board layout for rj45 shield when using adn4652

Hi,

Your cable shield (or shields) should be earthed. There are different RJ-45 connector footprints (e.g. surface-mount vs. through-hold, different shield connections) but in general it should be possible to connect the shield of the connector (connects to cable shield) to a distinct PCB copper plane that is coupled to chassis/earth.

I recommend keeping this at the edge of the board, avoiding overlap with other PCB planes (e.g. isolated power, ground). An example is shown below (RJ-45 + ADN4651 + ADuM5000 footprints) - the area on the left is for the shield - the area on the right is isolated (top area) or non-isolated PCB ground (this might also be coupled to earth, or even to the shield area). Typically the shield area would be connected to the device chassis. The isolated planes may only have the isolators connecting them to the rest of the circuit (sometimes a high-voltage filter capacitor might be connected). The rest of the PCB ground can be coupled to chassis, maybe with some filtering.

Some other boards have the connector side ground coupled to chassis, with the MCU side kept floating (main PCB ground is the "isolated" ground).

The shield area could be an internal layer if you need to maintain larger PCB clearance on the outside layers. You really only need one layer for this section - the rest of the PCB can follow a standard stack-up (e.g. Layer 1: Signal+Ground, Layer 2: ground, Layer 3: Power, Layer 4: Signal + ground)

Hi,

Your cable shield (or shields) should be earthed. There are different RJ-45 connector footprints (e.g. surface-mount vs. through-hold, different shield connections) but in general it should be possible to connect the shield of the connector (connects to cable shield) to a distinct PCB copper plane that is coupled to chassis/earth.

I recommend keeping this at the edge of the board, avoiding overlap with other PCB planes (e.g. isolated power, ground). An example is shown below (RJ-45 + ADN4651 + ADuM5000 footprints) - the area on the left is for the shield - the area on the right is isolated (top area) or non-isolated PCB ground (this might also be coupled to earth, or even to the shield area). Typically the shield area would be connected to the device chassis. The isolated planes may only have the isolators connecting them to the rest of the circuit (sometimes a high-voltage filter capacitor might be connected). The rest of the PCB ground can be coupled to chassis, maybe with some filtering.

Some other boards have the connector side ground coupled to chassis, with the MCU side kept floating (main PCB ground is the "isolated" ground).

The shield area could be an internal layer if you need to maintain larger PCB clearance on the outside layers. You really only need one layer for this section - the rest of the PCB can follow a standard stack-up (e.g. Layer 1: Signal+Ground, Layer 2: ground, Layer 3: Power, Layer 4: Signal + ground)