Cirrus Logic CRD4202-2 - Manual (Page 4)

CRD4202-2
4 DS549RD1B1
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.
The CS4202 features a pseudo-differential CD in-
put that minimizes common mode noise and inter-
ference. Each CD signal acts as one side of the
differential input and CD_C acts as the other side.
CD_C is used as the common return path for both
the left and right channels.
2.3 Center, LFE, and Surround Outputs
The audio outputs in Figure 4 drive the rear speak-
ers (surround), center speaker (CNT), and sub-
woofer (LFE) in six channel applications. These
four outputs are driven digitally from the CS4202
through two serial output ports and converted to an-
alog audio through two high-performance CS4334
24-bit stereo DACs.
2.4 Front Channel and Headphone
Outputs
Figure 5 details the Headphone and Line Output
circuits. The Line Outputs are the main analog out-
puts in a two channel system, and become the Front
Outputs in a six channel audio system.
The CS4202 has a built in headphone amplifier on
pins 39 and 41. These outputs are capable of driv-
ing headphones with impedances as low as 32
Ω
.
The headphone outputs are AC-coupled through
220
µ
F capacitors. These large capacitor values
create excellent low frequency response even under
32
Ω
loads.
2.5 S/PDIF Optical Output
The S/PDIF (IEC-958) digital output shown in
Figure 6 is compatible with digital inputs on con-
sumer devices such as Mini Disk recorders and
consumer stereo receivers. The S/PDIF output op-
erates at a fixed sampling frequency of 48 kHz. It
uses an industry standard Toshiba TOTX-173 opti-
cal TOSLINK transmitter.
2.6 CNR Connector and EEPROM
The CNR connector is shown in Figure 7. CNR is a
motherboard interface that supports audio, modem,
and LAN subsystems. CNR applications are target-
ed at OEMs, system manufacturers, and system in-
tegrators who wish take advantage of physically
separating their audio, modem, or LAN circuitry
from the PC motherboard. CNR accomplishes this
without the additional cost associated with the in-
terface circuitry required for a PCI bus add-in card.
The CRD4202-2 uses the AC-Link, SMBus, and
power supply pins. The SMBus signals are con-
nected to an AT24C02 EEPROM to provide Plug-
and-Play functionality for the CNR card. The EE-
PROM holds the Subsystem Vendor ID and Sub-
system ID. It also contains other information for
implementing a Plug-and-Play CNR card. For ad-
ditional information on the CNR design specifica-
tions, programming utilities, and information on
programming the EEPROM, visit the Intel
® Com-
munications and Network Riser (CNR) homepage
at http://developer.intel.com/technology/cnr/.
2.7 Auto Demotion Circuit
The configuration of the codec on the CRD4202-2
will always be set as the primary audio codec in
PLL mode. In crystal mode operation it can auto-
matically demote to a secondary codec in the pres-
ence of a motherboard codec when R54 is changed
to 100 k
Ω
(Figure 9). This feature is in accordance
with the AC '97 Codec Disable and Demotion
Rules.
2.8 Phase Locked Loop
The CRD4202-2 reference design is configured to
operate the CS4202 in Phase Locked Loop (PLL)
mode as the primary codec. The external clock
must be one of the three supported rates, and the co-
dec ID pins must be properly configured to identify