Datasheet

LTC4270/LTC4271
15
42701fc
OVERVIEW
Power over Ethernet, or PoE, is a standard protocol for send-
ing DC power over copper Ethernet data wiring. The IEEE
group that administers the 802.3 Ethernet data standards
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 cur-
rent monitoring, V
EE
monitoring, port current policing,
one second current averaging and four general purpose
input/output pins.
42701 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
1/12
LTC4270/
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
Figure 10. Power over Ethernet System Diagram