WM8988 datasheet(53/56 Pages) WOLFSON

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Production Data

WM8988

PD, Rev 4.0, October 2008

LINE INPUT CONFIGURATION

When LINPUT1/RINPUT1 or LINPUT2/RINPUT2 are used as line inputs, the microphone boost and

ALC functions should normally be disabled.

In order to avoid clipping, the user must ensure that the input signal does not exceed AVDD. This

may require a potential divider circuit in some applications. It is also recommended to remove RF

interference picked up on any cables using a simple first-order RC filter, as high-frequency

components in the input signal may otherwise cause aliasing distortion in the audio band. AC signals

with no DC bias should be fed to the WM8988 through a DC blocking capacitor, e.g. 1

µF.

HEADPHONE OUTPUT CONFIGURATION

Analogue outputs LOUT1/ROUT1 and LOUT2/ROUT2, can drive a 16

Ω or 32Ω headphone load, as

shown in Figure 45.

Figure 45 Recommended Headphone Output Configurations

The DC blocking capacitors C1 and C2 and the load resistance together determine the lower cut-off

frequency, fc. Increasing the capacitance lowers fc, improving the bass response. Smaller

capacitance values will diminish the bass response. Assuming a 16 Ohm load and C1, C2 = 220

µF:

fc = 1 / 2

π RLC1 = 1 / (2π x 16Ω x 220µF) = 45 Hz

LINE OUTPUT CONFIGURATION

The analogue outputs, LOUT1/ROUT1 and LOUT2/ROUT2, can be used as line outputs.

Recommended external components are shown below.

Figure 46 Recommended Circuit for Line Output

The DC blocking capacitors and the load resistance together determine the lower cut-off frequency,

fc. Assuming a 10 kΩ load and C1, C2 = 1

µF:

fc = 1 / 2

π (RL+R1) C1 = 1 / (2π x 10.1kΩ x 1µF) = 16 Hz

Increasing the capacitance lowers fc, improving the bass response. Smaller values of C1 and C2 will

diminish the bass response. The function of R1 and R2 is to protect the line outputs from damage

when used improperly.

WM8988 Datasheet(PDF) 53 Page - Wolfson Microelectronics plc