ISL84521 Ver la hoja de datos (PDF) - Intersil

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ISL84521

Low-Voltage, Single and Dual Supply, Quad SPST, Analog Switches

Intersil 

ISL84521, ISL84522, ISL84523

Test Circuits and Waveforms (Continued)

V+

C

V+

SIGNAL

GENERATOR

NO1 OR NC1

COM1

50Ω

NO OR NC

IN2

0V or 2.4V

IN2 0V OR 2.4V

ANALYZER

RL

COM2

NO2 OR NC2

GND

NO

CONNECTION

C

V-

FIGURE 6. CROSSTALK TEST CIRCUIT

Detailed Description

The ISL84521, ISL84522, ISL84523 quad analog switches

offer precise switching capability from a bipolar ±2V to ±6V or

a single 2V to 12V supply with low on-resistance (65Ω) and

high speed switching (tON = 45ns, tOFF = 15ns). The devices

are especially well suited to portable battery powered

equipment thanks to the low operating supply voltage (2V),

low power consumption (1µW) and low leakage currents (1nA

max). High frequency applications also benefit from the wide

bandwidth, and the very high OFF isolation and crosstalk

rejection.

Supply Sequencing And Overvoltage Protection

As with any CMOS device, proper power supply sequencing

is required to protect the device from excessive input

currents which might permanently damage the IC. All I/O

pins contain ESD protection diodes from the pin to V+ and to

V- (Figure 8). To prevent forward biasing these diodes, V+

and V- must be applied before any input signals, and input

signal voltages must remain between V+ and V-. 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 (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 of using a low RON switch, so two small signal

diodes can be added in series with the supply pins to provide

overvoltage protection for all pins (Figure 8). These

additional diodes limit the analog signal from 1V below V+ to

1V above V-. The low leakage current performance is

IMPEDANCE

ANALYZER

IN 0V OR 2.4V

COM

GND

V-

FIGURE 7. CAPACITANCE TEST CIRCUIT

unaffected by this approach, but the switch resistance may

increase, especially at low supply voltages.

OPTIONAL

PROTECTION

RESISTOR

INX

VNO OR NC

OPTIONAL PROTECTION

DIODE

V+

VCOM

V-

OPTIONAL PROTECTION

DIODE

FIGURE 8. OVERVOLTAGE PROTECTION

Power-Supply Considerations

The ISL8452X construction is typical of most CMOS analog

switches, in that they have three supply pins: V+, V-, and

GND. V+ and V- drive the internal CMOS switches and set

their analog voltage limits, so there are no connections

between the analog signal path and GND. Unlike switches

with a 13V maximum supply voltage, the ISL8452X 15V

maximum supply voltage provides plenty of room for the

10% tolerance of 12V supplies (±6V or 12V single supply),

as well as room for overshoot and noise spikes.

This family of switches performs equally well when operated

with bipolar or single voltage supplies, and bipolar supplies

need not be symmetrical. The minimum recommended

supply voltage is 2V or ±2V. 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 and Typical Performance Curves for

details.

7

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