PoE (Power over Ethernet) Devices

The Si3402 and Si3404 are industry’s most highly-integrated, IEEE 802.3at Type 1-compliant, PoE PD interface and pulse-width-modulated (PWM) switching regulator devices. By setting a new bar for device integration, lowest overall BOM cost, efficiency and reliability, the Si3402 and Si3404 enable designers to easily add PoE functionality to their Ethernet products. When included in the design of a PoE-enabled system, such as a wireless access point or VoIP phone, the Si3402 and Si3404 convert the high voltage (typically ±48 V) supplied over Ethernet copper UTP cabling into a regulated, low-voltage dc supply. In addition, the Si3402 and Si3404 combine all the required IEEE 802.3at Type 1 detection, classification and hot swap interfaces with a complete, high efficiency, PWM switching regulator.

The Si3402-B is a pin-compatible replacement for the End-of-Life Si3402-A. Existing customer products which were based on Si3402-A EVB reference designs can be readily re-used with minimal change to a few on-board components.  The Si3402 is a strong legacy device with long-term support, and is available in a 5mm x 5mm QFN package.  The newer Si3404 offers additional features in a compact 4mm x 4mm QFN package.  The Si3404 does not include input diode bridges on-chip, whereas the Si3402 includes input diode bridges on-chip.


  • Supports non-isolated and isolated switching topologies
  • Fully integrated high-voltage devices
  • Two complete diode bridges (Si3402)
  • Transient voltage suppressor
  • Switching regulator driver FET
  • Dual current-limited hot swap switch
  • Tunable switching frequency (Si3404)
  • Comprehensive protection circuitry
  • Transient over-voltage protection
  • Under voltage lockout
  • Thermal shutdown protection
  • Fold back current limiting
  • Low-EMI slew rate control
  • Transformer bias winding support (Si3404)

Getting Started with PoE Devices

Si3404 Buck PD Evaluation Kit

The easiest way to begin development with the Si3404 PoE Powered Device is with the Si3404BKC2-KIT.  An Isolated version is also available.

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PoE Devices Product Matrix

Part Number Data Sheet Evaluation Kit Description IEEE Specification Maximum Output Power (W) Package Type Package Size (mm) Auto MPS Support Aux Adapter Support Transformer Bias Winding Input DCDC Efficiency (%) Sleep Mode Switching Frequency Range (kHz) Synchronous FET Driver Temperature Range (ºC)
Si3402BISO-EVB PoE PD interface with dc-dc converter 802.3at Type 1 15 QFN20 5x5 No No No Yes 78 350 350 No -40 85
Si3404BKC2-KIT PoE PD interface with compact footprint 802.3at Type 1 15 QFN20 4x4 No No Yes Yes 80 100 500 No -40 85
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