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Altera_Forum
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10 years ago

Enpirion EN5322QI: AGND/PGND

Hello Members,

I have some questions about the PCB-design for EN5322QI:

I planning to have a PCB with EN5322QI and EN6310QI. The board will have one complete GND-plane (Layer2).

1) PGND

For me this is just the GND which I connect to the GND-plane, correct? This also means that all Input/Output caps are just connected to this GND-plane through VIAs?!

But if this is correct, why in the datasheet for EN6310QI they seperate the Input/Output caps to two different PGND pin groups? (Pin 3,4 for output caps || Pin 21, 22 for input caps)

What does this mean for my PCB-Design? Do I have to route these caps first to the pins and then from this Pin with a VIA to my GND-Plane?

2) AGND

How to seperate the AGND from PGND. On which specific point on the PCB I have to connect them together (through a NetTie?).

Thanks so far!

3 Replies

  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    Electrically, both PGND & AGND are going to connect to your ground plane.

    Locate the input/output caps close to the controller and nail all their GND pins to your plane with vias.

    Pins 3, 4, 21 & 22 are all PGND and will be nailed to your plane. The datasheet is simply guiding you to ensure input/output caps are close to the controller by offering PGND pins close to the input/output power pins. Keep things tight, lots of vias to your ground plane.

    AGND will connect to your ground plane through a single via, close to the AGND pin. More importantly, keep the local decoupling cap for AVIN close and keep the traces short. Don't be tempted to connect the AGND pin to the thermal pad (or any other ground copper) under the controller.

    Finally, follow the layout recommendations in each datasheet. I'd suggest this is (pretty much) all covered there.

    Cheers,

    Alex
  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    Thanks for your explanations a_x_h_75!

    a_x_h_75: The datasheet is simply guiding you to ensure input/output caps are close to the controller by offering PGND pins close to the input/output power pins

    => For me that was not written clearly in the datasheet ;)

    a_x_h_75: AGND will connect to your ground plane through a single via.

    => This is not mentioned anywhere in the datasheet! The only comment in the datasheet is: EN5322QI => AGND: Analog Ground for the Controller Circuit || EN6310QI => AGND: Quit analog ground for control circuits. Connect to system ground plane.

    a_x_h_75: Finally, follow the layout recommendations in each datasheet. I'd suggest this is (pretty much) all covered there.

    => The correct connection between PGND(GND) and AGND is not mentioned in both datasheets :/
  • Altera_Forum's avatar
    Altera_Forum
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    10 years ago

    The recommended layout is shown in the EN5322QI data sheet (Figure 7). As Fizzjo indicates, AGND connects to the ground plane with a single via near the AGND pin. The intent is to keep any current from the PGND plane from flowing through the AGND plane and influencing the control circuitry.