原标题：TI TPS23754 Class 4 PoE电源转换器参考设计

　　TI公司的tps23754和TPS23756组合了以太网供电(PoE)用电设备(PD)接口和电流模式DC/DC控制器,PoE接口支持IEEE 802.3at标准,支持高效率的拓朴,功率高达30W,主要用在IEEE 802.3at标准兼容的设备,视频和VoIP电话,RFID读卡器,多波段接如点和安全照相机.本文介绍了TPS23754/6主要特性,框图,典型应用电路,以及Class 4 PoE电源转换器参考设计主要特性,电路图,材料清单和PCB设计图.

　　The TPS23754 and TPS23756 devices have a combined power-over-ethernet (PoE) powered-device (PD) interface and current-mode DC/DC controller optimized specifically for isolated converters. The PoE interface supports the IEEE 802.3at standard.

　　The TPS23754 and TPS23756 support a number of input voltage ORing options including highest voltage, external adapter preference, and PoE preference. These features allow the designer to determine which power source will carry the load under all conditions.

　　The PoE interface features the new extended hardware classification necessary for compatibility with high-power midspan power sourcing equipment (PSE) per IEEE 802.3at. The detection signature pin can also be used to force power from the PoE source off. Classification can be programmed to any of the defined types with a single resistor.

　　The DC/DC controller features two complementary gate drivers with programmable dead time. This simplifies the design of active-clamp forward converters or optimized gate drive for highly-efficient flyback topologies. The second gate driver may be disabled if desired for single MOSFET topologies. The controller also features internal softstart, bootstrap startup source, current-mode compensation, and a 78% maximum duty cycle. A programmable and synchronizable oscillator allows design optimization for efficiency and eases use of the controller to upgrade existing power supply designs. Accurate programmable blanking, with a default period, simplifies the usual current-sense filter design trade-offs.

　　The TPS23754 device has a 15-V converter startup while the TPS23756 device has a 9-V converter startup. The TPS23754-1 replaces the PPD pin with a no-connect for increased pin spacing.

　　TPS23754/6主要特性:

　　Powers up to 30-W (Input) PDs

　　DC/DC Control Optimized for Isolated Converters

　　Supports High-Efficiency Topologies

　　Complete PoE Interface

　　Enhanced Classification per IEEE 802.3at With Status Flag

　　Adapter ORing Support

　　Programmable Frequency With Synchronization

　　Robust 100-V, 0.5-Ω Hotswap MOSFET

　　–40°C to 125°C Junction Temperature Range

　　Industry Standard PowerPAD TSSOP-20

　　TPS23754/6应用:

　　• IEEE 802.3at Compliant Devices

　　• Video and VoIP Telephones

　　• RFID Readers

　　• Multiband Access Points

　　• Security Cameras

　　图1. TPS23754/6框图

　　图2.采用TPS23754的高效转换器电路图

　　图3.驱动同步的反激电路图

　　Class 4 PoE电源转换器参考设计

　　This converter reference design is used for Class 4 PoE applications where high efficiency is required. The active clamp forward converter with synchronous rectifiers provides excellent efficiency and small size for PoE applications such as a wireless access point. The TPS23754 contains both the PoE Powered Device and the PWM controller functions.

　　Class 4 PoE电源转换器参考设计主要特性:

　　High efficiency(90%)

　　3.3V at 7.6A output

　　Isolated Forward with synchornous rectifier

　　Uses TPS23754 high-power, high-efficiency PoE interface PD and PWM controller

　　Small size solution

　　This circuit design is full-functional tested and recommended for new designs

　　图4. Class 4 3.3V/7.6A PoE电源转换器参考设计外形图

　　Class 4 PoE电源转换器参考设计材料清单: