Datasheet Linear Technology LTC4257CDD#PBF

Manufacturer	Linear Technology
Series	LTC4257
Part Number	LTC4257CDD#PBF

IEEE 802.3af PD Power over Ethernet Interface Controller

Datasheets

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PDF, 270 Kb, Revision: B, File uploaded: Oct 25, 2017

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Packaging

Package	3x3 DFN-8
Package Code	DD
Package Index	05-08-1698

Parametrics

Number of Channels	1
Design Tools	LTspice Model
Export Control	no
I2C Interface	no
IEEE-Compliant Classification	One Event
IEEE-Compliant Detection	Yes (Internal 25k resistor)
IEEE-Compliant Disconnection	N/A
Max Power	13 W
Operating Temperature Range	0 to 70 °C
PSE/PD	PD
PoE Type	1

Eco Plan

RoHS

Compliant

Design Notes

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Power over Ethernet Isolated Power Supply Delivers 11.5W at 90% Efficiency &mdash DN338
PDF, 80 Kb, File published: May 2, 2004
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Power over Ethernet Isolated Power Supply
Delivers 11.5W at 90% Efficiency вЂ“ Design Note 338
Jesus Rosales
fewer switches to turn on and off the better. A push-pull
converter could be used, but the additional complexity
is not justiп¬Ѓed at this power level. A single transistor
forward converter is another option, but requires
an additional output inductor and rectiп¬Ѓer. A п¬‚yback
converter is the simplest choice. Flyback converters
are thought to be less efп¬Ѓcient than forward and pushpull converters, but that changes when the output is
synchronously rectiп¬Ѓed (a MOSFET is used instead of
a diode to rectify the output). When powering IP telephones, wireless access points,
PDA charging stations and other PDs (Powered Devices)
from an Ethernet cable, designers have at most 12.95W
of available power per the IEEE 802.3af standard. Increased demands for power mandate a very efп¬Ѓcient
power converter especially for classВ 3 devices (consuming between 6.49W and 12.95W). The more power lost
in the converter, the less power available for the PD.
The voltage available from the PSE (Power Sourcing
Equipment) ranges from 44V to 57V, but PDs need to
operate with as much as 20О© of series wire resistance.
A PD can never draw more than 350mA or 12.95W
continuously. With the maximum input current of
350mARMS, the input voltage can droop as much as …

Model Line

Series: LTC4257 (8)

LTC4257CDD#PBF LTC4257CDD#TRPBF LTC4257CS8#PBF LTC4257CS8#TRPBF LTC4257IDD#PBF LTC4257IDD#TRPBF LTC4257IS8#PBF LTC4257IS8#TRPBF

Manufacturer's Classification

Monitor, Control and Protection > Power-over-Ethernet (PoE) Interface Controllers > PoE Powered Device (PD)

Other Names:

LTC4257CDDPBF, LTC4257CDD PBF