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