small as possible.  The input bypass capacitor must be as close to the IC as possible and directly connect to the VIN and ground pin with wide traces or copper pours.  Let me know if any of this helps.

  • 0 in reply to JohnTucker
    TI__Guru**** 191445 points

    Did this ever get resolved?