LTC4257 Datasheet, PDF (1/20 Pages) Linear Technology – IEEE 802.3af PD Power over Ethernet Interface Controller

LTC4257
IEEE 802.3af PD
Power over Ethernet
Interface Controller
FEATURES
■ _{Complete Power Interface Port for IEEE 802.3af}^®
Powered Devices (PDs)
■ _{Onboard 100V, 400mA Power MOSFET}
■ _{Precision Input Current Limit}
■ _{Onboard 25k Signature Resistor}
■ _{Programmable Classification Current (Class 0-4)}
■ _{Undervoltage Lockout}
■ _{Smart Thermal 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 provides complete signature and power
interface functions for a device operating in an IEEE
802.3af Power over Ethernet (PoE) system. The LTC4257
simplifies Powered Device (PD) design by incorporating
the 25k signature resistor, the classification current source,
input current limit with thermal foldback, undervoltage
lockout and power good signalling, all in a single 8-pin
package. By incorporating a high voltage power MOSFET
onboard, the LTC4257 provides the system designer with
reduced cost while also saving board space.
The LTC4257 can interface directly with a variety of Linear
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
solutions for Power Sourcing Equipment (PSE) applica-
tions with quad network power controllers.
The LTC4257 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
–48V FROM
POWER SOURCING
EQUIPMENT
(PSE)
~+
DF01SA ^0.1µF
~–
Powered Device (PD)
SMAJ58A
LTC4257
GND
R_CLASS
100k
R_CLASS
PWRGD
5µF ⁺
MIN
V_IN
V_OUT
V_IN
SWITCHING
POWER SUPPLY
SHDN
RTN
+
3.3V
TO LOGIC
–
4257 TA01
LTC4257 Charging 300µF
Load Capacitor
V_IN
50V/DIV
V_OUT
20V/DIV
I_IN
200mA/DIV
PWRGD
50V/DIV
5ms/DIV
4225 TA02
4257fb
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