SA572 Datasheet, PDF (9/12 Pages) NXP Semiconductors – Programmable analog compandor

SA572
C₁₊
2.2 mF
R_X
R₁
3.3k
ATTACK
CAP
+
C_A 1 mF
3, 13
4, 12
2, 14
BUFFER
RECOVERY
CAP
+
C_R 10 mF
R₄
100k
5, 11
6.8k
D
G ^R2
C₂
7, 9 ⁺
2.2 mF
R_DC1
9.1k
R_DC2
+
9.1k
C_DC
10 mF
C₃₊
V_IN
2.2 mF
TO THD
TRIM PIN
OF 572
PINS 6, 10
R₃
17.3k
R₅
1k
V+
2
−
3 ⁵⁵³²
+
+
C₅ 22 mF
V−
1 VOUT DC
+
2.2 mF
V_OUT
Figure 9. Automatic Level Control
Automatic Level Control (ALC)
In the ALC configuration, the variable gain cell is placed
in the feedback loop of the operational amplifier and the
rectifier is connected to the input. As the input amplitude
increases above the crossover point, the overall system
gain decreases proportionally, holding the output
amplitude constant. As the input amplitude decreases
below the crossover point, the overall system gain
increases proportionally, holding the output amplitude at
the same constant level.
Gain
+
2
R1 R2 I1
R3 VIN(avg)
where:
R₁ = 6.8 kW (Internal)
R₂ = 3.3 kW
R₃ = 17.3 kW
I₁ = 140 mA
The output DC level can be set using the following
equation:
ǒ Ǔ V_OUT DC +
1
)
R_DC1
)
R₄
R_DC2
V _REF
where:
R₄ = 100 kW
R_DC1 = R_DC2 = 9.1 kW
V_REF = 2.5 V
The output level is calculated using the following
equation:
ǒ Ǔ VOUT_LEVEL
+
R1
2
R2
R3
I1
VIN
VIN (avg)
where:
R₁ = 6.8 kW (Internal)
R₂ = 3.3 kW
R₃ = 17.3 kW
I₁ = 140 mA
VIN
VIN (avg)
+
p
2 ^Ǹ2
+
1.11
(for
sine
waves)
Note that for very low input levels, ALC may not be
desired and to limit the maximum gain, resistor R_X has
been added.
Gain
max.
+
ǒ Ǔ R1)Rx
VREF
2
· R2
R3
·
IB
Rx ^ ((desired max gain) 26 kW) * 10 kW
http://onsemi.com
9