This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.


Other Parts Discussed in Thread: LMZ31704


We have a customer that is using the LMZ31704 in a new design.   They mentioned reading a note on an evaluation board stating AGND and PGND are connected internally in the LMZ31704 module.   I don't think this is the case.  Would you confirm this please?  They also referred to the LMZ31704 EVM schematic which does not connect the AGND to PGND making the customer believe they must be connected internally to the module. The EVM does have a jumper (R15) connecting AGND and PGND on the board, but the jumper states that the component is not populated.  Below is how the customer implemented their LMZ31704 design.

The customer stated that they don't connect their AGND and DGND (PGND on the LMZ31704) on their board, but that both signals are connected together somewhere else in the system.  

I believe that AGND and PGND are intentionally not connected internally to the chip so that they can be connected externally somewhere in the system which allows some isolation between the two signals.   In the case of the customer's application, as long as their AGND and DGND signals both have a low impedance path to the main system ground and connect at a single point this would be the best practice.  Please confirm this is the best practice.

Thanks for your help.


John Wiemeyer

  • Hi E2e,

    Looks like the picture of the schematic that I pasted into the post didn't get saved so I am uploading it here.

    The note about AGND and PGND not needing a connection on the PWB because it is connected internally is below.


    John Wiemeyer

  • Hi John,

    The AGND to PGND connection is made internal to the device. It is not recommended to connect them on the PCB. See the Layout Considerations section of the datasheet. It lists keeping AGND and PGND separate from one another.