CS4225
46.5dB of gain in 1.5dB steps. The gain is ad-
justable only by software control. Level changes
only take effect on zero crossings to minimize
audible artifacts. If there is no zero crossing,
then the requested level change will occur after a
time-out of 511 frames (10.6ms at 48kHz frame
rate). There is a separate zero crossing detector
for each channel.
ADC and DAC Coding
The CS4225 converters use 2’s complement cod-
ing. Table 1 shows the ADC and DAC transfer
functions.
16-bit ADC/DAC
Input/ 2’s
Output Complement Complement Voltage*
12-bit ADC
2’s Input
Analog Outputs
Voltage*
+1.400000
+1.399957
Code
7FFF
7FFE
Code
Line Level Outputs
7FF
+1.40000
+139864
7FE
AOUT1, AOUT2, AOUT3 and AOUT4 output a
1V
level for full scale, centered around
+0.000064
+0.000021
-0.000021
-0.000064
0001
0000
FFFF
FFFE
001
000
FFF
FFE
+0.00204
+0.00068
-0.00068
-0.00204
rms
+2.1V. Figure 1 shows the recommended 1.0µF
dc blocking capacitor with a 40kΩ resistor to
ground. When driving impedances greater than
10kΩ, this provides a high pass corner of 20Hz.
These outputs may be muted.
-1.399957
-1.400000
8001
8000
801
800
-1.39864
-1.40000
Output Level Attenuator
*Nominal voltage relative to CMOUT (Typ 2.1V), no
gain or attenuation. Actual measured voltage will be
modified by the gain error and offset error specifica-
tions.
The DAC outputs are each routed through an at-
tenuator, which is adjustable in 1dB steps.
Output attenuation is available via software con-
trol only. Level changes are implemented such
that the noise is attenuated by the same amount
as the signal (equivalent to using an analog at-
tenuator after the signal source), until the
residual output noise is equal to the noise floor
in the mute state. Level changes only take effect
on zero crossings to minimize audible artifacts.
If there is no zero crossing, then the requested
level change will occur after a time-out of 511
frames (10.6ms at 48kHz frame rate). There is a
separate zero crossing detector for each channel.
Table 1 - ADC/DAC Input and Output Coding Table
Calibration
Both output offset voltage and input offset error
are minimized by an internal calibration cycle.
At least one calibration cycle must be invoked
after power up. A calibration will occur any time
the part comes out of reset, including the power-
up reset. For the most accurate calibration, some
time must be allowed between powering up the
CS4225, or exiting the power-down state, and in-
itiating a calibration cycle, to allow the voltage
reference to settle. This is achieved by holding
RST/PDN low for at least 50ms after power up
or exiting power-down mode. Input offset error
will be calibrated for all inputs and outputs.
Each output can be independently muted via
mute control bits. In addition, the CS4225 has an
optional mute on consecutive zeros feature,
where each DAC output will mute if it receives
512 consecutive zeros. A single non-zero value
will unmute the DAC output.
A calibration takes 192 frames to complete,
based on the frequency of the VCO of the inter-
DS86PP8
11
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