8

FN6044.3

January 16, 2006

Detailed Description

The ISL43410 operates from a single 2V to 12V supply with

low on-resistance (115

Ω) and high speed operation

suited to portable battery powered equipment thanks to the

low operating supply voltage (2.0V), low power consumption

and QFN

packaging. High frequency applications also benefit

from the wide bandwidth, and the very high off isolation

(75dB) and crosstalk rejection (-85dB).

Supply Sequencing And Overvoltage Protection

With any CMOS device, proper power supply sequencing is

required to protect the device from excessive input currents

which might permanently damage the IC. All I/O pins contain

ESD protection diodes from the pin to V+ and GND (see

Figure 8). To prevent forward biasing these diodes, V+ must

be applied before any input signals, and input signal

voltages must remain between V+ and GND. If these

conditions cannot be guaranteed, then one of the following

two protection methods should be employed.

Logic inputs can easily be protected by adding a 1k

Ω

resistor in series with the input (see Figure 8). The resistor

limits the input current below the threshold that produces

permanent damage, and the sub-microamp input current

produces an insignificant voltage drop during normal

operation.

This method is not applicable for the signal path inputs.

Adding a series resistor to the switch input defeats the

diodes can be added in series with the supply pins to provide

overvoltage protection for all pins (see Figure 8). These

additional diodes limit the analog signal from 1V below V+ to

1V above GND. The low leakage current performance is

unaffected by this approach, but the switch resistance may

increase, especially at low supply voltages.

Power-Supply Considerations

The ISL43410 construction is typical of most CMOS analog

switches, except that they have only two supply pins: V+ and

GND. V+ and GND drive the internal CMOS switches and

set their analog voltage limits. Unlike switches with a 13V

maximum supply voltage, the ISL43410’s 15V maximum

supply voltage provides plenty of room for the 10% tolerance

of 12V supplies, as well as room for overshoot and noise

spikes.

The minimum recommended supply voltage is 2.0V. 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 also power the internal logic and level shifters.

The level shifters convert the input logic levels to switched

V+ and GND signals to drive the analog switch gate

terminals.

This device cannot be operated with bipolar supplies,

because the input switching point becomes negative in this

configuration.

Logic-Level Thresholds

The ISL43410 is TTL compatible (0.8V and 2.4V) over a

level is about 2.5V. This is still below the TTL guaranteed

high output minimum level of 2.8V, but noise margin is

reduced. For best results with a 12V supply, use a logic

The digital input stages draw supply current whenever the

digital input voltage is not at one of the supply rails (see

Figure 12). Driving the digital input signals from GND to V+

with a fast transition time minimizes power dissipation. The

ISL43410 has been designed to minimize the supply current

whenever the digital input voltage is not driven to the supply

rails (0V to V+). For example driving the device with 3V logic

(0V to 3V) while operating with a 5V supply the device draws

devices of competitors can draw 8 times this amount of

current.

High-Frequency Performance

In 50

Ω systems, signal response is reasonably flat even past

100MHz (see Figure 17). Figure 17 also illustrates that 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 18 details the high Off Isolation and Crosstalk

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

about 55dB in 50

Ω systems, decreasing approximately 20dB

FIGURE 8. OVERVOLTAGE PROTECTION

GND

OPTIONAL PROTECTION

V+

IN

DIODE

OPTIONAL PROTECTION

DIODE

OPTIONAL

PROTECTION

RESISTOR

FOR LOGIC

INPUTS

1k

Ω

ADD

1k

Ω

ISL43410