SSM2315CBZ-REEL Datasheet, PDF (13/16 Pages) Analog Devices – Filterless, High Efficiency, Mono 3 W Class-D Audio Amplifier

LAYOUT
As output power continues to increase, care must be taken to lay
out PCB traces and wires properly among the amplifier, load,
and power supply. A good practice is to use short, wide PCB
tracks to decrease voltage drops and to minimize inductance.
Ensure that track widths are 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. A 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 guidelines help 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 that a large ground plane be used for minimum
impedances.
In addition, good PCB layouts isolate critical analog paths from
sources of high interference. High frequency circuits (analog
and digital) should be separated from low frequency circuits.
Properly designed multilayer printed circuit boards can reduce
EMI emission and increase immunity to the 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 crossover.
If the system has separate analog and digital ground and power
planes, the analog ground plane should be underneath the analog
power plane. 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.
SSM2315
INPUT CAPACITOR SELECTION
The SSM2315 does not require input coupling capacitors if the
input signal is biased from 1.0 V to VDD − 1.0 V. Input capacitors are
required if the input signal is not biased within this recommended
input dc common-mode voltage range, if high-pass filtering is
needed, or if a single-ended source is used. If high-pass filtering
is needed at the input, the input capacitor and the input resistor
of the SSM2315 form a high-pass filter whose corner frequency
is determined by the following equation:
fC = 1/(2π × RIN × CIN)
The input capacitor can significantly affect the performance of
the circuit. Not using input capacitors degrades both the output
offset of the amplifier and the dc 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, low ESR capacitor, usually of 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 SSM2315 helps maintain
efficient performance.
Rev. A | Page 13 of 16