Cirrus Logic CRD4202-2 - Manual (Page 3)

CRD4202-2
DS549RD1B1 3
1. GENERAL INFORMATION
The CRD4202-2 CNR reference design features six
channel CD quality analog and S/PDIF digital au-
dio outputs. The card includes the CS4202 AC '97
audio codec operating in PLL mode, and two
CS4334 24-bit serial stereo DACs. This combina-
tion gives the CRD4202-2 a rich feature set and in-
dustry leading audio performance.
The CS4202 audio codec includes a stereo 20-bit
DAC, a stereo 18-bit ADC, and a very flexible an-
alog audio mixer. The serial data outputs are paired
with two CS4334 DACs to provide four additional
channels of analog audio. The CS4202 also fea-
tures three stereo pairs of line level analog inputs, a
microphone input, and a stereo pseudo-differential
CD input. The input signals can be routed to the
ADC for recording or mixed together for recording
and direct playback. The CS4202 has internal reg-
isters that are used to control its various features
such as volume levels, audio muting, and signal
routing. The CS4202 maintains high audio quality
and exceeds the Microsoft
® PC 2001 audio perfor-
mance specifications.
The CS4202 audio codec communicates to the au-
dio controller across the CNR interface using the
AC-Link. The AC-Link is a 5-wire serial digital in-
terface that transfers digital audio data and GPIO
control/status data between the two devices, sends
commands from the audio controller to the codec,
and provides codec status information to the con-
troller. For additional information on the AC-Link,
see the Intel
® AC '97 revision 2.2 specification.
2. SCHEMATIC DESCRIPTION
The block diagram in Figure 1 illustrates the inter-
connections between the schematic pages found at
the end of this document. Sections 2.1 through 2.8
describe the circuitry contained in these schemat-
ics.
2.1 CS4202 Audio Codec
The CS4202 audio codec is shown in Figure 2. The
analog input signals to the CS4202 originate from
the inputs in Figure 3, while the analog outputs are
shown in Figure 4 and Figure 5. AFLT1 and
AFLT2 (pins 29, 30) require 1000 pF NPO/C0G
capacitors connected to analog ground. These ca-
pacitors provide a single pole lowpass filter to the
inputs of the CS4202 ADC. No other input filtering
is required.
The AC-Link may require series termination resis-
tors to prevent reflections. These are normally
placed as close as possible to the transmitting end
of the AC-Link signal. The CS4202 SDATA_IN
(pin 8) and BIT_CLK (pin 6) outputs have 47
Ω
se-
ries termination resistors.
The CS4202 is powered by separate analog and
digital power supplies, each with their own respec-
tive grounds. The AGND symbols refer to analog
ground and DGND symbols refer to digital ground.
For best results, connect the grounds together at a
single point with a 0.050 inch trace underneath the
CS4202. Each power pin requires an individual de-
coupling capacitor. These decoupling capacitors
are placed as close as possible to their respective
pins. The CS4202 audio codec uses a 0.1
µ
F ce-
ramic capacitor for each of the +3.3 V digital and
+5 V analog supply pins.
2.2 Analog Inputs
The LINE_IN, VIDEO_IN, and AUX_IN stereo
inputs shown in Figure 3 are AC-coupled to the
CS4202 codec with 1
µ
F capacitors to minimize
low frequency roll-off. The pull down resistors are
recommended to prevent noise from coupling to
the analog inputs when they are not in use. Loca-
tions for 6 dB dividers were provided for 2.0 Vrms
input compatibility, but are not required for
PC 2001 compliance.
The microphone input is AC-coupled with a 1
µ
F
capacitor to minimize low frequency roll-off. The