CS4299 Datasheet, PDF (38/52 Pages) Cirrus Logic – CrystalClear SoundFusion Audio Codec 97

CS4299
6.1.5 Phone Input
One application of the PHONE input is to interface
to the output of a modem analog front end (AFE)
device so that modem dialing signals and protocol
negotiations may be monitored through the audio
system. Figure 16 shows a design for a modem
connection where the output is fed from the
CS4299 MONO_OUT pin through a divider. The
divider ratio 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 re-
placed with appropriate values, as long as the total
load on the output is kept greater than 10 kΩ. The
PHONE input is divided by 6 dB to accommodate
a line-level source of 2 V_RMS.
6.2 Analog Outputs
The analog line-level output section provides two
stereo outputs and a mono output. The
LINE_OUT_L/R, ALT_LINE_OUT_L/R, and
MONO_OUT pins require 680 pF to 1000 pF NPO
capacitors between the corresponding pin and ana-
log ground. Each analog output is DC-biased up to
the Vrefout signal reference, nominally 2.3 V. This
requires the outputs be AC-coupled to external cir-
cuitry (AC load must be greater than 10 kΩ) or DC
coupled to a buffer op-amp biased at Vrefout.
6.2.1 Stereo Outputs
See Figure 18 for a line-level stereo output refer-
ence design. See Figure 17 for a recommended
headphone stereo output reference design.
6.2.2 Mono Output
The mono output, MONO_OUT, can be either a
sum of the left and right output channels, attenuat-
ed by 6 dB to prevent clipping at full scale, or the
selected Mic signal. The mono out channel can
drive the PC internal mono speaker using an appro-
priate buffer circuit
PHONE
MONO_OUT
6.8 kΩ
0Ω
1.0 µ F
1.0 µ F
PHONE
MONO_OUT
6.8 kΩ 47 kΩ _{1000 pF}
AGND
AGND
Figure 16. Modem Connection
ALT_LINE_OUT_R
ALT_LINE_OUT_L
1000 pF
NPO
1
4
2
3
27 kΩ
1000 pF
NPO
VREFOUT
0.1 µF
Y5V
AGND
1 µF
AGND
2-
3+
T DA1308
1
22 pF
NPO
220 µF
+
ELEC
10 Ω
1/4 WATT
HP_OUT_R
1
4
2
3
39 kΩ
22 pF
NPO
220 µF
+
ELEC
6-
5+
7
T DA1308
10 Ω
1/4 WATT
HP_OUT _L
43
47 kΩ
12
AGND
Figure 18. Stereo Output
ALT_LINE_OUT_R
Vrefout
ALT_LINE_OUT_L
27 kΩ
27 kΩ
1000 pF 1000 pF
NPO NPO
39 kΩ
22 pF
NPO
2-
1
3+
TDA1308
5+
7
6-
22 pF
NPO
39 kΩ
220 µ F
+ ELEC
220 µ F
+ ELEC
47 kΩ
10 Ω
1/4 Watt
10 Ω
1/4 Watt
47 kΩ
Headphone
Out
AGND
AGND
Figure 17. Alternate Line Output as Headphone Output
38