9

FN6357.4

August 15, 2007

High-Frequency Performance

In 50

Ω systems, the ISL54056 has a -3dB bandwidth of

104MHz (see Figure 22). The frequency response is very

consistent over a wide V+ range, and for varying analog

signal levels.

An OFF switch acts like a capacitor and passes higher

frequencies with less attenuation, resulting in signal

feedthrough from a switch’s input to its output. Off isolation is

the resistance to this feedthrough, while crosstalk indicates

the amount of feedthrough from one switch to another.

Figure 23 details the high off isolation and crosstalk rejection

provided by this part. At 100kHz, off isolation is about 65dB

in 50

Ω systems, decreasing approximately 20dB per decade

as frequency increases. Higher load impedances decrease

off isolation and crosstalk rejection due to the voltage divider

action of the switch OFF impedance and the load

impedance.

Leakage Considerations

Reverse ESD protection diodes are internally connected

between each analog-signal pin and both V+ and GND. One of

these diodes conducts if any analog signal exceeds V+ or

GND.

Virtually all the analog leakage current comes from the ESD

diodes to V+ or GND. Although the ESD diodes on a given

signal pin are identical and therefore fairly well balanced,

they are reverse biased differently. Each is biased by either

V+ or GND and the analog signal. This means their leakages

will vary as the signal varies. The difference in the two diode

leakages to the V+ and GND pins constitutes the analog signal

path leakage current. All analog leakage current flows between

each pin and one of the supply terminals, not to the other

switch terminal. This is why both sides of a given switch can

show leakage currents of the same or opposite polarity.

There is no connection between the analog signal paths and

V+ or GND.

FIGURE 10. ON-RESISTANCE vs SUPPLY VOLTAGE vs

SWITCH VOLTAGE

FIGURE 11. ON-RESISTANCE vs SUPPLY VOLTAGE vs

SWITCH VOLTAGE

FIGURE 12. ON-RESISTANCE vs SUPPLY VOLTAGE vs

SWITCH VOLTAGE

FIGURE 13. ON-RESISTANCE vs SWITCH VOLTAGE

01

23

45

0.32

0.33

0.34

0.35

0.36

0.37

0.38

0.39

0.40

V+ = 4.5V

V+ = 4.3V

V+ = 3.9V

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.36

0.37

0.38

0.39

0.40

0.41

0.42

0.43

0.44

0.45

0.46

V+ = 3.3V

V+ = 3V

V+ = 2.7V

00.5

1.0

1.5

2.0

0.4

0.5

0.6

0.7

0.8

V+ = 2V

V+ = 1.8V

V+ = 1.65V

01

2345

0.25

0.30

0.35

0.40

0.45

V+ = 4.3V

+85°C

-40°C

+25°C

ISL54056