8

FN6033.4

April 12, 2005

Detailed Description

The ISL43120–ISL43122 and ISL43210 bidirectional, dual

analog switches offer precise switching capability from a

single 2.7V to 12V supply with low on-resistance (19

Ω) and

are especially well suited to portable battery powered

equipment thanks to the low operating supply voltage (2.7V),

low power consumption (5

µW), low leakage currents (100pA

max), and the tiny SOT-23 packaging. High frequency

applications also benefit from the wide bandwidth, and the

very high off isolation and crosstalk rejection.

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.

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 ISL43XXX 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 ISL43XXX 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 2.7V. 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.

FIGURE 6. CROSSTALK TEST CIRCUIT

FIGURE 7. CAPACITANCE TEST CIRCUIT

0V or 2.4V

ANALYZER

V+

C

NO1 or NC1

SIGNAL

GENERATOR

GND

COM1

50

Ω

NC

COM2

NO2 or NC2

V+

C

GND

NO or NC

COM

IMPEDANCE

ANALYZER

FIGURE 8. OVERVOLTAGE PROTECTION

GND

OPTIONAL PROTECTION

V+

DIODE

OPTIONAL PROTECTION

DIODE

OPTIONAL

PROTECTION

RESISTOR

ISL43120, ISL43121, ISL43122, ISL43210