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EVAL-SSM3515Z User Guide

UG-580

Rev. A | Page 5 of 19

OUTPUT CONFIGURATION

The OUT− and OUT+ output terminals connectors provide
convenient attachment points for speakers or other load devices
with standard banana connectors. In addition, 2-pin, 0.100 inch
headers are provided. J7 is inserted before the EMI filtering
portion, and J8 is inserted after the EMI filtering portion.
Because the

SSM3515

does not typically require any external

audio band LC output filtering due to a low noise modulation
scheme, a low cost, high performance common-mode, choke-
based filter can optionally be inserted on the evaluation board
for EMI suppression.
For optimal performance measurement, remove this filtering by
inserting 0 Ω links or a thick wire short across B1 and B2. In
this case, leave the C39 to C41 filter capacitors unpopulated.
To safeguard against system radiated emission failure, especially
if the speaker cable length exceeds 20 cm, it may be necessary
to include an output filter. The recommended filter uses a
common-mode choke, L5 in the output path, plus capacitors,
C39 to C41, to couple the output terminals to ground. A
schematic of this configuration is shown in Figure 10, with
recommended values for the filter components given. The
recommended common-mode chokes are listed in Table 2.
Alternatively, a carefully selected pair of ferrite beads can be
used in place of the common-mode choke to save space. Take
care with the component selection to avoid degradation of
THD + N or signal-to-noise ratio (SNR) as a result of the
nonlinear performance of the ferrite beads. A summary of
the recommended ferrite beads is shown in Table 3.
For the best THD and SNR performance as specified in the

SSM3515

data sheet, remove the output filters and insert a short

across L1 and L2.

EDGE MODE

To reduce the radiated emissions from the

SSM3515

amplifier,

an edge rate control mode is available. To enable the reduced
EMI mode, send an I

C control register write to activate Bit D4

of Register 0x01. The efficiency is slightly reduced when low
EMI mode is enabled. To return to the ordinary (fast edge)
operating mode, write a 0 to Bit D4 of Register 0x01.

COMPONENT SELECTION

Selecting the proper components is the key to achieving the
performance required at the cost budgeted.

Common-Mode Choke Coil—L5

The L5 common-mode choke coil is a necessary component for
filtering out the EMI caused at the switching output nodes
when the length of the speaker wire is greater than 20 cm.
Recommended components are shown in Table 2.

Output Shunt Capacitors

There are three output shunt capacitors, C39 to C41, that work
with the L1 common-mode chokes coil. Use small size (0603 or
0402), multilayer ceramic capacitors made of X7R or C0G (NP0)
materials. The recommended value is 220 pF.

Output Ferrite Beads

If ferrite beads are preferred for EMI filtering at the output
nodes, choose only the selected ferrite beads in Table 3 to
avoid excessive noise induced by the nonlinear behavior of
ferrite beads.

Table 2. Recommended Common-Mode Chokes

Part No.

Manufacturer

Z (Ω at 100 MHz)

MAX

(mA)

DCR (Ω)

Size (mm)

DLW5BTN251SQ2

Murata Manufacturing Co.

250

5000