4 April 2019 : A new chipset from STMicroelectronics lets users quickly build reliable and space-efficient Powered Devices (PDs) to take advantage of the latest IEEE 802.3bt Power-over-Ethernet (PoE) specification.
The PM8804 and PM8805 provide the PoE-converter circuitry for PDs up to class-8, which defines a usable power budget of 71 Watts. The chipset saves space, enhances reliability, and cuts time to market for next-generation connectivity equipment including 5G “small cells,” WLAN access points, switches, and routers. ST’s new PoE chipset also targets smart-building and smart-office applications such as IP cameras, access-control systems, display panels, lighting, curtain or shutter controllers, video-call systems, IP phones, and tabletop consoles.
The PM8804 implements a complete PWM controller for a 48V isolated flyback or forward converter, including dual low-side gate drivers for high-efficiency forward active-clamp topologies. The operating frequency is selectable up to 1MHz, allowing the use of small external filter and decoupling components for high power density. Also featuring a high-voltage start up regulator with 20mA output capability, the PM8804 helps save on board space and bill of materials.
The PM8805 companion chip contains two active bridges, a charge pump for driving high-side MOSFETs, a hot-swap FET, and the IEEE 802.3bt compliant interface. Integrating the active bridges saves the real-estate otherwise occupied by eight discrete MOSFETs and their driving circuitry. The PM8805 generates a Power-good signal for enabling the PM8804 and other circuitry such as an LED driver, and supports Maintain Power Signature (MPS) current control that allows the PD to enter power-saving standby without being disconnected.
Both devices are in production now. The PM8804 is packaged as a 3mm x 3mm, 0.5mm-pitch VFQFPN-16, and priced at $0.60 for orders of 1000 pieces. The PM8805 in 8mm x 8mm thermally enhanced VFQFPN-43 featuring exposed pads is $4.50.
