Isolated Flyback 30W Class 4 PoE+ Evaluation Kit

March 23, 2020 by Paul Shepard

The Si34061FB12V4KIT 12V Class 4 Flyback evaluation kit from Silicon Laboratories demonstrates a complete IEEE 802.3at Power over Ethernet PD system using the Si34061 PoE+ PD device. A single Si34061 manages the PoE+ interface and dc-dc conversion. The isolated flyback converter outputs up to 2.5A at 12V for a total power of 30W while using a small EPD13 size transformer.

The Sifos IEEE compliance report, EMI test report, schematics, and layout, found in the User Guide, jump start new designs. The Si34061-EVB-EXT-12V maximum output is Class 4 power (30W with isolated 12V output). The Si34061 IC integrates an IEEE 802.03at compatible PoE+ interface as well as a peak-current-control dc-dc controller.

Kit Features

  • Included devices:
    • Si34061-GM (5x5 mm 24-pin QFN)
  • 30W, isolated flyback converter
    • 12V, 2.5A output
    • Up to 89.8% end to end efficiency
    • Small, EPD13 size transformer
  • 48V aux power supply input
  • Second RJ45 jack to pass through Ethernet data
  • Fully IEEE 802.3at compliant
  • EN 55032 class B conducted and radiated EMI compliant
  • Synchronous rectification
  • High flexibility
  • Integrated transient overvoltage protection
  • Thermal shutdown protection

Si34061FB12V4KIT 12V Class 4 Flyback evaluation kit schematic (click on schematic to enlarge)

Silicon Labs Si3406 Power Over Ethernet Plus (PoE+) Device

Silicon Labs Si3406 Power Over Ethernet Plus (PoE+) Powered Devices integrate all power management and control functions required in a Power-over-Ethernet Plus (PoE+) Powered Device (PD) application. These devices convert the high voltage supplied over a 10/100/1000BASE-T Ethernet connection to a regulated, low-voltage output supply. The optimized architecture of these devices minimizes the solution footprint and external BOM (Bill of Materials) cost and enables the use of low-cost external components while maintaining high performance.

The Si3406 PoE+ Devices integrate the required diode bridges and transient surge suppressor, enabling direct connection of the IC to the Ethernet RJ-45 connector. The switching power FET and all associated functions are also integrated. The Si3406 Devices support Isolated Flyback, Non-Isolated Flyback, and Buck Converter Topologies.

The switching frequency for the regulator is tunable with a simple external resistor value to help avoid unwanted harmonics for better emissions control. A synchronous driver is provided to optionally drive a secondary side FET to improve efficiency of power conversion. Connection to the PSE switch is maintained during sleep by an optional automated maintain-power-signature (MPS) signal.

Si3406 Devices fully support the IEEE 802.3at specification for the cases of single or two event classification. Standard external resistors provide the proper IEEE 802.3 signatures for the detection function and programming of the classification mode, and internal startup circuits ensure well-controlled soft-start initial operation of both the hots-wap switch and the voltage regulator.

The Si34061 and Si34062 variants add main transformer bias winding support for ultra-high-efficiency operation.

The Si34061 includes support for external augmentation or full bypass of the internal hot swap and/or switching FET for best power handling and thermal management at the high end of Class 4, plus offers a further boost in power conversion efficiency when needed.

The Si34062 includes support for sleep modes with wake function, as well as LED drive capability. These features can be utilized to minimize standby current, control sleep and wake states, and provide application status information using a solid or blinking LED.

The Si3406 PoE PD is available in a low-profile, 20-pin, 5mm x 5mm QFN package. The Si34061 and Si34062 variants are offered in low-profile, 24-pin, 5mm x 5mm QFN packages.