MAXREFDES1266

描述

The MAXREFDES1266 is a 65W, 24V Power-over-Ethernet (POE) solution that delivers up to 2.7A load current. The design is optimized for applications with a 37V to 57V input voltage range. The design is a fully assembled, surface-mount circuit board featuring an Ethernet port, network-powered device (PD) interface controller, and a downstream CCM flyback converter. The design receives power from an IEEE^® 802.3bt-compliant power-sourcing equipment (PSE).

The MAXREFDES1266 employs a MAX5974A fixed-frequency, current-mode PWM controller in continuous mode flyback configuration. The MAX5974A features unique circuitry to achieve output regulation without using an optocoupler. The device features a unique feed-forward maximum duty-cycle clamp that makes the maximum clamp voltage during transient conditions independent of the line voltage, allowing the use of a power MOSFET with lower breakdown voltage. The programmable frequency dithering feature provides low-EMI, spread-spectrum operation.

The MAX5995B is used to provide a complete interface for a PD to comply with the IEEE 802.3bt standard in a POE system. It provides the PD with a detection signature, classification signature, and an integrated isolation power switch with startup inrush current control. The devices support a multi-event classification method, as specified in the IEEE 802.3bt standard. They provide a signal to indicate a Type 1 to Type 4 PSE. The devices can detect the presence of a wall adapter power source connection and allow a smooth switchover from the PoE power source to the wall power adapter. The devices also provide a power-good (PG) signal, two-step current limit, and foldback control and overtemperature protection.

优势和特点

Features

• Wide 37V to 57V input voltage range
• Highly regulated output voltage with ±1% ripple
• IEEE 802.3bt-compliant PD interface
• Multi-event classification
• Demonstrates a 65W PD design with isolated CCM flyback topology DC-DC converter
• 24V output at 2.7A
• Startup inrush current limit of 135mA (typ)
• Flyback controller internal UVLO at +16V
• Reduced BOM cost by employing primary sensing feedback
• High-efficiency flyback design using synchronous rectification

Applications

• Industrial Power Supplies
• Access Control
• E-Buildings
• POE-Enabled Devices (e.g., IP phone, IP camera)