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The IEEE 802.3af-Compliant Power-Over-Ethernet power-suplly ICs

Maxim introduces the MAX5941/MAX5942, the industry's first power-over-Ethernet (PoE) DC-DC controllers that integrate an interface controller for powered devices such as IP phones, wireless LAN access point, and IP cameras. These ICs provide regulated power to a device's system and allow it to be safely powered over the network category-5 (CAT-5) data cable.


Rated for up to +67V operation and over 15W output power, the MAX5941/MAX5942 are fully compliant to the IEEE802.3af standard and allow design of isolated or nonisolated power supplies. Each device provides a valid 25k ohms signature discovery, classification signature, and programmable inrush current. During detection, these devices draw less than the 10iA of offset current, allowing accurate detection of the 25k ohms signature.

The MAX5941/MAX5942 include a current-mode PWM controller with an integrated startup circuit suitable for the high-performance, isolated or non-isolated power supplies.
Other features include current-mode control, leading-edge blanking, soft-start, overcurrent shutdown, undervoltage lockout, and thermal shutdown.

The MAX5941 is recommended for isolated forward and flyback converters. The MAX5942 is recommended for nonisolated designs.

MAX5941A, MAX5941B

The MAX5941A/MAX5941B integrate a complete power IC for powered devices (PD) in a power-over-ethernet (PoE) system. The MAX5941A/MAX5941B provide a PD interface and a compact DC-DC PWM controller suitable for flyback and forward converters in either isolated or nonisolated designs.

The MAX5941A/MAX5941B PD interface complies with the IEEE 802.3af standard, providing the PD with a detection signature, a classification signature, and an integrated isolation switch with programmable inrush current control. These devices also feature power-mode undervoltage lockout (UVLO) with wide hysteresis and power-good status outputs.

The MAX5941A/MAX5941B also integrate all the building blocks necessary for implementing DC-DC fixed-frequency isolated power supplies. These devices are a current-mode controller with an integrated high startup circuit suitable for isolated telecom/industrial voltage-range power supplies. A high-voltage startup circuit allows the PWM controller to draw power directly from the 18V to 67V input supply during startup.
The switching frequency is internally trimmed to 275kHz ±10%, thus reducing magnetics and filter components. The MAX5941A allows an 85% operating duty cycle and can be used to implement flyback converters. The MAX5941B limits the operating duty cycle to less than 50% and can be used in single-ended forward converters. The MAX5941A/MAX5941B are designed to work with or without an external diode bridge in front of the PD.

The temperature range & package

The MAX5941/MAX5942 are available in the extended (-40°C to +85°C) and commercial (0°C to +70°C) temperature ranges in the surface-mount, 16-pin SO package.




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