wm8987 Wolfson Microelectronics plc, wm8987 Datasheet - Page 56

• Manufacturer Part Number: wm8987
• Description: Stereo Codec For Portable Audio Applications
• Manufacturer: Wolfson Microelectronics plc

WM8987L
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MICROPHONE INPUT CONFIGURATION
Figure 48 Driving single-ended headphones without DC-blocking capacitors
It requires the following register settings:
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As the OUT3 pin produces a DC voltage of AVDD/2 (=VREF), there is no DC offset between
LOUT2/ROUT2 and OUT3, and therefore no DC blocking capacitors are required. This saves space
and material cost in portable applications. However, compared to the single-ended configuration
using capacitors, the WM8987L power consumption is higher, due to the additional power consumed
in the OUT3 driver.
It is recommended to connect the capless headphone outputs only to headphones, and not to the
line input of another system. Although the built-in thermal shutdown circuit will prevent any damage
to the headphone outputs, such a connection may be noisy, and may not function properly if the
other system is grounded.
Figure 49 Recommended Circuit for Line Input
MICROPHONE
Set only the LOUT2, ROUT2 and OUT3 bits in R26 to ‘1’ to enable LOUT2, ROUT2,
OUT3 and the associated mixers. The ROUT1 and MONO bits should remain at ‘0’.
Set LD2LO (R34) and RD2RO (R37) to ‘1’ to enable the correct audio paths (in the case
of audio playback from an analogue source, select the input pin using LMIXSEL and
RMIXSEL, and set LI2LO/RI2RO instead of LD2LO/RD2RO).
Leave OUT3SW = 0 in R24, so that the potential at OUT3 is the same as VREF.
Leave ROUT2INV = 0 in R24, so that the right-channel signal going to ROUT2 is not
inverted.
The left channel volume is controlled by LOUT2VOL.
The right channel volume is controlled by ROUT2VOL.
FROM
AGND
47kOhm
R2
AGND
R1
680 Ohm to 2.2kOhm
check microphone's specification
AGND
220pF
C1
1uF
C2
MICBIAS
LINPUT1/2
RINPUT1/2
PD Rev 4.0 August 2008
Production Data
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