SA575
Low Voltage Compandor
The SA575 is a precision dual gain control circuit designed for low
voltage applications. The SA575’s channel 1 is an expandor, while
channel 2 can be configured either for expandor, compressor, or
automatic level controller (ALC) application.
Features
•
Operating Voltage Range from 3.0 V to 7.0 V
•
Reference Voltage of 100 mV
RMS
= 0 dB
•
One Dedicated Summing Op Amp Per Channel and Two Extra
•
•
•
•
•
•
•
•
•
•
•
•
•
Uncommitted Op Amps
600
W
Drive Capability
Single or Split Supply Operation
Wide Input/Output Swing Capability
Pb−Free Packages are Available*
20
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20
1
SOIC−20 WB
D SUFFIX
CASE 751D
Applications
TSSOP−20
DTB SUFFIX
CASE 948E
1
Portable Communications
Cellular Radio
Cordless Telephone
Consumer Audio
Portable Broadcast Mixers
Wireless Microphones
Modems
Electric Organs
Hearing Aids
PDIP−20
N SUFFIX
CASE 738
20
1
PIN CONNECTIONS
D* and DTB Packages
+V
IN1
-V
IN1
V
OUT1
RECT. IN1
1
2
3
4
20 V
CC
19 +V
IN2
18 -V
IN2
17 V
OUT2
16 RECT.IN2
15 C
RECT2
14 SUM OUT2
13 COMP.IN2
12 SUM NODE 2
11 GAIN CELL IN2
C
RECT1
5
SUM OUT 1
COMP. IN1
6
7
V
REF
8
GAIN CELL IN1 9
GND 10
*Available in large SOL package only.
ORDERING INFORMATION
See detailed ordering and shipping information in the package
dimensions section on page 13 of this data sheet.
*For additional information on our Pb−Free strategy and soldering details, please
download the ON Semiconductor Soldering and Mounting Techniques Reference
Manual, SOLDERRM/D.
DEVICE MARKING INFORMATION
See general marking information in the device marking
section on page 13 of this data sheet.
©
Semiconductor Components Industries, LLC, 2006
1
September, 2006 − Rev. 3
Publication Order Number:
SA575/D
SA575
MAXIMUM RATINGS
Rating
Single Supply Voltage
Voltage Applied to Any Other Pin
Operating Ambient Temperature Range
Operating Junction Temperature
Storage Temperature Range
Thermal Impedance
SOIC
TSSOP
PDIP
SOIC
TSSOP
PDIP
Symbol
V
CC
V
IN
T
A
T
J
T
STG
q
JA
Value
−0.3 to 8.0
−0.3 to (V
CC
+ 0.3)
-40 to +85
150
150
87
124
70
1116
1068
1344
Unit
V
V
°C
°C
°C
°C/W
Maximum Power Dissipation
P
D
mW
Maximum ratings are those values beyond which device damage can occur. Maximum ratings applied to the device are individual stress limit values
(not normal operating conditions) and are not valid simultaneously. If these limits are exceeded, device functional operation is not implied, damage
may occur and reliability may be affected.
temperature range: -40 to +85
°
C for SA575, except SSOP package is tested at +25°C only. V
CC
= 5.0 V, unless otherwise stated. Both
channels are tested in the Expandor mode (see Test Circuit).
Characteristic
Symbol
Test Conditions
Min
Typ
Max
DC ELECTRICAL CHARACTERISTICS
Typical values are at T
A
= 25
°
C. Minimum and Maximum values are for the full operating
Unit
FOR COMPANDOR, INCLUDING SUMMING AMPLIFIER
Supply Voltage (Note 1)
Supply Current
Reference Voltage (Note 2)
Summing Amp Output Load
Total Harmonic Distortion
Output Voltage Noise
Unity Gain Level
Output Voltage Offset
Output DC Shift
V
CC
I
CC
V
REF
R
L
THD
E
NO
0dB
V
OS
−
No Signal
V
CC
= 5.0 V
−
1.0 kHz, 0 dB, BW = 3.5 kHz
BW = 20 kHz, R
S
= 0
W
1.0 kHz
No Signal
No Signal to 0 dB
Gain Cell Input = 0 dB, 1.0 kHz
Rectifier Input = 6.0 dB, 1.0 kHz
Tracking Error Relative to 0 dB
Crosstalk
FOR OPERATIONAL AMPLIFIER
Output Swing
Output Load
Input Common-Mode Range
Common-Mode Rejection Ratio
Input Bias Current
Input Offset Voltage
Open-Loop Gain
Slew Rate
Bandwidth
Input Voltage Noise
Power Supply Rejection Ratio
V
O
R
L
CMR
CMRR
I
B
V
OS
A
VOL
SR
GBW
E
NI
PSRR
R
L
= 10 kW
1.0 kHz
−
−
V
IN
= 0.5 V to 4.5 V
−
R
L
= 10 kW
Unity Gain
Unity Gain
BW = 20 kHz
1.0 kHz, 250 mV
V
CC
-0.4
600
0
60
-1.0
−
−
−
−
−
−
V
CC
−
−
80
−
3.0
80
1.0
3.0
2.5
60
−
−
V
CC
−
1.0
−
−
−
−
−
−
V
W
V
dB
mA
mV
dB
V/ms
MHz
mV
dB
Gain Cell Input = 0 dB, 1.0 kHz
Rectifier Input = -30 dB, 1.0 kHz
1.0 kHz, 0 dB, C
REF
= 220
mF
3.0
3.0
2.4
10
−
−
-1.5
-150
-100
-1.0
-1.0
−
5.0
4.2
2.5
−
0.12
6.0
−
−
−
−
−
-80
7.0
5.5
2.6
−
1.5
30
1.5
150
100
1.0
1.0
-65
V
mA
V
kW
%
mV
dB
mV
mV
dB
dB
dB
1. Operation down to V
CC
= 2.0 V is possible, but performance is reduced. See curves in Figures 6 and 7.
