[FAQ] Why is high efficiency important in PoE applications?

Customers tend to care about high efficiency in PoE applications for two main reasons:

1. When wanting to stay within a certain Class range

That is, it is common in PoE applications for customers to want to stay within a certain Class range in order to avoid additional system level BOM costs. Let's walk through an example to understand this in more detail. Imagine designing a 23W load using a Class 4 PoE PD. For this scenario, in order to stay within the Class 4 range of <25W on the PD input, an efficiency of 92% is needed to obtain 23W at the load. However, if unable to achieve 92% efficiency, an IEEE802.3bt Class 5 PoE PD will be needed as well as other system level components. Since IEEE802.3bt PDs solutions tend to have a higher cost than IEEE802.3at PD solutions, this causes the system level solution cost to increase making it important to stay within the Class 4 range if at all possible. In addition, an IEEE802.3bt PSE switch would be needed to power the IEEE802.3bt PD, further increasing system level costs.

2. When thermal performance is important

For applications such as small solution size designs, thermal performance becomes increasingly of interest as smaller systems do not tend to have fans, heatsinks, or other methods of getting heat out. For situations like this, high efficiency enables less heat to be dissipated in the system and better thermal performance overall.

 Additional Resources

• Check out TI's PoE landing page: www.TI.com/PoE

• Learn about the IEEE802.3bt standard: Power over Ethernet: Getting Started with the New Standard