Geneva, Switzerland STMicroelectronics has launched two families of Power-over-Ethernet (PoE) interface controllers for networked devices. The STHS4257 and STHS237x PoE powered device interface controllers families are fully compliant with the IEEE 802.3af specification for powered devices (PD), which provide all the control functions needed to enable a PD to request and draw power from an Ethernet network via a power source.
By using the STHS4257 and STHS237x controllers, designers will be able to eliminate the 110/220V AC power lines to many wired LAN devices such as Voice over IP (VoIP) phones and security cameras, said ST. Other applications include webcams, wireless LAN (WLAN) access points, point of sale (POS) terminals and RFID readers. The controllers are drop-in replacements for competitors' products.
Each device consists of two main sections: the IEEE802.3af-compliant interface to the PoE-powered RJ-45 wall socket, which includes basic PD Detection and Classification functions; and the hot swap controller (HSC), which protects the PD during insertion, operation and power withdrawal. The controllers integrate a high-voltage power MOSFET (low-side switch), with low RDS ON, and with the capability to accept transients as high as 100 V. The hot swap features include functions such as inrush current limiting, under-voltage lockout (UVLO), and thermal overload protection.
All the devices include an open drain PowerGOOD (PWRGD) signal to indicate normal operation, and a 1.5-V voltage offset to accommodate the input-diode bridge which is used to make the PD polarity insensitive. The basic parts the STHS2375, STHS2376, STHS2377, STHS4257A/L and STHS4257A1/L1 are available with either Latched Operation (L) or Automatic Retry (A), after fault conditions. The STHS4257 part integrates a 25-kOhm signature resistor, with a signature disable function. The STHS237x requires an external signature resistor.
The STHS237x family consists of devices for all the UVLO limits configurations: IEEE compliant (STHS2375), programmable (STHS2376), and for legacy systems (STHS2377). The STHS4257A1/L1 includes a dual-level current-limit circuit, which allows it to interface with legacy PoE systems while maintaining compatibility with the current IEEE 802.3af specification.
Pricing: The STHS4257 in a SO8 package (DFN8 on request) is priced at $1.35 and the STHS237x in a SO8 package (TSSOP8 on request) is priced at $1.01 in quantities of 1,000.
Availability: Available now in volume production.
Product information: STHS4257 and STHS237x
STMicroelectronics, Inc., 1-781-861-2650, www.st.com