Production Data WM8524
w
PD, Rev 4.1, October 2011
21
RECOMMENDED ANALOGUE LOW PASS FILTER
Figure 16 Recommended Analogue Low Pass Filter (one channel shown)
An external single-pole RC filter is recommended if the device is driving a wideband amplifier. Other
filter architectures may provide equally good results.
The filter shown in Figure 16 has a -3dB cut-off at 105.26kHz and a droop of 0.15dB at 20kHz. The
typical output from the WM8524 is 2.1Vrms – when a 10kΩ load is placed at the output of this
recommended filter the amplitude across this load is 1.99Vrms.
RECOMMENDED PCB LAYOUT
C1
AVDD
C2
C5
LINEGND
CPCB
CPCA
CPVOUTN
LINEVDD
AGND
To LINEVDD
Supply
To AVDD
Supply
VMID
C4
WM8524
C3
Top Layer Copper
Via
Figure 17 Recommended PCB Layout
Notes:
1. C5 should be placed as close to WM8524 as possible, with minimal track lengths to reduce inductance and maximise
performance of the charge pump. Vias should be avoided in the tracking to C5.
2. C1 is then next most important and should also be placed as close as possible to the WM8524. Again, minimise track
lengths and avoid vias to reduce parasitic inductance.
3. C2 and C4 are then next most important, and lastly C3.
4. The WM8524 evaluation board, details available at www.wolfsonmicro.com
, shows an example of good component
placement and layout to maximise performance with a minimal BOM.
