ISL84521 Intersil Corporation, ISL84521 Datasheet - Page 7

• Manufacturer Part Number: ISL84521
• Description: Low-Voltage/ Single and Dual Supply/ Quad SPST/ Analog Switches
• Manufacturer: Intersil Corporation

Test Circuits and Waveforms
Detailed Description
The ISL84521, ISL84522, ISL84523 quad analog switches
offer precise switching capability from a bipolar
or a single 2V to 12V supply with low on-resistance (65Ω)
and high speed switching (t
devices are especially well suited to portable battery
powered equipment thanks to the low operating supply
voltage (2V), low power consumption (1µW) and low leakage
currents (1nA 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- (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 1kΩ
resistor in series with the input (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 R
diodes can be added in series with the supply pins to provide
overvoltage protection for all pins (Figure 8). These
additional diodes limit the analog signal from 1V below V+ to
1V above V-. The low leakage current performance is
SIGNAL
GENERATOR
ANALYZER
FIGURE 6. CROSSTALK TEST CIRCUIT
R
0V or 2.4V
L
ON
NO1 OR NC1
COM2
IN2
ON
switch, so two small signal
7
= 45ns, t
GND
NO2 OR NC2
COM1
OFF
V+
V-
IN2
(Continued)
ISL84521, ISL84522, ISL84523
= 15ns). The
C
C
0V OR 2.4V
±
CONNECTION
NO
2V to
50Ω
±
6V
unaffected by this approach, but the switch resistance may
increase, especially at low supply voltages.
Power-Supply Considerations
The ISL8452X 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 ISL8452X 15V
maximum supply voltage provides plenty of room for the
10% tolerance of 12V supplies (
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
supply voltage is 2V or
input signal range, switching times, and ON-resistance
degrade at lower supply voltages. Refer to the electrical
specification tables and Typical Performance Curves for
details.
IMPEDANCE
ANALYZER
OPTIONAL
PROTECTION
RESISTOR
FIGURE 7. CAPACITANCE TEST CIRCUIT
FIGURE 8. OVERVOLTAGE PROTECTION
IN
V
NO OR NC
X
±
2V. It is important to note that the
NO OR NC
COM
V-
V+
±
6V or 12V single supply),
OPTIONAL PROTECTION
DIODE
OPTIONAL PROTECTION
DIODE
GND
V-
V
V+
IN
COM
0V OR 2.4V