Power Over Ethernet (PoE) Solutions Featuring the LM5xxx Family

Power over Ethernet (PoE) integrates data and power over standard LAN infrastructures. Since PoE devices do not require wall-mounted power supplies, overall system costs are lower. For IP telephony, uninterruptible power supplies (UPS) guarantee higher reliability and less susceptibility to power surges, theft, interruption, or disconnection. Worldwide usage of the RJ-45 power connector ensures global compatibility of PoE devices. For wireless access-point applications, these systems do not require AC power sources, power lines, or outlets. PoE-enabled devices offer superior management flexibility with remote power up/down capability.

National Semiconductor provides innovative and robust Power Over Ethernet (POE) single and integrated solutions for the receiving (PD) side of the IEEE 802.3af application.

National’s PD Interfaces for PoE

• IEEE 802.3af Compliant with Power over Ethernet Consortium Test Data (Interoperability Cluase 33, PD Performance)
• Support for Isolated or Non-Isolated Applications
• Robust Auxiliary Poewr Support Including Aux Dominant Interface
• Programmable Current Limit and UVLO for High Power PoE Applications

IEEE 802.3af

The IEEE 802.3af standard for delivering power over Cat-5/5E cables eliminates the need for AC-adapters for equipment plugged into the Ethernet. A PoE system essentially consists of two major components; the Power Sourcing Equipment (PSE), which delivers power, and Powered Devices (PD), which receive and use the power. A PSE will only deliver power to the load if it detects a valid signature resistance, which distinguishes a compliant PD from a device that cannot receive power. It does this by applying a small current-limited voltage to the cable and checks for the presence of a 25k ohm resistor in the remote device. Only if the resistor is present is the full 48V is applied, but this is still current-limited to prevent damage to cables and equipment in fault conditions. Once the PD receives power, it must also convert the –48V PoE to the required power supply voltage.

Applications

Power Over Ethernet technology allows IP telephones, wireless LAN Access Points, webcams and many other appliances to receive power as well as data over existing LAN cabling.
Some Popular Applications for PoE include:

• VoIP (Voice over Internet Protocol) telephones
• IEEE802.11 Wireless LAN Access Points
• Bluetooth Access Points
• Web cameras
• Vending machines
• Gaming machines
• Retail point of information systems
• EPOS systems
• Building access control systems including RFID Card Readers and Lock Activators
• Time and attendance systems
• Battery chargers for mobile phones and PDAs
• Electronic musical instruments

Select

Power over Ethernet (PoE) Controller

Device	Description	Comments	Application Notes
LM5070	Integrated Power-over-Ethernet PD Interface and PWM Controller	For isolated and non-isolated applications	AN-1346 LM5070 'HE' Evaluation Board AN-1358 LM5070 AE Evaluation Board
LM5071	Integrated Power-over-Ethernet PD Interface and PWM Controller	Specifically designed for the PD that must accept power from auxiliary sources such as ac adapters	AN-1430  LM5071 Evaluation Board
LM5072	Integrated 100V Power Over Ethernet PD Interface and PWM Controller with Aux Support	Programmable DC current limit up to 800mA; versatile auxiliary power options with 9V minimum range; integrated hot-swap-MOSFET (100V/0,7 Ohm)	AN-1455 LM5072 Evaluation Board AN-1474 LM507X PoE Family FAQs
LM5073	Integrated 100V Power Over Ethernet PD Interface with Aux Support	Allows for flexible DC/DC converter selection	AN-1574 LM5073 Evaluation Board