wm9001 Wolfson Microelectronics plc, wm9001 Datasheet - Page 22

• Manufacturer Part Number: wm9001
• Description: 1w Dual-mode Class Ab/d Speaker Driver
• Manufacturer: Wolfson Microelectronics plc

WM9001
w
PCB LAYOUT CONSIDERATIONS
The efficiency of the speaker drivers is affected by the series resistance between the WM9001 and
the speaker (e.g. inductor ESR) as shown in Figure 12. This resistance should be as low as possible
to maximise efficiency.
Figure 12 Speaker Connection Losses
The distance between the WM9001 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 13. When additional passive filtering is used, low ESR
components should be chosen to minimise series resistance between the WM9001 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 13 EMI Reduction Techniques
WM9001
WM9001
WM9001
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
WM9001
WM9001
SPKP
SPKN
SPKP
SPKN
LOW ESR
LOW ESR
Short connection reduces EMI
PP, June 2009, Rev 3.2
LC Filtering
reduces EMI
Pre-Production
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