PoE chipset facilitates converter circuitry for powered devices

By Majeed Ahmad, contributing writer

The chipset from STMicroelectronics  built around the IEEE 802.3bt  Power over Ethernet (PoE) specification provides the PoE-converter circuitry for powered devices (PDs) in a usable power budget of 71 W. It’s targeted at connectivity devices such as 5G small cells, Wi-Fi access points, switches, and routers.

Comprised of the PM8804  and PM8805  chips, ST’s new PoE chipset also targets smart building and smart office applications like IP cameras, IP phones, access-control systems, display panels, lighting, curtain or shutter controllers, video-call systems, and tabletop consoles.

The PM8804 chip implements a complete PWM controller for a 48-V isolated flyback or forward converter. That includes dual low-side gate drivers for high-efficiency forward active-clamp topologies. The operating frequency, selectable up to 1 MHz, allows the use of small external filter and decoupling components for high power density. The PM8804, packaged in a 3 × 3-mm, 0.5-mm-pitch VFQFPN-16, is priced at $0.60 for orders of 1,000 pieces.

The PM8805 companion chip, on the other hand, contains two active bridges, a charge pump for driving high-side MOSFETs, a hot-swap FET, and the IEEE 802.3bt-compliant interface. Here, the integration of active bridges saves the real estate otherwise occupied by eight discrete MOSFETs and their driving circuitry. The PM8805, available in an 8 × 8-mm thermally enhanced VFQFPN-43, is priced at $4.50.