ISL84524 Intersil Corporation, ISL84524 Datasheet - Page 9

• Manufacturer Part Number: ISL84524
• Description: Low-Voltage/ Single Supply/ 4 to 1 Multiplexer and DPDT Analog Switches
• Manufacturer: Intersil Corporation

Detailed Description
The ISL84524 and ISL84525 operate from a single 2V 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 (2.7V), low power consumption (3µW), low leakage
currents (25nA max), and the tiny
frequency applications also benefit from the wide bandwidth,
and the very high off isolation (75 dB) and crosstalk rejection
(-85dB).
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 GND (see
Figure 8). 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 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.
This method is not applicable for the signal path inputs.
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 8). 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
FOR LOGIC
INPUTS
FIGURE 8. OVERVOLTAGE PROTECTION
1kΩ
1kΩ
V
ADD
IN
NO or NC
H
X
ON
switch, so two small signal
GND
9
V+
MSOP
OPTIONAL PROTECTION
DIODE
OPTIONAL PROTECTION
DIODE
packaging. High
V
COM
ISL84524, ISL84525
Power-Supply Considerations
The ISL8452X construction is typical of most CMOS analog
switches, except that they have only two supply pins: V+ and
GND. V+ and GND drive the internal CMOS switches and
set their analog voltage limits. 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.
The minimum recommended supply voltage is 2V. 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 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.
Logic-Level Thresholds
This switch family is TTL compatible (0.8V and 2.4V) over a
supply range of 2V to 11V. At 12V the V
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 even past
100MHz (see Figure 13). Figure 13 also illustrates that the
frequency response is very consistent over varying analog
signal levels.
An OFF switch acts like a capacitor and passes higher
frequencies with less attenuation, resulting in signal feed
through from a switch’s input to its output. Off Isolation is the
resistance to this feed through, while Crosstalk indicates the
amount of feed through from one switch to another. Figure
14 details the high Off Isolation and Crosstalk rejection
provided by this family. At 10MHz, Off Isolation is about
55dB in 50Ω systems, decreasing approximately 20dB per
decade as frequency increases. Higher load impedances
decrease Off Isolation and Crosstalk rejection due to the
voltage divider action of the switch OFF impedance and the
load impedance.
OH
greater than 3V.
IH
level is about