WM1811A datasheet(324/328 Pages) WOLFSON

324 / 328 page

WM1811A

Production Data

PD, November 2013, Rev 4.1

324

PCB LAYOUT CONSIDERATIONS

Poor PCB layout will degrade the performance and be a contributory factor in EMI, ground bounce

and resistive voltage losses. All external components should be placed as close to the WM1811A

device as possible, with current loop areas kept as small as possible. Specific factors relating to Class

D loudspeaker connection are detailed below.

CLASS D LOUDSPEAKER CONNECTION

Long, exposed PCB tracks or connection wires will emit EMI. The distance between the WM1811A

and the loudspeaker should therefore be kept as short as possible. Where speakers are connected to

the PCB via a cable form, it is recommended that a shielded twisted pair cable is used. The shield

should be connected to the main system, with care taken to ensure ground loops are avoided.

Further reduction in EMI can be achieved using PCB ground (or VDD) planes and also by using

passive LC components to filter the Class D switching waveform. When passive filtering is used, low

ESR components should be chosen in order to minimise the series resistance between the WM1811A

and the speaker, maximising the power 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 can also be used. These should be positioned

as close to the device as possible.

These techniques for EMI reduction are illustrated in Figure 97.

SPKP

SPKN

EMI

SPKP

SPKN

SPKP

SPKN

LOW ESR

SPKP

SPKN

SPKP

SPKN

Long, exposed tracks emit EMI

Short connection wires will reduce EMI emission

Shielding using PCB ground (or VDD)

planes will reduce EMI emission

LC filtering will reduce EMI emission

up to around 30MHz

Ferrite beads will reduce EMI emission

at frequencies above 30MHz.

Figure 97 EMI Reduction Techniques

WM1811A Datasheet(PDF) 324 Page - Wolfson Microelectronics plc

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