UG325: Class 3 Isolated Evaluation Board
for the Si3404
The Si3404 isolated Flyback topology based evaluation board is a
KEY FEATURES
reference design for a power supply in a Power over Ethernet
(PoE) Powered Device (PD) application.
IEEE 802.03af Compatible
Very Small Application PCB Surface
This Si3404-ISO-FB EVB maximum output level is Class 3 power ( x 15.4 W).
High Efficiency
The Si3404-ISO-FB EVB board is shown below. The Si3404 IC integrates an IEEE
High Integration
802.03af compatible PoE interface as well as a current control based dc/dc converter.
Low-Profile 4 x 4 mm 20-pin QFN
Thermal Shutdown Protection
The Si3404 PD integrates a detection circuit, classification circuit, dc/dc switch, hot-
Low BOM Cost
swap switch, TVS overvoltage protection, dynamic soft-start circuit, cycle-by-cycle cur-
rent limit, thermal shutdown, and inrush current protection. Transient Overvoltage Protection
The switching frequency of the converter is tunable by an external resistor.
silabs.com | Building a more connected world. Rev. 0.1 UG325: Class 3 Isolated Evaluation Board for the Si3404
Kit Description
1. Kit Description
The Si3404-ISO-FB isolated Flyback topology based evaluation board is a reference design for power supplies in Power over Ethernet
(PoE) Powered Device (PD) applications. The Si3404 device is described more completely in the data sheet and application notes. This
document describes the evaluation board.
The Si3404-ISO-FB EVB is shown on the cover page. The schematic is shown in Figure 2.3 Si3404 Isolated Flyback EVB Schematic: 5
V, Class 3 PD on page 4, and the layout is in 16. Board Layout. The dc output is at connectors J11(+) and J12().
Boards are shipped configured to produce 5 V output voltage but can be configured for different output voltages, such as 3.3 or 12 V,
for example, by changing resistors R14, R15, and a few other components. Refer to AN1130: Using the Si3406/Si34061/Si34062 PoE
+ and Si3404 PoE PD Controller in Isolated and Non-Isolated Designs for more information. The preconfigured Class 3 signature can
also be modified, which is described as well in AN1130.
The silicon type diode bridge can be replaced with Schottky type diode bridges to achieve higher overall board efficiency.
To compensate the reverse leakage of the Schottky type diodes at high temperature, the recommended detection resistor should be
adjusted to the values listed in the following table:
Table 1.1. Recommended Detection Resistor Values
External Diode Bridge R
DET
Silicon Type 24.3 k
Schottky Type 24.9 k
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