Datasheet

(1)
(1) Decay hold time, (2) Slow Decay, (3) Quick Attack
(2)
(3)
12 dB
10 dB
14 dB
12 dB
signal below target
attack
decay
microphone gain
target level
signal above target
peak detection
and ADC output
LM49350, LM49350RLEVAL
SNAS359D –SEPTEMBER 2008–REVISED JUNE 2012 www.ti.com
signal amplitude instantaneously, but tracks decreases in audio input signal amplitude at programmable rate
(PEAK DECAY TIME). ATTACK RATE, DECAY RATE, HOLD TIME, and PEAK DECAY TIME are fully
adjustable which allows flexible operation of the ALC circuit. The ALC’s timers are based on the sample rate of
the DAC or ADC, so the closest corresponding sample rate must be programmed into the ALC SAMPLE RATE
setting (for DAC ALC) or the ALC MODE setting (for ADC ALC).
Figure 65. ALC Example
Table 49. ADC_ALC_1 (0x81h)
Bits Field Description
2:0 SAMPLE_RATE This programs the timers on the ALC with the closest sample rate of the ADC.
SAMPLE_RATE ADC Fs
000 8kHz
001 12kHz
010 16kHz
011 24kHz
100 32kHz
101 48kHz
110 96kHz
111 192kHz
3 LIMITER If set, the circuit will never apply gain to the signal, no matter how small, but it will attenuate the signal
as soon as it reaches target and release it at the decay rate, once signal level reduces below target.
The I
2
C gain setting (at the time the LIMITER is enabled) is the maximum gain that the ALC will apply.
Care should be taken when choosing the optimum I
2
C gain setting whenever enabling the Limiter.
4 STEREO LINK If set, the ALC circuit uses the stereo average of the input signals to control the gain of the stereo
output. This maintains stereo imaging. If this bit is cleared, then both channels operate as dual mono.
5 SOURCE_SEL If SOURCE_OVR is set then this manually overrides the selection of the input amplifier that is used to
alter the gain for ALC operation.
0 = Both ALCs control AUX gain
1 = Both ALCs control MIC gain
6 SOURCE_OVR If set, the output of the ALC is not set automatically but is controlled by the SOURCE_SEL bit. If
cleared each ALC controls the input gain of the amplifier (AUX or MIC) that is set to that ADC channel
(or MIC if both are selected).
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