Production Data

WM9082

w

PD, August 2012, Rev 4.1

17

APPLICATIONS INFORMATION

RECOMMENDED EXTERNAL COMPONENTS

POWER SUPPLY DECOUPLING

Electrical coupling exists particularly in digital logic systems where switching in one sub-system

causes fluctuations on the power supply. This effect occurs because the inductance of the power

supply acts in opposition to the changes in current flow that are caused by the logic switching. The

resultant variations (or ‘spikes’) in the power supply voltage can cause malfunctions and unintentional

behaviour in other components. A decoupling (or ‘bypass’) capacitor can be used as an energy

storage component which will provide power to the decoupled circuit for the duration of these power

supply variations, protecting it from malfunctions that could otherwise arise.

Coupling also occurs in a lower-frequency form when ripple is present on the power supply rail

caused by changes in the load current or by limitations of the power supply regulation method. In

audio components such as the WM9082, these variations can alter the performance of the signal

path, leading to degradation in signal quality. A decoupling (or ‘bypass’) capacitor can be used to filter

these effects, by presenting the ripple voltage with a low impedance path that does not affect the

circuit to be decoupled.

These coupling effects are addressed by placing a capacitor between the supply rail and the

corresponding ground reference. In the case of systems comprising multiple power supply rails,

decoupling should be provided on each rail.

The recommended power supply decoupling capacitors for WM9082 are listed below in Table 9.

POWER SUPPLY

DECOUPLING CAPACITOR

DVDD

0.1

F ceramic

SPKVDD

4.7

F ceramic

Table 9 Power Supply Decoupling Capacitors

All decoupling capacitors should be placed as close as possible to the WM9082 device.

Due to the wide tolerance of many types of ceramic capacitors, care must be taken to ensure that the

selected components provide the required capacitance across the required temperature and voltage

ranges in the intended application. For most application the use of ceramic capacitors with capacitor

dielectric X5R is recommended.

CLASS D SPEAKER CONNECTIONS

The WM9082 incorporates a Class D speaker driver, which offers high amplifier efficiency at large

signal levels. As the Class D output is a sigma-delta modulated signal, the choice of speakers and

tracking of signals is important for ensuring good performance and reducing EMI.

The efficiency of the speaker drivers is affected by the series resistance between the WM9082 and

the speaker (e.g. PCB track loss and inductor ESR) as shown in Figure 4. This resistance should be

as low as possible to maximise efficiency.