8

FN6098.1

Detailed Description

The ISL43L420 is a bidirectional, quad single pole/double

throw (SPDT) analog switch that offers precise switching

capability from a single 1.1V to 4.5V supply with low on-

resistance (0.24

battery powered equipment due to its low operating supply

voltage (1.1V), low power consumption (2.7

µW max), low

leakage currents (150nA max), and the tiny QFN package.

insertion loss and distortion to applications that require signal

reproduction.

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 to GND (See

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

be applied before any input signals, and the 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 acceptable 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 signal range is

reduced and the resistance may increase, especially at low

supply voltages.

Power-Supply Considerations

The ISL43L420 construction is typical of most single supply

CMOS analog switches, in that they have two supply pins:

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

switches and set their analog voltage limits. Unlike switches

with a 4V maximum supply voltage, the ISL43L420 4.7V

maximum supply voltage provides plenty of room for the

10% tolerance of 4.3V supplies, as well as room for

overshoot and noise spikes.

The minimum recommended supply voltage is 1.1V. 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 V+

ANALYZER

V+

C

NO or NC

SIGNAL

GENERATOR

GND

COM

50

Ω

N.C.

COM

NC or NO

V+

C

GND

NO or NC

COM

IN

IMPEDANCE

ANALYZER

0V or V+

FIGURE 8. OVERVOLTAGE PROTECTION

GND

OPTIONAL PROTECTION

V+

DIODE

OPTIONAL PROTECTION

DIODE

OPTIONAL

PROTECTION

RESISTOR

ISL43L420