Research On High-efficiency Power Integrated Circuit Of Powered Device Based On IEEE802.3at Power Over Ethernet (PoE) Standard

Power over Ethernet(Po E)represents a standardized technology to transfer data along with electrical power on Ethernet cabling,allowing devices to be powered via their network ports.Since it is compatible with existing Ethernet cable infrastructure,the PoE technology can work properly without making any modification,greatly reducing the overall installation and maintenance cost.Compared with the traditional power sypply mode,PoE technology has great advantages in easy installation,high reliability,cost savings and providing unified and secure power standards for users around the world.PoE technology can effectively solve the problem of centralized power supply for terminal equipment such as video and Vo IP telephones,multiband access points,RFID readers,security cameras,and so on.Therefore,PoE technology continues to receive attention and has wide-ranging prospects in the global networking market.In order to unified standards to be comparible with PoE devices between different vendors,PoE special group of Institute of Electrical and Electronics Engineers(IEEE)has been working on relevant standards since 1999,and released the 802.3af standard in 2003 and802.3at standard in 2009 respectively.In additon,devices compliant with IEEE802.3af and IEEE802.3at are referred to as type 1 and type 2 devices,respectively.A typical PoE system consists of a power sourcing equipment(PSE)and a powered device(PD).In order to ensure the smooth power transmission process and meet the IEEE802.3at standard,both the PSE and PD need to have appropriate power management ICs to manage and control the entire power transmission process.The power management ICs of the PD include a PoE interface and DC-DC controller and are the interface between the Ethernet cable and IP devices.The PoE interface is responsible for the communication with PSE and supports all the functions that comply with the IEEE802.3at standard such as detection,classification,current-limit,and so on.Meanwhile,the DC-DC controller is suitable for a variety of topologies to employ voltage conversion.Based on IEEE802.3at standard,the paper provides a power managament IC for PD.Using Silicon-on-Insulator(SOI)BCD process,a prototype converter integrates the PoE interface and DC-DC controller to drastically reduce the power consumption and the size of PCB,and proposes a complete set of solution for PD.The system can work with power either from an Ethernet cable or from an external adapter.During the detection phase,the other modules of chip are not active and therefore the traditional comparison method with reference level cannot be used.Based on bandgap reference structure,a detection comparator is provided to detect input voltage without extra voltage reference,and reduces chip size and detection time.The chip uses an algorithm to accuratey distinguish between type 1 and type 2 devices by two-event classification logic control(latching the states of classification and mark twice).Using a PTAT current generation circuit,a low offset voltage amplifier and base current compensation technology to tackle the problem of current-liniting point drift caused by metal resistor with low-resistance,a low-loss current-limiting technique is proposed to achieve a high precision current-limit point.DC-DC controller uses peak current mode,integrates a hotswap MOSFET to isolate its ground and that of PoE and has complete protection circuit to ensure the safe operation of the system.A dual-mode(PWM&PSM)controlled scheme is provided to achieve high efficiency over a wide load range.A circuit multiplexed oscillator structure is proposed to achieve the programmable and synchronous clock frequency.The maximum duty cycle is set precisely to reduce the voltage stress of the main MOSFET.The chip is fabricated in a 0.5?m 65V SOI BCD process,occupies a die size(with pads)of1.79×2.76 mm~2,and adopts TSSOP-20 package form.The experimental results are measured for an active clamp forward converter with a wide range of DC input voltages from 33 to 57 V.The experimental results show that the chip can be compatible with IEEE802.3af and IEEE802.3at standard and provides maximum output power of 30W.The chip achieves peak power efficiency of 90%and 90.63%on DC(at 53 V)and ASS(at 48V),respectively.Measurements further show that the peak-to-peak ripple voltage of the chip is 161mV at 53 V and the load regulation at different input voltages can be measured to be within±0.11%.In addtion,for the 2-A load step,the output voltage peak and drop during load stepping down and stepping up are 396 and 364 mV,respectively.The recovery time is less than 1.2 ms for the final settled voltage for both load step up and step down.