Datasheet
LM49370
SNAS356D –FEBRUARY 2007–REVISED MARCH 2012
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Table 15. AGC_2 (0x09h) (continued)
Bits Field Description
7 AGC_TIGHT If set, the AGC algorithm controls the microphone preamplifier more exactly.
(1)
AGC_TIGHT = 0 AGC_TARGET Min Level Max Level
000
2
−6 dB −3 dB
001
2
−8 dB −4 dB
010
2
−10 dB −5 dB
011
2
−12 dB −6 dB
100
2
−14 dB −7 dB
101
2
−16 dB −8 dB
110
2
−18 dB −9 dB
111
2
−20 dB −10 dB
AGC_TIGHT = 1 000
2
−6 dB −3 dB
001
2
−8 dB −5 dB
010
2
−10 dB −7 dB
011
2
−12 dB −9 dB
100
2
−14 dB −11 dB
101
2
−16 dB −13 dB
110
2
−18 dB −15 dB
111
2
−20 dB −17 dB
(1) The AGC can be used to control the analog path of the microphone to the output stages or to optimize the microphone path for
recording on the ADC. When the analog path is used this bit should be set to ensure the target is tightly adhered to. If the ADC is the
only destination of the microphone or the desired analog mixer level is line level then AGC_TIGHT should be cleared, allowing greater
dynamic rage of the recorded signal. For further details see the AGC Overview.
AGC_3 CONFIGURATION REGISTER
This register is used to control the LM49370's Automatic Gain Control.
(2)
Table 16. AGC_3 (0x0Ah)
Bits Field Description
4:0 AGC_HOLDTIME This programs the amount of delay before the AGC algorithm begins to adjust the gain of the microphone
preamplifier.
AGC_HOLDTIME No. of speech segments
00000
2
0
00001
2
1
00010
2
2
00011
2
3
00100
2
to 11100
2
4 to 28
11101
2
29
11110
2
30
11111
2
31
(2) See the AGC Overview.
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