ISL43681IR datasheet(14/18 Pages) RENESAS

14 / 18 page

ISL43681, ISL43741

FN6053 Rev 3.00

Page 14 of 18

Mar 13, 2006

recommended supply voltage is 2V or 2V. It is important to

note that the input signal range, switching times, and on-

resistance degrade at lower supply voltages. Refer to the

electrical 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.

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 2.7V

to 10V. At 12V the VIH level is about 3.3V. This is still below

the CMOS guaranteed high output minimum level of 4V, but

noise margin is reduced. For best results with a 12V supply,

use a logic family that provides a VOH greater than 4V.

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 50

 systems, signal response is reasonably flat even past

100MHz (see Figures 18 and 19). Figures 18 and 19 also

illustrates that the frequency response is very consistent

over 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

20 details the high Off Isolation and Crosstalk rejection

provided by this family. At 10MHz, Off Isolation is about

55dB in 50

 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.

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