WM8987LGECOSLASHV datasheet(55/58 Pages) WOLFSON

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Pre-Production

WM8987L

PP Rev 3.0 January 2007

Figure 48 Driving single-ended headphones without DC-blocking capacitors

It requires the following register settings:

•

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.

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 short circuit protection 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.

MICROPHONE INPUT CONFIGURATION

Figure 49 Recommended Circuit for Line Input

47kOhm

220pF

1uF

AGND

LINPUT1/2

RINPUT1/2

FROM

MICROPHONE

680 Ohm to 2.2kOhm

check microphone's specification

MICBIAS

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