WM8725 Wolfson Microelectronics plc, WM8725 Datasheet - Page 11

• Manufacturer Part Number: WM8725
• Description: 99db Stereo Dac
• Manufacturer: Wolfson Microelectronics plc

WM8725
RECOMMENDED EXTERNAL COMPONENTS
Figure 7 Recommended External Components
DETAIL OF RECOMMENDED EXTERNAL COMPONENTS SHOWING THE EXTERNAL
LOW PASS FILTER
PCB LAYOUT
w
ANALOGUE
FOR RIGHT
CHANNEL
OUTPUT
GND
VDD
FROM AUDIO
PROCESSOR
10µF
External
LPF
Figure 8 Third-Order Low Pass Filter (LPF) Example
An external low pass filter is recommended (see Figure 8) if the device is driving a wideband
amplifier. In some applications, second-order or passive RC filter may be adequate.
1.
2.
3.
4.
5.
10µF
VOUTR
VOUTL
0.1µF
External LPF
x2 for Stereo Operation
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.
Separate analogue and digital ground planes should be situated under respective
analogue and digital device pins.
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.
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.
Analogue output signal tracks should be kept as short as possible and over the
analogue ground plane reducing the possibility of losing signal quality.
+
10k
1
2
3
4
5
6
7
680pF
LRCIN
DIN
BCKIN
NC
CAP
VOUTR
GND
10k
WM8725
1500pF
10k
100pF
DEEMPH
FORMAT
+
-
VOUTL
MUTE
SCKI
VDD
NC
13
11
14
12
10
9
8
Filtered
Analogue
Output
External
LPF
256fs/384fs CLK
PD Rev 4.1 August 2004
ANALOGUE
OUTPUT FOR
LEFT
CHANNEL
Production Data
11