As I mentioned in my May meeting recap, an ad hoc was formed to collect use cases for 4-pair PoE. Not only is this an important topic, but it gives me a chance to ask for some reader input again. Regular readers of my posts know that in addition to keeping you up to date on the progress of the 4-pair task force, collecting your ideas so that I can bring them to the task force is the driving force behind my blog entries. As such, I want to give some examples of use cases and ask for your feedback as to which of them you see end users implementing. In addition, if there are use cases you are aware of that aren’t discussed here, please let me know.
The first set of use cases I want to discuss are the power level use cases.
The most obvious use case of 4-pair PoE is the higher power applications it enables. However, the highest volume applications that use PoE are those that use the least amount of power (4W or 7W loads), we don’t want to place an undue burden on these applications in the new standard. In other words, we want to enable low power applications to use 4-pair PoE without increasing cost and complexity. If you design or use PoE for low power applications, do you see yourself (or your customers) upgrading to 4-pair PoE if all that is required is a new switch or midspan? What if a new switch and new powered devices (PDs) are required? How about for slightly higher power applications (13W or 25W)?
The other set of use cases I want to discuss is powered devices that could use 4-pair PoE to power two independent loads inside a PD. In other words, the PD would present individual detection and classification signatures on each alternative to enable the switch or midspan to power them individually. One example of this that I often hear cited is a security camera that would use separate power feeds for the camera and the motor/heater.
I have also heard it suggested that a possible use case is to use two independent power feeds (one on each alternative) to provide redundant power to a PD. In fact, the redundancy can be extended past the PD hot-swap FET to include independent DC-DC converters. Can you see yourself or your customers building PDs with independent loads? How about using redundant power feeds?
Ok, one last request for your input. Are there use cases that you know of that I didn’t discuss here? What else should we be aware of when we are writing the new standard? Please answer these questions and the ones throughout the post by commenting below.
PoE resources:
- Read all IEEE blogs here
- App note: Implementing a 60-W, End-to-End PoE System
- PoE PD efficiency calculator tool
- PoE system block diagram
- PoE powered device (PD) products
- PoE power sourcing equipment (PSE) products