ISL84582 查看數據表（PDF） - Renesas Electronics

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ISL84582

Low-Voltage, Single and Dual Supply, Differential 4-to-1 Multiplexer

Renesas Electronics 

ISL84582

Detailed Description

The ISL84582 multiplexer offers precise switching capability

from a bipolar ±2V to ±6V or a single 2V to 12V supply with

low ON-resistance (39) and high speed operation

(tON = 38ns, tOFF = 19ns) with dual 5V supplies. The device

is especially well suited to portable battery-powered

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

low power consumption (3µW), low leakage currents (0.2nA).

High frequency applications also benefit from the wide

bandwidth, and the very high off-isolation and crosstalk

rejection.

Supply Sequencing and Overvoltage Protection

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- (see

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 1k

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.

This method is not applicable for the signal path inputs.

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 (see Figure 8). These

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

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

unaffected by this approach, but the switch resistance may

increase, especially at low supply voltages.

OPTIONAL

PROTECTION

RESISTOR

FOR LOGIC

INPUTS

OPTIONAL PROTECTION

DIODE

V+

1k

LOGIC

VNO OR NC

VCOM

V-

OPTIONAL PROTECTION

DIODE

FIGURE 8. INPUT OVERVOLTAGE PROTECTION

FN6213 Rev 3.00

May 6, 2009

Power-Supply Considerations

The ISL84582 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 absolute maximum voltage, the ISL84582 15V

absolute maximum 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.

The ISL84582 performs equally well when operated with

bipolar or single voltage supplies. 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 beginning on page 5 and

“Typical Performance Curves” beginning on page 11 for

details.

V+ and GND power the internal logic (thus setting the digital

switching point) and level shifters. The level shifters convert

the logic levels to switched V+ and V- signals to drive the

analog switch gate terminals.

Logic-Level Thresholds

V+ and GND power the internal logic stages, so V- has no

affect on logic thresholds. This ISL84582 is TTL compatible

(0.8V and 2.4V) over a V+ supply range of 2.7V to 10V. At

12V the VIH level is about 3.3V. This is still below the CMOS

guaranteed high output minimum level of 4V, but noise

margin is reduced. For best results with a 12V supply, use a

logic family that provides a VOH greater than 4V.

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 50 systems, signal response is reasonably flat even past

100MHz (see Figures 17 and 18). Figures 17 and 18 also

illustrates that the frequency response is very consistent

over 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, while Crosstalk indicates the

amount of feed through from one switch to another. Figure 19

details the high Off-Isolation and Crosstalk rejection

provided by this family. At 10MHz, Off-Isolation is about

55dB in 50 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.

Page 10 of 14

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