7

FN6111.0

January 27, 2005

Detailed Description

The ISL8499 is a bidirectional, quad single pole/double

throw (SPDT) analog switch that offers precise switching

capability from a single 1.65V to 4.5V supply with low on-

resistance (0.24

portable battery powered equipment due to its low operating

supply voltage (1.65V), low power consumption (2.7

µW

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

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

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

100mA

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+

ISL8499