MAXREFDES1009: IEEE 802.3af/at compliant, PD interface with 3 ultra-small size, high efficiency, synchronous DC-DC Buck converters

Power over Ethernet (PoE) is a technology that allows network cables to deliver power to a powered device (PD) via power-sourcing equipment (PSE) or midspan, and has many advantages over traditional methods of delivering power.

PoE allows power and data to be combined, removing the need for altering the AC mains infrastructure and can be installed by non-electricians. PoE is an intelligent system designed with protection at the forefront, preventing overload, underpowering, and installation errors, while allowing simple scalability and reliability.

High-efficiency, step-down switching regulators minimize power loss with efficiencies greater than 90%, allowing reductions in excessive heat, longer lifetime of ICs, and maximum power available to the PD. Ultra-small packaging, no Schottky diode, and the use of all ceramic capacitors reduce the overall size of the design.

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Key Features

• IEEE 802.3af/at Compliance
• 2-Event Classification
• No Schottky-Synchronous Operation for High Efficiency and Reduced Cost
• Internal Compensation and Feedback Divider for 5V Fixed Output Saves Space
• All-Ceramic Capacitors, Ultra-Compact Layout
• Peak Efficiency > 90%
• 3mm × 2mm, 10-Pin TDFN and 5mm × 4.4mm, 14-Pin TSSOP Packages (MAX17502)
• Thermally Enhanced, 3mm × 3mm, 10-Pin TDFN (MAX5969B)

Designed, Built, Tested

This document describes the hardware shown in Figure 1. It provides a detailed technical guide to designing a complete interface for a PD to comply with the IEEE^® 802.3af/at standard in a power-over-Ethernet (PoE+/Type II) Class 4 system and provides a 3-output, non-isolated, ultra-small, high-efficiency, synchronous, step-down DC-DC conversion.

Design Resources