®

20

PCM3501

APPLICATIONS INFORMATION

BASIC CIRCUIT CONNECTIONS

The basic connection diagram for the PCM3501 is shown in

Figure 16. Included are the required power supply bypass and

reference decoupling capacitors. The DAC output, VOUT, and

the ADC input, VIN, should be AC-coupled to external cir-

cuitry.

Reference Pin Connections

The VCOM voltage is used internally to bias the input and

output amplifier stages of the PCM3501. It is brought out

FIGURE 16. Basic Connection Diagram.

unbuffered on pin 1 for decoupling. A 1

µF to 10µF alumi-

num electrolytic or tantalum capacitor is recommended for

decoupling purposes. This capacitor should be located as

close as possible to pin 1.

The VCOM voltage is typically equal to VCC/2, and may be

used to bias external input and output circuitry. However,

since the VCOM pin is not a buffered output, it must drive a

high impedance load to avoid excessive loading. Buffering

the VCOM pin with an external op amp configured as a

voltage follower is recommended when driving multiple bias

nodes. Figure 17 shows an example of using VCOM with

external circuitry.

FIGURE 17. Using VCOM to Bias External Circuitry.

V

COM

V

REF1

V

REF2

V

IN+

V

IN–

M/S

TSC

BCK

FS

DIN

DOUT

FSO

V

CC

AGND

V

OUT+

V

OUT–

PDWN

LOOP

HPFD

XTI

XTO

SCKIO

DGND

V

DD

1

2

3

4

5

6

7

8

9

10

11

12

24

23

22

21

20

19

18

17

16

15

14

13

PCM3501

+

+

+

+

C

3

C

4

C

5

C

6

Serial

Interface

+

+

C

1

+3.3V

Power supply

External Reset

Power-Down Control

External Clock System

Analog Line Interface Circuit

Telecom Line

+

C

2

C

9

C

1, C2: Power supply bypass capacitors. Parallel combination of 1µF to 10µF aluminum electrolytic capacitor and 0.1µF ceramic capacitor.

C

3, C4, C5: VREF and VCOM bypass capacitors. 1µF to 10µF aluminum electrolytic capacitor.

C

6-C9: Input/output AC-coupling capacitors. 0.1µF to 10µF. If VIN+, VIN–, VOUT+, VOUT– are operated in reference

to V

COM, these capacitors are not required.

+

C

7

+

C

8

PCM3501

OPA337

+

4.7

µF

Use voltage follower

to buffer V

COM

To Bias

Nodes

V

COM