LTC4263 datasheet(16/32 Pages) LINER

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LTC4270/LTC4271

42701f

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-

dards added PoE powering capability in 2003. This original

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

power sourcing equipment, while a device that draws power

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.

Midspans are typically used to add PoE capability to existing

non-PoE networks. PDs are typically IP phones, wireless

access points, security cameras, and similar devices.

PoE++ Evolution

Even during the process of creating the IEEE PoE+ 25.5W

specification it became clear that there was a significant

and increasing need for more than 25.5W of delivered

power. The A-grade LTC4270/LTC4271 chipset responds

to this market by allowing a reliable means of providing up

APPLICATIONS INFORMATION

to 90W of delivered power to a LTPoE++ PD. The LTPoE++

specification provides reliable detection and classification

extensions to the existing IEEE PoE protocols that are

backward compatible and interoperable with existing Type

1 and Type 2 PDs. Unlike other proprietary PoE++ solutions

Linear’s LTPoE++ provides mutual identification between

the PSE and PD. This ensures the LTPoE++ PD knows it

may use the requested power at start-up because it has

detected a LTPoE++ PSE. LTPoE++ PSEs can differentiate

between a LTPoE++ PD and all other types of IEEE compli-

ant PDs allowing LTPoE++ PSEs to remain compliant and

interoperable with existing equipment.

LTC4270/LTC4271 Product Family

The LTC4270/LTC4271 family is a fourth generation

12-port PSE controller that implements 12 PSE ports in

either an endpoint or midspan design. Virtually all neces-

sary circuitry is included to implement an IEEE 802.3at

compliant PSE design, requiring only an external power

MOSFET and sense resistor per channel; these minimize

power loss compared to alternative designs with onboard

MOSFETs and increase system reliability in the event a

single channel fails.

All grades of the LTC4270/LTC4271 family offer advanced

fourth generation PSE features, including per-port current

monitoring, global temperature and VEE monitoring, port

current policing, one second current averaging and four

general purpose input/output pins.

42701 F10

S1B

SMAJ58A

0.22μF

100V

X7R

1μF

100V

X7R

SMAJ58A

58V

DATA PAIR

VEE

SENSE GATE OUT

VDD33

INT

SCL

SDAIN

SDAOUT

0.25Ω

SPARE PAIR

1/12

LTC4270/

LTC4271

DGND

AGND

I2C

3.3V

INTERRUPT

–48V

CAT 5

20Ω MAX

ROUNDTRIP

0.05μF MAX

RJ45

1N4002

PSE

RCLASS

–48VIN

PWRGD

–48VOUT

LTC4265

GND

DC/DC

CONVERTER

5μF ≤ CIN

≤ 300μF

–

VOUT

GND

0.1μF

Figure 10. Power over Ethernet System Diagram

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