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| FAB2200 Datasheet, PDF (16/33 Pages) Fairchild Semiconductor – Audio Subsystem with Stereo Class-G Headphone Amplifier and 1.2W Mono Class-D Speaker Amplifier | |||
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Table 9.
THMAX
[3:0]
0000
0001
0010
0011
0100
0101
0110
0111
THMAX Threshold
Maximum
Output
Threshold
(Vpk)
Maximum Power with
Sine Wave and 8ï
Load (mW)
THMAX Threshold Disabled
2.2
302.5
2.4
360.0
2.6
422.5
2.8
490.0
3.0
562.5
3.2
640.0
3.4
722.5
THMAX
[3:0]
1000
1001
1010
1011
1100
1101
1110
1111
Maximum
Output
Threshold
(Vpk)
3.6
3.8
4.0
4.2
4.4
4.6
4.8
5.0
Maximum Power
with Sine Wave and
8ï Load (mW)
810.0
902.5
1000.0
1102.5
1210.0
1322.5
1440.0
1562.5
THVBATT limits the amount of clipping allowed by the
AGC. As VBATT falls, the maximum output amplitude
falls. THVBATT defines the threshold as a fraction of the
VBATT supply voltage. When the fraction is less than 1,
the AGC attempts to adjust gain to prevent clipping. For
values greater than 1, some clipping is allowed before
the AGC reduces gain (see Table 10).
Table 10. THVBATT Threshold
THVBATT [4:0]
VBATT Fraction
(V/V)
THD with 1KHz
Sine Wave (%)
(VBATT=3.7V,
8ï Load)
THVBATT [4:0]
VBATT Fraction
(V/V)
THD with 1KHz
Sine Wave (%)
(VBATT=3.7V,
8ï Load)
0000
THVBATT Threshold Disabled
1000
1.25
13.0
0001
0.90
1.0
1001
1.30
14.4
0010
0.95
3.0
1010
1.35
15.6
0011
1.00
4.9
1011
1.40
16.7
0100
1.05
6.7
1100
1.45
17.7
0101
1.10
8.5
1101
1.50
18.7
0110
1.15
10.0
1110
1.55
19.6
0111
1.20
11.6
1111
1.60
20.5
Ultimately, the AGC threshold is whichever voltage is
5.0
lower between THVBATT and THMAX. For example, if
THMAX = 0111, THVBATT = 0001, and VBATT = 4.2V,
the AGC threshold is 3.4V as defined by THMAX. If
4 .5
VBATT falls to 3.6V, the AGC threshold falls to 3.24V as
defined by THVBATT (see Figure 21). If THVBATT and
4.0
THMAX are both set to 0, the AGC is disabled.
3 .5
THVBATT
AGC Threshold
© 2009 Fairchild Semiconductor Corporation
FAB2200 ⢠Rev. 1.0.1
3.0
AGC Threshold
2 .5
2.0
THMAX
2 .5
3.0
3 .5
4.0
4 .5
5.0
5 .5
VBATT (V)
Figure 21. AGC Threshold, THMAX = 0111,
THVBATT = 0001
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