LTC4257-1_15 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
■ _{Complete Power Interface Port for IEEE 802}^®_.3af
Powered Devices (PDs)
■ _{Onboard 100V, 400mA Power MOSFET}
■ _{Precision Dual Level Current Limit}
■ _{Onboard 25k Signature Resistor with Disable}
■ _{Programmable Classification Current (Class 0-4)}
■ _{Undervoltage Lockout}
■ _{Thermal Overload Protection}
■ _{Power Good Signal}
■ _{Available in 8-Pin SO and Low Profile (3mm × 3mm)}
DFN Packages
U
APPLICATIO S
■ _{IP Phone Power Management}
■ _{Wireless Access Points}
■ _{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.
All other trademarks are the property of their respective owners.
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
42571fb
1