ISL43L841_14 Datasheet, PDF (8/12 Pages) Intersil Corporation – Ultra Low ON-Resistance, Low-Voltage,Single Supply, Differential 4 to 1 Analog Multiplexer

ISL43L841
Detailed Description
The ISL43L841 analog multiplexer offers precise switching
capability from a single 1.65V to 4.5V supply with low on-
resistance (0.47Ω) and high speed operation (t_ON = 24ns,
t_OFF = 14ns). The devices are especially well suited to
portable battery powered equipment thanks to the low
operating supply voltage (1.65V), low power consumption
(0.23µW), low leakage currents (50nA max). High frequency
applications also benefit from the wide bandwidth, and the
very high off isolation and crosstalk rejection.
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 8). To prevent forward biasing these diodes, V+ must
be applied before any input signals, and the input signal
voltages must remain between V+ and GND.
If these conditions cannot be guaranteed, then precautions
must be implemented to prohibit the current and voltage at
the logic pins and signal pins from exceeding the maximum
ratings of the switch. The following two methods can be used
to provided additional protection to limit the current in the
event that the voltage at a signal pin or logic pin goes below
ground or above the V+ rail.
Logic inputs can be protected by adding a 1kΩ resistor in
series with the logic input (see Figure 8). The resistor limits
the input current below the threshold that produces
permanent damage, and the submicroamp input current
produces an insignificant voltage drop during normal
operation.
This method is not acceptable for the signal path inputs.
Adding a series resistor to the switch input defeats the
purpose of using a low R_ON switch. Connecting schottky
diodes to the signal pins as shown in Figure 8 will shunt the
fault current to the supply or to ground thereby protecting the
switch. These schottky diodes must be sized to handle the
expected fault current.
OPTIONAL
SCHOTTKY
DIODE
OPTIONAL
V+
PROTECTION
RESISTOR
ADD_X
INH
V_NOx
V_COM
OPTIONAL
SCHOTTKY
DIODE
GND
FIGURE 8. OVERVOLTAGE PROTECTION
Power-Supply Considerations
The ISL43L841 construction is typical of most CMOS analog
switches, in that they have two supply pins: V+ and GND. V+
and GND drive the internal CMOS switches and set their
analog voltage limits. Unlike switches with a 4V maximum
supply voltage, the ISL43L841 4.7V maximum supply
voltage provides plenty of room for the 10% tolerance of
4.3V supply, as well as room for overshoot and noise spikes.
The minimum recommended supply voltage is 1.65V but the
part will operate with a supply below 1.65V. 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 logic (thus setting the digital
switching point) and level shifters. The level shifters convert
the logic levels to switch V+ and GND signals to drive the
analog switch gate terminals.
This device cannot be operated with bipolar supplies,
because the input switching point becomes negative in this
configuration.
Logic-Level Thresholds
These devices are 1.8V CMOS compatible (0.5V and 1.4V)
over a supply range of 2.5V to 4.5V (see Figure 15). At 2.5V
the V_INL level is about 0.52V. This is still above the 1.8V
CMOS guaranteed minimum level of 0.4V, but noise margin
is reduced.
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. The ISL43L841 has been
designed to minimize the supply current whenever the digital
input voltage is not driven to the supply rails (0V to V+). For
example driving the device with 2.85V logic (0V to 2.85V)
while operating with a 4.2V supply, the device draws only
10µA of current when both address inputs are high (see
Figure 13 for V_LOGIC = 2.85V).
High-Frequency Performance
In 50Ω systems, signal response is reasonably flat even past
10MHz with a -3dB bandwidth of 70MHz (see Figure 19).
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 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 20 details the high Off Isolation and Crosstalk
rejection provided by this family. At 100kHz, Off Isolation is
about 65dB in 50Ω systems, decreasing approximately 20dB
per decade as frequency increases. Higher load
impedances decrease Off Isolation and Crosstalk rejection
8
FN6212.1
June 30, 2006