Analog Devices Inc./Maxim Integrated MAXREFDES98#

Overview

MAXREFDES98# from Maxim Integrated is a non-isolated Power over Ethernet (PoE) powered device (PD) reference design module integrating the MAX5969A IEEE 802.3af-compliant PD controller and the MAX17503 4.5V–60V input, 2.5A synchronous step-down converter. It delivers 5V ±3% at up to 2.5A (12.5W) from a 36V–57V PoE input, uses low forward voltage Schottky bridge rectifiers for improved efficiency, and targets compact, cost-sensitive PoE endpoints such as IP cameras and LED lighting.

For engineers reviewing the MAXREFDES98# datasheet, MAXREFDES98# pinout, MAXREFDES98# application, or MAXREFDES98# equivalent, this page provides verified technical context, validated pin functions, confirmed performance metrics (86% peak efficiency, ±3% output accuracy, 300kHz switching), and production-ready design resources including schematics, Gerber files, and BOM - all aligned with Maxim's official reference design documentation.

Technical Context

The MAXREFDES98# implements a two-stage non-isolated PoE power architecture: first, the MAX5969A performs IEEE 802.3af detection, classification (Class 3 via 619Ω resistor), and inrush-controlled hot-swap switching; second, the MAX17503 executes regulated 5V/2.5A DC-DC conversion with internal compensation, 300kHz fixed-frequency operation, and soft-start timing of 3.2ms.

Input compatibility is ensured by dual bridge rectifiers accepting either polarity across VA1/VA2 and VB1/VB2 terminals; output stability is maintained with <1.5% load regulation and <100mV ripple across 5mA–2.5A, while the open-drain RESET signal (active low, asserts for 3.4ms after VOUT exceeds 4.75V) enables coordinated system initialization.

Key Specifications

Availability

MAXREFDES98# is available at Aetrix Electronics and suitable for IP cameras, LED lighting systems, industrial sensors, and non-isolated Ethernet equipment requiring stable component supply, rapid prototyping, and production-ready PoE PD implementation.

Supply support for MAXREFDES98# includes scheduled delivery planning, volume procurement assistance, BOM continuity management, traceable sourcing, and lifecycle availability coordination for OEM customers, industrial embedded developers, connected-device designers, and electronics production programs.

Manufacturer

Maxim Integrated (now part of Analog Devices) designs precision analog, mixed-signal, and power management ICs for industrial, communications, and computing applications.

MAXREFDES98# belongs to Maxim's reference design portfolio targeting cost-optimized, non-isolated PoE powered devices - specifically engineered to eliminate transformer-based isolation where safety standards permit, reducing bill-of-materials and thermal overhead.

FAQ

What is the exact function of MAXREFDES98# in a PoE system?

MAXREFDES98# is a complete non-isolated PoE powered device (PD) reference design module that integrates both the IEEE 802.3af-compliant PD interface (via MAX5969A) and the regulated 5V/2.5A DC-DC power supply (via MAX17503). It enables direct connection to PoE power sourcing equipment without isolation transformers, delivering clean, efficient power to downstream loads such as imaging sensors or microcontrollers. The MAXREFDES98# handles detection, classification, inrush control, and regulation in a single compact board.

Does MAXREFDES98# support IEEE 802.3at (PoE+)?

MAXREFDES98# is explicitly designed and tested for IEEE 802.3af compliance (Class 3, up to 12.95W), with a fixed 619Ω classification resistor. While its 36V–57V input range overlaps with 802.3at PSE outputs, it does not implement 802.3at-specific features such as two-event classification or higher power negotiation. Therefore, MAXREFDES98# operates reliably on 802.3at PSEs only in af-compatible mode and cannot draw more than Class 3 power. Its behavior remains fully defined under 802.3af.

What are the pin functions of the 6-pin J1 and J2 connectors on MAXREFDES98#?

J1 (input side) pins are: VA1/VA2 and VB1/VB2 - dual bridge rectifier inputs accepting either polarity from PoE pairs; CP1/CP2 - connect to the onboard 619Ω classification resistor for IEEE 802.3af Class 3 identification. J2 (output side) pins are: VOUT (×2), GND (×2), NX (no connect), and RESET - an open-drain active-low reset signal that goes high 3.4ms after VOUT exceeds 4.75V, intended for microcontroller synchronization.

Can MAXREFDES98# be used without the MAXREFDES98EV# evaluation board?

Yes, MAXREFDES98# is a standalone module with 12 through-hole pins (2.54mm pitch) designed for direct soldering onto custom PCBs. It requires no MAXREFDES98EV# for operation - the EV board merely adds RJ45 connectivity, current sensing (via MAX9643), and LED indicators for rapid lab validation. All critical circuitry, including PD control, DC-DC conversion, and protection, resides entirely on the MAXREFDES98# board itself.

What efficiency and thermal performance can be expected from MAXREFDES98# in real-world use?

MAXREFDES98# achieves 86% peak efficiency at 48V input and 2.5A load, with efficiency remaining above 82% across 0.5A–2.5A at 48V. Measured output ripple stays below 100mV from 5mA to full load, and thermal performance is robust due to Schottky bridge rectifiers (KMB110F) and optimized inductor selection (e.g., TDK SLF12575T-150M4R7-PF). No heatsink is required under continuous 12.5W operation in still air, per Maxim's lab validation data.