9

FN6356.4

November 22, 2008

Frequency Performance

In 50

Ω systems, the ISL54050 has a -3dB bandwidth of

25MHz (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

feed-through from a switch’s input to its output. OFF-

isolation is the resistance to this feed-through, while

crosstalk indicates the amount of feed-through 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 62dB 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.

Typical Performance Curves

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

2345

0.25

0.26

0.27

0.28

0.29

0.30

V+ = 4.5V

V+ = 4.3V

V+ = 3.9V

0

0.5

1.0

1.5

2.0

2.5

3.0

3.5

0.28

0.29

0.30

0.31

0.32

0.33

0.34

0.35

V+ = 3.3V

V+ = 3V

V+ = 2.7V

0

0.5

1.0

1.5

2.0

0.30

0.35

0.40

0.45

0.50

0.55

0.60

0.65

0.70

V+ = 2V

V+ = 1.65V

V+ = 1.8V

01

23

45

V+ = 4.3V

+85°C

-40°C

+25°C

0.20

0.25

0.30

0.35

ISL54050