wm8988 Wolfson Microelectronics plc, wm8988 Datasheet - Page 53

• Manufacturer Part Number: wm8988
• Description: Stereo Codec For Portable Audio Applications
• Manufacturer: Wolfson Microelectronics plc

Production Data
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LINE INPUT CONFIGURATION
HEADPHONE OUTPUT CONFIGURATION
LINE OUTPUT 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. 1µF.
Analogue outputs LOUT1/ROUT1 and LOUT2/ROUT2, can drive a 16Ω 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, f
capacitance values will diminish the bass response. Assuming a 16 Ohm load and C1, C2 = 220µF:
f
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,
f
f
Increasing the capacitance lowers f
diminish the bass response. The function of R1 and R2 is to protect the line outputs from damage
when used improperly.
c
c
c
. Assuming a 10 kΩ load and C1, C2 = 1µF:
= 1 / 2π R
= 1 / 2π (R
L
L
C
c
+R
. Increasing the capacitance lowers f
1
= 1 / (2π x 16Ω x 220µF) = 45 Hz
1
) C
1
= 1 / (2π x 10.1kΩ x 1µF) = 16 Hz
c
, improving the bass response. Smaller values of C1 and C2 will
c
, improving the bass response. Smaller
PD, Rev 4.0, October 2008
WM8988
53