STMicroelectronics’ PM8804 and PM8805 chipset 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 chips provide the PoE-converter circuitry for PDs up to class-8, which defines a usable power budget of 71W. The 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. Other features include a startup regulator with a 20-mA.
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 3 mm x 3 mm, 0.5 mm-pitch VFQFPN-16, and priced at $0.60 each/1,000. The PM8805 in an 8 mm x 8 mm thermally enhanced VFQFPN-43 featuring exposed pads costs $4.50.