11

FN6054.2

February 27, 2006

Detailed Description

The ISL43231 analog switch offers a precise switching

supply with low on-resistance (39

Ω) and high speed

It has an inhibit and inhibit bar pin to simultaneously open all

signal paths. It also has a latch bar pin to lock in the last

switch address.

The device is especially well suited for applications using

Leakage, Charge Injection, etc.) is best in class.

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 to V- (see

Figure 9). To prevent forward biasing these diodes, V+ and

V- must be applied before any input signals, and input signal

voltages must remain between V+ and V-. 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 9). 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 9). These

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

1V above V-. 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 ISL43231 construction is typical of most CMOS analog

switches, in that they have three supply pins: V+, V-, and

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

their analog voltage limits, so there are no connections

between the analog signal path and GND. Unlike switches

with a 13V maximum supply voltage, the ISL43231 15V

maximum supply voltage provides plenty of room for the

as well as room for overshoot and noise spikes.

This switch device performs equally well when operated with

bipolar or single voltage supplies.The minimum

FIGURE 7. CROSSTALK TEST CIRCUIT

FIGURE 8. CAPACITANCE TEST CIRCUIT

0V or V+

ANALYZER

SIGNAL

GENERATOR

GND

50

Ω

N.C.

EN

V-

C

V+

C

EN, LE

GND

NO or NC

COM

IMPEDANCE

ANALYZER

0V or V+

EN

V-

C

V+

C

EN, LE

FIGURE 9. INPUT OVERVOLTAGE PROTECTION

V-

OPTIONAL PROTECTION

V+

LOGIC

DIODE

OPTIONAL PROTECTION

DIODE

OPTIONAL

PROTECTION

RESISTOR

FOR LOGIC

INPUTS

1k

Ω

ISL43231