
ASAHI KASEI
[AK4632]
MS0396-E-00
2005/06
- 38 -
SPK-ALC Operation
The ALC (Automatic Level Control) operation of speaker output is done by ALC2 block when ALC2 bit is
“
1
”
. Input
resistance of the ALC2 is 24k
(typ) and centered around VCOM voltage. The ALC2 level diagram is shown in Figure
37
~
Figure 40.
The limiter detection level is proportional to SVDD voltage. The output level is limited by the ALC2 circuit when the
input signal exceeds –7.1dBV (@SPKG1 bit =
“
0
”
, SVDD=3.3V or @SPKG1 bit =
“
1
”
, SVDD = 5V). When a
continuous signal of –7.1dBV or greater is input to the ALC2 circuit, the change period of the ALC2 limiter operation is
250
μ
s (=2/fs@fs=8kHz) and the attenuation level is 0.5dB/step.
The ALC2 recovery operation uses zero crossings and gains of 1dB/step. The ALC2 recovery operation is done until the
input level of the Speaker-amp goes to –9.1dBV (@SPKG1 bit =
“
0
”
, SVDD=3.3V or @SPKG1 bit =
“
1
”
, SVDD = 5V).
Maximum gain of the ALC2 recovery operation is set by RFS5-0 bits.
When the input signal is between –9.1dBV and –7.1dBV, the ALC2 limiter or recovery operations are not done.
When the PMSPK bit changes from
“
0
”
to
“
1
”
, the initilization cycle (512/fs = 64ms @fs=8kHz at ROTM bit =
“
0
”
) starts.
The ALC2 is disabled (The ALC2 gain is fixed to
“
-3.5dB
”
.) during the initilization cycle and the ALC2 starts from
“
–2dB
”
after completing the initilization cycle. The ROTM bit and RFS5-0 bits set during the PMSPK bit =
“
0
”
.
When the ALC2 is disable, a gain of the ALC2 block is fixed to -3.5dB. Therefore, a gain of internal speaker block is
shown in Table 22.
Parameter
ALC2 Limiter operation
Operation Start Level
5.2dBV
fs=8kHz
2/fs = 250
μ
s
Period
fs=16kHz
2/fs = 125
μ
s
Zero-crossing Detection
No
ATT/GAIN
0.5dB step
Table 21. Limiter /Recovery of ALC2 (ROTM bit =
“
0
”
)
SPKG1-0 bits
00
01
10
11
Table 22. Gain of Speaker-Amp at ALC2 OFF(Full-differential Output)
ALC2 Recovery operation
7.2dBV
512/fs=64ms
512/fs=32ms
Yes (Timeout = Period Time)
1dB step
Gain
+4.4dB
+6.4dB
+10.6dB
+12.7dB