Pull up and pull down placement

Question

Hi, We are planning to use W5500 with RP2040 in our design. We have two board approach for our design Main PCB will have the W5500 chip Sub PCB will have the Magnetics and the RJ45 connector. These two boards are connected by a FPC cable. I have a query on the pull up and pull down resistors and capacitors placement on the IC side of the magnetic transformer. Should those be placed on the main board or the sub board? Please suggest. 11111111642×531 51.2 KB Appreciate your quickest response. Thanks, Naveen

Eugeny · Answer

You can find layout guide here. Block A and B may be better placed as close to magnetic as possible. This must answer your question. But using FPC cable… not sure it is good way to extend the conductors. I used board-to-board through-hole connection (no connectors, soldering) and the cumulative length of each conductor was less than 2 inches, and it worked well, but using cables… You probably need twisted pair FPC cable!

Eugeny · Answer

Not sure if there’s such service. If layout is not a secret post related pics here.

Naveen S Kurdekar · Answer

RJ45_EVT.pdf Hi Eugeny, PFA the layout in pdf format. This is the sub board where we have Discrete magnetics and Ethernet connector. The W5500 chip is on a main board. There is an FPC running from the main board to Ethernet sub board. The length of the TX and RX lines are less than 12cm. Thanks, Naveen

Eugeny · Answer

If the pinout of the connector is not fixed, you can reassign the pins to eliminate lane crossings at different board levels. The board is not serviceable (if serviceability is assumed at all) - you get the guidelines too literally putting components the way you would not be able to replace them if needed. I am not sure, but you may need to increase clearance between signal ground and network connector ground polygons. In addition the right hole for network connector mounting significantly decreases strength of the board, and therefore its durability for forcing/bending.