Data Sheet SSM2306
Rev. A | Page 13 of 16
LAYOUT
As output power continues to increase, careful layout is needed
for proper placement of PCB traces and wires between the ampli-
fier, load, and power supply. A good practice is to use short, wide
PCB tracks to decrease voltage drops and minimize inductance.
Make track widths at least 200 mil for every inch of track length
for lowest DCR, and use 1 oz. or 2 oz. of copper PCB traces to
further reduce IR drops and inductance. Poor layout increases
voltage drops, consequently affecting efficiency. Use large traces
for the power supply inputs and amplifier outputs to minimize
losses due to parasitic trace resistance. Proper grounding guide-
lines help to improve audio performance, minimize crosstalk
between channels, and prevent switching noise from coupling
into the audio signal.
To maintain high output swing and high peak output power, the
PCB traces that connect the output pins to the load and supply
pins should be as wide as possible to maintain the minimum
trace resistances. It is also recommended to use a large area
ground plane for minimum impedances.
Good PCB layouts isolate critical analog paths from sources of
high interference; furthermore, separate high frequency circuits
(analog and digital) from low frequency ones. Properly designed
multilayer printed circuit boards can reduce EMI emission and
increase immunity to RF field by a factor of 10 or more compared
with double-sided boards. A multilayer board allows a complete
layer to be used for the ground plane, whereas the ground plane
side of a double-sided board is often disrupted with signal cross-
over. If the system has separate analog and digital ground and
power planes, the analog ground plane should be underneath
the analog power plane, and, similarly, the digital ground plane
should be underneath the digital power plane. There should be
no overlap between analog and digital ground planes or analog
and digital power planes.
INPUT CAPACITOR SELECTION
The SSM2306 does not require input coupling capacitors if the
input signal is biased from 1.0 V to V
DD
− 1.0 V. Input capacitors
are required if the input signal is not biased within this recom-
mended input dc common-mode voltage range, if high-pass
filtering is needed (see Figure 32), or if using a single-ended
source (see Figure 33). If high-pass filtering is needed at the
input, the input capacitor together with the input resistor of
the SSM2306 form a high-pass filter whose corner frequency
is determined by the following equation:
f
C
= 1/(2π × R
IN
× C
IN
)
Input capacitors can have very important effects on the circuit
performance. Not using input capacitors degrades the output
offset of the amplifier as well as the PSRR performance.
PROPER POWER SUPPLY DECOUPLING
To ensure high efficiency, low total harmonic distortion (THD),
and high PSRR, proper power supply decoupling is necessary.
Noise transients on the power supply lines are short duration
voltage spikes. Although the actual switching frequency can range
from 10 kHz to 100 kHz, these spikes can contain frequency
components that extend into the hundreds of megahertz. The
power supply input needs to be decoupled with a good quality,
low ESL and low ESR capacitor, usually around 4.7 µF. This
capacitor bypasses low frequency noises to the ground plane.
For high frequency transients noises, use a 0.1 µF capacitor as
close as possible to the VDD pin of the device. Placing the
decoupling capacitor as close as possible to the SSM2306
helps maintain efficiency performance.
