原标题：Linear LT4275 90W以太网受电控制方案

　　Linear 公司的LT4275是引脚兼容的IEEE 802.3和LTPoE++受电设备(PD)控制器,在PD RJ45连接器上提供38.7W,52.7W,70W或90W的功率,支持LTPoE++ 38.7W, 52.7W, 70W和90W,EEE 802.3at 25.5W,EEE 802.3af 高达13W标准,最大输入电压100V,主要用在大功率无线数据系统,户外安全照相系统,商业和公共信息显示屏,高温工业应用.本文介绍了LT4275A 主要特性,框图,多种受电电路图,以及演示板DC1788A电路图和材料清单.

　　The LT275 is a pin-for-pin compatible family of IEEE 802.3 and LTPoE++ powered device (PD) controllers.

　　The LT4275A employs a proprietary LTPoE++ classification scheme, delivering 38.7W, 52.7W, 70W or 90W of power at the PD RJ45 connector. The LT4275A is fully compatible with IEEE 802.3. The LT4275B is an IEEE 802.3at compliant, Type 2 (PoE+) PD delivering up to 25.5W. The LT4275C is an IEEE 802.3af compliant, Type 1 (PoE) PD delivering up to 13W.

　　The LT4275 internal charge pump provides an N-channel MOSFET solution, eliminating a larger and more costly P-channel MOSFET. A low RDS(ON) MOSFET also maximizes power delivery and efficiency, reduces power and heat dissipation, and eases thermal design. Startup inrush current is adjustable with an external capacitor. The LT4275 also includes a power good output, on-board signature resistor, undervoltage lockout, and thermal protection. The LT4275A/LT4275B drives a single opto-coupler to indicate the power level of the attached PSE. Pin-selectable support for non-standard low voltage operation is provided.

　　Auxiliary power override is supported with the AUX pin.

　　The LT4275A can be configured to support all possible LTPoE++, 802.3at and 802.3af power levels with external component changes.

　　LT4275A主要特性:

　　IEEE 802.3af/at and LTPoE++™ Powered Device (PD) Controller

　　LTPoE++ Supports Power Levels Up to 90W

　　LT4275A 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

　　LT4275B is IEEE 802.3at/af Compliant

　　LT4275C is IEEE 802.3af Compliant

　　100V Absolute Maximum Input Voltage

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

　　Overtemperature Protection

　　Integrated Signature Resistor

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

　　Programmable Aux Power Support as Low as 9V

　　Optional Support of Non-Standard Low Voltage PoE

　　Available in 10-Lead MSOP and 3mm × 3mm DFN

　　Packages

　　LT4275A 应用:

　　High Power Wireless Data Systems

　　Outdoor Security Camera Equipment

　　Commercial and Public Information Displays

　　High Temperature Industrial Applications

　　图1.LT4275A方框图

　　图2.LT4275A IEEE 802.3af (Type 1) 13W受电设备(PD)电路图

　　图3.LT4275A IEEE 802.3at (Type 2) 25.5W 受电设备(PD)电路图

　　图4.LT4275A LTPoE++ 38.7W - 90W 受电设备(PD)电路图

　　演示板DC1788A

　　Demonstration circuit 1788A features the LT®4275, a fourth generation powered device (PD) controller for Power over Ethernet (PoE) applications.

　　The DC1788A is available in DC1788A-A, DC1788A-B, and DC1788A-C versions to meet the power level required by the PD application. The DC1788A-A features the LT4275A PD controller. This controller supports the IEEE 802.3at (Type 2, PoE+), IEEE 802.3af (Type 1, PoE) and LTPoE++™ specification. LTPoE++ adds four power levels to the existing IEEE standard with 38.7W, 52.7W, 70W, and 90W of delivered PD power at the RJ45 jack. The DC1788A-B features the LT4275B PD controller and is compliant with the IEEE 802.3at and IEEE 802.3af specifications. The DC1788A-C features the LT4275C PD controller and is compliant with the IEEE 802.3af specification.

　　The DC1788A includes an RJ45 Ethernet port, a high power Ethernet magnetic, a discrete active bridge rectifier, a surge protector, an external N-channel FET, and the LT4275. The discrete active bridge rectifier is used to achieve higher efficiency than a conventional diode bridge rectifier. Many of the main features from the previous generation PD controller are included in this generation PD L, LT, LTC, LTM, Linear Technology and the Linear logo are registered trademarks and LTPoE++ and Hot Swap are trademarks of Linear Technology Corporation. All other trademarks are the property of their respective owners.

　　controller. These include a power good indicator, a power sourcing equipment (PSE) type indicator, and support for an auxiliary power input. The major difference from the previous generation PD controller is that the LT4275 drives an external N-channel Hot Swap™ FET at the PoE high side voltage rail. This allows the user to choose a lowRDS(ON) N-channel MOSFET to maximize power efficiency, reduce heat dissipation, and ease thermal design. An LED status indicator is included to indicate the Hot Swap FET is fully turned on and the PSE is powering the PD. A sufficient load to sink more than 10mA is also included to assure the PSE maintains power to the PD and to meet the DC maintain power signature current required by the IEEE 802.3at/IEEE 802.3af specification.

　　Simply connect the output of the DC1788A to the DC/DC converter that is right for the application. Linear Technology offers a variety of DC/DC converter solutions that can be

　　used with the DC1788A (eg DC894, DC1317, etc).

　　演示板DC1788A材料清单: