ISL84581 Intersil Corporation, ISL84581 Datasheet - Page 10

• Manufacturer Part Number: ISL84581
• Description: 8 to 1 Multiplexer
• Manufacturer: Intersil Corporation

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 ISL84581 construction is typical of most CMOS analog
switches, in that it has three supply pins: V+, V-, and GND.
V+ and V- drive the internal CMOS switches and set their
analog voltage limits, so there are no connections between
the analog signal path and GND. Unlike switches with a 13V
maximum supply voltage, the ISL84581 15V maximum
supply voltage provides plenty of room for the 10% tolerance
of 12V supplies (
for overshoot and noise spikes.
The part performs equally well when operated with bipolar or
single voltage supplies.The minimum recommended supply
voltage is 2V single supply or
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” on page 11 for details.
V+ and GND power the internal logic setting the digital
switching point of the level shifters. The level shifters convert
the logic levels to switched V+ and V- signals to drive the
analog switch gate terminals.
Logic-Level Thresholds
V+ and GND power the internal logic stages, so V- has no
affect on logic thresholds. This ISL84581 is TTL compatible
(0.8V and 2.4V) over a V+ supply range of 2.7V to 10V. At
12V the V
guaranteed high output minimum level of 4V, 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.
OPTIONAL
PROTECTION
RESISTOR
FOR LOGIC
INPUTS
FIGURE 7. INPUT OVERVOLTAGE PROTECTION
IH
1kΩ
level is about 3.3V. This is still below the CMOS
±
6V or 12V single supply), as well as room
LOGIC
V
NOx
OH
10
±
2V dual supply. It is important
V+
V-
greater than 4V.
OPTIONAL PROTECTION
DIODE
OPTIONAL PROTECTION
DIODE
V
COM
ISL84581
High-Frequency Performance
In 50Ω systems, signal response is reasonably flat even past
100MHz (see Figures 16 and 17). Figures 16 and 17 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. Figure 18 details the high Off
Isolation of the ISL84581. At 10MHz, Off Isolation is about
55dB 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.
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 GND.
February 9, 2007
FN6416.0