MAXREFDES1015: Using MAX5971B, the PSE controller with the fewest components supports detection of IEEE 802.3af/at devices

The MAX5971B is a single-port power controller designed for use in IEEE® 802.3af/at-compliant power-sourcing equipment (PSE). This device provides powered device (PD) discovery, classification, current limit, and DC and AC load-disconnect detections. The MAX5971B supports both fully automatic operation and software programmability, and features an integrated power MOSFET and sense resistor. The device supports detection and classification operation from a single 54V supply. In addition, it supports 2-event classification and new Class 5 classification of high-power PDs. The MAX5971B provides up to 40W to a single port (Class 5 enabled) and still provides high-capacitance detection for legacy PDs.

Key Features

• IEEE 802.3af/at Compliant
• Up to 40W for Single-Port PSE Applications
• Integrated Power MOSFET and Sense Resistor
• Supports 54V Single-Supply Operation
• PD Detection and Classification
• Supports Both AC Load and DC Load Detections
• LED Indicator for Port Status

This board is not available for purchase.

This is a minimum component design of a PSE controller board using the MAX5971B for the detection and classification of PD, especially for DC disconnect detection.

Designed, Built, Tested

This document describes the hardware shown in Figure 1. It provides a detailed systematic technical guide to designing the MAX5971B PSE controller for DC-disconnect. Refer to the MAX5971B IC data sheet and MAX5971B EV kit data sheet for device operation details. The controller design been built and tested, details of which follow later in this document.

Design Resources