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R

1

R

3

R

4

R

2

C

1

C

2

V

IN

V

OUT

OP A2 134

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