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LMZ30604 AGND area connected to PGND pour

Borut Cadez
Prodigy 50 points
Other Parts Discussed in Thread: LMZ30604

Hello,

we have a LMZ30604 design which does not have a separate AGND area. AGND area is connected to a overall PGND pour on top layer. There is a direct connection between AGND pad and PGND pads of Cin/Cout on top layer (in addition to vias as explained in datasheet). Otherwise design is prepared as described in datasheet. Can this kind of layout have any issues (Noise, EMC)?  What is the purpose of having isolated AGND area, they are connected on the GND plane anyway?

We believe that the LMZ30604 has problems (not sure what kind yet) when ESD event hits near PCB. This layout is the only difference from recommendation that I can find. Any help would be highly appreciated.

Thank you.

Best regards,

Borut

  • 0
    TI__Mastermind 28020 points

    Hi Borut,

    If the AGND is not isolated and connected to PGND at only one point, it can introduce ground loops and noise. By combining AGND and PGND on the top layer, high current switching noise can flow through the AGND and introduce noise on the internal analog circuitry. Please contact me directly at jarrigo@ti.com to discuss in more detail.

    Thanks, Jason