TYPICAL APPLICATION
EXAMPLES
DF1704 or Other
The audio interface connections for a stereo audio applica-
tion is shown in Figure 4. The audio data is input to the
digital filter, which then oversampleS the data by a factor of
8. The audio data is then filtered digitally and output to the
PCM1704 DACs.
Digital Filter
PCM1704
DOR
WCKO
BCKO
DATA
WCLK
BCLK
24-Bit
96kHz
Data
Figure 5 shows single channel circuit connections for a
typical PCM1704 application. It shows the PCM1704 inter-
face to the digital filter, the I/V converter, and the DAC post
filter. Selection of an appropriate op amp for the I/V con-
verter is critical for obtaining optimum dynamic perfor-
mance from the PCM1704. The OPA627 is recommended
for this application. Op amps with similar characteristics and
faster settling times may also be used.
PCM1704
DATA
WCLK
BCLK
DOL
The suggested DAC post filter is a second-order lowpass
active filter, using the multiple feedback (MFB) circuit
technique. The OPA2134 is an excellent choice for the op
amp in this circuit, since it is designed for high performance
audio applications. The post filter is used to reconstruct and
band limit the DAC output signal.
FIGURE 4. Audio Interface Connections for Stereo Audio
Application.
100µF
+
DAC
I/V
Post Filter
0.1µF
100µF
+
24-Bit
–5V
96kHz Data
PCM1704U
0.1µF
C3
+
DATA
BCLK
NC
–VCC
REF DC
NC
1
2
20
19
18
17
16
15
14
13
12
11
C4
C5
+15V
+
+
2.5kΩ
3
8X
C1
C2
Oversampling
Interpolation
Filter
47pF
–VDD
SERVO DC
AGND
AGND
IOUT
4
DGND
+VDD
WCLK
NC
5
4.7µF
+
4.7kΩ
4.7kΩ
560pF
+
4.7µF
+
6
7
2kΩ
U1
OPA627
4.7µF
NC
8
Audio
Output
1/2
OPA2134
U2
C6
+
20BIT
INVERT
BPO DC
+VCC
9
Digital
Controls
2200pF
4.7µF
C7
+
+
10
+
C1 = 4.7µF
C2 = 4.7µF
C3 = 4.7µF
+5V
–15V
0.1µF
0.1µF
Aluminum
Electrolytics
C
4 = 47µF
C5 = 47µF
C6 = 100µF
C7 = 4.7
100µF
100µF
+
+
FIGURE 5. Typical Application Circuit (one channel shown).
®
9
PCM1704
TI [ TEXAS INSTRUMENTS ]
