Production Data
WM8945
100 uF
100 uF
SPKOUTL
32 ohm
load
SPKOUTR
GND
GND = 0V
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
4.7F ceramic
LDOVOUT
VMIDC
2.2F ceramic
4.7F 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.
PD, May 2011, Rev 4.1
163
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WOLFSON [ WOLFSON MICROELECTRONICS PLC ]
