Datasheet

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ANALOG OUTPUTS
V
COM
Output
–
–
V
COM
OPA337
+
10 µF
+
PCM1780/81/82
Buffered V
COM
V
CC
V
OUT
X
†
+
PCM1780/81/82
A
V
+ *1, where A
V
+ *
R
2
R
1
V
COM
†
X = L or R
1/2
OPA2353
+
V
CC
2
3
1
C
1
R
3
R
2
C
2
R
1
10 µF
+
(a) Using V
COM
to Bias a Single-Supply Filter Stage
(b) Using a Voltage Follower to Buffer V
COM
When Biasing Multiple Nodes
S0054-01
R
4
R
5
PCM1780 , PCM1781 , PCM1782
SLES132B – MARCH 2005 – REVISED AUGUST 2006
The PCM1780/81/82 includes two independent output channels, V
OUT
L and V
OUT
R. These are unbalanced
outputs, each capable of driving 3.9 Vp-p typical into a 5-k Ω ac-coupled load. The internal output amplifiers for
V
OUT
L and V
OUT
R are biased to the dc common voltage, equal to 0.5 V
CC
.
The output amplifiers include an RC continuous-time filter, which helps to reduce the out-of-band noise energy
present at the DAC outputs due to the noise-shaping characteristics of the PCM1780/81/82 delta-sigma D/A
converters. The frequency response of this filter is shown as ANALOG FILTER in the Typical Performance
Curves section. By itself, this filter is not enough to attenuate the out-of-band noise to an acceptable level for
many applications. An external low-pass filter is required to provide sufficient out-of-band noise rejection. Further
discussion of DAC post-filter circuits is provided in the Application Information section of this data sheet.
One unbuffered common voltage output pin, V
COM
(pin 13), is brought out for decoupling purposes. This pin is
nominally biased to the dc common voltage, equal to V
CC
/2. This pin can be used to bias external circuits.
Figure 27 shows an example of using the V
COM
pin for external biasing applications.
Figure 27. Biasing External Circuits Using the V
COM
Pin
25
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