Si3400/1/2-EVB
Rev. 0.82 11
d. Begin entering your design targets in cells B9 through B13 of the Excel worksheet:
i. If using the Si3401/2, select on-chip “diode bypass” option in cell B9 in the Excel spreadsheet
utility. By entering a “1” in this cell, the Si3400/1/2’s on-chip diodes are assumed to be bypassed
with external diode bridges in your schematic. A “0” in this cell means the Si3400/1/2’s on-chip
diode bridges will be used.
ii. Enter V
IN
into cell B10. This voltage is the input voltage at the diode bridge output, which is 2 to
3 V less than the PSE input voltage, or typically 46 V.
iii. Enter your design’s desired output current, I
O
in Amperes, into cell B11.
iv. Enter your design’s desired output voltage, V
O
in Volts, in cell B12.
v. Enter your design’s maximum ambient operating temperature in °C into cell B13.
e. If you are using the “Non-isolated” worksheet:
i. The feedback resistor network values (R5 and R6) for your design are calculated and displayed in
cells G13 and G12, respectively. Use these resistor values to update your schematic.
ii. To use the default diode and inductor components used in the Si3400-EVB non-isolated
schematic, Silicon Labs strongly recommends leaving each default values “as-is” in cells B15
through B18.
iii. To ensure your design is operating within the acceptable operating ranges for all the external
components you use in your schematic, carefully review the calculated values found in cells B20
through B27.
iv. Carefully review the calculated values in the Summary section (cells B29 through B33).
1. Cell B29: PSE input voltage. Make sure the PSE input voltage is compatible with the PSE
intended to power your PD.
2. Cell B30: PSE input power. If the power is >12.95 W (more than the IEEE 802.3af limits),
then this cell is shaded in light RED and your PSE must be capable of sourcing the power
level shown in cell B30.
3. Cell B33: If the calculated junction temperature is >
140 °C, then this cell is shaded in light
red. Consider bypassing the on-chip diodes to lower the effective junction temperature, or
reducing the output current (if possible). Other inputs in cells B9 through B13 may also need
to be adjusted to lower the calculated junction temperature.
f. If you are using either of the “Isolated” worksheets, enter in the input values to determine if your design
will be operating in the “continuous” mode or the “discontinuous mode”:
i. Check the value of the current calculated in cell H11.
1. If your desired output current (B11) is less than the value shown in cell H11, then use the
“Isolated Discontinuous” worksheet.
2. If your desired output current (B11) is greater than the value shown in cell H11, then use
the “Isolated Continuous” worksheet.
ii. The feedback resistor network values (R5 and R6) for your design are calculated and displayed in
cells E12 and E13, respectively. Use these resistor values to update your schematic.
iii. Select transformer turns ratio: use 3.3, 2.5 or 1 as standard choices for 3.3, 5, and 12 V output,
respectively. Leave the rest of the options as defaults. If you have different output voltage, then
contact Silicon Labs for recommendations.
iv. To use the default transformer, snubber and diode components used in the Si3400ISO-EVB
isolated schematic, Silicon Labs strongly recommends leaving each default values “as-is” in cells
B15 through B23. Always select the EP13 core if you require short circuit protection.
v. To ensure your design is operating within the acceptable operating ranges for all the external
components you use in your schematic, carefully review the calculated values found in cells B25
through B35.
