SSM2335

Rev. 0 | Page 13 of 1

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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 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 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, as well as the PCB traces to

the 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 interference. 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

ground plane side of a double-sided board is often disrupted by

signal crossover.

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 SSM2335 does not require input coupling capacitors if the

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 SSM2335 form a high-pass filter whose

corner frequency is determined by the following equation:

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.

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, with a minimum value of 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 SSM2335 helps

to maintain efficient performance.