100W PoE Chipset for Connectivity and Smart Buildings

A new chipset from STMicroelectronics lets users quickly build reliable and space-efficient powered devices to take advantage of the latest IEEE 802.3bt Power-over-Ethernet (PoE) specification. The PM8804 and PM8805 provide the PoE-converter circuitry for power devices up to class-8, which defines a usable power budget of 71W.

The chipset enhances reliability, saves space, 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 including IP cameras, access control systems, lighting, display panels, curtain or shutter controllers, IP phones, video-call systems, and tabletop consoles.

PM8804

The PM8804 implements a forward converter, including dual low-side gate drivers for high-efficiency forward active-clamp topologies, or a complete PWM controller for a 48V isolated flyback topologies.

PM8804 block diagram (Click on image to enlarge)

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.

PM8805

The PM8805 companion chip contains a hot-swap FET, two active bridges, a charge pump for driving high-side MOSFETs, 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.

PM8805 block diagram (Click on image to enlarge)

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 power device to enter power-saving standby without being disconnected.

Features of PM8804

• PWM peak current mode controller
• Input operating voltage up to 75V
• Internal high-voltage start-up regulator with 20mA current capability
• Current sense with programmable blanking time up to 200ns
• Programmable fixed frequency up to 1MHz
• Soft-start up with settable time
• Soft turn off (optionally disabled)
• Dual low-side complementary gate drivers
• Programmable dead time from 10ns to 200ns between GATE1 and GATE2
• Gate drivers have 1A peak capability
• GATE2 optionally turned off for reduced consumption
• 80% maximum duty cycle with internal slope compensation
• Internal pull-up resistor on CTL pin enables the optocoupler connection
• Operating current consumption <1.5mA
• Embedded protections:
  • Severe overcurrent protection with latch after 4 events
  • Delayed overload protection with automatic restart
  • Feedback disconnection (OV) protection on VC
  • Thermal shutdown
• High efficiency topologies:
  • Flyback, forward
  • Flyback with synchronous rectification
  • Flyback with active clamp
  • Forward with active clamp

Features of PM8805

• Dual active bridge, hot-swap MOSFET and PoE-Power-Device interface in a system-in-package
• 100V N-ch MOSFETs with 0.2Ω total path resistance for each active bridge.
• 100V, 0.1Ω high-side N-ch hot swap MOSFET
• PoE-PD single-signature interface compliant with IEEE 802.3bt / at / af
• Supports 4-pair PoE applications
• Supports 12V auxiliary sources
• Identifies which kind of PSE (standard or legacy) is connected with and provides successful IEEE802.3bt / at / af classification indication as a combination of the T0, T1 and T2 signals (open drain)
• Smart operational modes
• Programmable classification current with
• 3.3ms delay.
• Optional Autoclass feature
• Advanced energy-saving MPS timings
• Two-step hot swap current protection: DC with
• 1ms delay and short-circuit with 10μs delay.
• Controlled pre-charge of the output capacitor
• PGD signal (open drain) to enable an external
• PWM controller
• Thermal shutdown protection

Both devices are now in production. The PM8805 is in an 8mm x 8mm thermally enhanced VFQFPN-43 package featuring exposed pads and is priced at $4.50. The PM8804 is in a 3mm x 3mm, 0.5mm-pitch VFQFPN-16, and priced at $0.60 for orders of 1000 pieces.