1 Summary description
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
● 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 (see Figure 4 on page 8).
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
(see Figure 1 on page 6 and Table 2 on page 6). 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). See Table 1 on page 1.
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. For product options overview see Table 1 on page 1.