Interface Controllers for PoE Powered Device Applications

The STHS237x 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 RDS ON and the capability to accept transients as high as 100V. Since the pins (such as VDD and VSS) 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 VDD and VSS pins.

The IEEE802.3af-compliant interface includes the basic PD Detection and Classification functions, whereas the 'Hot Swap' functions include other basic features, such as Inrush Current Limiting, Undervoltage Lockout (UVLO), and Thermal Overload Protection. All of the devices include an open drain Power Good (PG) signal to indicate normal steady operation. The STHS237x family also incorporates a voltage offset (two series diodes) to accommodate the input diode bridge used to make the PD polarity insensitive.

The STHS237x family comprises devices for all the UVLO limits configurations: IEEE standard compliant (STHS2375), programmable (STHS2376) and for legacy systems (STHS2377).

Each of the basic part types, the STHS2375, STHS2376 and the STHS2377, is available either with Latched Operation (L) Mode or with Automatic Retry (A) Mode after fault conditions.