ISL54053_14 Datasheet, PDF (8/12 Pages) Intersil Corporation – Ultra Low ON-Resistance, Low Voltage, Single Supply, SPDT Analog Switch

ISL54053
OPTIONAL
SCHOTTKY
DIODE
OPTIONAL
PROTECTION
RESISTOR
V+
IN_X
V_NX
V_COM
OPTIONAL
SCHOTTKY
DIODE
GND
FIGURE 8. OVERVOLTAGE PROTECTION
Power-Supply Considerations
The ISL54053 construction is typical of most single
supply 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 4.5V maximum supply voltage, the
ISL54053 5.5V maximum supply voltage provides plenty
of room for the 10% tolerance of 4.3V supplies, as well
as room for overshoot and noise spikes.
The minimum recommended supply voltage is 1.8V but
the part will operate with a supply below 1.8V. It is
important to note that the input signal range, switching
times, and ON-resistance degrade at lower supply
voltages. Refer to the “Electrical Specifications” tables
starting on page 3 and “Typical Performance Curves” on
page 9 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 1.8V CMOS compatible (0.5V and
1.4V) over a supply range of 2V to 5V (see Figure 15). At
5V the V_IH level is about 1.2V. This is still below the 1.8V
CMOS guaranteed high output minimum level of 1.4V,
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.
High-Frequency Performance
In 50Ω systems, the ISL54053 has a -3dB bandwidth of
190MHz (see Figure 16). 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, while
crosstalk indicates the amount of feedthrough from one
switch to another. Figure 17 details the high off isolation
and crosstalk rejection provided by this family. At
100kHz, off isolation is about 80dB 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.
Leakage Considerations
ESD protection diodes are internally connected between
each analog-signal pin and both V+ and GND. One of
these diodes conducts if any analog signal exceeds V+ or
GND.
Virtually all the analog leakage current comes from the
ESD diodes to V+ or GND. 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 GND 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 GND
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 GND.
8
FN6460.3
October 19, 2009