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LM5175 13V, 10A Large spikes in output waveform

Tim Finks89
Prodigy 40 points
Other Parts Discussed in Thread: LM5175

Greetings, I have an LM5175 design showing large, fast spikes in the output waveform. The design is required to accommodate a 10-15V  input, and provide a regulated 13.0V 10A (max) output. The switching frequency is set to 500KHz. With a 13.0V input and a 6.5A load, we see the following waveform:

Any suggestions concerning cause?

  • 0
    TI__Genius 11490 points

    Hi Tim,

    The fast spikes may not have anything to do with the controller IC. This seems like the switching noise coupling to the probes.

    If you use short probe tips (GND and VOUT) close to the ceramic capacitorss the high frequency spikes should go away or decrease.

    Regards,

  • 0 in reply to Vijay86929
    Prodigy 40 points
    I have traced the larger spikes to ringing at the L1 MOSFET gate. The smaller spikes occur at every MOSFET state change. I concur that the controller is not a problem here.

    I observe that the controller switches constantly between boost and buck, since I see constant switching at L1 (buck mode) and L2 (boost mode). How does the controller sense the appropriate mode? Are there concerns when the constant mode switching occurs?