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LMG2100EVM-078: AGND vs PGND riddle, do they have to be externally connected?

Erfan Sadeghi
Prodigy 10 points
Part Number: LMG2100EVM-078
Other Parts Discussed in Thread: LMG2100R044

Tool/software:

Hi,

According to LMG2100R044 datasheet, AGND and PGND pins are internally connected. I could also confirm it by desoldering the external jumper in the EVM (R10) that connects those grounds. 

My questions are:

1. If the pins are internally connected, then what is the need to connect them externally? I read somewhere in the forum that it is for debugging purposes when the device is not installed on the board. Is this the only reason?

2. Why the R10 resistor in the EVM is laid out far away from the device? isn't it a possible cause for ground loops? 

Thank you in advance for your help,

Erfan

  • +1
    TI__Intellectual 1230 points

    Hi Erfan,

    The PGND and AGND pins are internally connected but it is important to keep the power plane and signal plane separate from each other to avoid the power switching noise interference with the signal path.

    Hence the PGND plane as you see in the layout is used only below the power components for creating a flux cancellation power return path.

    But the AGND plane is kept separate and is used for shielding all the signal related paths. 

    There is no need to connect them externally and the R10 can be used as DNP. In absence of device it can be used to connect the two planes.

    Thanks,

    Subhransu