LM49370_08 Datasheet, PDF (36/100 Pages) National Semiconductor (TI) – Audio Sub-System with an Ultra Low EMI, Spread Spectrum, Class D Loudspeaker Amplifier, a Dual-Mode

12.16 MIC_1 CONFIGURATION REGISTER
This register is used to control the microphone configuration.
TABLE 17. MIC_1 (0x0Bh)
Bits
Field
Description
3:0 PREAMP_GAIN This programs the gain applied to the microphone preamplifier if the AGC is not in use.
PREAMP_GAIN
Gain
0000₂
0001₂
0010₂
0011₂
0100₂ to 1100₂
1101₂
1110₂
1111₂
4
MIC_MUTE If set, the microphone preamplifier is muted.
6 dB
8 dB
10 dB
12 dB
14 dB to 30 dB
32 dB
34 dB
36 dB
5
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.
6
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 20)
Note 20: 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 for a 1 µF 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.
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