Since the IEEE Std 802.3af, or Power-over-Ethernet (PoE), standard was ratified in June 2003, millions of PoE-enabled VoIP phones, WAPs (wireless access points) and security cameras have shipped worldwide. PoE is being built into a wide array of applications, such as Point of Sale terminals, networked sensors and building automation, because it conveniently and simultaneously delivers data and power. Projected shipments of PoE-enabled products for power sourcing equipment (PSEs) and powered devices (PDs) will exceed 100 million ports in 2008. While a substantial number, the 100 million ports represent less than one third of all wired Ethernet port shipments in 2008. Reducing the design effort and incremental cost of adding PoE to new and existing Ethernet products will encourage even higher levels of PoE adoption.
One approach to facilitate simpler, more compact and less costly PoE PD solutions is to integrate the high-voltage, typically discrete, silicon components. Multiple diode bridges, a transient voltage suppressor (TVS), and a power MOSFET for the PWM switching regulator are examples of components which can be integrated, but typically are not due to the complex nature of high voltage integrations. This paper provides an overview of key system-level requirements one must consider when integrating these devices into a PoE powered device interface and power management controller and the resultant benefits.
Powered device interfaces for PoE-enabled products have evolved from the early, fully-discrete implementations to the current generation of single-chip solutions that integrates the detection, classification and hot swap interface functions (required by the IEEE 802.3af standard), and a companion pulse width modulator (PWM) for dc-dc conversion. A typical solution is shown in the diagram below, including the external components required for a common isolated power supply.
Figure 1 Traditional PoE PD Interface and Switching Regulator (without high voltage device integration)