
SSM2380
Rev. A | Page 17 of 32
Attack Time, Hold Time, and Release Time
When the amplifier input signal exceeds a preset threshold,
the ALC reduces amplifier gain rapidly until the output voltage
settles to a target level. This target level is maintained for a certain
period. If the input voltage does not exceed the threshold again,
the ALC increases the gain gradually.
The attack time is the time taken to reduce the gain from maxi-
mum to minimum. The hold time is the time that the reduced
gain is maintained. The release time is the time taken to increase
the gain from minimum to maximum. These times are shown
Table 9. Attack, Hold, and Release Times for I2C Control Mode
Duration
Attack Time
32 μs to 4 ms (per 0.5 dB step)
Hold Time
90 ms to 120 ms
Release Time
4 ms to 512 ms (per 0.5 dB step)
1 The attack time and release time can be adjusted using the I2C interface.
The hold time cannot be adjusted.
Soft-Knee Compression
Often performed using sophisticated DSP algorithms, soft-knee
compression provides maximum sound quality with effective
speaker protection. Instead of using a fixed compression setting
prior to limiting, the SSM2380 allows for a much more subtle
transition into limiting mode, preserving the original sound
various soft-knee compression settings. If desired, compression
can be disabled. When compression is disabled, the part operates
in limiter-only mode.
0
0.5
1.0
1.5
2.0
2.5
0
0.05
0.10 0.15 0.20
0.30 0.35
0.40
0.45
0.25
0.50
INPUT VOLTAGE (V)
O
UT
P
UT
V
O
L
T
AG
E
(
V
)
08
75
2-
00
7
00 (LIMITER MODE)
01 (COMPRESSION MODE 1)
10 (COMPRESSION MODE 2)
11 (COMPRESSION MODE 3)
2.5V × 0.77 = 1.925V
Figure 38. Adjustable Compression Settings, VDD = 2.5 V,
ALC Threshold Level = 77%
0
0.5
1.5
2.0
2.5
1.0
3.0
3.5
0
0.1
0.2
0.3
0.4
0.6
0.7
0.8
0.9
0.5
1.0
INPUT VOLTAGE (V)
OU
T
P
U
T
V
O
LT
A
G
E
(
V
)
08
75
2-
018
00 (LIMITER MODE)
01 (COMPRESSION MODE 1)
10 (COMPRESSION MODE 2)
11 (COMPRESSION MODE 3)
3.6V × 0.77 = 2.772V
Figure 39. Adjustable Compression Settings, VDD = 3.6 V,
ALC Threshold Level = 77%
0
0.5
1.5
2.0
2.5
1.0
3.0
4.0
3.5
4.5
0
0.2
0.4
0.6
0.8
1.2
1.4
1.6
1.8
1.0
2.0
INPUT VOLTAGE (V)
OU
T
P
U
T
V
O
LT
A
G
E
(
V
)
08
75
2-
019
00 (LIMITER MODE)
01 (COMPRESSION MODE 1)
10 (COMPRESSION MODE 2)
11 (COMPRESSION MODE 3)
5.0V × 0.77 = 3.85V
Figure 40. Adjustable Compression Setting, VDD = 5.0 V,
ALC Threshold Level = 77%
ALC Soft Transition
The ALC operation of the SSM2380 incorporates techniques to
reduce the audible artifacts associated with gain change transi-
tions. First, the gain is changed in small increments of 0.5 dB.
In addition to this small step size, the rate of gain change is
reduced, proportional to the attack time setting. This feature
drastically reduces and virtually eliminates the presence of zipper
noise and other artifacts associated with gain transitions during
ALC operation.
Figure 41 shows the soft transition operation.
08
75
2-
008
SOFT TRANSITION (32s TO 256s)
NORMAL TRANSITION
0.5dB
Figure 41. Soft Transition