SSM2404

REV. B

–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

Ω typically, which causes very

little signal attenuation even with a load resistor.

TOP VIEW

(Not to Scale)

1

2

3

4

5

6

7

8

20

19

18

17

16

15

14

13

SSM2404

SW1

SW4

SW2

SW3

IN1

OUT1

DGND

SW1 CONTROL

SW2 CONTROL

OUT2

IN2

IN4

OUT4

+12V

SW4 CONTROL

SW3 CONTROL

9

10

12

11

R IS OPTIONAL

L

–12V

OUT3

IN3

SW

CONTROL

SWITCH

STATE

0

1

OFF

ON

Figure 20. Basic Circuit Configuration

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

Ω 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

Ω 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

Ω 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

Ω

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.

10

90

100

0%

10V

5V

0

5V

0

ANALOG

OUTPUT

V

A (OUT)

LOGIC

INPUT

5ms/div

10

90

100

0%

50mV

50

µs

OPEN

(SWITCH OFF)

CLOSED

(SWITCH ON)

10

90

100

0%

50mV

50

µs

CLOSED

(SWITCH ON)

OPEN

(SWITCH OFF)

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