LTC4257-1 Datasheet, PDF (1/20 Pages) Linear Technology – Power over Ethernet Interface Controller with Dual Current Limit

LTC4257-1
IEEE 802.3af PD
Power over Ethernet Interface
Controller with Dual Current Limit
FEATURES
s _{Complete Power Interface Port for IEEE 802}^®_.3af
Powered Devices (PDs)
s _{Onboard 100V, 400mA Power MOSFET}
s _{Precision Dual Level Current Limit}
s _{Onboard 25k Signature Resistor with Disable}
s _{Programmable Classification Current (Class 0-4)}
s _{Undervoltage Lockout}
s _{Thermal Overload Protection}
s _{Power Good Signal}
s _{Available in 8-Pin SO and Low Profile (3mm × 3mm)}
DFN Packages
U
APPLICATIO S
s _{IP Phone Power Management}
s _{Wireless Access Points}
s _{Telecom Power Control}
DESCRIPTIO
The LTC^®4257-1 provides complete signature and power
interface functions for a device operating in an IEEE
802.3af Power over Ethernet (PoE) system. The LTC4257-1
simplifies Powered Device (PD) design by incorporating
the 25k signature resistor, classification current source,
input current limit, undervoltage lockout, thermal over-
load protection, signature disable and power good signal-
ling, all in a single 8-pin package. The LTC4257-1 includes
a precision, dual level current limit circuit. This allows it to
charge large load capacitors and interface with legacy
Power over Ethernet systems while maintaining compat-
ibility with the current IEEE 802.3af specification. By
incorporating a high voltage power MOSFET onboard, the
LTC4257-1 provides the system designer with reduced
cost while also saving board space.
The LTC4257-1 can interface directly with a variety of Lin-
ear Technology DC/DC converter products to provide a cost
effective power solution for IP phones, wireless access
points and other PDs. Linear Technology also provides
network power controllers for Power Sourcing Equipment
(PSE) applications.
The LTC4257-1 is available in the 8-pin SO and low profile
(3mm × 3mm) DFN packages.
, LTC and LT are registered trademarks of Linear Technology Corporation.
802 is a registered trademark of Institute of Electrical and Electronics Engineers, Inc.
TYPICAL APPLICATIO
Powered Device (PD)
–48V FROM
POWER SOURCING
EQUIPMENT
(PSE)
~+
DF01SA
~–
0.1µF
SMAJ58A
LTC4257-1
GND
R_CLASS SIGDISA
R_CLASS
PWRGD
V_IN
V_OUT
+
5µF
MIN
100k
V_IN
SWITCHING
POWER SUPPLY
SHDN
RTN
+
3.3V
TO LOGIC
–
42571 TA01
42571fa
1