WM8945ECSSLASHR datasheet(163/169 Pages) WOLFSON

163 / 169 page

Production Data

WM8945

PD, May 2011, Rev 4.1

163

GND = 0V

SPKOUTL

SPKOUTR

GND

100 uF

32 ohm

load

Figure 60 DC-blocking Components for Headphone Output

BTL SPEAKER OUTPUT CONNECTION

The BTL speaker output connection is a differential mode of operation. The loudspeaker may be

connected directly across the SPKOUTL and SPKOUTR pins. No additional external components are

required in this case.

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 WM8945, 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 WM8945 are listed below in Table 72.

POWER SUPPLY

DECOUPLING CAPACITOR

DCVDD, DBVDD, LDOVDD, SPKVDD

4.7

F ceramic

LDOVOUT

2.2

F ceramic

VMIDC

4.7

F ceramic

Table 72 Power Supply Decoupling Capacitors

All decoupling capacitors should be placed as close as possible to the WM8945 device. The

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

be made at a single point as close as possible to the GND ball of the WM8945.

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 ball of the WM8945.

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