LTC4257IS8-1#PBF

The LTC4257IS8-1#PBF is a highly integrated power management solution which satisfies the Power over Ethernet (PoE) end-span PD and Midspan PSE requirements from the prestandard 802.3af as well as the 802.3at/4PPoE standards.

The LTC4257IS8-1#PBF features two independent ports for supplying, controlling and monitoring power to two high power Class 0, 1, 2 and 3 compliant PDs. It provides constant current and voltage outputs under the control of a single external resistor. In addition, the device incorporates a multiple-phase voltage regulators, two low noise and low dropout linear regulators and two low dropout linear regulators, all packaged in a low profile 8-lead MSOP and with a space-saving pinout.

Application Field

The LTC4257IS8-1#PBF is ideal for applications in Power over Ethernet such as Video Surveillance, Wireless Repeaters, Battery Back-up Systems, Access Point, Controls and other applications with multifunctional output requirements. It is also suitable for applications requiring 10/100/1000 Base-T compliance.

Working Principle

The LTC4257IS8-1#PBF integrates two ports for supplying, controlling and monitoring power to two high power Class 0, 1, 2 and 3 compliant PDs. One port is intended to drive low power PDs, while the other port is intended to drive high power PDs. Each port includes a multiple-phase voltage regulator, two low noise and low dropout linear regulators, two low dropout (LDO) linear regulators and a current source for deriving the current source for deriving the current source for deriving the currents required for PDs.

The LTC4257IS8-1#PBF provides an adjustable constant current or current limiting at the PD port, allowing a wide input voltage range. This is especially important for long cable runs where input voltage may be lower than expected. Controlled output voltage is achieved by controlling the output current while keeping the output voltage at the desired level.

In addition, the device includes ample protection to ensure reliable operation of the system in harsh environment conditions. The LTC4257IS8-1#PBF also features a power fail sequence circuitry that prevents a collapse of the input voltage during system shutdown.