Si3400/1/2-EVB

10

Rev. 0.82

Introduction

Although all four EVB designs are pre-configured as a Class 3 PD for Si3400/1 and Class 4 for Si3402 with a 5 V

output, the schematics and layouts can easily be adapted to meet a wide variety of common output voltages and

power levels.

The

complete

EVB

design

databases

for

the

standard

5 V/Class 3

configuration

are

located

at

www.silabs.com/PoE under the “Documentation” link. Silicon Labs strongly recommends using these EVB

schematics and layout files as a starting point to ensure robust performance and to help avoid common mistakes in

the schematic capture and PCB layout processes.

Following are recommended design checklists that can assist in trouble-free development of robust PD designs:

Refer also to the Si3400/01 and Si3402 data sheets and AN296 when using the checklists below.

1. Design Planning Checklist:

a. Determine if your design requires an isolated or non-isolated topology. For more information, see

Section 4 of AN296.

b. To begin integrating the Si3400, Si3401, or Si3402 into your schematics, download the schematic and

layout database for your particular isolation requirements from www.silabs.com/PoE.

c. Silicon Labs strongly recommends using the EVB schematics and layout files as a starting point as you

begin integrating the Si3400/1/2 into your system design process.

typical expected transient surge conditions). In general, to achieve the highest overall efficiency

performance of the Si3400/1/2, choose the highest voltage used in your PD and then post regulate to the

lower supply rails, if necessary.

e. If your PD’s total power is <10 W, select the Si3400.

f.

If your PD design consumes >10 W, then select the Si3401 and make sure you bypass the Si3401/2’s

on-chip diode bridges with external diode bridges or discrete diodes. Bypassing the Si3401/2’s on-chip

diode bridges with external bridges or discrete diodes is required to help spread the heat generated in

designs dissipating >10 W.

g. Based on your required PD power level, select the appropriate class resistor value by referring to Table 2

of AN296. This sets the Rclass resistor (R3 in Figure 1 on page 2).

2. Calculate design-specific external components (for all designs which are not for a 5 V, Class 3 output

configuration):

a. To help guide the selection of the other application-specific external component values needed for your

design’s isolation requirements, access the Excel spreadsheet utility at the following address:

https://www.silabs.com/products/power/poe/Pages/default.aspx

i.

Use the “Non-isolated” worksheet if your design is intended for a non-isolated output supply.

ii. Use either the “Isolated Continuous” or the “Isolated Discontinuous” worksheets if your design is

for an isolated output supply (“continuous” versus “discontinuous” mode is determined by the

current value calculated in cell H11 of the spreadsheet).

b. If your design is a 5 V output Class 3 design, you do not need to change any external components.

c. To avoid potential performance issues for non-5 V output configurations, Silicon Labs strongly

recommends using the exact components and component values shown and calculated in the Excel

worksheets.