W7500S2E-R1 EMI/EMC issues & force 10Base-T mode

Question

After doing many tests with our pre-production board using the W7500S2E-R1 module, we’ve noticed very strong unwanted emissions at the 25 MHz harmonics, especially 175 MHz, 225 MHz, 425 MHz etc. In fact, the W7500S2E-R1 module is not able to pass the EMC tests, neither Class A. After doing a research, I’ve found the reason: 25 MHz clock signals TXCLK and RXCLK going through the MII interface on a very bad designed PCB. If I disconnect the RJ45 cable, the module auto-negotiates to 10Base-T mode which uses only 2.5 MHz clock so the emissions are acceptable in this mode. So in my opinion, the W7500S2E-R1 module is not able to operate in 100Base-T mode because the RF emissions are above limits in this mode. This should be mentioned in the documentation by the way. Now I’m asking Wiznet for a software solution which will allow me to switch to force 10Base-T mode to reduce the emissions to acceptable level. I’m sure that such modification is possible in the firmware. Also it would be nice if possible future hardware revision of the W7500S2E-R1 will use better PCB design. The performance/price ratio of this module is unmatched but some fixes in HW and SW would be very useful if I had to consider the wider use of this module.

lokman402 · Answer

@FMLab Hi, I’m Ron from WIZnet HK. Sorry for the late reply. About your issues, we found that you have serval other questions about our W7500S2E-R1. Would you mind gather all your questions and send an email to support@wiznet.hk? Therefore, we could let our WIZnet HK FAE to answers all your questions. Best Regards, Ron