2. Reference voltage, V
REF
, is typically at 1/2 V
CC
.
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SA575
Functional Description
This section describes the basic subsystems and
applications of the SA575 Compandor. More theory of
operation on compandors can be found in AND8159 and
AND8160. The typical applications of the SA575 low
voltage compandor in an Expandor (1:2), Compressor (2:1)
and Automatic Level Control (ALC) function are
explained. These three circuit configurations are shown in
Figures 2, 3, and 4 respectively.
The SA575 has two channels for a complete companding
system. The left channel, A, can be configured as a 1:2
Expandor while the right channel, B, can be configured as
either a 2:1 Compressor, a 1:2 Expandor or an ALC. Each
channel consists of the basic companding building blocks
of rectifier cell, variable gain cell, summing amplifier
and V
REF
cell. In addition, the SA575 has two additional
high performance uncommitted op amps which can be
utilized for application such as filtering, pre-emphasis/
de-emphasis or buffering.
Figure 5 shows the complete schematic for the
applications demo board. Channel A is configured as an
expandor while channel B is configured so that it can be
used either as a compressor or as an ALC circuit. The
switch, S
1
, toggles the circuit between compressor and
ALC mode. Jumpers J
1
and J
2
can be used to either include
the additional op amps for signal conditioning or exclude
them from the signal path. Bread boarding space is
provided for R
1
, R
2
, C
1
, C
2
, R
10
, R
11
, C
10
and C
11
so that
the response can be tailored for each individual need. The
components as specified are suitable for the complete
audio spectrum from 20 Hz to 20 kHz.
The most common configuration is as a unity gain
non-inverting buffer where R
1
, C
1
, C
2
, R
10
, C
10
and C
11
are
eliminated and R
2
and R
11
are shorted. Capacitors C
3
, C
5
,
C
8
, and C
12
are for DC blocking. In systems where the
inputs and outputs are AC coupled, these capacitors and
resistors can be eliminated. Capacitors C
4
and C
9
are for
setting the attack and release time constant.
C
6
is for decoupling and stabilizing the voltage reference
circuit. The value of C
6
should be such that it will offer a
very low impedance to the lowest frequencies of interest.
Too small a capacitor will allow supply ripple to modulate
the audio path. The better filtered the power supply, the
smaller this capacitor can be. R
12
provides DC reference
voltage to the amplifier of channel B. R
6
and R
7
provide a
DC feedback path for the summing amp of channel B,
while C
7
is a short-circuit to ground for signals. C
14
and C
15
are for power supply decoupling. C
14
can also be
eliminated if the power supply is well regulated with very
low noise and ripple.
Demonstrated Performance
The applications demo board was built and tested for a
frequency range of 20 Hz to 20 kHz with the component
values as shown in Figure 5 and V
CC
= 5.0 V. In the
expandor mode, the typical input dynamic range was from
-34 dB to +12 dB where 0 dB is equal to 100 mV
RMS
. The
typical unity gain level measured at 0 dB @ 1.0 kHz input
was
"0.5
dB and the typical tracking error was
"0.1
dB
for input range of -30 to +10 dB.
In the compressor mode, the typical input dynamic range
was from -42 dB to
"18
dB with a tracking error +0.1 dB
and the typical unity gain level was
"0.5
dB.
In the ALC mode, the typical input dynamic range was
from -42 dB to +8.0 dB with typical output deviation of
"0.2
dB about the nominal output of 0 dB. For input
greater than +9.0 dB in ALC configuration, the summing
amplifier sometimes exhibits high frequency oscillations.
There are several solutions to this problem. The first is to
lower the values of R
6
and R
7
to 20 kW each. The second
is to add a current limiting resistor in series with C12 at
Pin 13. The third is to add a compensating capacitor of
about 22 to 30 pF between the input and output of summing
amplifier (Pins 12 and 14). With any one of the above
recommendations, the typical ALC mode input range
increased to +18 dB yielding a dynamic range of over
60 dB.
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4
SA575
Expandor
The typical expandor configuration is shown in Figure 2.
The variable gain cell and the rectifier cell are in the signal
input path. The V
REF
is always 1/2 V
CC
to provide the
maximum headroom without clipping. The 0 dB ref is
100 mV
RMS
. The input is AC coupled through C
5
, and the
output is AC coupled through C
3
. If in a system the inputs
and outputs are AC coupled, then C
3
and C
5
can be
eliminated, thus requiring only one external component,
C
4
. The variable gain cell and rectifier cell are DC coupled
so any offset voltage between Pins 4 and 9 will cause small
offset error current in the rectifier cell. This will affect the
accuracy of the gain cell. This can be improved by using an
extra capacitor from the input to Pin 4 and eliminating the
DC connection between Pins 4 and 9.
The expandor gain expression and the attack and release
time constant is given by Equation 1 and Equation 2,
respectively.
Expandor gain =
4V
IN
(avg)
3.8 kW x 100
mA
2
(eq. 1)
where V
IN
(avg) = 0.95V
IN(RMS)
t
R
=
t
A
= 10 kW x C
RECT
= 10 kW x C
4
(eq. 2)
7, 13
C
5
EXP IN
10mF
10kW
9, 11
D
G
S
10kW
6, 14
C
3
EXP OUT
10mF
4, 16
3.8kW
5, 15
2.2mF
V
REF
8
C
4
Figure 2. Typical Expandor Configuration
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