SSM2375 Datasheet, PDF (11/13 Pages) Analog Devices – Filterless High Efficiency Mono 3 W Class-D Audio Amplifier

Preliminary Technical Data
SSM2375
Σ-Δ output modulation. This feature ensures that the current
flowing through the inductive load is small.
ground plane side of a double-sided board is often disrupted by
signal crossover.
When the user wants to send an input signal, an output pulse is
generated to follow input voltage. The differential pulse density
is increased by raising the input signal level. Figure 7 depicts
three-level, Σ-Δ output modulation with and without input
stimulus.
OUTPUT = 0V
+5V
OUT+
0V
+5V
OUT–
0V
+5V
VOUT
0V
–5V
OUTPUT > 0V
+5V
OUT+
0V
+5V
OUT–
0V
+5V
VOUT
0V
OUTPUT < 0V
+5V
OUT+
0V
+5V
OUT–
0V
0V
VOUT
–5V
Figure 7. Three-Level, Σ-Δ Output Modulation With and
Without Input Stimulus
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 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. 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 to improve audio performance,
minimize crosstalk between channels, and prevent switching
noise from coupling into the audio signal.
If the system has separate analog and digital ground and power
planes, the analog ground plane should be directly beneath the
analog power plane, and, similarly, the digital ground plane should
be directly beneath the digital power plane. There should be no
overlap between analog and digital ground planes or between
analog and digital power planes.
INPUT CAPACITOR SELECTION
The SSM2375 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 recom-
mended 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 SSM2375 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. These spikes can contain frequency components
that extend into the hundreds of megahertz. The power supply
input must be decoupled with a good quality, low ESL, low ESR
capacitor, greater than 4.7 μF. This capacitor bypasses low
frequency noises to the ground plane. For high frequency
transient 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 SSM2375 helps to maintain efficient
performance.
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
layout isolates critical analog paths from sources of high inter-
ference. High frequency circuits (analog and digital) should be
separated from low frequency circuits.
Properly designed multilayer PCBs 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
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