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.