STMicroelectronics Launches PoE Interface Controllers For Networked Devices

STMicroelectronics (ST) announced two new families of Power-over-Ethernet (PoE) interface controllers. All devices in the 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 these new controllers, ST claims that designers will be able to eliminate the 110/220Vac power lines to many wired LAN devices such as VoIP (Voice over IP) phones and security cameras. Other applications benefiting from PoE include webcams, wireless LAN (WLAN) access points, point of sale (POS) terminals and RFID readers.

The STHS4257 and STHS237x PoE Powered Device Interface Controllers enable greater flexibility in installation locations, and lower overall product cost, by removing the external power supplies; the standard CAT5 Ethernet cabling can now carry power and data to devices on the network. The controllers are described as 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 100V. The ‘hot swap’ features include functions such as inrush current limiting, undervoltage lockout (UVLO), and thermal overload protection.

All the devices include an open drain PowerGOOD (PWRGD) signal to indicate normal operation, and a 1.5V 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 25kΩ Signature Resistor, with 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.

Both families are available in volume now, the STHS4257 in an SO8 package (DFN8 available upon request), priced at $1.35 in 1k quantities and the STHS237x in SO8 package (TSSOP8 available upon request), priced at $1.01 in 1k quantities.