Hot W5100 with POE++ (MAX5996C Eval kit)

Question

Hello, We are using a W5100 with a Pulsejack (J1011F01PNL) RJ45 on a PCB, and have been using this PCB design for many years without issue. Recently we have added an additional POE++ PCB to the product which is the same as the MAX5996C Eval kit. This POE++ PCB plugs into our original W5100 PCB with a normal network cable. The W5100 circuit we are using is the same as in the Hardware Design Guide Schematics V2.1 Data sheet links are below. A few of the W5100 appear to be failing to function and get very hot after a few weeks of operation. They seem to fail after a power cycle, ie they never fail during usage. Is this a known issue with the W5100 and POE? Is the W5100S version more resilient to POE usage? Any help would be greatly appreciated. MAX5996C eval Kit: https://www.analog.com/media/en/technical-documentation/data-sheets/MAX5996CEVKIT.pdf W5100 Hardware Design Guide Schematics V2.1 : docs.wiznet.io Documents | WIZnet Document System Download

Alan · Answer

W5100, W5100S and PoE are not related. PoE simply serves to get power from an Ethernet cable. PoE++ can provide up to 60W of power, and it is very difficult to hold 5V of power without noise. In other words, the correlation between PoE and W5100 can only be determined to affect W5100 due to voltage fluctuation while using PoE++. Of course, there may be other effects, but a well-designed PoE will not affect the W5100 error.

Eugeny · Answer

AJW: They seem to fail after a power cycle, ie they never fail during usage. Sounds like reset problem related to power voltage rise profile. What is the circuit for reset pin?

Christopher Binnie · Answer

Which POE++ solution are you using? btw - POE++ can provide over 80W of power according to the IEEE802.3bt spec