Datasheet

LTC4290/LTC4271
15
429071fa
For more information www.linear.com/LTC4290
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 LTC4290/LTC4271 chipset responds
ApplicAtions inForMAtion
to this market by allowing a reliable means of providing up
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.
LTC4290/LTC4271 Product Overview
The LTC4290/LTC4271 is a fourth generation 8-port PSE
controller that implements eight PSE ports in either an
endpoint or midspan design. Virtually all necessary 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 LTC4290/LTC4271 offer advanced fourth
generation PSE features, including per-port current monitor
-
ing, V
EE
monitoring, port current policing, one second cur-
rent averaging and four general purpose input/output pins.
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
V
EE
SENSE GATE OUT
V
DD33
INT
SCL
SDAIN
SDAOUT
0.25Ω
SPARE PAIR
SPARE PAIR
1/8
LTC4290/
LTC4271
DGND AGND
I
2
C
3.3V
INTERRUPT
–48V
CAT 5
20Ω 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
R
CLASS
–48V
IN
PWRGD
–48V
OUT
LTC4265
GND
DC/DC
CONVERTER
5µF ≤ C
IN
≤ 300µF
+
–
V
OUT
GND
0.1µF