Si3402 PD Interface and Switching Regulator

The Si3402 is the industry’s most highly-integrated, IEEE 802.3at Type 1-compliant, PoE PD interface and pulse-width-modulated (PWM) switching regulator. By setting a new bar for device integration, lowest overall BOM cost, efficiency and reliability, the Si3402 enables 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 converts the high voltage (typically ±48 V) supplied over Ethernet copper UTP cabling into a regulated, low-voltage dc supply. In addition, the Si3402 combines 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.


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


Design Tools

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Schematics/Layout (2)

Si3402-B Isolated EVB Database
1175 kB
Si3402-B Non-Isolated EVB Database
1151 kB
Product Matrix
Part NumberDatasheetTemperature RangeDescriptionPackage TypeMaximum Output Power
-40 to 85 °CPoE PD Interface with DCDC ConverterQFN2017 W


    • Complete IEEE 802.3af compliant PD interface, hot swap controller and efficient PWM switching regulator
    Compared to competing PD solutions, which typically require several external high-voltage discrete devices to complete a PD interface, the Si3402 uniquely integrates two full diode bridges, a transient voltage suppressor and a switching regulator driver FET on chip. Depending on the application’s power supply isolation requirements, the primary benefits of the Si3402 regulator's unmatched integration level are:
    • Elimination of four critical high-voltage BOM components: Two full diode bridges, a transient voltage suppressor and a switching regulator driver FET
    • Reduction in external BOM savings of at least $0.30 to $0.40 USD
    • Reduction of typical PCB layout footprints of 30%
    • Direct connection to RJ-45 jack for reduced EMI
    • Simplified design, PCB layout and validation processes
    Leveraging Silicon Labs' proven high-voltage design and manufacturing expertise, the Si3402 also enables enhanced PoE functionality, such as intelligent, system-level circuit protection and an early power loss indicator for reliable shut down of the PD when power is lost.


    Product Matrix





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