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Maxim IEEE802.3af-compliant PSE controller suits PoE apps

Posted: 30 Sep 2005 ?? ?Print Version ?Bookmark and Share

Keywords:maxim integrated products? max5945? ieee802.3af? power-sourcing-equipment controller? pse controller?

Maxim Integrated Products unveiled a quad IEEE802.3af-compliant power-sourcing-equipment (PSE) controller for power-over-ethernet (poe). In full compliance with the IEEE802.3af standard, the new MAX5945 controller provides discovery, classification, current limit, and both DC and AC load disconnect detection to a powered device (PD).

In addition, this controller is fully software configurable and provides three extra features not available from the competition. These features are:

? Supports both midspan (power injector) or endpoint switch/router (LAN) PSE applications. A cadence-timing feature allows the MAX5945 to be used in midspan systems.

? A watchdog feature allows system hardware to gracefully take over control if the system software crashes.

? Guaranteed operation over the extended -40C to 85C and the commercial 0 to 70C temperature ranges.

Maxim added that its new product's features add robustness, design flexibility and safety to PoE systems. During a system software crash or loss of communication between the system and the PSE controller, high-voltage conditions can exist at the output of the PSE controller causing a safety hazard. The watchdog feature ensures that the PSE controller goes into a shutdown mode or a user-defined default state during this event, while the cadence-timing feature allows the device to support both the midspan (power injector) and endpoint switch/router (LAN) PSE applications.

To ensure interoperability, both the PSE and PD devices must comply with the IEEE802.3af standard. A valid IEEE802.3af PSE device can deliver a maximum power of 15.4W per RJ-45 port and a valid IEEE802.3af PD device can consume a maximum power of 12.95W. Before applying power, the PSE must probe the PD and determine if a valid PD device is connected. The PD device must, in turn, exhibit a valid detection and classification signature prior to drawing power from the PSE. A valid PD detection signature is 25k and valid PD classes are Class 0 through Class 4.

The MAX5945's gate charging current, current-limit threshold, startup timeout, overcurrent timeout and autorestart duty-cycle features are all programmable. A class-overcurrent detection function enables the system to determine if a powered device (PD) is drawing more current than allowed for its class. Other standard features include input under-/overvoltage lockout, output-voltage slew-rate limit, overtemperature protection, power-good and fault status outputs. The device can operate autonomously or be controlled by software through an I?C compatible interface. These basic features improve system reliability, ensure design flexibility and provide field diagnostic and debug capabilities.

Maxim offers PoE reference designs with supporting software for both endpoint or midspan PSE applications. The MAX5945 is housed in a 36-pin SSOP package, with pricing starting at $6.81 (1,000-up, FOB USA). Samples and evaluation kits are already available.

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