PCM1742
16 SBAS176
to operate external mute circuits, or used as status indicators
for a microcontroller, audio signal processor, or other digitally
controlled functions.
The active polarity of Zero Flag output can be inverted by
setting the ZREV bit of Control Register 22 to “1”. The reset
default is active high output, or ZREV = 0.
The L-channel and R-channel common Zero Flag can be
selected by setting the AZRO bit of Control Register 22 to “1”.
The reset default is L-channel and R-channel independent
Zero Flag, or AZRO = 0.
APPLICATIONS INFORMATION
CONNECTION DIAGRAMS
A basic connection diagram is shown in Figure 11, with the
necessary power-supply bypassing and decoupling compo-
nents. Texas Instruments recommends using the component
values shown in Figure 11 for all designs.
The use of series resistors (22Ω to 100Ω) are recommended
for the SCK, LRCK, BCK, and DATA inputs. The series
resistor combines with stray PCB and device input capaci-
tance to form a low-pass filter that reduces high-frequency
noise emissions and helps to dampen glitches and ringing
present on clock and data lines.
FIGURE 10. Dual-Supply Filter Circuit.
FIGURE 11. Basic Connection Diagram.
1
2
3
4
5
6
7
8
BCK
DATA
LRCK
DGND
V
DD
V
CC
V
OUT
L
V
OUT
R
16
15
14
13
12
11
10
9
SCK
ML
MC
MD
ZEROL/NA
ZEROR/ZEROA
V
COM
AGND
Post LPF
+3.3V
Regulator
Mode
Control
Zero Mute
Control
System Clock
PCM
Audio Data
Input
+5V V
CC
L-Chan OUT
10µF
10µF
+
+
10µF
+
Post LPF
R-Chan OUT
R
1
R
3
R
4
R
2
C
1
C
2
V
IN
V
OUT
OPA2134
2
3
1
R
2
R
1
A
V
≈ –
POWER SUPPLIES AND GROUNDING
The PCM1742 requires a +5V analog supply (V
CC
) and a +3.3V
digital supply (V
DD
). The +5V supply (V
CC
) is used to power the
DAC analog and output filter circuitry, while the +3.3V (V
DD
)
supply is used to power the digital filter and serial interface
circuitry. For best performance, the +3.3V (V
DD
) supply should
be derived from the +5V (V
CC
) supply using a linear regulator,
as shown in Figure 11. The REG1117-3.3 from Texas Instru-
ments is an ideal choice for this application.
Proper power-supply bypassing is shown in Figure 11. The
10µF capacitors should be tantalum or aluminum electro-
lytic.
DAC OUTPUT FILTER CIRCUITS
Delta-sigma DACs utilize noise-shaping techniques to im-
prove in-band Signal-to-Noise Ratio (SNR) performance at
the expense of generating increased out-of-band noise above
the Nyquist Frequency, or fS/2. The out-of-band noise must
be low-pass filtered in order to provide the optimal converter
performance. This is accomplished by a combination of
on-chip and external low-pass filtering.
Figures 9(a) and 10 show the recommended external low-
pass active filter circuits for single- and dual-supply applica-
tions. These circuits are second-order Butterworth filters
using a Multiple FeedBack (MFB) circuit arrangement that
reduces sensitivity to passive component variations over
frequency and temperature. For more information regarding
MFB active filter design, please refer to Burr-Brown Appli-
cations Bulletin #34 AB-034 (SBFA001), available from our
web site at http://www.ti.com.
Since the overall system performance is defined by the
quality of the DACs and their associated analog output
circuitry, high-quality audio op amps are recommended for
the active filters. The OPA2353 and OPA2134 dual op amps
from Texas Instruments are recommended for use with the
PCM1742, see Figures 9(a) and 10.