Datasheet

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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
≈
−
PCB LAYOUT GUIDELINES
PCM1742
V
CC
V
DD
DGND
Return Path for Digital Signals
Analog
Ground
Digital
Ground
AGND
Output
Circuits
DIGITAL SECTION ANALOG SECTION
Digital Logic
and
Audio
Processor
Digital Power
+V
D
DGND
Analog Power
+5V
A
+V
S
AGND
REG
−V
S
PCM1742
SBAS176A – DECEMBER 2000 – REVISED APRIL 2005
APPLICATION INFORMATION (continued)
Figure 29. Dual-Supply Filter Circuit
Because the overall system performance is defined by the quality of the DACs and their associated analog
output circuitry, high-quality audio operational amplifiers are recommended for the active filters. The OPA2353
and OPA2134 dual operational amplifiers from Texas Instruments are recommended for use with the PCM1742;
see Figure 27 (a) and Figure 29 .
A typical PCB floor plan for the PCM1742 is shown in Figure 30 . A ground plane is recommended, with the
analog and digital sections being isolated from one another using a split or cut in the circuit board. The PCM1742
should be oriented with the digital I/O pins facing the ground plane split/cut to allow for short, direct connections
to the digital audio interface and control signals originating from the digital section of the board.
Separate power supplies are recommended for the digital and analog sections of the board. This prevents the
switching noise present on the digital supply from contaminating the analog power supply and degrading the
dynamic performance of the PCM1742. In cases where a common 5-V supply must be used for the analog and
digital sections, an inductance (RF choke, ferrite bead) should be placed between the analog and digital 5-V
supply connections to avoid coupling of the digital switching noise into the analog circuitry. Figure 31 shows the
recommended approach for single-supply applications.
Figure 30. Recommended PCB Layout
26