WM8725

Production Data

WOLFSON MICROELECTRONICS LTD

PD Rev 2.0 July 2000

8

RECOMMENDED EXTERNAL COMPONENTS

GND

VOUTR

CAP

VDD

NC

BCKIN

LRCIN

DIN

5

6

7

1

2

3

4

10

9

8

14

13

12

11

VOUTL

MUTE

NC

DEEMPH

SCKI

FORMAT

WM8725

GND

VDD

ANALOGUE

OUTPUT

FOR RIGHT

CHANNEL

FROM AUDIO

PROCESSOR

ANALOGUE

OUTPUT FOR

LEFT

CHANNEL

256fs/384fs CLK

10µF

0.1µF

10µF

+

External

LPF

External

LPF

Figure 5 Recommended External Components

DETAIL OF RECOMMENDED EXTERNAL COMPONENTS SHOWING THE EXTERNAL

LOW PASS FILTER

External LPF

x2 for Stereo Operation

100pF

-

+

10k

Ω

1500pF

10k

Ω

680pF

10k

Ω

Filtered

Analogue

Output

VOUTR

VOUTL

Figure 6 Third-Order Low Pass Filter (LPF) Example

An external low pass filter is recommended (see Figure 6) if the device is driving a wideband

amplifier. In some applications, second-order or passive RC filter may be adequate.

PCB LAYOUT

1.

Place all supply decoupling capacitors as close as possible to their respective supply

pins and provide a low impedance path from the capacitors to the appropriate ground.

2.

Separate analogue and digital ground planes should be situated under respective

analogue and digital device pins.

3.

Avoid noise on the CAP reference pin. The decoupling capacitor should be placed as

close to this pin as possible with a low impedance path from the capacitor to analogue

ground.

4.

Digital input signals should be screened from each other and from other sources of

noise to avoid cross-talk and interference. They should also run over the digital ground

plane to avoid introducing unwanted noise into the analogue ground plane.

5.

Analogue output signal tracks should be kept as short as possible and over the

analogue ground plane reducing the possibility of losing signal quality.