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LM2842: Switching Network Waveform

Charles Gervasi
Expert 2270 points
Part Number: LM2842

What could be causing this waveform at the switching node?

By the switching node, I mean the cathode of the diode.

I tried adding input and output capacitance, changing the inductor, and increasing the boost cap.  The waveform remains about the same.  

  • 0
    TI__Genius 13735 points

    hi, Charles,

    What's you Vin Vout Iout condition. and could you share you SCH with components value so I could check . this waveform  test point is on SW pin right?

    Elena

  • 0 in reply to Elena Gao
    Expert 2270 points

    Thanks for responding immediately.

    Vin = 12V.  Vout = 5V.  This is the original circuit.

    The buck controller was originally AOZ1280CI.  I changed it to LM2842 because the AOZ1280CI failed.  I had to change the feedback network slightly by placing a 140kΩ resistor on top of (in parallel to) R17.  I also tried larger inductor values since I'm using LM2842XMK, with a switching frequency of 550kHz.  

    The LM2842XMK failed too, possibly because of this problem or possibly something else.  

  • 0 in reply to Charles Gervasi
    TI__Genius 13735 points

    hi, Charles,

    please try 0.1uf cboot cap ,C1,  and 47uh or 33uh inductor for L1. higher voltage cap of C5 ,like 25V/ 50V, should be better .

    Elena