FAB2200 Datasheet, PDF (18/33 Pages) Fairchild Semiconductor – Audio Subsystem with Stereo Class-G Headphone Amplifier and 1.2W Mono Class-D Speaker Amplifier

AGC Attack
AGC attack occurs when the AGC determines that, after
applying present gain, the output signal amplitude would
be too high and gain should be stepped down by 1dB.
The AGC checks an approximation of the amplitude of
the output signal that includes present gain, but
excludes clipping that may occur in the final output
stage. All of the following conditions must be true to
trigger an AGC attack:
 The amplitude is above the AGC threshold, AND
 Present gain is above the minimum gain point, AND
 Attack speed is not exceeded.
The minimum gain is determined by the AGCMIN
register. The rate of gain reduction is determined by the
AGCATTACK register.
AGC Release
When the output signal is below the AGC threshold,
gain is stepped up by 1dB. The rate of gain increase is
determined by the AGCRELEASE registers. Gain is
increased until it reaches the starting gain or an AGC
attack is triggered again.
Table 12. AGC Attack Speed
AGCATTACK [2:0] AGC Attack Speed (µs/Step) AGCATTACK [2:0] AGC Attack Speed (µs/Step)
000
12.5
100
200
001
25.0
101
400
010
50.0
110
800
011
100.0
111
1600
Table 13. AGC Release Speed
AGCRELEASE [2:0]
AGC Release Speed
(ms/Step)
000
12.5
001
25.0
010
50.0
011
100.0
AGCRELEASE [2:0]
100
101
110
111
AGC Release Speed
(ms/Step)
200
400
800
1600
© 2009 Fairchild Semiconductor Corporation
FAB2200 • Rev. 1.0.1
18
www.fairchildsemi.com