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The Si3400 and Si3401 are complete power supply solutions for Power over Ethernet (PoE) Powered Device (PD) applications. 
The Si3400 is the industry’s most highly integrated, IEEE 802.3af 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 Si3400 enables designers to easily add PoE functionality to their Ethernet products. When connected in a PoE-enabled system, such as a wireless access point or VoIP phone, the Si3400 converts the high voltage (typically ±48 V) supplied over Ethernet copper UTP cabling into a regulated, low voltage DC supply. In addition, the Si3400 combines all the required IEEE 802.3af detection, classification and hot swap interfaces with a complete, high efficiency, PWM switching regulator, including programmable soft start.
Compared to competing PD solutions, which typically require several external high voltage discrete devices to complete a PD interface, the Si3400 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 Si3400’s unmatched integration level are:
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Elimination of four critical high voltage BOM components:
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Two full diode bridges, a transient voltage suppressor and a switching regulator driver FET
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Reduction in external BOM savings of at least $0.30 to $0.40 USD
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Reduction of typical PCB layout footprints of 30%
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Direct connection to RJ-45 jack for reduced EMI
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Simplified design, PCB layout and validation processes
Leveraging Silicon Laboratories' proven high voltage design and manufacturing expertise, the Si3400 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.
Si3401
For PD applications which require more power than the 11 W (max) capability of the Si3400, the Si3401 provides the same feature set as the Si3400 but adds an increased hot swap switch current limit of 470 mA (min), versus the Si3400’s 350 mA (min). The Si3401’s higher current limit enables it to support applications in the 14 to 16 W range.
 Learn more about Silicon Labs' portfolio of products for the embedded PSE market.
Si3400/01 Block Diagram
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