A Design Of Powered Device Interface Chip Under PoE System

Power over Ethernet technology refers to ensuring the safety of the existing structured cabling, without making any changes to the existing Ethernet cabling infrastructure Cat.5, it is not only to ensure the normal operation of the existing network, but at the same time for some IP-based terminals, such as IP telephones, wireless LAN access point AP, network cameras, to provide DC power supply technology to minimize transmission costs. Power over Ethernet technology is also known as LAN-based power supply system or Active Ethernet, which is using the existing IEEE802.3af/at standard Ethernet cable to simultaneously transmit data and power, and maintained compatibility with the existing Ethernet system and user.Standard Ethernet-powered devices with the power supply system is divided into two parts by the electrical equipment. The main principle is to provide and control supply voltage variations throughout the various stages of the process by power supply equipment, after the powered device receives the voltage signals to control within the various modules enable off and analyzed to adjust, and finally feedback to a certain power supply equipment current signal, thus completing various functions such as detection and classification.This paper designed an interface chip which is compatible with IEEE802.3at powered device communication protocol and used to control the electrical power over Ethernet system by the end. The design uses Hangzhou Silan company100V high voltage BCD process, with all the features required standards IEEE802.3at, support of not less than25.5W of power. This chip includes ten basic function modules of pre-regulator, band-gap reference current source, comparators, signature resistance detection, classification regulator, mark&reset, two-event classification logic control, current limiting, complementary power good output signal. Specific innovations of the chip are140mA inrush current limiting, complementary output enable signal, the threshold30V-36V voltage protection, threshold is71V-73V overvoltage protection, threshold of122℃-148℃over temperature protection, an optional external power adapter input, IEEE802.3at type2powered devices display the new signal, as well as two-event classification logic implementation.This thesis completed all the circuit design and layout design, front schematic simulation and post simulation. The circuit simulation results show that this article has reached the above design goals.