W5100 is one of classical hardwired TCP/IP chip which developed by WIZnet. It offloaded all TCP/IP protocol from MCU in order to release more memory resources to enhance the network performance of overall system. It has been proven in various applications for several years. Easy to use and excellent performance has also been recognized by many developers. But many developers also found that the operating temperature of W5100 is a little high. They (Chinese user) also discussed this issue with other developers in some website, forum, etc. We had summarized it as following for your reference:
Come from “极客工坊(Geek-workshop)”：http://www.geek-workshop.com/forum.php?mod=viewthread&tid=1179
User “电源插头” asking ：“Beginning to use W5100，when power ON, the temperature of chip become heating, even hot. It just working at beginning, but it can’t ping at some time later. I don’t know why this situation happened. My board had implemented the SD card.”
Internet user reply as following：
—“I think that your W5100 board seems have some problem. I also use W5100 and run it for sending data to Internet over a night. It still keeps working until next day. For temperature issue, I don’t think that it is very hot, just heating.”
—“Hot is seems a little hot. But my device already running for a week continuously (one data per minutes) which is using W5100.”
Come from “阿莫西电子论坛(AM OSBBS Forum)”：http://www.amobbs.com/thread-4702243-1-1.html
User “Andiwxz” asking : “The operating temperature of W5100 is too high，even heating. What happen? When testing W5100, I already found that it is heating. But I can’t found the reason. Can someone help me to solve this issue?”
Internet user reply as following：
—“Heating of W5100 is normal case as it embedded PHY core, the operating current is around 130mA.”
Come from “百度知道(Baidu knowledge)”：
“The operating temperature of W5100 is a little bit high. Is it means the chip is damaged？”
Internet user reply as following：
—“W5100’s operating temperature is higher than other WIZnet’s chip because of W5100 embedded PHY core(Analog part). But it will affect the performance of W5100. W5100 also pass the relative temperature reliability test. ”
—————————————————————————————————————
Summary：
Since W5100 embedded Ethernet PHY core and the package size of W5100 is small. Therefore W5100 will become heat when operating. The heating is mainly come from the Ethernet PHY core. Normally, the current of PHY is relative high. Such as RTL8201CP，IP101A, etc. In 3.3V operating voltage, the power consumption of 1ooBaseT is around 120mA. W5100 is industry version chip, the operating temperature is -40°C to 85°C. Normally, it not needs any radiating process. If the temperature of working environment is really worst (such as have some device will generate the heating), user can consider adding the heat sink or ventilation heat exchanger.
But W5100 is working well for a lot of Industry application, even not adding heat sink or ventilation heat exchanger. W5100 have passed the relative temperature test. So user can have confidence in W5100.
Relative document: http://beta.dacomwest.de/pdf/w5100_test_report.pdf
http://wenku.baidu.com/view/70c8b4c189eb172ded63b7ec.html