CS4297 Datasheet, PDF (32/46 Pages) Cirrus Logic – CrystalClear SoundFusion Audio Codec 97

CS4297
CrystalClear™ SoundFusion™ Audio Codec ’97
Miscellaneous Analog Signals
The AFILT1 and AFILT2 pins must have a 390 pF
NPO capacitor (must not be smaller than 390 pF) to
analog ground. These capacitors, along with an in-
ternal 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 filters 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
(see Figure 10 in the Grounding and Layout section
for an example). 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.
Power Supplies
The power supplies providing analog power should
be as clean as possible to minimize coupling into
the analog section which could degrade analog per-
formance. The pins AVdd1 and AVdd2 supply
power to all the analog circuitry on the CS4297.
This 5 Volt analog supply should be generated
from a voltage regulator (7805 type) connected to a
+12 Volt supply. This helps isolate the analog cir-
cuitry from noise typically found on +5 V digital
supplies which power many digital circuits in a PC
environment. A typical voltage regulator circuit for
analog power using an MC78M05CDT is shown in
Figure 9.
The digital power pins DVdd1 and DVdd2 should
be connected to the same digital supply as the
AC’97 Controller’s AC-Link interface. Since the
digital interface on the CS4297 may operate at ei-
ther 3.3 V or 5 V, proper connection of these pins
will depend on the digital power supply of the
AC’97 Controller.
+12VD
MC78M05CDT
Y5V
0.1µF
1 _IN
+ _ELEC
10µF
OUT ³
GND
2
Y5V
0.1µF
+5VA
+ _ELEC
10µF
DGND
Figure 9. Voltage Regulator
AGND
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DS242F5