The Si3402 integrates all power management and control functions required in a
Power-over-Ethernet (PoE) powered device (PD) application. The Si3402
converts the high voltage supplied over the 10/100/1000BASE-T Ethernet
connection into a regulated, low-voltage output supply. The optimized
architecture of the Si3402 minimizes the solution footprint, reduces external
BOM cost, and enables the use of low-cost external components while
maintaining high performance. The Si3402 integrates the required diode bridges
and transient surge suppressor, thus enabling direct connection of the IC to the
Ethernet RJ-45 connector. The switching power FET and all associated
functions are also integrated. The integrated switching regulator supports
isolated (flyback) and non-isolated (buck) converter topologies. The Si3402
supports IEEE 802.3 Type 1 (Class 3 and below) Powered Device applications.
Standard external resistors connected to the Si3402 provide the proper IEEE
802.3 signatures for the detection function and programming of the requested
power class. Startup circuits ensure well-controlled initial operation of both the
hotswap switch and the voltage regulator. The Si3402 is available in a lowprofile,
20-pin, 5 x 5 mm QFN package. The Si3402-C is a pin-compatible
replacement of the obsolete Si3402-A. PCB layouts designed for Si3402-A can
be reused with Si3402-C, but some component value changes are required.
The Si3402-C’s functionality is similar to that of the Si3402-B but without the
requirement to make a connection between the Ethernet jack and CT1, CT2,
SP1, or SP2 pins when bypassing the integrated diode bridge with external
Schottky diodes. Further, PLOSS functionality is removed from the Si3402-C.
