WM9001

Production Data

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PD, March 2010, Rev 4.1

22

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 aximizi 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 aximizi series resistance between the WM9001 and the speaker,

aximizing 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.

WM9001

SPKP

SPKN

EMI

WM9001

SPKP

SPKN

Short connection reduces EMI

WM9001

SPKP

SPKN

LC Filtering

reduces EMI

LOW ESR

LOW ESR

WM9001

SPKP

SPKN

Shielding using PCB ground

plane (or Vdd) reduces EMI

WM9001

SPKP

SPKN

Ferrite beads reduce 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

Long, exposed tracks emit more EMI

Figure 13 EMI Reduction Techniques