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LM5122: The Output much more spike and noise even no load

Simon Poon
Prodigy 240 points
Part Number: LM5122
Other Parts Discussed in Thread: LM9036

Hi all, I have planning to design a DCDC converter with 15-20V input and 30V ~6A output, here is my part of the circuit, when first try, the output have so much "noise", seems like the voltage is very fluctuate and much "spike" at voltage output, also, I check the LM9036 output also same symptom, the 3V3 is very noise too, and the behavior is same as output voltage. However, this problem also happen when no load, is there any possible issues occur? Thanks so much!

  • 0
    TI__Guru* 75370 points
    Do you get 30Vout? Would you please show some scope shots of the Vout? Also, the schematic is not very clear to review: I cannot tell whether a joint is a real joint when two wires cross.
  • 0 in reply to Youhao Xi
    Prodigy 240 points

    Hi Youhao Xi, yes, here are some photo of the scope to the 3.3V out and 30V out,(Blue is 3.3V output, and Yellow is 30V output)

    You can see the spike Vpk-Vpk is very high, especially the 3.3V, the Vmax is 12.2V, the 30V output also have spike, but it around 2~4V only.

    Thanks.