CS4218 Datasheet, PDF (12/44 Pages) Cirrus Logic – 16-Bit Stereo Audio Codec

CS4218
OVERVIEW
The CS4218 contains two analog-to-digital con-
verters, two digital-to-analog converters,
adjustable input gain, and adjustable output level
control. Since the converters contain all the re-
quired filters in digital or sampled analog form,
the filters’ frequency responses track the sample
rate of the CS4218. Only a single-pole RC filter
is required for the analog inputs and outputs.
Communication with the CS4218 is via a serial
port, with separate pins for data input and out-
put. The filters and converters operate over a
sample rate range of 4 kHz to 50 kHz.
Line In
Right
Line In
Left
5.6K
5.6K
5.6K
5.6K
0.33 uF
300 pF
NPO
NPO
300 pF
0.33 uF
RIN1
or
RIN2
LIN1
or
LIN2
FUNCTIONAL DESCRIPTION
Analog Inputs and Outputs
Figure 8 illustrates the suggested connection dia-
gram for the CS4218. The line level inputs,
LIN1 or LIN2 and RIN1 or RIN2, are selected
by an internal input multiplexer. This multiplexer
is a source selector and is not designed for real-
time switching between inputs at the sample rate.
When using the CS4218 as a drop-in replace-
ment for the CS4216, existing recommended
circuits (shown in the CS4216 data sheet) may
be used as is without any noticeable degradation
in performance. Performance may vary with
user-specific input circuits and should be
checked when contemplating the use of CS4218
in existing CS4216 designs.
Unused analog inputs that are not selected have
a very high input impedance, so they may be
tied to AGND directly. Unused analog inputs
that are selected should be tied to AGND
through a 0.1 µF capacitor. This prevents any
DC current flow.
The analog inputs are single-ended and inter-
nally biased to the REFBUF voltage (nominally
Figure 9. Line Inputs.
2.1 V). The REFBUF output should be buffered
if it is to be used for microphone phantom
power.
The use of a single-pole RC filter is recom-
mended for use as an external anti-alias filter for
the CS4218. The maximum cutoff frequency
(lowpass) should not exceed 200 kHz. A lower
value for cuttoff frequency may be used, and is
dependent upon the application’s input band-
width.
The CS4218 inputs will accept a 1Vrms signal,
so a divide by two resistor network will serve as
a front-end interface to 2 Vrms line level sys-
tems. Figure 9 shows a simple input circuit that
includes a gain of 0.5 and the required RC filter.
The gain of 0.5 yields a full scale input sensitiv-
ity of 2 V_rms with the CS4218 programmable
gain set to 0.
The analog outputs are also single-ended and
centered around the REFBUF voltage. AC cou-
pling capacitors of >1 µF are recommended.
Refer to Figure 8 for the recommended analog
output circuit.
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