LM4935 datasheet(37/112 Pages) NSC

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12.0 Status & Control Registers (Continued)

12.16 MIC_1 CONFIGURATION REGISTER

This register is used to control the microphone configuration.

TABLE 16. MIC_1 (0x0Bh)

Bits

Field

Description

3:0

PREAMP_GAIN

Programs the gain applied to the microphone preamplifier if the AGC is not in use.

PREAMP_GAIN

Gain

0000

6dB

0001

8dB

0010

10 dB

0011

12 dB

0100

2 to 11002

14 dB to 30 dB

1101

32 dB

1110

34 dB

1111

36 dB

MIC_MUTE

If set the microphone preamplifier is muted.

INT_SE_DIFF

If set the internal microphone is assumed to be single ended and the negative connection is

connected to the ADC common mode point internally. This allows a single-ended internal

microphone to be used.

INT_EXT

If set the single ended external microphone is used and the negative microphone input is grounded

internally, otherwise internal microphone operation is assumed. (Note 19)

Note 19: On changing INT_EXT from internal to external note that the dc blocking cap will not be charged so some time should be taken (300 ms fora1µF cap)

between the detection of an external headset and the switching of the output stages and ADC to that input to allow the DC points on either side of this cap to stabilize.

This can be accomplished by deselecting the microphone input from the audio outputs and ADC until the DC points stabilize.

An active MIC path to CPOUT or the ADC may result in the microphone DC blocking caps causing audio pops under the following situations:

1) Switching between internal and external microphone operation while in chip modes ’10’ or ’11’.

2) Toggling in and out of powerdown/standby modes.

3) Toggling between chip modes ’10’ and ’11’ whenever external microphone operation is selected.

4) The insertion/removal of a headset while in chip modes ’10’ or ’11’ whenever external microphone operation is selected.

To avoid these potential pop issues, it is recommended to deselect the microphone input from CPOUT and ADC until the DC points stabilize.

LM4935 Datasheet(PDF) 37 Page - National Semiconductor (TI)

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