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LM25118: LM25118: When work at BOOST or buck-boost mode,when Vin=8~16V ,Vout=12V, there are some spike in the Vout ,the spike similar to the Switch frequency ,pleace help to check it ,many thanks ~

Andrew Liu74
Intellectual 970 points
Part Number: LM25118

LM25118: When work at BOOST or buck-boost mode,when Vin=8~16V ,Vout=12V, there are some spike in the Vout ,the spike similar to the Switch frequency ,pleace help to check it ,many thanks ~

when Vin=17~30V,Vout=12V ,the Vout seems normal ,

  • 0
    TI__Guru 73150 points
    Hi Andrew,

    Thank you fro considering the LM25118. Two questions: (1) where did you place your probe to monitor the Vout? (2) did you use the short ground leads to measure?

    The reason that I asked the 1st question is to understand where do you place your ground reference. The 2nd question regarding the measurement method. Long ground leads can pick noise and the scope picture may not be realistic.

    In the buck mode the LM25118 output is like a normal buck and the output capacitor sees the continuous inductor current with small ripple current, thus the Vout is more clean. In the buck-boost mode, the diagonal switches are switched together, hence the output capacitor sees pulsing current. You should place the cermaic capacitors closest to the rectifier diode such that the ac current components are immediately get filtered.

    Thanks,
    Youhao Xi