LTC4267CGN-1#PBF Linear Technology, LTC4267CGN-1#PBF Datasheet - Page 9

• Manufacturer Part Number: LTC4267CGN-1#PBF
• Description: IC POE 802.3AF INTERFACE 16SSOP
• Manufacturer: Linear Technology

Specifications of LTC4267CGN-1#PBF

• Controller Type: Power over Ethernet Controller (POE)
• Interface: IEEE 802.3af
• Current - Supply: 3mA
• Operating Temperature: 0°C ~ 70°C
• Mounting Type: Surface Mount
• Package / Case: 16-SSOP
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Voltage - Supply: -

BLOCK DIAGRAM
APPLICATIO S I FOR ATIO
OVERVIEW
The LTC4267-1 is partitioned into two major blocks: a
Powered Device (PD) interface controller and a current
mode fl yback switching regulator. The Powered Device
(PD) interface is intended for use as the front end of a
PD adhering to the IEEE 802.3af standard, and includes
a trimmed 25k signature resistor, classifi cation current
source, and an input current limit circuit. With these
functions integrated into the LTC4267-1, the signature
and power interface for a PD can be built that meets all
the requirements of the IEEE 802.3af specifi cation with a
minimum of external components.
The switching regulator portion of the LTC4267-1 is a
constant frequency current mode controller that is opti-
mized for Power over Ethernet applications. The regulator
is designed to drive a 6V N-channel MOSFET and features
soft-start and programmable slope compensation. The
integrated error amplifi er and precision reference give the
PD designer the option of using a nonisolated topology
without the need for an external amplifi er or reference. The
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LTC4267-1 has been specifi cally designed to interface with
both IEEE compliant Power Sourcing Equipment (PSE)
and legacy PSEs which do not meet the inrush current
requirement of the IEEE 802.3af specifi cation. By setting
the initial inrush current limit to a low level, a PD using
the LTC4267-1 minimizes the current drawn from the PSE
during start-up. After powering up, the LTC4267-1 switches
to the high level current limit, thereby allowing the PD to
consume up to 12.95W if an IEEE 802.3af PSE is present.
This low level current limit also allows the LTC4267-1 to
charge arbitrarily large load capacitors without exceeding
the inrush limits of the IEEE 802.3af specifi cation. This
dual level current limit provides the system designer with
fl exibility to design PDs which are compatible with legacy
PSEs while also being able to take advantage of the higher
power available in an IEEE 802.3af system.
Using an LTC4267-1 for the power and signature inter-
face functions of a PD provides several advantages. The
LTC4267-1 current limit circuit includes an onboard 100V
power MOSFET. This low leakage MOSFET is specifi ed to
LTC4267-1
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