The reference design simplifies making devices with power and internet over a single cable suitable for various applications.
Power Over Ethernet (PoE) is a pivotal technology that enables electrical power to be passed along with data on Ethernet cables, streamlining the installation and operation of networked devices. This technology simplifies the infrastructure by allowing power and data transmission through a single cable, eliminating the need for additional electrical wiring and reducing overall installation costs. PoE is crucial in supporting a wide range of devices, such as IP cameras, VoIP phones, wireless access points, and IoT devices, enhancing flexibility and scalability in network deployment. Additionally, its capability for intelligent power management and support for advanced smart building technologies highlights its critical role in modern networking environments. The reference design from STMicroelectronics, featuring a 3.3V/20A active clamp forward converter and IEEE 802.3bt compliant Power Over Ethernet (PoE), streamlines the design process.
The reference design from STMicroelectronics features a 3.3 V, 20 A DC-DC active clamp forward converter, perfectly suited for various applications, including wireless access points. Enhanced with a Power Over Ethernet (PoE) PD interface, it incorporates the PM8805 system in a packaged device. This integration includes two active bridges and an IEEE 802.3bt-compliant Powered Device (PD) interface. It is highly effective across a broad spectrum of medium-to-high power applications in both 2-pair and 4-pair high-efficiency PoE and PoE+ systems.
Equipped with 100 V N-channel MOSFETs, the PM8805 offers a low total path resistance of 0.2 Ω for each bridge. It can identify the type of Power Sourcing Equipment (PSE)—whether standard or legacy—and provides clear IEEE 802.3af/at/bt classification indications through the T0, T1, and T2 signals. This allows for precise control and adaptability in various networking environments, ensuring compatibility and performance.
Additionally, the PM8805 interface enhances operational flexibility. It features smart mode selection controlled via STBY, FAUX, and RAUX signals, allowing users to tailor the device’s function to specific application requirements. The system’s packaging in a compact QFN 56 8x8mm format with 43 pins and 6 exposed pads facilitates straightforward integration into existing systems, meeting the needs of diverse and demanding applications.
Complementing the PM8805, the PM8804 PWM controller provides advanced power management solutions for 48 V converters. It operates with an input voltage of up to 75 V and includes a programmable oscillator for adjusting the switching frequency up to 1 MHz. Features such as a high-voltage startup regulator, a soft startup with settable time, and optional soft turn-off enhance its efficiency and power conservation capabilities. The controller also features dual 1 APK, low-side complementary gate drivers, with the option to turn off GATE2 to reduce power consumption, all housed in a space-efficient QFN 16 3x3mm package. This design optimization makes it ideal for compact, high-efficiency applications.
STMicroelectronics has tested this reference design. It comes with a bill of materials (BOM), schematics, assembly drawing, printed circuit board (PCB) layout, etc. You can find additional data about the reference design on the company’s website. To read more about this reference design, click here.
