W5100 - grounding

TCP/IP Chip W5100
1

Below questions are in relation to W5100 IC.

  1. Is it recommended to have separate Digital and Analog power/ground for the IC? or maintain a single (digital) power/ground?
  2. The signals TXOP/N, RXIP/N (Pins 8,9,5,6) are connected to RJ45 jack which has integrated magnetics. In that case, what Ground should be used for the Bob-Smith termination - analog/digital?
  3. What ground connection needs to be used for RSET_BG (pin 1)?

Thanks

2

Power - yes, ground - no. You do not bother about separating ground unless this ground somehow goes out of the ethernet connector (e.g. shielded cable).
Link. Check datasheet for your jack. it may already have this circuit, you just connect the pin to the ground.
This pin is in the “phy signals” group, therefore belongs to analog power reference.

3

Thank you Eugeny.

“Check datasheet for your jack. it may already have this circuit, you just connect the pin to the ground.”

In case of J1B121ZCCD, GH_GND pin has 1000pF capacitor and Bob-smith termination is internally present.
May I ask why in that case which of these two would be a better approach?

  1. Shorting GH_GND and MH (connector Mounting hole) GNDs together and then connecting a 1nF to signal ground OR
  2. Connecting GH_GND to signal ground and connecting 1nF between the signal ground and MH GNDs
4

I connect such pin to common ground. It already has the capacitor, two capacitors in series make no sense. If you are bothered by the separating connector’s chassis and the signal ground, then it is up to requirements. For example, in industrial applications the connector must be grounded either to signal ground or to PE (if these two are connected).