CS4297A_06 Datasheet, PDF (39/52 Pages) Cirrus Logic – CrystalClear® SoundFusion™ Audio Codec ‘97

C_CS_S4₄2₂9₉7₇A_A
7. SONY/PHILIPS DIGITAL
INTERFACE (S/PDIF)
The S/PDIF digital output is used to interface the
CS4297A to consumer audio equipment external to
the PC. This output provides an interface for stor-
ing digital audio data or playing digital audio data
to digital speakers. Figure 20 illustrates the circuits
necessary for implementing the IEC-958 optical or
consumer interface. For further information on
S/PDIF operation see application note AN22: Over-
view of Digital Audio Interface Data Structures [3].
For further information on S/PDIF recommended
transformers see application note AN134: AES and
S/PDIF Recommended Transformers [4].
8. GROUNDING AND LAYOUT
Figure 21 on page 40 shows the conceptual layout
for the CS4297A. The decoupling capacitors
should be located physically as close to the pins as
possible. Also note the connection of the REFFLT
decoupling capacitors to the ground return trace
connected directly to the ground return pin, AVss1.
It is strongly recommended that separate analog
and digital ground planes be used. Separate ground
planes keep digital noise and return currents from
modulating the CS4297A ground potential and de-
grading performance. The digital ground pins
should be connected to the digital ground plane and
kept separate from the analog ground connections
of the CS4297A and any other external analog cir-
cuitry. All analog components and traces should be
located over the analog ground plane and all digital
components and traces should be located over the
digital ground plane.
The common connection point between the two
ground planes (required to maintain a common
ground voltage potential) should be located under
the CS4297A. The AC-link digital interface con-
nection traces should be routed such that the digital
ground plane lies underneath these signals (on the
internal ground layer). This applies along the entire
length of these traces from the AC ’97 controller to
the CS4297A.
Refer to the Application Note AN18: Layout and
Design Rules for Data Converters and Other
Mixed Signal Devices [2] for more information on
layout and design rules.
S/PDIF_OUT ^R1
SPDO/SDO2
R₂
DVdd 3.3V 5V
R₁ 247.5 Ω 375 Ω
R₂ 107.6 Ω 93.75 Ω
DGND
DS318PP6
J1
T₁
+5V_PCI
0.1 µ F
SPDO/SDO2 ⁴
3
8.2 kΩ ₂
1
5
DGND
6
DGND
TOTX-173
DGND
Figure 20. S/PDIF Output
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