The LTC4257 is a complete power interface power supply chip designed for IEEE 802.3af PoE systems. It integrates 25k signature resistors, classification current sources, input current limiting with thermal foldback, undervoltage lockout, and power good signaling, all in a single 8-pin package. The chip integrates a high-voltage power MOSFET, which reduces the cost for system designers and saves board space. LTC4257 can directly interface with Linear Technology's various DC/DC converter products to provide an economical power solution for IP phones, wireless access points and other PDs. Linear Technology also provides solutions for PSE applications based on quad network power controllers. LTC4257 is available in 8-pin SO and low profile (3mm x 3mm) DFN packages.
The LTC4257 is a Power over Ethernet (PoE) PD interface controller that integrates a 25 kΩ signature resistor, classification current source, input‑current limit with thermal foldback, undervoltage lockout, and power‑good signalling in an 8‑lead package. It is intended for IP phones, wireless access points and other IEEE 802.3af powered devices.
The datasheet provides absolute maximum ratings, electrical characteristics, pin descriptions, package dimensions, typical performance curves, and application notes on detection, classification and thermal protection. It also lists ordering information for the SO and DFN package variants.
| On‑board Power MOSFET Rating | 100 V, 400 mA |
|---|