ISL84514 Intersil Corporation, ISL84514 Datasheet - Page 7

• Manufacturer Part Number: ISL84514
• Description: Low-Voltage/ Single Supply/ SPST/ Analog Switches
• Manufacturer: Intersil Corporation

Detailed Description
The ISL84514 and ISL84515 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 (2nA
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
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
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
FIGURE 6. OVERVOLTAGE PROTECTION
IN
V
NO OR NC
ON
switch, so two small signal
GND
7
V+
OPTIONAL PROTECTION
DIODE
OPTIONAL PROTECTION
DIODE
V
COM
ISL84514, ISL84515
Power-Supply Considerations
The ISL8451X 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 ISL8451X 15V maximum supply voltage provides plenty
of room for the 10% tolerance of 12V supplies, as well as
margin 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.
This family of switches cannot be operated with bipolar
supplies, because the input switching point becomes
negative in this configuration. For a ±5V single SPST switch,
see the ISL84516, ISL84517 data sheet.
Logic-Level Thresholds
This switch family is TTL compatible (0.8V and 2.4V) over a
supply range of 3V to 11V, and the full temperature range
(see Figure 10). At 12V the low temperature V
about 2.5V. This is still below the TTL guaranteed high
output minimum level of 2.8V, but noise margin is reduced.
For best results with a 12V supply, use a logic family that
provides a V
The digital input stages draw supply current whenever the
digital input voltage is not at one of the supply rails. Driving
the digital input signals from GND to V+ with a fast transition
time minimizes power dissipation.
High-Frequency Performance
In 50Ω systems, signal response is reasonably flat to
20MHz, with a -3dB bandwidth exceeding 200MHz (see
Figure 13). Figure 13 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 14 details the
high Off Isolation provided by this family. At 10MHz, off
isolation is about 50dB in 50Ω systems, 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.
OH
greater than 3V.
IH
level is