ISL43210A

8

FN7876.0

June 24, 2011

Detailed Description

The ISL43210A bidirectional, single SPDT analog switch offers

precise switching capability from a single 2.7V to 15V supply

with low ON-resistance (11Ω) and high speed operation.

The device is especially well suited for 3D TV and 3D eyeware

equipment thanks to the high single supply operating voltage

(15V), low power consumption (27µW max), fast switching

packaging. High frequency applications also benefit from the

wide bandwidth and the very high off isolation rejection.

Supply Sequencing and Overvoltage

Protection

With any CMOS device, proper power supply sequencing is

required to protect the device from excessive input currents

that might permanently damage the IC. All I/O pins contain

ESD protection diodes from the pin to V+ and GND (see

Figure 8). To prevent forward biasing these diodes, V+ must be

applied before any input signals, and input signal voltages

must remain between V+ and GND. If these conditions cannot

be guaranteed, then one of the following two protection

methods should be employed.

Logic inputs can easily be protected by adding a 1kΩ resistor in

series with the input (see Figure 8). The resistor limits the input

current below the threshold that produces permanent

damage, and the sub-microamp input current produces an

insignificant voltage drop during normal operation.

Adding a series resistor to the switch input defeats the purpose

added in series with the supply pins to provide overvoltage

protection for all pins (see Figure 8). These additional diodes

limit the analog signal from 1V below V+ to 1V above GND. 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 ISL43210A construction is typical of most CMOS analog

switches, except that it has only two supply pins: V+ and GND.

V+ and GND drive the internal CMOS switches and set their

analog voltage limits. Unlike switches with a 13V absolute

maximum voltage, the ISL43210A 16.5V absolute maximum

supply voltage provides plenty of room for the 10% tolerance

of 15V supplies, as well as room for overshoot and noise

spikes.

The minimum recommended supply voltage is 2.7V. It is

important to note that the input signal range, switching times,

and ON-resistance degrade at lower supply voltages. Refer to

the “Electrical Specification” tables beginning on page 3 and

“Typical Performance Curves” beginning on page 9 for details.

V+ and GND also power the internal logic and level shifter. The

level shifter converts the input logic levels to switch V+ and

GND signals to drive the analog switch gate terminals.

This device cannot be operated with bipolar supplies because

the input switching point becomes negative in this

configuration.

Logic-Level Thresholds

This switch is TTL compatible (0.8V and 2.4V) over a supply

about 2.5V. This is still below the TTL guaranteed high output

minimum level of 2.8V, but noise margin is reduced. For best

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 feed-

through from a switch’s input to its output. Off isolation is the

resistance to this feed-through. Figure 17 details the high off

isolation rejection provided by this part. At 10MHz, off isolation

is about 50dB in 50Ω systems, 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.

FIGURE 8. OVERVOLTAGE PROTECTION

GND

OPTIONAL PROTECTION

V+

DIODE

OPTIONAL PROTECTION

DIODE

OPTIONAL

PROTECTION

RESISTOR