CS4294 Datasheet, PDF (31/42 Pages) Cirrus Logic – SoundFusion Audio/Docking Codec 97 (AMC 97)

CS4294
7.3 Line Level Outputs
The analog output section provides a stereo line-
level output and an alternate stereo line-level out-
put.
LINE_OUT_L,
LINE_OUT_R,
ALT_LINE_OUT_L, and ALT_LINE_OUT_R
outputs should be capacitively coupled to external
circuitry.
Each of the 4 analog outputs, if used in the design,
require 680 pF or larger NPO dielectric capacitors
between the corresponding pin and AGND. Each
analog output is DC biased up to the Vrefout volt-
age signal reference which is nominally 2.2 V. This
requires that the output either be AC coupled to ex-
ternal circuitry (AC load must be greater than 10
kΩ) or DC coupled to a buffer op-amp biased at the
Vrefout voltage (see Figure 13 for the recommend-
ed headphone op-amp circuit).
7.4 Miscellaneous Analog Signals
The AFILT1 and AFILT2 pins must have a
1000 pF NPO capacitor (must not be smaller than
390 pF) to analog ground. These capacitors, along
with an internal resistor, provide a single-pole low-
pass filter at the inputs to the ADCs. By placing
these filters at the input to the ADCs, low-pass fil-
ters at each analog input pin are not necessary.
The REFFLT pin lowers the noise of the internal
voltage reference. A 1 µF (must not be greater than
1 µF) and 0.1 µF capacitor to analog ground should
be connected with a short, wide trace to this pin. No
other connection should be made, as any coupling
onto this pin will degrade the analog performance
of the Codec. Likewise, digital signals should be
kept away from REFFLT for similar reasons.
The Vrefout pin is typically 2.2 V and provides a
common mode signal for single-supply external
circuits. Vrefout only supports light DC loads and
should be buffered if AC loading is needed. For
typical use, a 0.1 µF in parallel with a 1 µF capaci-
tor should be connected to Vrefout.
DS326PP4
68 kΩ
+5 VA
U1A
1
8
+ ^{3 MC33078D}
-2
4
AGND
+5 VA
47 kΩ
+1
10 µF
2
47 kΩ
100 kΩ
AGND
AGND
2.7 kΩ
47 kΩ
4
AGND
3
5
2
0.068 µF
1
X7R
220 pF 220 pF
AGND
CGND
+1
6.8 kΩ
10 µF
2
AGND
+5 VA _U1B
5+
8
MC33078D
7
1 µF
6-
MIC1
4
X7R
AGND
220 pF
47 kΩ
Figure 12. PC ‘99 Microphone Pre-amplifier
31