MAX5974F

• IEEE 802.3af/at-Compliant PD Interface Circuit
• -39V to -57V Startup Input Voltage Range
• 91% Efficiency (at VIN = +48V)
• Nonisolated +3.3V Output at 1.8A
• PD Detection and Configurable Classification Signatures
• 2-Event Classification and Wall-Adapter Detect Output
• Inrush Current Limit of 180mA (max)
• Internal UVLO at -38.6V
• Evaluates Endspan and Midspan Ethernet Systems
• Simplified Wall-Adapter Interface
• Proven PCB Layout
• Fully Assembled and Tested

The MAX5974E evaluation kit (EV kit) is a fully assembled and tested surface-mount circuit board featuring the MAX5974E spread-spectrum, current-mode PWM controller for Power-over-Ethernet (PoE) powered device (PD) applications. The EV kit circuit is a nonisolated, compact, and low-cost design used in Power-over-LAN (PoLAN) applications requiring DC power from an Ethernet network port for PDs such as IP phones, wireless access nodes, and security cameras.

The EV kit features a Class 2 PD with a 200kHz switching frequency flyback DC-DC converter using the IC. The circuit achieves high efficiency up to 91% using a synchronous rectifier. The surface-mount transformer provides energy storage for the output, which is configured for +3.3V and provides up to 1.8A load current.

The EV kit includes the MAX5969B IEEE® 802.3af/at-compliant PD interface-controller IC that provides PD detection signature, PD classification signature, inrush current control, undervoltage lockout (UVLO), and current limit after the PD is on.

The EV kit circuit receives its power from IEEE 802.3af/at-compliant power-sourcing equipment (PSE). The PSE provides the required -39V to -57V DC power over a twisted-pair Ethernet network cable to the EV kit's RJ45 MagJack®. The EV kit features a 1 x 1Gb RJ45 MagJack and two full-bridge diodes for separating the DC power provided by an endspan or midspan Ethernet system.

The EV kit circuit can also be powered by a +39V to +57V wall-adapter power source applied at the WAD_IN and WAD_GND PCB pads. When a wall-adapter power source is detected, it always takes precedence over the PSE source, allowing the wall adapter to power the EV kit.

Warning: The EV kit is designed to operate with high voltages. Dangerous voltages are present on this EV kit and on equipment connected to it. Users who power up this EV kit or power the sources connected to it must be careful to follow safety procedures appropriately to work with high-voltage electrical equipment.

Under severe fault or failure conditions, this EV kit may dissipate large amounts of power, which could result in the mechanical ejection of a component or of component debris at high velocity. Operate this kit with care to avoid possible personal injury.

Applications

• High-Power PD (Beyond the 802.3af/at Standard)
• IP Phones
• PoE IEEE® 802.3af/at Powered Devices
• Security Cameras
• Wireless Access Nodes