ISL54051_0709 Datasheet, PDF (7/10 Pages) Intersil Corporation – Ultra Low ON-Resistance, Low Voltage, Single Supply, Single SPST Analog Switches

ISL54051, ISL54052
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 6) 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
PROTECTION
RESISTOR
V+
IN_X
V_NX
V_COM
OPTIONAL
SCHOTTKY
DIODE
GND
FIGURE 6. OVERVOLTAGE PROTECTION
Power-Supply Considerations
The constuction of the ISL54051 and the ISL54052 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
ISL54051 and the ISL54052’s 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” starting 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 CMOS compatible (0.5V and 1.4V)
over a supply range of 2V to 5V (see Figure 13). 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 ISL54051 and the ISL54052 have a
-3dB bandwidth of 190MHz (see Figure 14). 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 15 details the high
off isolation 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
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.
7
FN6459.2
September 25, 2007