WM8959 Wolfson Microelectronics Ltd., WM8959 Datasheet - Page 152

• Manufacturer Part Number: WM8959
• Description: Mobile Multimedia DAC with Dual-mode Class AB/D Speaker Driver
• Manufacturer: Wolfson Microelectronics Ltd.

WM8959
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WM8959
WM8959
WM8959
The distance between the WM8959 and the speakers should be kept to a minimum to reduce series
resistance, and also to reduce EMI. Further reductions in EMI can be achieved by additional passive
filtering and/or shielding as shown in Figure 99. When additional passive filtering is used, low ESR
components should be chosen to minimise series resistance between the WM8959 and the speaker,
maximising efficiency.
LC passive filtering will usually be effective at reducing EMI at frequencies up to around 30MHz. To
reduce emissions at higher frequencies, ferrite beads placed as close to the device as possible will
be more effective.
Figure 99 EMI Reduction Techniques
SPKP
SPKN
SPKP
SPKN
SPKP
SPKN
Long, exposed tracks emit more EMI
Ferrite beads reduce EMI
Shielding using PCB ground
plane (or Vdd) reduces EMI
EMI
LC filtering is more effective at removing EMI at
frequencies below ~30MHz
Ferrite beads are more effective at removing
EMI at frequencies above ~30MHz
WM8959
WM8959
SPKP
SPKN
SPKP
SPKN
LOW ESR
LOW ESR
Short connection reduces EMI
LC Filtering
reduces EMI
PP, May 2008, Rev 3.1
Pre-Production
152