8

Detailed Description

The ISL8391–ISL8393 quad analog switches offer precise

to 12V supply with low on-resistance (20

Ω) and high speed

especially well suited to portable battery powered equipment

thanks to the low operating supply voltage (2V), low power

consumption (1

µW), low leakage currents (2.5nA max). High

frequency applications also benefit from the wide bandwidth,

and the very high OFF isolation and crosstalk rejection.

Supply Sequencing And Overvoltage Protection

As 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 8). 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 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 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 ISL839X 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 ISL839X 15V

maximum supply voltage provides plenty of room for the

as well as room for overshoot and noise spikes.

This family of switches performs equally well when operated

with bipolar or single voltage supplies, and bipolar supplies

need not be symmetrical. The minimum recommended

input signal range, switching times, and ON-resistance

degrade at lower supply voltages. Refer to the electrical

FIGURE 6. CROSSTALK TEST CIRCUIT

FIGURE 7. CAPACITANCE TEST CIRCUIT

0V OR 2.4V

ANALYZER

V+

C

NO1 OR NC1

SIGNAL

GENERATOR

GND

IN1

COM1

IN2

50

Ω

0V OR 2.4V

NO

COM2

NO2 OR NC2

C

V-

CONNECTION

V+

GND

NO OR NC

COM

IN

IMPEDANCE

ANALYZER

0V OR 2.4V

V-

FIGURE 8. OVERVOLTAGE PROTECTION

V-

OPTIONAL PROTECTION

V+

DIODE

OPTIONAL PROTECTION

DIODE

OPTIONAL

PROTECTION

RESISTOR

ISL8391, ISL8392, ISL8393