UG-704
EVAL-SSM4567Z User Guide
Rev. 0 | Page 10 of 23
PASSIVE COMPONENT SELECTION
Although the evaluation board is preloaded with the passive components required for a basic configuration, the same circuit can be
evaluated with different component values or filter designs. Selecting the proper components is the key to achieving the performance
required at the budgeted cost.
OUTPUT FERRITE BEADS (FB5 TO FB6)
The output beads, FB5 to FB6, are suggested components for filtering out the EMI caused at the switching output nodes. The penalty for
using ferrite beads for EMI filtering is slightly worse noise and distortion performance at the system level due to the nonlinearity of the
beads. Ensure that these beads have enough current conducting capability while providing sufficient EMI attenuation. The current rating
needed for an 8 Ω load is approximately 420 mA, and impedance at 100 MHz must be ≥120 Ω. In addition, the lower the dc resistance (DCR)
of these beads, the better for minimizing their power consumption. Table 4 describes suggested beads.
Table 4. Suggested Output Beads
Part No.
Manufacturer
Z (Ω)
I
MAX
(mA)
DCR (Ω)
Size (mm)
BLM18PG121SN1D
Murata
120
2000
0.05
1.6 × 0.8 × 0.8
MPZ1608S101A
TDK
100
3000
0.03
1.6 × 0.8 × 0.8
MPZ1608S221A
TDK
220
2000
0.05
1.6 × 0.8 × 0.8
BLM18EG221SN1D
Murata
220
2000
0.05
1.6 × 0.8 × 0.8
OUTPUT SHUNTING CAPACITORS (C26 AND C27)
There are two output shunt capacitors, C26 and C27, that work with the FB5 to FB6 ferrite beads, if they are used. Use small size (0603
or 0402), multilayer ceramic capacitors that are made of X7R or C0G (NP0) materials. Note that the capacitors can be used in pairs: a
capacitor with small capacitance (up to 100 pF) plus a capacitor with a larger capacitance (less than 1 nF). This configuration provides
thorough EMI reduction for the entire frequency spectrum. Alternatively, a single capacitor of approximately 470 pF can be used if reducing
the bill of materials is a priority.
