ISL43120_05 Datasheet, PDF (9/13 Pages) Intersil Corporation – Low-Voltage, Single Supply, Dual SPST, SPDT Analog Switches

ISL43120, ISL43121, ISL43122, ISL43210
V+ and GND also power the internal logic and level shiftier.
The level shiftier 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 3V to 11V (see Figure 15). At 12V the V_IH
level is 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 the provides a V_OH greater than 3V.
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
300MHz (see Figure 16). Figure 16 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, 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 10MHz, Off
Isolation is about 50dB 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
Reverse 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.
Typical Performance Curves T_A = 25°C, Unless Otherwise Specified
40
35
30
85°C
25
20
15
25°C
-40°C
10
5
3 4 5 6 7 8 9 10 11 12 13
V+ (V)
FIGURE 9. ON RESISTANCE vs SUPPLY VOLTAGE
45
V+ = 3.3V
40
35
30
25
20
15
30
25
20
15
10
20
85°C
15
85°C
25°C
-40°C
25°C
85°C
25°C
-40°C
V+ = 5V
V+ = 12V
10
5 ^-40°C
0
2
4
6
8
V_COM (V)
10
12
FIGURE 10. ON RESISTANCE vs SWITCH VOLTAGE
9
FN6033.4
April 12, 2005