Datasheet
ANALOG OUTPUTS
V
COM
OUTPUT
–V
OUT
X
+
PCM1680
A
V
+ *
R
2
R
1
V
COM
OPA2134
+
V
CC
2
3
1
C
1
R
3
R
2
C
2
R
1
C
3
10 µF
+
S0056-01
R
4
R
5
+
OPA337
−
To Additional
Low-Pass
Filter Circuits
PCM1680
SLES133B – MARCH 2005 – REVISED OCTOBER 2008 ..................................................................................................................................................
www.ti.com
The PCM1680 includes eight independent output channels, V
OUT
1 through V
OUT
8. These channels are
unbalanced outputs, each capable of driving 3.9 V
PP
typical into a 5-k Ω ac load with V
CC
= 5 V. The internal
output amplifiers for V
OUT
1 through V
OUT
8 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 PCM1680 Δ Σ DACs. The frequency
response of this filter is shown in Figure 11 . By itself, this filter is not enough to attenuate the out-of-band noise
to an acceptable level for most 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 25), is brought out for decoupling purposes. This pin is
nominally biased to the dc common voltage, equal to V
CC
/2. If this pin is to be used to bias external circuitry, a
voltage follower is required for buffering purposes. Figure 31 shows an example of using the V
COM
pin for
external biasing applications.
Figure 31. Single-Supply Filter Circuit Using V
COM
for External Biasing Applications
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