WM8978GEFLSLASHV datasheet(20/78 Pages) WOLFSON

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WM8978

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PP Rev 1.7 January 2005

AUXILLIARY INPUTS

There are two auxilliary inputs, AUXL and AUXR which can be used for a variety of purposes such

as stereo line inputs or as a ‘beep’ input signal to be mixed with the outputs.

The AUXL/R inputs can be used as a line input to the input BOOST stage which has gain adjust of -

12dB to +6dB in 3dB steps (plus off). See the INPUT BOOST section for further details.

The AUXL/R inputs can also be mixed into the output channel mixers, with a gain of -15dB to +6dB

plus off.

In addition the AUXR input can be summed into the Right speaker output path (ROUT2) with a gain

adjust of -15 to +6dB. This allows a ‘beep’ input to be output on the speaker outputs only without

affecting the headphone or lineout signals.

INPUT BOOST

Each of the stereo input PGA stages is followed by an input BOOST circuit. The input BOOST

circuit has 3 selectable inputs: the input microphone PGA output, the AUX amplifier output and the

L2/R2 input pin (can be used as a line input, bypassing the input PGA). These three inputs can be

mixed together and have individual gain boost/adjust as shown in Figure 7.

Figure 7 Input Boost Stage

The input PGA paths can have a +20dB boost (PGABOOSTL/R=1) , a 0dB pass through

(PGABOOSTL/R=0) or be completely isolated from the input boost circuit (INPPGAMUTEL/R=1).

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