WM8788

Preliminary Technical Data

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PTD, December 2010, Rev 2.2

18

APPLICATIONS INFORMATION

RECOMMENDED EXTERNAL COMPONENTS

AUDIO INPUT PATHS

The WM8788 provides 2 analogue audio inputs. The maximum analogue input signal level varies

with AVDD and with the input circuit configuration, as described in the following equation:

Ω.

For 1Vrms (0dBV) maximum input signal level when AVDD = 3.3V, the recommended input

For 2Vrms (6dBV) maximum input signal level when AVDD = 3.3V, the recommended input

The input pins INL and INR are referenced to the internal DC reference, VMID. A DC blocking

capacitor is required for each input. The choice of capacitor is determined by the filter that is formed

Figure 14 Input Signal Path External Components

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 4.7

μF capacitance is used for all WM8788 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.