WM8944BECSSLASHR datasheet(159/165 Pages) CIRRUS

159 / 165 page

WM8944B

Rev 4.3

159

BTL SPEAKER OUTPUT CONNECTION

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

connected directly across the SPKOUTP and SPKOUTN 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 WM8944B, 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 WM8944B are listed below in Table 73.

POWER SUPPLY

DECOUPLING CAPACITOR

DCVDD, DBVDD, LDOVDD, SPKVDD

4.7

F ceramic

LDOVOUT

2.2

F ceramic

VMIDC

4.7

F ceramic

Table 73 Power Supply Decoupling Capacitors

All decoupling capacitors should be placed as close as possible to the WM8944B 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 WM8944B.

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 WM8944B.

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.

WM8944BECS/R 数据表(PDF) 159 Page - Cirrus Logic

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WM8944BECS/R 数据表(PDF) 159 Page - Cirrus Logic

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