IEEE 802.3af PD Interface and PWM Controllers with Integrated Power MOSFETs

The MAX5953A/MAX5953B/MAX5953C/MAX5953D integrate a complete power IC solution for Powered Devices (PD) in a Power-Over-Ethernet (PoE) system, in compliance with the IEEE 802.3af standard. The MAX5953A/MAX5953B/MAX5953C/MAX5953D provide the PD with a detection signature, a classification signature, and an integrated isolation switch with programmable inrush current control. These devices also integrate a voltage-mode PWM controller with two power MOSFETs connected in a two-switch voltage-clamped DC-DC converter configuration.

An integrated MOSFET provides PD isolation during detection and classification. All devices guarantee a leakage current offset of less than 10µA during the detection phase. A programmable current limit prevents high inrush current during power-on. The devices feature power-mode undervoltage lockout (UVLO) with wide hysteresis and long deglitch time to compensate for twisted-pair-cable resistive drop and to assure glitch-free transition between detection, classification, and power-on/-off phases. The MAX5953A/MAX5953C have an adjustable UVLO threshold with the default value compliant to the 802.3af standard, while the MAX5953B/MAX5953D have a lower and fixed UVLO threshold compatible with some legacy pre-802.3af power-sourcing equipment (PSE) devices.

The DC-DC converters are operable in either forward or flyback configurations with a wide input voltage range from 11V to 76V and up to 15W of output power. The voltage-clamped power topology enables full recovery of stored magnetizing and leakage inductive energy for enhanced efficiency and reliability. When using the high-side MOSFET, the controller can be configured as a buck converter. A look-ahead signal for driving secondary-side synchronous rectifiers can be used to increase efficiency. A wide array of protection features include UVLO, over-temperature shutdown, and short-circuit protection with hiccup current limit for enhanced performance and reliability. Operation up to 500kHz allows for smaller external magnetics and capacitors.

The MAX5953A/MAX5953B/MAX5953C/MAX5953D are available in a high-power (2.22W), 7mm x 7mm thermally enhanced thin QFN package.

Applications

* Computer Telephony * IEEE 802.3af Powered Devices * Internet Appliances * IP Phones * Security Cameras * Wireless Access Nodes

* Powered Device Interface

* Fully Integrated IEEE 802.3af-Compliant PD Interface

* PD Detection and Programmable Classification Signatures

* Less than 10µA Leakage Current Offset During Detection

* Integrated MOSFET for Isolation and Inrush Current Limiting

* Gate Output Allows External Control of the Internal Isolation MOSFET

* Programmable Inrush Current Control

* Programmable Undervoltage Lockout (MAX5953A/MAX5953C)

* DC-DC Converter

* Clamped, Two-Switch Power IC for High Efficiency

* Integrated High-Voltage 0.4Ω Power MOSFETs Up to 15W Output Power

* Bias Voltage Regulator with Automatic High-Voltage Supply Turn-Off

* 11V to 76V Wide Input Voltage Range

* Feed-Forward Voltage-Mode Control for Fast Input Transient Rejection

* Programmable Undervoltage Lockout

* Overtemperature Shutdown

* Indefinite Short-Circuit Protection with Programmable Fault Integration

* Integrated Look-Ahead Signal for Secondary-Side Synchronous Rectification

* > 90% Efficiency with Synchronous Rectification

* Up to 500kHz Switching Frequency

* High-Power (2.22W), 7mm x 7mm Thermally Enhanced Lead-Free Thin QFN Package