9

FN6356.2

June 11, 2007

Frequency Performance

In 50

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

120MHz (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.

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

234

5

V+ = 4.3V

+85°C

-40°C

+25°C

0.20

0.25

0.30

0.35

ISL54050