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PSE controller has unique fit for PoE apps

Maxim Integrated Products introduces the MAX5945, a quad IEEE802.3af-compliant power-sourcing-equipment (PSE) controller for Power-over-Ethernet (PoE). In full compliance with the IEEE802.3af standard, the MAX5945 provides discovery, classification, current limit, and both DC and AC load disconnect detection to a powered device (PD). This controller is fully software configurable and, most importantly, provides three significant extra features not available from the competition.

PoE is a power distribution technique used to carry DC power and data from a PSE like the MAX5945 controller over Ethernet CAT-5 cable to a PD. Examples of PSEs are network switches, routers, hubs, and midspan power injectors. Since the ratification of the IEEE802.3af standard, industry quickly adopted PoE technology for networking applications. A variety of IEEE802.3af PD devices include IP phones, wireless network access points, and security cameras.

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.

While the MAX5945 meets all required IEEE802.3af requirements (see below), this PSE controller also provides three key features lacking from the competitive solution.

1. 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. The competitive solution handles switch/router PSE applications only.

2. A watchdog feature allows system hardware to gracefully take over control if the system software crashes. This feature is not available from the competition.

3. Guaranteed over the extended -40 degrees Celsius to +85 degrees Celsius and the commercial 0 to +70 degrees Celsius temperature ranges. The competition guarantees only the 0 to +70 degrees Celsius temperature range.

These unique features add robustness, design flexibility, and safety to PoE systems. The wider temperature range supports the requirements of extended-temperature 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. The cadence-timing feature allows the device to support both the midspan (power injector) and endpoint switch/router (LAN) PSE applications.

As a high-performance PoE controller, the MAX5945 has all the capabilities a designer needs to meet IEEE802.3af requirements. 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 I2 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. Customers can contact the factory for evaluation kits.

The MAX5945 is packaged in a 36-pin SSOP package. Prices start at $6.81 (1000-up, FOB USA). Samples are available.

A preliminary Data Sheet for this product is available at
www.maxim-ic.com/MAX5945

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