7
FN6038.3
March 13, 2006
Detailed Description
The ISL8394 quad analog switches offer precise switching
capability from a bipolar ±2V to ±6V or a single 2V to 12V
supply with low on-resistance (17
) and high speed
operation (tON =50ns, tOFF = 30ns). The devices are
especially well suited to portable battery powered equipment
thanks to the low operating supply voltage (2V), low power
consumption (5
W), 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
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
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
purpose of using a low RON switch, so two small signal
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
Repeat test for all switches.
FIGURE 4. OFF ISOLATION TEST CIRCUIT
Repeat test for all switches.
FIGURE 5. RON TEST CIRCUIT
FIGURE 6. CROSSTALK TEST CIRCUIT
FIGURE 7. CAPACITANCE TEST CIRCUIT
Test Circuits and Waveforms (Continued)
ANALYZER
RL
SIGNAL
GENERATOR
V+
C
0V OR 2.4V
NO OR NC
COM
IN
GND
C
V-
V+
C
0.8V OR 2.4V
NO OR NC
COM
IN
GND
VNX
V1
RON = V1/1mA
1mA
C
V-
0V or 2.4V
ANALYZER
V+
C
NO1 OR NC1
SIGNAL
GENERATOR
RL
GND
IN1
COM1
IN2
50
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-
ISL8394