Cirrus Logic CS4202 - Manual (Page 51)

CS4202
DS549PP2 51
Mic Volume Register (Index 0Eh) the pre-amplifier
gain can be set to 0 dB, 10 dB, 20 dB, or 30 dB.
10.1.4 PC Beep Input
The PC_BEEP input is useful for mixing the output
of the “beeper” (timer chip), provided in most PCs,
with the other audio signals. When the CS4202 is
held in reset, PC_BEEP is passed directly to the line
output. This allows the system sounds or “beeps” to
be available before the AC ’97 interface has been ac-
tivated. Figure 21 illustrates a typical input circuit for
the PC_BEEP input. If PC_BEEP is driven from a
CMOS gate, the 4.7 k
Ω resistor should be tied to an-
alog ground instead of +5VA. Although this input is
described for a low-quality “beeper”, it is of the same
high-quality as all other analog inputs and may be
used for other purposes.
10.1.5 Phone Input
One application of the PHONE input is to interface
to the output of a modem analog front end (AFE) de-
vice so that modem dialing signals and protocol ne-
gotiations may be monitored through the audio
system. Figure 22 shows a design for a modem con-
nection where the output is fed from the CS4202
MONO_OUT pin through a divider. The divider ra-
tio shown does not attenuate the signal, providing an
output voltage of 1 V
RMS
. 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 PHONE input is di-
vided by 6 dB to accommodate a line-level source of
2 V
RMS
.
10.2 Analog Outputs
The analog output section provides a stereo, a head-
phone, and a mono output. The MONO_OUT,
LINE_OUT_L, and LINE_OUT_R pins require
680 pF to 1000 pF NPO dielectric capacitors be-
tween the corresponding pin and analog ground.
Each analog output is DC-biased up to the Vrefout
voltage signal reference, nominally 2.4 V. This re-
quires the outputs be AC-coupled to external circuit-
ry (AC loads must be greater than 10 k
Ω for the line
output or 32
Ω for the headphone output). The head-
phone coupling capacitors should be 220
µF or great-
er to minimize low frequency roll-off.
10.2.1 Stereo Outputs
The LINE_OUT and HP_OUT stereo outputs de-
pend on the configuration of the HPCFG pin. As
shown in Figure 23, if the HPCFG pin is left floating,
0.1 µ F
X7R
100 Ω
0.1 µ F
X7R
MIC1/MIC2
10 µF
ELEC
AGND
+5VA
2.2 k Ω
1.5 k Ω
AGND
AGND
+
Figure 20. Microphone Input
4.7 k Ω
PC_BEEP
+5VA (Low Noise) or
AGND if CMOS Source
PC-BEEP-BUS
47 k Ω
2.7 nF
X7R
0.1 µF
X7R
AGND
Figure 21. PC_BEEP Input
PHONE
MONO_OUT
PHONE
MONO_OUT
6.8 k Ω 1.0 µF
0 Ω
6.8 k Ω
1.0 µF
47 k Ω
AGND AGND
1000 pF
Figure 22. Modem Connection