ISL54054 Datasheet, PDF (8/13 Pages) Intersil Corporation – Ultra Low ON-Resistance, Low Voltage, Single Supply, Single SPST/1:2 Distribution Analog Switch

ISL54054, ISL54055
Power-Supply Considerations
The construction of the ISL54054 and the ISL54055 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 ISL54054 and the
ISL54055’s 5.5V maximum supply voltage provides
plenty of room for the 10% tolerance of 4.5V supplies,
as well as room for overshoot and noise spikes.
The minimum recommended supply voltage is 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 8 for details.
V+ and GND also power the internal logic and level
shiftier. The level shiftier converts 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 logic compatible (0.5V and
1.4V) over a supply range of 2.5V to 5V (see
Figure 19). At 5V the V_IH level is about 1.38V. This is
still below the 1.8V CMOS guaranteed high output
minimum level of 1.4V, but noise margin is reduced. At
1.8V operation the V_IL level is around 0.1V and can
only be used in 1.8V applications with minimal ground
bounce.
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 ISL54054 and the ISL54055 have a
-3dB bandwidth of 72MHz with Nx pins connected and
138MHz for a single Nx input (see Figure 20). 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.
Figure 21 details the high off isolation rejection
provided by this family. At 100kHz, off isolation in 50Ω
systems is about 74dB with Nx pins connected and
83dB with a single Nx input, decreasing approximately
20dB per decade as frequency increases. Higher load
impedances decrease off isolation 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
1.2
1.4
I_COM = 100mA
V+ = 1.8V
1.1
I_COM = 100mA
1.2
1.0
V+ = 1.8V
0.9
1.0
0.8
+85°C
0.7
0.6
0.5
V+ = 2.7V
0.4
V+ = 4.5V
V+ = 3V
0.3
V+ = 5V
0.2
0
1
2
3
4
5
V_COM (V)
FIGURE 7. ON-RESISTANCE vs SUPPLY VOLTAGE vs
SWITCH VOLTAGE (NX PINS CONNECTED)
0.8
+25°C
0.6
-40°C
0.4
0.2
0
0.5
1.0
V_COM (V)
1.5
1.8
FIGURE 8. ON-RESISTANCE vs SWITCH VOLTAGE
(NX PINS CONNECTED)
8
FN6461.2
October 19, 2009