ISL43112, ISL43113
8
FN6029.3
December 11, 2015
Submit Document Feedback
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 V-. The low
leakage current performance is unaffected by this approach, but
the switch resistance may increase, especially at low supply
voltages.
Power-Supply Considerations
The ISL4311x construction is typical of most CMOS analog
switches, except that there are only two supply pins: V+ and V-.
The power supplies need not be symmetrical for useful
operation. As long as the total supply voltage (V+ to V-, including
supply tolerances, overshoot, and noise spikes) is less than the
15V maximum supply rating, and the digital input switching point
remains reasonable (see “
Logic-Level Thresholds” section), the
ISL43112, ISL43113 function well. The 15V maximum supply
rating provides the designer of 12V systems much greater
flexibility than switches with a 13V maximum supply voltage.
The minimum recommended supply voltage is ±1.5V. It is
important to note that the input signal range, switching times
and On-resistance degrade at lower supply voltages, and the
digital input V
IL
becomes negative at V
S
±2V. Refer to the
“Typical Performance Curves” for details.
V+ and V- 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 V- signals to drive the analog switch gate
terminals.
This family of switches is not recommended for single supply
applications. For single supply, similar performance, pin
compatible, TTL compatible versions of these switches, see the
ISL43110, ISL43111
datasheet.
Logic-Level Thresholds
Due to the lack of a GND pin, the switching point of the digital
input is referenced predominantly to V+. The digital input is
CMOS compatible at ±5V supplies, and is TTL compatible for
±3.3V supplies. For other supply combinations refer to Figures 13
and 14.
The switching point has a very low temperature sensitivity, and
changes by only 100mV from +85°C to -40°C, regardless of
supply voltage.
High-Frequency Performance
In 5Ωsystems, signal response is reasonably flat to 30MHz,
with a -3dB bandwidth of nearly 400MHz (see Figure 15).
Figure 15
also illustrates that the frequency response is very
consistent over a wide V+ range, and for varying analog signal
levels.
An OFF switch acts like a capacitor and passes higher
frequencies with less attenuation, resulting in signal feedthrough
from a switch’s input to its output. OFF Isolation is the resistance
to this feedthrough. Figure 16 details the high OFF Isolation
provided by this family. At 10MHz, OFF Isolation is about 50dB in
50Ωsystems, decreasing approximately 20dB per decade as
frequency increases. Higher load impedances decrease OFF
Isolation due to the voltage divider action of the switch OFF
Impedance and the load impedance.
Leakage Considerations
Reverse ESD protection diodes are internally connected between
each analog-signal pin and both V+ and V-. One of these diodes
conducts if any analog signal exceeds V+ or V-.
Virtually, all the analog leakage current comes from the ESD
diodes to V+ or V-. Although the ESD diodes on a given signal pin
are identical and therefore fairly well balanced, they are reverse
biased differently. Each is biased by either V+ or V- and the
analog signal. This means their leakages will vary as the signal
varies. The difference in the two diode leakages to the V+ and V-
pins constitutes the analog-signal path leakage current. All
analog leakage current flows between each pin and one of the
supply terminals, not to the other switch terminal. This is why
both sides of a given switch can show leakage currents of the
same or opposite polarity. There is no connection between the
analog-signal paths and V+ or V-.
