WM8783 Datasheet, PDF (14/17 Pages) Wolfson Microelectronics plc – Stereo Low Power 96kHz ADC

WM8783
Production Data
APPLICATIONS INFORMATION
RECOMMENDED EXTERNAL COMPONENTS
AUDIO INPUT PATHS
The WM8783 provides 2 analogue audio inputs. Each of these inputs is referenced to the internal DC
reference, VMID. A DC blocking capacitor is required for each input pin. The choice of capacitor is
determined by the filter that is formed between that capacitor and the input impedance of the input
pin. The circuit is illustrated in Figure 9.
Figure 9 Audio Input Path DC Blocking Capacitor
The input impedance is noted in the “Electrical Characteristics”. It is recommended that an input
capacitor is selected such that the Fc cut-off frequency is less than 20Hz.
It is recommended that a 1μF capacitance is used for all WM8783 input connections. Tantalum
electrolytic capacitors are particularly suitable as they offer high stability in a small package size.
See Wolfson Applications Note WAN_0176 for further guidance on the choice of capacitor types.
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 WM8783, 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 WM8783 are listed below in Table 2.
POWER SUPPLY
DECOUPLING CAPACITOR
AVDD
4.7μF ceramic
VMIDC
4.7μF ceramic
Table 2 Power Supply Decoupling Capacitors
All decoupling capacitors should be placed as close as possible to the WM8783 device.
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PD, August 2010, Rev 4.0
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