Isolated 12-port PoE PSE controller chipset eliminates optos to reduce costs
May 02, 2011 // Paul Buckley
Linear Technology Corporation has introduced an isolated 12-port Power Source Equipment (PSE) controller chipset designed for use in IEEE 802.3at (PoE+) Type 1 and Type 2 compliant Power over Ethernet (PoE) systems. The LTC4270/71 provides 12 independent PSE channels for simpler, lower component count designs, reduced board space and lower solution costs.
The LTC4271 provides a digital interface to the PSE host, while the LTC4270 proffers the high voltage Ethernet interface; the two ICs are then bridged by inexpensive Ethernet transformers. The transformer-isolated communication protocol replaces up to six expensive opto-couplers and a complex isolated 3.3 V supply used in traditional designs, resulting in cost savings and a more robust and manufacturable design.
The LTC4270/LTC4271 is suitable for a wide variety of PSE applications, including next generation switches, routers, hubs and midspans. Users will appreciate the robustness provided by 80 V port pins and lowest-in-industry power dissipation, making thermal design significantly easier than designing with PSEs that integrate more fragile normally higher RDS(ON) MOSFETs. Powered Device (PD) discovery is accomplished using a proprietary dual-mode, four point detection mechanism that ensures the best immunity from false PD detection. Advanced power management includes prioritized fast shutdown, 14-bit per-port voltage and current readback, 8-bit programmable current limits and 7-bit programmable overload current limits and field-upgradeable firmware. A 1 MHz I2C interface allows a host controller to digitally configure the IC or query port readings. “C” libraries are available to reduce engineering costs and improve time to market.
The LTC4270 is available in three power grades: A-grade uses Linear's LTPoE++ signaling to support up to 90W PDs, B-Grade uses PoE+ signaling to support up to 25.5 W PDs, and C-grade uses PoE signaling to support up to 13W PDs. All chipsets are offered in industrial temperature grades. The LTC4270 is in a RoHS-compliant 52-pin 7 mm x 8 mm QFN package, while the LTC4271 is in a 24-pin 4 mm x 4 mm QFN package.
The LTC4270/71 chipset is priced starting at $12.00 each in 1,000 piece quantities and is now available in production quantities. The LTC4270/LTC4271 is backward compatible with the LTC4266 4-port PoE+ PSE controller and LTC4274 single-port PoE+ PSE controller, supported by Linear's extensive technical experience in PoE circuit design, ensuring a smooth transition to the new PoE+ standard or higher power levels.
More information about the LTC4270 chipset at www.linear.com/product/LTC4270.
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