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LM43603: LM43603 unstable output voltage

Lin Zhao
Intellectual 1230 points
Part Number: LM43603

Hi, 

My customer met a urgent issue on LM43603, during no load condition, IC behaves normally.

When Io goes above 100mA, Vout begin decrease. and FB pin voltage decrease as well.

when Io goes up to 1.5A, Vo begin to oscillate between 0~4.5V, measured SW and found frequency was changing all the time.

Specific measured waveform and schematic and layout file and inductor datasheet could be found in below.

I found that FB trace is long and adjacent to inductor, it may be a concern. looking forward to your suggestion.

DPE.zip

  • 0
    TI__Guru 57555 points

    We have several comments:

    1.  The FB trace is too long and the FB resistors and Cff should be near the FB pin.  Should not route near inductor or SW node.

    2.  You should have a small value input bypass capacitor, 0.1uF,  in parallel with the 10uF input cap.  This should be close to the device.

    3.  Be sure that the DAP is well soldered to the ground plane.

    4.  It looks like you only have 2x22uF on the output; more output cap will help with load transient and stability.

  • 0 in reply to Frank De Stasi
    TI__Intellectual 1230 points
    Hi Frank,

    Thanks for your comments, it's found that PAD is not well soldered and caused thermal oscillation.