原标题：Linear LT4276IEEE 802.3af/at和LTPoE++受电设备解决方案

　　Linear公司的LT4276是LTPoE++/PoE+/PoE PD正激式/反激式控制器,支持LTPoE++ 38.7W,52.7W,70W和90W标准以及EEE 802.3at (25.5W) 规范,IEEE 802.3af (高达 13W) 规范,具有出众的浪涌保护能力,主要用在大功率无线数据系统,户外监视照相机设备,商用和公共信息显示器以及高温应用.本文介绍了LT4276主要特性,框图,多种应用电路以及演示板2046A-A特性,电路图和材料清单.

　　The LTR4276 is a pin-for-pin compatible family of IEEE802.3 and LTPoE++ Powered Device (PD) controllers. Itincludes an isolated switching regulator controller capableof synchronous operation in both forward and flybacktopologies with auxiliary power support.

　　The LT4276A employs the LTPoE++ classification scheme,receiving 38.7W, 52.7W, 70W or 90W of power at the PDRJ45 connector, and is backwards compatible with IEEE802.3. The LT4276B is a fully 802.3at compliant, 25.5WType 2 (PoE+) PD. The LT4276C is a fully 802.3af compliant,13W Type 1 (PoE) PD.

　　The LT4276 supports both forward and flyback powersupply topologies, configurable for a wide range of PoEapplications. The flyback topology supports No-Optofeedback. Auxiliary input voltage can be accurately sensedwith just a resistor divider connected to the AUX pin.

　　The LT4276 utilizes an external, low RDS(ON) N-channelMOSFET for the Hot Swap function, maximizing powerdelivery and efficiency, reducing heat dissipation, andeasing the thermal design.

　　LT4276主要特性:

　　IEEE802.3af/at and LTPoE++™ 90W Powered Device(PD) with Forward/Flyback Controller

　　LT4276A Supports All of the Following Standards:

　　LTPoE++ 38.7W, 52.7W, 70W and 90W

　　IEEE 802.3at 25.5W Compliant

　　IEEE 802.3af up to 13W Compliant

　　LT4276B is IEEE 802.3at/af Compliant

　　LT4276C is IEEE 802.3af Compliant

　　Superior Surge Protection (100V Absolute Maximum)

　　Wide Junction Temperature Range (–40℃ to 125℃)

　　Auxiliary Power Support as Low as 9V

　　No Opto-Isolator Required for Flyback Operation

　　External Hot Swap™ N-Channel MOSFET for LowestPower Dissipation and Highest System Efficiency

　　>94% End-to-End Efficiency with LT4321 Ideal Bridge

　　Available in a 28-Lead 4mm × 5mm QFN Package

　　LT4276应用:

　　High Power Wireless Data Systems

　　Outdoor Security Camera Equipment

　　Commercial and Public Information Displays

　　High Temperature Applications

　　图1.LT4276框图

　　图2.LT4276应用电路图:正激模式70W电源

　　图3.LT4276应用电路图:反激模式13WPoE电源

　　图4.LT4276应用电路图:反激模式25.5W PoE+电源

　　图5.LT4276应用电路图:正激模式70W LTPoE+电源

　　图6.LT4276应用电路图:正激模式90W LTPoE+电源

　　图7.LT4276应用电路图:反激模式38.7W LTPoE++电源

　　图8.LT4276应用电路图:反激模式25.5W PoE+和9V-57V辅助输入电源

　　图9.LT4276应用电路图:反激模式25.5W PoE+电源

　　图10.LT4276应用电路图:反激模式25.5W PoE+电源

　　演示板2046A-A

　　Demonstration circuit 2046A-A is a PoE powered device(PD) with an isolated power supply using synchronousflyback topology, featuring the LTR4276 and ideal diodebridge controller (LT4321).

　　The LT4276 provides IEEE802.3af (PoE, Type 1),IEEE802.3at (PoE+, Type 2), and LTPoE++™ PD interfacingand power supply control. When the PD is fully powered,the PD interface switches power over from the powersourcing equipment (PSE) to the switcher through anexternal, low resistance, high power N-channel FET. Thehighly integrated LT4276 controls a high power, smallsizedpower supply that utilizes a highly efficient flybacktopology with synchronous rectification. The LT4321provides further efficiency improvement by minimizingthe bridge losses.

　　The DC2046A-A supplies a 3.3V output at up to 6.8A. Italso demonstrates the use of an optional auxiliary powersupply input of 48V. When present, the auxiliary supplybecomes the dominant supply over PoE to provide power.

　　图11.演示板2046A-A外形图

　　演示板2046A-A材料清单: