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LTC4270/ Datasheet(PDF) 16 Page - Linear Technology |
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LTC4270/ Datasheet(HTML) 16 Page - Linear Technology |
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16 / 32 page  LTC4290/LTC4271 16 429071f OVERVIEW Power over Ethernet, or PoE, is a standard protocol for sending DC power over copper Ethernet data wiring. The IEEE group that administers the 802.3 Ethernet data stan- dardsaddedPoEpoweringcapabilityin2003.Thisoriginal PoE spec, known as 802.3af, allowed for 48V DC power at up to 13W. This initial specification was widely popular, but 13W was not adequate for some requirements. In 2009, the IEEE released a new standard, known as 802.3at or PoE+, increasing the voltage and current requirements to provide 25W of power. The IEEE standard also defines PoE terminology. A device that provides power to the network is known as a PSE, or powersourcingequipment,whileadevicethatdrawspower from the network is known as a PD, or powered device. PSEs come in two types: Endpoints (typically network switches or routers), which provide data and power; and Midspans, which provide power but pass through data. MidspansaretypicallyusedtoaddPoEcapabilitytoexisting non-PoE networks. PDs are typically IP phones, wireless access points, security cameras, and similar devices. APPLICATIONS INFORMATION LTC4290/LTC4271 Product Overview The LTC4290/LTC4271 is a fourth generation 8-port PSE controller that implements eight PSE ports in either an endpointormidspandesign.Virtuallyallnecessarycircuitry is included to implement an IEEE 802.3at compliant PSE design,requiringonlyanexternalpowerMOSFETandsense resistorperchannel;theseminimizepowerlosscompared toalternativedesignswithonboardMOSFETsandincrease system reliability in the event a single channel fails. The LTC4290/LTC4271 offers advanced fourth generation PSE features, including per-port current monitoring, VEE monitoring, port current policing, one second current averaging and four general purpose input/output pins. The LTC4290/LTC4271 chipset implements a proprietary isolation scheme for inter-chip communication. This architecture dramatically reduces BOM cost by replacing expensive opto-isolators and isolated power supplies with a single low-cost transformer. LTC4290/LTC4271 is a fully IEEE-compliant Type 2 PSE supporting autonomous detection, classification and powering of Type 1 and Type 2 PDs. Figure 10. Power over Ethernet System Diagram 429071 F10 S1B S1B SMAJ58A 0.22µF 100V X7R 1µF 100V X7R Tx Rx Rx Tx SMAJ58A 58V DATA PAIR DATA PAIR VEE SENSE GATE OUT VDD33 INT SCL SDAIN SDAOUT 0.25 SPARE PAIR SPARE PAIR 1/8 LTC4290/ LTC4271 DGND AGND I2C 3.3V INTERRUPT –48V CAT 5 20 MAX ROUNDTRIP 0.05µF MAX RJ45 4 5 4 5 1 2 1 2 3 6 3 6 7 8 7 8 RJ45 1N4002 ×4 1N4002 ×4 PSE PD RCLASS –48VIN PWRGD –48VOUT LTC4265 GND DC/DC CONVERTER 5µF ≤ CIN ≤ 300µF + – VOUT GND 0.1µF |
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