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Switching Node - TPS5450 - No Load

RNJ
Prodigy 45 points
Other Parts Discussed in Thread: TPS5450

Hi,

I'm doing tests with the DC-DC STEP-DOWN TPS5450 and I had a strange behavior in my switching node with no load connected. Follows the picture.

Can anyone help me to understand the waveform in the switching node when the DCDC has no load connected? Is this common? Or is it a design error?

Thanks!!

  • 0
    TI__Mastermind 35185 points

    Hi Ricardo,

    This is expected and is called discontinuous conduction mode (DCM) operation. When the current in the inductor reaches zero, there is ringing caused by the output LC filter. In this case, the ringing stops when the high-side FET turns on for the next switching cycle.

    Best Regards,
    Anthony

  • 0
    TI__Guru**** 191445 points

    That is the typical waveform you should expect for DCM (Discontinuous Conduction Mode) operation.  When inductor current falls to zero the PH nod will go to the output voltage (there can be no voltage across an inductor without rising or falling current, V = L di/dt).  When teh current stops, the circuit will oscillate for some time before settling at PH = Vout.  In this case, the next switching cycle starts before the resonant circuit damps out.  What you see is normal operation.