®

9

PCM1704

FIGURE 4. Audio Interface Connections for Stereo Audio

Application.

FIGURE 5. Typical Application Circuit (one channel shown).

DOR

WCKO

BCKO

DOL

DATA

WCLK

BCLK

DATA

WCLK

BCLK

DF1704 or Other

Digital Filter

PCM1704

PCM1704

24-Bit

96kHz

Data

TYPICAL APPLICATION

EXAMPLES

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.

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.

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.

20

19

18

17

16

15

14

13

12

11

1

2

3

4

5

6

7

8

9

10

C

1

C

2

C

4

C

3

C

5

+

Digital

Controls

Aluminum

Electrolytics

–5V

100

µF

0.1

µF

+

C

7

+

+

+

4.7

µF

OPA627

1/2

OPA2134

47pF

+

4.7

µF

+

C

6

+

+

100

µF

0.1

µF

+

100

µF

0.1

µF

+

+5V

–15V

Audio

Output

+15V

100

µF

0.1

µF

+

PCM1704U

DATA

BCLK

NC

–V

DD

DGND

+V

DD

WCLK

NC

20BIT

INVERT

–V

CC

REF DC

NC

SERVO DC

AGND

AGND

I

OUT

NC

BPO DC

+V

CC

8X

Oversampling

Interpolation

Filter

2.5k

Ω

U1

U2

4.7k

Ω

4.7k

Ω

2k

Ω

4.7

µF

560pF

2200pF

+

4.7

µF

+

DAC

I/V

Post Filter

24-Bit

96kHz Data

C

C

C

C

C

C

C