ltc4266a Linear Technology Corporation, ltc4266a Datasheet - Page 15

• Manufacturer Part Number: ltc4266a
• Description: Quad Poe/poe+/ltpoe++ Pse Controller
• Manufacturer: Linear Technology Corporation

OPERATION
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
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 spec 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 LTC4266A family responds to this market by
allowing a reliable means of providing up to 90W of deliv-
ered power to a LTPoE ++ PD. The LTPoE ++ specification
provides reliable detection and classification extensions to
the existing IEEE PoE technique that are backward com-
patible and interoperable with existing Type 1 and Type 2
PDs. Unlike other proprietary PoE ++ solutions, Linear’s
LTPoE ++ solution provides mutual identification between
the PSE and PD. This ensures that 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.
LTC4266 Product Family
The LTC4266 is a third-generation quad PSE controller
that implements four PSE ports in either an end-point 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 resis-
tor per channel; these minimize power loss compared to
alternative designs with on-board MOSFETs and increase
system reliability in the event a single channel fails.
The LTC4266 comes in three grades which support dif-
ferent PD power levels.
The A-grade LTC4266 extends PoE power delivery capabili-
ties to LTPoE ++ levels. LTPoE ++ is a Linear Technology
proprietary specification allowing for the delivery of up to
90W to LTPoE ++ compliant PDs. The LTPoE ++ architecture
extends the IEEE physical power negotiation to include 35W,
45W, 70W and 90W power levels. The A-grade LTC4266
also incorporates all B- and C-grade features.
The B-grade LTC4266 is a fully IEEE-compliant Type 2
PSE supporting autonomous detection, classification
and powering of Type 1 and Type 2 PDs. The B-grade
LTC4266 also incorporates all C-grade features. The
B-grade LTC4266 is marketed and numbered without the
B suffix for legacy reasons; the absence of power grade
suffix infers a B-grade part.
The C-grade LTC4266 is a fully autonomous 802.3at Type 1
PSE solution. Intended for use only in AUTO pin mode,
the C-grade chipset autonomously supports detection,
classification and powering of Type 1 PDs. As a Type 1
PSE, 2-event classification is prohibited and Class 4 PDs
are automatically treated as Class 0 PDs.
LTC4266A/LTC4266C
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