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TPSM84824: Is there any reason against connecting AGND with shortest trace possible without separate Plane?

Mateusz Maciag1
Prodigy 30 points
Part Number: TPSM84824

Hi,

As we know the AGND and PGND are connected internally to the TPSM84824. The TPSM84824 datasheet recommendation is to create separate plane for AGND however. In the layout guidelines (10.1) it was indicated however that VIN, VOUT and PGND are subject to conduction loss and thermal stress, but not AGND.

My questions are:

- What is the purpose of separate ground plane for AGND? Is it EMI / capacitive coupling related reason?

- Do you recommend against connecting all AGND pins with just shortest path possible? (i.e. using trace instead of large area ground plane).

--

Best regards,

Matthew

  • 0
    TI__Mastermind 35165 points

    Hi Matthew,

    The primary reason to avoid connecting AGND to PGND externally is this would create multiple return paths between AGND and PGND. This could result in noise pickup on AGND and this noise could interfere with the analog control circuits.

    It's ok to connect the AGND pins together using a short trace instead of a large ground plane as all of the AGND pins are also connected internally. However, the safest option would be to place a via near each AGND pin and use a small AGND island on another layer big enough to cover all of the vias.

    Anthony

  • 0 in reply to Anthony F
    Prodigy 30 points

    Thank you for quick response and valuable hint regarding AGND island. Looks like we weren't far from understanding AGND role here.

    Matthew,

    Firmware/Hardware Engineer