MAX5974E

• 符合IEEE 802.3af/at标准的PD接口电路
• -39V至-57V启动输入电压范围
• 效率高达91% (VIN = +48V)
• 非隔离+3.3V电源，可输出1.8A电流
• PD检测和可配置分级信号
• 2级事件分级和墙上适配器检测输出
• 180mA (最大值)浪涌电流抑制
• -38.6V内部UVLO
• 评估端点和中跨以太网系统
• 简化墙上适配器接口
• 经过验证的PCB布局
• 完全安装并经过测试

MAX5974E评估板(EV kit)是完全安装并经过测试的表贴电路板，用于评估MAX5974E扩频、电流模式PWM控制器，该器件适用于以太网供电(PoE)中的用电设备(PD)。评估板采用紧凑的低成本设计，用于LAN供电(PoLAN)，可直接从以太网端口获取直流电源为PD (如：IP电话、无线接点和安全摄像头等)供电。

评估板具有一个2级PD，安装了200kHz开关频率的反激式DC-DC转换IC。利用同步整流器，电路可获得高达91%的效率。表贴变压器为输出储存能量，输出电压配置为+3.3V，可提供1.8A的负载电流。

评估板包含符合IEEE® 802.3af/at标准的PD接口控制IC MAX5969B，提供PD侦测信号、PD分级信号、浪涌电流控制、欠压锁定(UVLO)以及PD开启后的限流。

评估板电路从IEEE 802.3af/at兼容供电设备(PSE)取电。PSE提供所需要的-39V至-57V直流电压，经过非屏蔽双绞线以太网电缆连接到评估板的RJ45 MagJack®。评估板具有1 x 1Gb RJ45 MagJack和两个全桥二极管，用于分离由端点或中跨以太网系统提供的直流电源。

评估板也可以由+39V至+57V墙上适配器供电(作用在WAD_IN和WAN_GND PCB焊盘)。当检测到墙上适配器电源时，将优先选择墙上适配器给评估板供电。

警告：评估板设计工作在高压环境。该评估板及其相连设备都存在危险的高压。用户为评估板或评估板连接电源上电时，须谨慎操作并严格遵守高压电气设备的安全操作规程。

在严重故障或失效条件下，评估板会产生非常大的功耗，可能导致元件或元件碎片高速飞溅。须谨慎操作该评估板，以避免可能的人身伤害。

应用

• 大功率PD (高于802.3af/at标准要求)
• IP电话
• PoE IEEE® 802.3af/at用电设备
• 安全监控摄像机
• 无线接入点

• IEEE 802.3bt-compliant Class 6 PD
• Port telemetry with an isolated I²C interface
• 5V/9.2A isolated synchronous forward converter

The EVAL-LTC9105-AZ is an IEEE 802.3bt-compliant Type 3, Class 6 Power over Ethernet (PoE) powered device (PD) with port telemetry via I²C. The evaluation board features the LTC9105 PD interface controller, MAX5974C switching regulator controller, the LT4321 PoE ideal diode bridge controller, and the ADuM1252 I²C isolator.

The LTC9105 provides IEEE 802.3af-, IEEE 802.3at-, and IEEE 802.3bt-compliant interfacing with port voltage and current telemetry via I²C. It utilizes an external, low channel resistance, R_DS(ON) (34mΩ typical), N-channel, hot-swap metal-oxide semiconductor, field-effect transistor (MOSFET), and 50mΩ sense resistor. Automatic maintain power signature (MPS) keeps the port connected when the current drops to a low level.

The MAX5974C controls a DC/DC converter utilizing a highly efficient active-clamp forward converter topology with synchronous rectification and provides an isolated 5V/9.2A output. The LT4321 controls eight low R_DS(ON) (57mΩ typical), N-channel MOSFETs to further improve end-to-end power delivery efficiency and ease thermal design. The ADuM1252 isolates I²C data between the LTC9105 and a host controller on a nonisolated ground domain.

The EVAL-LTC9105-AZ is configured as a Class 6 PD and accepts up to 51W of delivered power from a power sourcing equipment (PSE) via its RJ45 connector (J1). The EVAL-LTC9105-AZ can be powered by a local 55V DC power supply using the auxiliary supply input terminals. With the DC590B I²C interface board connected to the EVAL-LTC9105-AZ, the EVAL-LTC9105-AZ graphical user interface (GUI) displays port telemetry and configuration options.