Linear Technology Corp. has introduced the LT4275, LTPoE++, PoE+ and PoE-compliant powered device (PD) interface controllers for applications requiring up to 90W of delivered power.
PoE+ limits the maximum PD power delivery to 25.5W, which is insufficient to power today’s new class of power-hungry applications, such as picocells, base stations, signage and heated outdoor cameras. Linear Technology’s LTPoE++ standard addresses this market by expanding the power budget to four different power levels (38.7W, 52.7W, 70W and 90W), enabling complete high power LTPoE++ systems.
The LTPoE++ standard employs a classification scheme that simply enables LTPoE++ power sourcing equipment (PSE) controllers and LTPoE++ PD controllers to reliably communicate with one another while maintaining interoperability with IEEE standard equipment. The LT4275A (LTPoE++), LT4275B (PoE+) and LT4275C (PoE) efficiently deliver power to PD loads using just one IC.
“What people want when they come to LTC is a complete solution: we give them the chipset at both ends of the cable” said Bob Reay, vice president, mixed signal products. “We have a proprietary scheme to figure out the handshake between both ends to make sure the right amount of power is delivered, and we’ve designed everything to minimize power dissipation at high power.”
When power is added to the cable, it creates heat problems. By using an external MOSFET, it allows designers to achieve lower on-resistance and in turn less power dissipation on the board, he added.
This approach allows users to size the MOSFET to their application’s specific heating and efficiency requirements, enabling the use of low RDS(ON) 30mOhm MOSFETs if necessary. The LT4275 recognizes a PSE as either Type 1 hardware complying with the IEEE 802.3af 13W power level, Type 2 hardware, complying with IEEE 802.3at 25.5W power level or LTPoE++ hardware complying with 38.7W to 90W power levels, and passes power accordingly. For efficient power allocation, PD users can configure a classification that represents the PD power usage. A 100V abs max rated input voltage means the LT4275 easily survives and protects PDs from the most common Ethernet line surges. A programmable auxiliary power pin with signature corrupt provides support down to 9V. The LT4275 also includes a power good output, onboard signature resistor, undervoltage lockout and comprehensive thermal protection.
The LT4275 is offered in industrial and automotive grades, supporting operating temperature ranges from -40°C to 85°C and -40°C to 125°C, respectively, and is available in small RoHS-compliant 10-pin MSOP or 3mm x 3mm DFN packages. The LT4275 is priced starting at $1.45 each in 1,000-piece quantities and is available in production quantities.
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