WM8956 datasheet(77/80 Pages) WOLFSON

77 / 80 page

Preliminary Technical Data

WM8956

PTD, July 2007, Rev 2.1

Figure 46 Speaker Equivalent Circuit

PCB LAYOUT CONSIDERATIONS

The efficiency of the speaker drivers is affected by the series resistance between the WM8956 and

the speaker (e.g. inductor ESR) as shown in Figure 47. This resistance should be as low as possible

to maximise efficiency.

VDD

GND

VMID

Losses due to resistance between WM8956 and speaker (e.g. inductor ESR)

This resistance must be minimised in order to maximise efficiency.

Switching

Losses

Class D

output

Figure 47 Speaker Connection Losses

The distance between the WM8956 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 48. When additional passive filtering is used, low ESR

components should be chosen to minimise series resistance between the WM8956 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.

WM8956 Datasheet(PDF) 77 Page - Wolfson Microelectronics plc