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Summary description

The STHS4257 is an IEEE802.3af-compliant family of interface controllers for Power over Ethernet (PoE) Powered Device (PD) applications. The devices consist of two main sections:

● The IEEE802.3af interface to the PoE powered RJ-45 wall socket, and

● the Hot Swap Controller (HSC) functions required to protect the PD during insertion, operation, and withdrawal from the RJ-45 socket.

These devices have an integrated high voltage power MOSFET (low-side switch) with low RON and the capability to accept transients as high as 100V. Since the pins (such as GND and VIN) which interface to the RJ-45 socket can routinely see high peak voltages in excess of 100V, it is strongly recommended that board designers protect the PD device with a transient voltage suppressor, such as the SMAJ58A (available from STMicroelectronics), connected between the GND and VIN pins (see Figure 4 on page 8).

Features

■ IEEE 802.3af-compliant interface for Powered Devices (PDs)

■ Integrated 100V, 450mA power MOSFET low side switch

■ Inrush current limit

■ Normal operation current limit

■ Integrated 25kΩ signature resistor

■ Signature disable (STHS4257A1/L1)

■ Resistor-programmable classification current (Class 0-4)

■ Power Good output, open drain

■ Undervoltage Lockout (UVLO)

■ Thermal overload protection (two-step for the STHS4257A/L)

■ Latch (L) or auto-retry (A) after repetitive thermal overload

■ Industrial temperature range: –40 to +85°C

■ SO8 and DFN8 (3mm x 3mm) packages

■ RoHS compliant

Applications

■ Voice over IP (VoIP) phones

■ Web cameras

■ WLAN access points

■ Internet appliances

■ POS terminals

■ RFID readers