Cirrus Logic CRD4297-1 AMR, Product Data Book

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DS242RD1B1 5
CRD4297-1 AMR
CrystalClear™ AC '97 AMR Audio Modem Riser Reference
CIRRUS LOGIC ADVANCED PRODUCT DATABOOK
ground pins are tied to digital ground except for B2,
which is tied to analog ground.
The AC-link, which consists of ASDOUT, ARST#,
ASYNC, ASDIN, and ABITCLK, transfers digital
audio data between the audio codec and the host.
PC_BEEP_BUS routes the motherboard
beep/speaker signal from the motherboard to the
audio subsystem, for use in hearing POST codes
(refer to the Intel Audio/Modem Riser Specification
[2]).
The PRIMARY_DN# signal indicates the presence
or the absence of a primary codec on the mother-
board. The MSTRCLK is the 24.576 MHz master
clock for the AC ‘97 link. Populate R51 since the
CS4297 is always the primary codec. Populate R50
for CS4297A/99, when they are the secondary co-
dec.
The CS4297 does not support S/PDIF, R3 is popu-
lated so the S/PDIF signal originates from the
AMR bus. For a CS4297A/99 by populating R2 in-
stead of R3, the SPDIF_CODEC signal is directly
routed to the S/PDIF circuit, bypassing the AMR
bus.
Figure
13
: Power Supply
The CS4297 requires both a d3.3 V and an
5 V supply. The digital power is supplied
from the AMR bus. A separate regulator is recom-
mended for the analog voltage supply to provide
good audio signal quality. A Motorola MC78L05
regulates the +12 V supply from the AMR bus
down to a clean +5 V analog supply. Two packag-
ing options are supported, where U5 is an SO8 sur-
face mount package and U4 is a TO-92 pin-in-hole
package. The -12 V power pin is decoupled
through C73/C74, and supplies power to the head-
phone circuit.
Figure
14
: CS4297
AC ‘97
Audio Codec
For the best audio performance, the analog voltage
regulator, an MC78L05, is located near the
CS4297. A 10 µF electrolytic capacitor should be
added next to pins 25 and 26 if the capacitor con-
nected to the output of the power regulator is locat-
ed far away from the CS4297. All filtering
capacitors of audio signals are NPO-type to ensure
minimal added distortion. Two footprints are pro-
vided for the crystal XTAL: a CA-301 pin-in-hole
footprint, Y1, for miniature crystal; and a standard
HC-49U package, Y2. The HC-49U package can
be bent over and soldered to the card. R47 is a ter-
mination resistor in the serial AC-link between the
CS4297 and the AMR bus.
Figure
15
: Analog Inputs
The inputs for AUX, VIDEO, CD, and LINE are
passed through a divider circuit that reduces the
voltage by 6 dB to allow connection of line level
sources up to 2 Vrms. The 220 pF capacitors are
provided on Line_In, Mic_In, CD_In, Aux_In,
Video_In, and Internal Modem connection for
EMC suppression. These may be removed if EMC
testing determines they are not required. 1 µF AC-
coupling capacitors are used on the Line_In,
Mic_In, CD_In, Aux_In, Video_In, and Internal
Modem circuit to minimize the low frequency roll-
off. The internal CD audio connection utilizes a
pseudo-differential interface with CD_GND as the
common return path for both the left and right
channels. Therefore, the input impedance of this
block is half of that of the other inputs.
The modem connection is both a mono input and
output. The output is fed from the CS4297’s
MONO_OUT pin through a divider made of
R22/23. The divider ratio is preset to 0 dB for an
output voltage of 1 Vrms. If a lower output voltage
is desired, the resistors can be replaced with appro-
priate values, as long as the total load on the output
is kept greater than 10 k
Ω
. The input is not divided
to accommodate line level sources up to 1 Vrms.
Figure
16
: Audio Outputs
The line out is driven directly by the CS4297. The
headphone out amplifier, a Motorola MC1458, is