CS4215
headphone outputs and a mono monitor speaker
output.
phone output lines are short-circuit protected.
These outputs may be muted.
Output Level Attenuator
Speaker Output
The DAC outputs are routed through an attenu-
ator, which provides 0 dB to 94.5 dB of
attenuation, adjustable in 1.5 dB steps. Level
changes are implemented using both analog and
digital attenuation techniques. Level changes
only take effect on zero crossings to minimize
audible artifacts. The requested level change is
forced if an analog zero crossing does not occur
within 511 frames (10.6 ms at a 48 kHz frame
rate). A separate zero crossing detector exists for
each channel.
MOUT1 and MOUT2 differentially drive a small
loudspeaker, whose impedance should be greater
than 32 Ω. The signal is a summed version of
the right and left line output, tapped off prior to
the mute function, but after the attenuator. The
speaker output may be independently muted.
With OLB = 0, the speaker output also contains
a 3 dB gain over the line outputs. When
OLB = 1, the speaker outputs are driven at the
same level as the line outputs.
Some small speakers distort heavily when pre-
sented with low frequency energy. A high-pass
filter helps eliminate the low frequency energy
and can be implemented by AC coupling both
speaker terminals with a resistor to ground, on
the speaker side of the DC blocking capacitors.
The values selected would depend on the speaker
chosen, but typical values would be 22 µF for
the capacitors, with the positive side connected
to the codec, and 50 kΩ resistors. This circuit is
contained on the CDB4215 evaluation board as
shown in the end of this data sheet.
Line Outputs
LOUTR and LOUTL output an analog signal,
centered around the CMOUT voltage. The mini-
mum recommended load impedance is 8 kΩ.
Figure 1 shows the recommended 1.0 µF DC
blocking capacitor with a 40 kΩ resistor to
ground. When driving impedances greater than
10 kΩ, this provides a high pass corner of
20 Hz. These outputs may be muted.
Headphone Outputs
Input Monitor Function
HEADR and HEADL output an analog signal,
centered around the HEADC voltage. The de-
fault headphone output level (OLB = 0) contains
an optional 3 dB gain over the line outputs
which provides reasonable listening levels, even
with small amplitude digital sources. These out-
puts have increased current drive capability and
can drive a load impedance as low as 48 Ω. Ex-
ternal 12 Ω series resistors reduce output level
variations with different impedance headphones.
The common return line from driving head-
phones should be connected to HEADC, which
is biased to the CMOUT voltage. This removes
the need for AC coupling, and also controls
where the return currents flow. All three head-
To allow monitoring of the input audio signal,
the output of the ADCs can be routed through a
monitor path attenuator, then digitally mixed into
the input data for the DACs (see the front page
block diagram). Changes in the input gain or
output level settings directly affect the monitor
level. If full scale data from the ADCs is added
to full scale digital data from the serial interface,
clipping will occur.
Calibration
Both output offset voltage and input offset error
are minimized by an internal calibration cycle.
At least one calibration cycle must be invoked
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