6

FN6099.1

December 27, 2004

Detailed Description

The ISL84780 is a bidirectional, quad single pole/double

throw (SPDT) analog switch that offers precise switching

capability from a single 1.6V to 3.6V supply with low on-

resistance (0.36

battery-powered equipment due to its low operating supply

voltage (1.6V), low power consumption (5.4

µW max), low

leakage currents (30nA max), and the tiny TQFN and TSSOP

packages. The ultra low on-resistance and Ron flatness

provide very low 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.

FIGURE 4. OFF ISOLATION TEST CIRCUIT

FIGURE 6. CROSSTALK TEST CIRCUIT

FIGURE 7. CAPACITANCE TEST CIRCUIT

ANALYZER

SIGNAL

GENERATOR

V+

C

0V or V+

NO or NC

COM

IN

GND

V+

C

0V or V+

NO or NC

COM

IN

GND

1mA

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+

ISL84780