WM9090ECSSLASHR datasheet(76/81 Pages) WOLFSON

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WM9090

Production Data

PD, November 2010, Rev 4.1

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 behavior 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 WM9090, 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 WM9090 are listed below in Table 36.

POWER SUPPLY

DECOUPLING CAPACITOR

AVDD

2.2

μF ceramic

SPKVDD

0.1

μF ceramic (see note)

VMIDC

2.2

μF ceramic (see text below)

Table 36 Power Supply Decoupling Capacitors

Note: 0.1

μF is required with 2.2μF a guide to the total required power rail capacitance.

All decoupling capacitors should be placed as close as possible to the WM9090 device. The

connection between GND, the AVDD decoupling capacitor and the main system ground should be

made at a single point as close as possible to the GND ball of the WM9090.

The VMID 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 ball of the WM9090.

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.

HEADPHONE OUTPUT PATH

The headphone output on WM9090 is ground referenced and therefore does not require the large,

expensive capacitors necessary for VMID-referenced solutions. For best audio performance, it is

recommended to connect a zobel network to the audio output pins. This network should comprise of

a 100nF capacitor and 20ohm resistor in series with each other (see “Analogue Outputs” section).

These components have the effect of dampening high frequency oscillations or instabilities that can

arise outside the audio band under certain conditions. Possible sources of these instabilities include

the inductive load of a headphone coil or an active load in the form of an external line amplifier.

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