8

FN6131.0

March 15, 2005

Detailed Description

The ISL43L210 is a bidirectional, 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

(0.34

device is especially well suited for portable battery powered

equipment due to its low operating supply voltage (1.1V), low

power consumption (1.8

µW max), low leakage currents

(100nA max), and the tiny SC70 packaging. The ultra low on-

resistance and Ron flatness provide very low insertion loss

and distortion to application 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 precautions

must be implemented to prohibit the current and voltage at

the logic pin and signal pins from exceeding the maximum

ratings of the switch. The following two methods can be used

to provided additional protection to limit the current in the

event that the voltage at a signal pin or logic pin goes below

ground or above the V+ rail.

Logic inputs can 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 to the signal pins as shown in Figure 8 will shunt the

fault current to the supply or to ground thereby protecting the

switch. These schottky diodes must be sized to handle the

expected fault current.

Power-Supply Considerations

The ISL43L210 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 ISL43L210 4.7V

maximum supply voltage provides plenty of room for the

10% tolerance of 4.2V 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

NC or NO

50

Ω

V+

C

GND

NO or NC

COM

IN

IMPEDANCE

ANALYZER

0V or V+

FIGURE 8. OVERVOLTAGE PROTECTION

GND

V+

OPTIONAL

PROTECTION

RESISTOR

OPTIONAL

SCHOTTKY

DIODE

OPTIONAL

SCHOTTKY

DIODE

ISL43L210