SSM-2404 Analog Devices, SSM-2404 Datasheet - Page 6

• Manufacturer Part Number: SSM-2404
• Description: Quad Audio Switch
• Manufacturer: Analog Devices

SSM2404
APPLICATIONS INFORMATION
The SSM2404 integrates four analog CMOS switches with
guaranteed “break-before-make” operation to provide high
quality audio switching. Each switch has complementary
N-channel and P-channel MOSFETs to allow the analog input
voltage range to include the positive and negative rails and
improve linearity. In addition, the topology permits fully
bilateral switching. When using the SSM2404 there is full
flexibility in configuring the switches. For example, they can be
used individually as shown in Figure 20, or as a double-pole,
double-throw (DPDT) switch, which is explained later. The
(SWITCH OFF)
(SWITCH ON)
Figure 19. Switch ON-to-OFF Transition (R
Figure 18. Switch OFF-to-ON Transition (R
CLOSED
OPEN
10V
5V
5V
Figure 17. t
0
0
100
90
10
0%
100
90
10
0%
100
90
10
0%
50mV
50mV
ON
/t
OFF
5ms/div
Switching Response
50 s
50 s
ANALOG
OUTPUT
V
LOGIC
INPUT
V
L
OPEN
(SWITCH OFF)
L
CLOSED
(SWITCH ON)
A (OUT)
INL/INH
= 5 k )
= 5 k )
–6–
SSM2404 can also be configured as a 4:1 multiplexer, or by
using additional packages, as 8:1 or 16:1 and up. The break-
before-make feature is guaranteed from part to part allowing
such multiple-package applications.
As Figure 20 shows, the SSM2404 is easy to use, and no ad-
ditional devices are needed. The load resistors are recommended
for improved OFF-isolation and charge injection. The ON
resistance of the switch is only 28
little signal attenuation even with a load resistor.
OPTIMIZING PERFORMANCE
As the performance curves show, the switch is optimized for
high impedance loads. The distortion performance is at its best
when the switch has a load impedance of 100 k or greater as
shown in Figure 1. However, even at lower values of load resis-
tances, the 1 kHz distortion performance is still excellent,
0.006% for a 10 k load. The main trade-off with THD is
OFF-isolation and crosstalk. This is shown in Figures 10 and
11, again with two different load conditions. As these graphs
show, the 10 k load yields approximately a 16 dB improve-
ment in both characteristics.
Thus, the optimum operating point depends on the most criti-
cal parameters. When THD is critical then high load imped-
ances should be used; however, when crosstalk and OFF-
isolation are critical, lower impedances on the order of 10 k
should be used. An additional benefit of using the smaller
load resistor is that any charge injected onto the output will be
shunted to ground through the resistor. If improved OFF-
isolation is needed, the SSM2404 dual audio switch should be
considered with its excellent 120 dB OFF-isolation at 20 kHz.
It is important that all of the AGND pins be connected to the
system analog ground. These pins isolate the input and output
of each switch. Without connecting these pins, the OFF-
isolation will degrade significantly.
SW1 CONTROL
SW2 CONTROL
OUT2
OUT1
DGND
Figure 20. Basic Circuit Configuration
R
L
IN2
IN1
R
L
10
1
2
3
4
5
6
7
8
9
SW1
SW2
R IS OPTIONAL
(Not to Scale)
L
SSM2404
TOP VIEW
SW4
SW3
19
18
20
17
16
15
14
13
12
11
typically, which causes very
R
IN3
+12V
IN4
SW4 CONTROL
SW3 CONTROL
–12V
L
R
L
CONTROL
OUT4
OUT3
SW
0
1
SWITCH
STATE
OFF
ON
REV. B