SSM2315

Rev. A | Page 13 of 16

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.

INPUT CAPACITOR SELECTION

The SSM2315 does not require input coupling capacitors if the

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:

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.