ISL43110_05 Datasheet, PDF (7/12 Pages) Intersil Corporation – Low-Voltage, Single Supply, SPST, High Performance Analog Switches

ISL43110, ISL43111
Test Circuits and Waveforms (Continued)
V+
IMPEDANCE
ANALYZER
NO or NC
IN ^{0V or V+}
COM
GND
FIGURE 5. CAPACITANCE TEST CIRCUIT
Detailed Description
The ISL43110 and ISL43111 analog switches offer precise
switching capability from a single 2.4V to 12V supply with
low on-resistance and high speed operation. The devices
are especially well suited to portable battery powered
equipment thanks to the low operating supply voltage (2.4V),
low power consumption (5µW), low leakage currents (1nA
max), and the tiny SOT-23 packaging. High frequency
applications also benefit from the wide bandwidth, and the
very high off isolation.
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
GND (see Figure 6). To prevent forward biasing these
diodes, V+ must be applied before any input signals, and
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 1kΩ
resistor in series with the input (see Figure 6). 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_ON switch, so two small signal
diodes can be added in series with the supply pins to provide
overvoltage protection for all pins (see Figure 6). 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 resistance may
increase, especially at low supply voltages.
OPTIONAL
PROTECTION
RESISTOR _IN
V_{NO or NC}
OPTIONAL PROTECTION
DIODE
V+
V_COM
GND
OPTIONAL PROTECTION
DIODE
FIGURE 6. OVERVOLTAGE PROTECTION
Power-Supply Considerations
The ISL4311X construction is typical of most CMOS analog
switches, except that there are only two supply pins: V+ and
GND. Unlike switches with a 13V maximum supply voltage,
the ISL4311X 15V maximum supply voltage provides plenty
of room for the 10% tolerance of 12V supplies, as well as
room for overshoot and noise spikes.
The minimum recommended supply voltage is 2.4V. It is
important to note that the 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.
V+ and GND power the internal CMOS switches and set
their analog voltage limits. These supplies also power the
internal logic and level shifters. The level shifters convert the
input logic levels to switched V+ and GND signals to drive
the analog switch gate terminals.
7
FN6028.3
April 12, 2005