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LMZ31704: Connecting a resistor divider to AGND from Vin and also number of board layers

Part Number: LMZ31704

Hi this device internally connects the GND and PGND but I would like to connect a divider on VIN to GND to get the voltage but I was wondering will this cause issues due to the fact VIN is referenced to PGND. Also the reference designs are all four layer boards for this component will it still work well with two layers?

I posted a picture of my PCB layout currently (no via stitching) and the green labels are the planes and the bottom layer is GND and the dark blue line is where I would like to connect a resistor across to go to the ADC.

Can anyone comment on the two layers and placing the divider? Thanks

  • Hello James,

    I think a resistor divider to GND to sense the input voltage will be OK.

    On the layout, I think two layers is possible, but be sure to connect the VIN pins together on the bottom layer. Right now, only pins 11 and 12 are connected to the input cap. Pins 1,40, and 39 seem to be on an island.
    Have a large PGND copper on the bottom and connect the PGND copper from top layer to bottom layer with several vias.

  • Oh the Island was a mistake thanks for pointing that out by placing a PGND plane on the bottom do you mean PGND only under the PGND above. Or do you mean PGND the entire bottom side of the board and under analog electronics?
    Assuming you mean break bottom layer into GND and PGND and run GND under the top GND and PGND under the top PGND?