Texas Instruments AN-1521 POEPHYTEREV-E, User Manual, Page: 16 / 22

A Note on the Use of Common-Mode Choke
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Horizontal Resolution: 50 µs/div.
Trace 1: The 3.3V output voltage ripples (AC coupled). 0.2V/div
Trace 2: The FFT of Trace 1 showing the peak value of the harmonics. Horizontal 500 kHz/div. Vertical 5 mV/div
Figure 13. Output Ripple Voltage under Full Load
23 A Note on the Use of Common-Mode Choke
A location is reserved on the evaluation board for an optional input common mode filter. For some special
applications that have very strict EMI requirements, the common mode filter consisting of the choke U6
and two Y capacitors CE12 and CE13 can be used. On the original evaluation board, these three
components are not populated, and U6’s pads are shorted with bus wires. When a common mode filter is
required, a Coilcraft D1882-AL or equivalent can be used for U6, along with a Syfer
1808JA250102MCTPY2 or equivalent for CE12 and CE13.
24 Bill of Materials
Table 2. Part 1. PoE Circuit BOM
(1)
ITEM PART NUMBER DESCRIPTION VALUE
BR1 CBR1-D020S DIODE BRIDGE, SMDIP, CENTRAL 1A, 200V
BR2 CBR1-D020S DIODE BRIDGE, SMDIP, CENTRAL 1A, 200V
CE1 C2012X7R1E474K CAPACITOR, CER, CC0805, TDK 0.47 µF, 25V
CE2 NU
CE3 NU
CE4 C5750X7R2A475M CAPACITOR, CER, CC2220, TDK 4.7 µF, 100V
CE6 C5750X7R2A475M CAPACITOR, CER, CC2220, TDK 4.7 µF, 100V
CE6 EEV-HA2A220P CAPACITOR, AL ELEC, PANASONIC 22 µF, 100V
CE7 C3216X5R0J226M CAPACITOR, CER, CC1206, TDK 22 µF, 6.3V
CE8 C3216X5R0J226M CAPACITOR, CER, CC1206, TDK 22 µF, 6.3V
CE9 C3216X5R0J226M CAPACITOR, CER, CC1206, TDK 22 µF, 6.3V
CE10 C3216X5R0J226M CAPACITOR, CER, CC1206, TDK 22 µF, 6.3V
CE11 C2012X7R1E474K CAPACITOR, CER, CC0805, TDK 0.47 µF, 25V
CE12 NU
(1)
Note: NU stands for Not Used, namely not populated.
16 AN-1521 POEPHYTEREV-I / -E Evaluation Board SNOA476C – October 2006 – Revised April 2013
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