ISL8391_04 Datasheet, PDF(9/12 Page) Intersil Corporation – Low-Voltage, Single and Dual Supply, Quad SPST, Analog Switches

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ISL8391_04 Datasheet, PDF (9/12 Pages) Intersil Corporation – Low-Voltage, Single and Dual Supply, Quad SPST, Analog Switches

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ISL8391, ISL8392, ISL8393

specification tables and Typical Performance Curves for

details.

V+ and GND power the internal logic (thus setting the digital

switching point) and level shifters. The level shifters convert

the logic levels to switched V+ and V- signals to drive the

analog switch gate terminals, so switch parameters -

especially RON - are strong functions of both supplies.

Logic-Level Thresholds

V+ and GND power the internal logic stages, so V- has no

affect on logic thresholds. This switch family is TTL

compatible (0.8V and 2.4V) over a V+ supply range of 2.5V

to 10V. At 12V the VIH level is about 2.7V, so for best results

use a logic family that provides a VOH greater than 3V.

The digital input stages draw supply current whenever the

digital input voltage is not at one of the supply rails. Driving

the digital input signals from GND to V+ with a fast transition

time minimizes power dissipation.

High-Frequency Performance

In 50â¦ systems, signal response is reasonably flat even past

200MHz (see Figure 15), with a small signal -3dB bandwidth

in excess of 300MHz, and a large signal bandwidth

exceeding 300MHz.

An off switch acts like a capacitor and passes higher

frequencies with less attenuation, resulting in signal

feedthrough from a switchâs 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 16 details the high OFF Isolation and

Crosstalk rejection provided by this family. At 10MHz, OFF

isolation is about 50dB in 50â¦ 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 V-. One

of these diodes conducts if any analog signal exceeds V+

or V-.

Virtually all the analog leakage current comes from the ESD

diodes to V+ or V-. 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 V- 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 V- 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 GND.

Typical Performance Curves TA = 25oC, Unless Otherwise Specified

62.5

37.5

12.5

V- = -5V

85oC

V- = 0V

25oC

-40oC

VCOM = (V+) - 1V

ICOM = 1mA

85oC

25oC

-40oC

9 10 11 12

V+ (V)

FIGURE 9. ON RESISTANCE vs SUPPLY VOLTAGE

ICOM = 1mA

85oC

25oC

-40oC

V+ = 2.7V

V- = 0V

85oC

25oC

-40oC

V+ = 3.3V

V- = 0V

V+ = 5V V- = 0V

25oC

VCOM (V)

-40oC

FIGURE 10. ON RESISTANCE vs SWITCH VOLTAGE

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