Cirrus Logic CRD4202-1 - Manual (Page 3)

CRD4202-1
DS549RD1A1 3
1. GENERAL INFORMATION
The CRD4202-1 reference design is a CNR card
that features six channel CD quality analog and
S/PDIF digital audio outputs. The card includes a
CS4202 AC '97 audio codec and two CS4334 24-
bit serial stereo DACs. This combination gives the
CRD4202-1 a rich feature set and industry 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 through the
AC-Link. The AC-Link is a 5-wire serial digital in-
terface that transfers digital audio between the two
devices and also sends commands from the audio
controller to the CS4202 registers. For more infor-
mation on the AC-Link, see the Intel
® AC '97 revi-
sion 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/COG
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 in Figure 3 are connected to 6 dB voltage di-
viders and AC-coupled to the CS4202 with 1
µ
F
capacitors to minimize low frequency roll-off. The
voltage divider allows input signal levels of up to
2 Vrms. The 6 dB dividers are for PC 99 compati-
bility and not required for PC 2001 compliance.
The microphone input is AC-coupled using a 1
µ
F
capacitor to minimize low frequency roll-off. The
microphone circuit provides low voltage phantom
power for electret microphones. Phantom power is
derived from the +5 V analog supply and provides
a maximum of 4.2 V under no load and a minimum
of 2.0 V under a 0.8 mA load, as required by
PC 2001 specifications.