lm4935rlx National Semiconductor Corporation, lm4935rlx Datasheet - Page 38

• Manufacturer Part Number: lm4935rlx
• Description: Audio Sub-system With Dual-mode Stereo Headphone And Mono High Efficiency Loudspeaker Amplifiers And Multi-purpose Adc
• Manufacturer: National Semiconductor Corporation

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Bits
12.0 Status & Control Registers
12.16 MIC_1 CONFIGURATION REGISTER
This register is used to control the microphone configuration.
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 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.
3:0
4
5
6
PREAMP_GAIN
INT_SE_DIFF
MIC_MUTE
INT_EXT
Field
Programs the gain applied to the microphone preamplifier if the AGC is not in use.
If set the microphone preamplifier is muted.
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.
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)
PREAMP_GAIN
0100
0000
0001
0010
TABLE 16. MIC_1 (0x0Bh)
0011
1101
1110
1111
2
to 1100
2
2
2
2
2
2
2
(Continued)
2
38
Description
14 dB to 30 dB
10 dB
12 dB
32 dB
34 dB
36 dB
Gain
6 dB
8 dB