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Original question:

LM2611AMF/NOPB

Shorting/No Output Voltage

Lidong Yu
Intellectual 1756 points

Hi team

I'm trying to generate -5 V from a 5 V supply using the LM2611AMF CUK converter, but I get very low voltage on the output and a large current draw (on the order of 400 mA) when I try to hook-up the device. Right now I'm only testing it from a power supply. I've attached my circuit schematic and layout. I realize that some of lines route over the switching paths, but the layout is on a 4 layer circuit board, which I was hoping would provide enough shielding. I've also try removing U10, but that does not fix the issue. I guess it could also be a soldering/board assembly issue, though I think this is unlikely as I've had this issue on multiple boards and they were assembled by a commercial vendor.

Is the an obvious issue with my layout for example that could cause this issue?

Any suggestions for things that I could try? Thanks!LM6211 Layout (1).pdf

  • +1
    TI__Guru 58225 points

    Hello Lidong,

    U10 is the coupling capacitor between the 2 inductors, correct? I recommend to increase the voltage rating as the one in your schematic seems to have 10V only.

    The schematic looks the same as the one given in the datasheet, so no major problem there.

    At the end, I expect that your layout is causing issues. It seems that the GND connection to the input output and IC is not solid enough to keep the voltage stable there while the device is switching. Please check out the layout of the EVM or in the datasheet.

    Best regards,
    Brigitte