LTC4257 - IEEE 802.3af PD Power over Ethernet Interface Controller

The LTC4257 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 signaling, 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) applications with quad network power controllers.

The LTC4257 is available in the 8-pin SO and low profile (3mm x 3mm) DFN packages.

  • 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 x 3mm)  DFN Packages
Typical Application

  • IP Phone Power Management
  • Wireless Access Points
  • Telecom Power Control

Order Information
Part NumberPackageTempPrice(1-99)Price (1k)*
LTC4257CDD#PBF3x3 DFN-8C$2.41$1.70
LTC4257CDD#TRPBF3x3 DFN-8C$1.76
LTC4257IDD#PBF3x3 DFN-8I$2.77$1.95
LTC4257IDD#TRPBF3x3 DFN-8I$2.01
Demo Boards
Part NumberDescriptionPrice
DC959ALTC4257-1 High-Power PD Demo Bd$50.00
Design Note
Reliability Data
Product Selector Card
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LTC4257 - IEEE 802.3af PD Power over Ethernet Interface Controller
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R413 Reliability Data
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LTC4257 Footprints and Symbols