WM9090ECSSLASHR datasheet(79/81 Pages) WOLFSON

79 / 81 page

Production Data

WM9090

PD, November 2010, Rev 4.1

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 WM9090

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 WM9090

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 WM9090

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 21.

Figure 21 EMI Reduction Techniques

WM9090ECS/R 数据表(PDF) 79 Page - Wolfson Microelectronics plc