ST's new chipset allows users to quickly develop reliable, space-saving powered devices (PDs) using the latest Power over Ethernet (PoE) specification, IEEE 802.3bt.
The PM8804 and PM8805 can be used in PoE converter circuits for powered devices, supporting Class 8 PoE devices with power ratings up to 71W. The new chipset saves board space, enhances product reliability, and reduces time-to-market for next-generation communication connectivity devices, including 5G "small cells," WLAN access points, switches, and routers. Target applications for ST's new PoE chipset include smart buildings and smart office equipment such as IP cameras, access control systems, display panels, lighting, electric curtains or blinds controllers, video calling systems, IP phones and desktop consoles .
The PM8804 implements a fully functional PWM controller for a 48V isolated flyback or forward converter and a dual low side gate driver for a highly efficient active clamp forward converter topology. The operating frequency is selectable up to 1MHz, allowing the use of small external filters and decoupling components in high power density applications. The PM8804 also features a high-voltage startup regulator with 20mA output, which helps save board space and bill of materials.
The PM8805 companion chip contains two active bridges, one charge pump for driving the high-side MOSFET, one hot-swap FET, and the IEEE 802.3bt standard interface. The integrated active bridge saves space in eight discrete MOSFETs and their drive circuitry. The PM8805 generates a power-good signal that enables the PM8804 and other circuits (for example, LED drivers) and supports maintenance power signature (MPS) current control, allowing the powered device to enter a power-saving standby state without disconnecting.
Both products are in volume production. The PM8804 is available in a 3mm x 3mm, 0.5mm pitch VFQFPN-16 package. The PM8805 is available in an 8mm x 8mm thermally enhanced VFQFPN-43 package with an exposed pad.