SSM2306

Rev. 0 | 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

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:

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 fre-

quency 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.