Ethernet standards require that the data cable be isolated from the system chassis due mainly to ground loops, which can corrupt data, and possible ground potential differences in the Ethernet cable plant.  By extension, PoE (Power over Ethernet) subsystems which leverage Ethernet architectures need to be isolated for the same reasons.  This normally calls for at least one isolated supply to power the PSE (power sourcing equipment) controller, as well as multiple opto-couplers to isolate the PSE-to-host digital communications, which is almost always an I²C serial bus interface.

The LTC4270/LTC4271 chipset is a self-isolating, 12-port PSE controller designed for use in PoE, PoE+ and LTPoE++^TM systems.  The LTC4271 provides a digital interface to the PSE host, while the LTC4270 provides a high voltage Ethernet interface, delivering power to 12 independent PoE ports; the two ICs are bridged by a pair of low-cost Ethernet transformers to provide the isolation.  This unique transformer-isolated communication protocol replaces up to six expensive opto-couplers and eliminates the need for an isolated 3.3V supply, resulting in significant BOM cost savings and a more robust and easy to manufacture design.

More Features - More Ports, More Power

When the latest PoE standard, IEEE 802.3at (PoE+), finalized in 2009, it increased the power available to powered devices (PDs) from 13W to 25.5W so that end applications could advance in feature set (for example, pan-tilt-zoom cameras).  Today, PoE+ PSEs and PDs are continuing to proliferate quickly in the field with many new applications emerging.  The LTC4270/LTC4271 provides a cost-effective 12-port PSE solution via reduced BOM cost, component count and board space, as well as an increase in reliability.

The LTC4270/LTC4271 chipset is the first PSE solution to offer LTPoE++, Linear Technology's implementation of a higher power PoE standard which provides up to 90W of delivered power to an LTPoE++ PD.  This proprietary scheme uses LTPoE++ signaling methods to identify LTPoE++ PDs requiring more than the 25.5W limit of the PoE+ specification.  LTPoE++ is interoperable and backward compatible with IEEE PoE/PoE+ compliant devices, so LTPoE++, PoE+ and PoE devices can work together seamlessly.

Positioning:

The LTC4270/LTC4271 chipset is Linear Technology's first 12-port PSE controller, and the first of a family of 4^th generation PoE products targeted for high power applications.  The integrated isolation and high port count provides the lowest BOM cost and component count solution in the market.  The use of external, low R_DS(ON) MOSFETs and 0.25Ω sense resistors increase port reliability and provide the lowest power dissipation through each port.  Very high reliability 4-point PD detection uses two test voltages and two test currents to guard against false PD detections.  A host of new advanced power management hardware and software features are now available to PSE designers, such as temperature monitoring and "C" libraries that address multiple implementation levels: from basic PSE operation to fully managed, over allocated and prioritized switch systems - simplifying PSE designs.

Market Strategy:

The LTC4270/71 chipset is targeted at both midspans and endspans, including next-generation routers, switches and hubs, for telecommunication, industrial and medical markets. High power PD applications include long range wireless access points (WAP), thin clients, heated surveillance cameras, and digital signage.  The cost savings afforded by the LTC4270/71's simple isolation scheme will be appreciated by the cost-sensitive PoE market.   Linear Technology offers a reliable solution on both the PSE and PD side for systems that require more than 25.5W, and has LTPoE++ application circuits available for designers to provide a faster path to the high power PoE market.