Embedian SMARC T335 Series, Руководство по конструкции аппаратуры

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SMARC T335x Carrier Board Hardware Design Guide, Document Revision 1.2
the analog input and voltage reference pins.
 Provide separate analog and digital ground planes with the digital
components over the digital ground plane, and the analog
components, including the analog power regulators, over the analog
ground plane. The split between planes must be a minimum of 0.05
inch wide.
 Route analog power and signal traces over the analog ground plane.
 Route digital power and signal traces over the digital ground plane.
 Position the bypassing and decoupling capacitors close to the IC pins,
or position the capacitors for the shortest connections to pins, with
wide traces to reduce impedance.
 Do not completely isolate the analog/audio ground plane from the rest
of the carrier board ground plane. Provide a single point (0.25 inch to
0.5 inch wide) where the analog/isolated ground plane connects to
the main ground plane. The split between planes must be a minimum
of 0.05 inch wide.
 Any signals entering or leaving the analog area must cross the
ground split in the area where the analog ground is attached to the
main carrier board ground. That is, no signal should cross the
split/gap between the ground planes, which would cause a ground
loop, thereby greatly increasing
EMI
emissions and degrading the
analog and digital signal quality
2.6.4. Unused I2S Signals Termination
All unused I2S interface signals can be left unconnected.