Preliminary Technical Data

WM8788

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PTD, December 2010, Rev 2.2

19

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 WM8788, 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 WM8788 are listed below in Table 5.

POWER SUPPLY

DECOUPLING CAPACITOR

AVDD

4.7

μF ceramic

REFVDD

4.7

μF ceramic

VMIDC

4.7

μF ceramic

Table 5 Power Supply Decoupling Capacitors

All decoupling capacitors should be placed as close as possible to the WM8788 device.

The VMIDC capacitor is not, technically, a decoupling capacitor. However, it does serve a similar

purpose in filtering noise on the VMID reference. The connection between GND, the VMID

decoupling capacitor and the main system ground should be made at a single point as close as

possible to the GND pin of the WM8788.

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.

See Wolfson Applications Note WAN_0176 for further guidance on the choice of capacitor types.

RECOMMENDED EXTERNAL COMPONENTS DIAGRAM

Figure 15 provides a summary of recommended external components for WM8788. Note that the

actual requirements may differ according to the specific target application.

Figure 15 WM8788 Recommended External Components Diagram