WM8978CGEFLSLASHV datasheet(28/118 Pages) WOLFSON

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WM8978

Production Data

PD, Rev 4.5, October 2011

AUXILIARY INPUTS

There are two auxiliary 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 14.

Figure 14 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).

ADDRESS

BIT

LABEL

DEFAULT

DESCRIPTION

R47

Left Input

BOOST

control

PGABOOSTL

Boost enable for left channel input

PGA:

0 = PGA output has +0dB gain through

input BOOST stage.

1 = PGA output has +20dB gain

through input BOOST stage.

R48

Right Input

BOOST

control

PGABOOSTR

Boost enable for right channel input

PGA:

0 = PGA output has +0dB gain through

input BOOST stage.

1 = PGA output has +20dB gain

through input BOOST stage.

Table 7 Input BOOST Stage Control

The Auxilliary amplifier path to the BOOST stages is controlled by the AUXL2BOOSTVOL[2:0] and

AUXR2BOOSTVOL[2:0] register bits. When AUXL2BOOSTVOL/AUXR2BOOSTVOL=000 this path

is completely disconnected from the BOOST stage. Settings 001 through to 111 control the gain in

3dB steps from -12dB to +6dB.

The L2/R2 path to the BOOST stage is controlled by the LIP2BOOSTVOL[2:0] and the

RIP2BOOSTVOL[2:0] register bits. When L2_2BOOSTVOL/R2_2BOOSTVOL=000 the L2/R2 input

pin is completely disconnected from the BOOST stage. Settings 001 through to 111 control the gain

in 3dB steps from -12dB to +6dB.

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