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IEEE 802.3af-Compliant, High-Efficiency, Class 1/Class 2 Powered Devices with Integrated DC-DC Converter

Integrated Powered Devices with Regulator Simplifies Designs

Product Details

Key Features

Simplified Block Diagram

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Key Features

  • High Integration Saves Space and BOM Cost
    • Efficient, Integrated DC-DC Converter (with Integrated Switches)
    • Built-In Output-Voltage Monitoring
    • Protects Against Overload, Output Short Circuit, Output Overvoltage, and Overtemperature
    • Integrated TVS Diode Withstands Cable Discharge Event (CDE)
    • Internal LDO Regulator with Up to 100mA Load
  • IEEE 802.3af-Compliant Features Reduce Design Time
    • PoE Class 1/Class 2 Classification Set with Single Resistor
    • Intelligent Maintain Power Signature (MPS) Complies with IEEE 802.3af Specification
    • Simplified Wall Adapter Interface
    • Pass 2kV, 200m CAT-6 Cable Discharge Event
  • High Efficiency During Light Loads Reduces Power Consumption
    • Sleep and Ultra-Low-Power Mode
    • Frequency Foldback for High-Efficiency Light-Load Operation
    • Back-Bias Capability to Optimize the Efficiency
  • Robust Performance
    • 8.7V to 60V Wide Input Voltage Range
    • Hiccup-Mode Runaway Current Limit
    • 49mA (typ) Inrush Current Limit
    • Open-Drain (Active-Low RESET) Output
  • Easy to Design With
    • 3.2V to 14V Programmable Output Voltage Range
    • Internal Compensation
    • Fixed 430kHz Switching Frequency

Applications/Uses

  • IEEE 802.3af-Powered Devices
  • IP Phones
  • IP Security Cameras
  • Wireless Access Nodes

Description

The MAX5991A/MAX5991B provide a complete power-supply solution as IEEE® 802.3af-compliant Class 1/Class 2 Powered Devices (PDs) in a Power-over-Ethernet (PoE) system. The devices integrate the PD interface with an efficient DC-DC converter, offering a low external part count PD solution. The devices also include a low-dropout regulator, MPS, sleep, and ultra-low power modes.

The PD interface provides a detection signature and a Class 1/Class 2 classification signature with a single external resistor. The PD interface also provides an isolation power MOSFET, a 60mA (max) inrush current limit, and a 321mA (typ) operating current limit.

The integrated step-down DC-DC converter uses a peak current-mode control scheme and provides an easy-to-implement architecture with a fast transient response. The step-down converter operates in a wide input voltage range from 8.7V to 60V and supports up to 6.49W of input power at 1.3A load. The DC-DC converter operates at a fixed 430kHz switching frequency, with an efficiency-boosting frequency foldback that reduces the switching frequency by half at light loads.

The devices feature an input undervoltage-lockout (UVLO) with wide hysteresis and long deglitch time to compensate for twisted-pair cable resistive drop and to assure glitch-free transition during power-on/-off conditions. The devices also feature overtemperature shutdown, short-circuit protection, output overvoltage protection, and hiccup current limit for enhanced performance and reliability.

All devices are available in a 20-pin, 4mm × 4mm, TQFN power package and operate over the -40°C to +85°C temperature range.

Simplified Block Diagram

MAX5991A, MAX5991B: Functional Diagram MAX5991A, MAX5991B: Functional Diagram Zoom icon

Technical Docs

Support & Training

Search our knowledge base for answers to your technical questions.

Filtered Search

Our dedicated team of Applications Engineers are also available to answer your technical questions. Visit our support portal .