I am using a DP83848I Ethernet Transceiver connected to a transformer exactly as given in Figure 2 of application note AN-1469: http://www.ti.com/lit/pdf/snla079. The transformer I am using is a Coilcraft ETH1-230LD transformer PoE. On our first run of boards (back in 2010), both 10 Mb/s and 100 Mb/s speeds operated correctly. We have another run of board (same layout, same components, but newer date codes) built in 2015 which operate at 10 Mb/s but not at 100 Mb/s. I have checked all of the signals around the PHY chip and they all look o.k. with the exception of the RXD0 and RXD1 signals which have overshoot (both in the 2010 boards and the 2015 boards). I installed series 50 ohm resistors in the RXD0 and RXD1 traces next to the PHY chip, and that corrected the overshoot, however the IC still would not communicate at 100 Mb/s.
Question: Does the use of a PoE transformer in a non-PoE application cause marginal operation that could affect 100 Mb/s functionality?
Thanks,
Bob
