CS4235 Datasheet, PDF (75/94 Pages) Cirrus Logic – CrystalClear Low Cost ISA Audio System

CS4235
CrystalClear ^TM Low Cost ISA Audio System
The AUX2 line-level inputs have an extra pin,
CMAUX2, which provides a pseudo-differential
input for both LAUX2 and RAUX2. This pin
takes the common-mode noise out of the AUX2
inputs when connected to the ground coming
from the AUX2 analog source. Connecting the
AUX2 pins as shown in Figure 19 provides extra
noise attenuation coming from the CDROM
drive, thereby producing a higher quality signal.
Since the better the resistors match, the better the
common-mode attenuation, one percent resistors
are recommended. If CMAUX2 is not used, it
should be connected through an AC cap to ana-
log ground.
(All resistors 1%)
6.8 kΩ
3.4 kΩ
1.0 µF
2.0 µF
RAUX2
CMAUX2
LAUX2
6.8 kΩ
6.8 kΩ
1.0 µF
3.4 kΩ ^{6.8 kΩ}
Figure 19. Differential CDROM In
Microphone Level Input
The microphone level input, MIC, include a se-
lectable -22.5 dB to +22.5 dB gain stage for
interfacing to an external microphone. An addi-
tional 20 dB gain block is also available. The
20 dB gain block can be switched off to provide
another mono line-level input. Figure 20 illus-
trates a single-ended microphone input buffer
circuit that will support lower gain mics. The cir-
cuit in Figure 20 supports dynamic mics and
phantom-powered mics that use the ring portion
of the jack for power.
Mono Input
The mono input, MIN, is useful for mixing the
output of the "beeper" (timer chip), provided in
all PCs, with the rest of the audio signals. The
MIN pin can be mixed into the output mixer
with at a 0 or -9 dB level. Also, the MIM and
2 kΩ
47 kΩ
0.1 µF
47 kΩ
+
1 µF
MC33078 or
MC33178
0.33 µF
4.7 kΩ ^X7R
VREF
MIC
600 Ω
+
2.7 nF
NPO
10 µF
Figure 20. Microphone Input
MIMR bits support muting the input to the left
and right channels respectively. Figure 21 illus-
trates a typical input circuit for the Mono In. If
MIN is driven from a CMOS gate, the 4.7 kΩ
should be tied to AGND instead of VA+. Al-
though this input is described for a low-quality
beeper, the input is of the same high-quality as
all other analog inputs and may be used for other
purposes.
+5VA (Low Noise) or
AGND - if CMOS Source
4.7 kΩ
1 47 kΩ
MIN
0.1 µF
2.7 nF
Figure 21. Mono Input
Line Level Outputs
The analog output section provides a stereo line-
level output. The other output types (headphone
and speaker) can be implemented with external
circuitry. LOUT and ROUT outputs should be
capacitively coupled to external circuitry. Both
LOUT and ROUT need 1000 pF NPO capacitors
between the pin and AGND.
DS252PP2
75