ISL84524 データシートの表示（PDF） - Renesas Electronics

部品番号

コンポーネント説明

一致するリスト

ISL84524

Low-Voltage, Single Supply, 4 to 1 Multiplexer and DPDT Analog Switches

Renesas Electronics 

ISL84524, ISL84525

Detailed Description

The ISL84524 and ISL84525 operate from a single 2V to

12V supply with low on-resistance and high speed operation.

The devices are especially well suited to portable battery

powered equipment thanks to the low operating supply

voltage (2.7V), low power consumption (3µW), low leakage

currents (25nA max), and the tiny MSOP packaging. High

frequency applications also benefit from the wide bandwidth,

and the very high off isolation (75dB) and crosstalk rejection

(-85dB).

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 GND (see

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

be applied before any input signals, and the input signal

voltages must remain between V+ and GND.

If these conditions cannot be guaranteed, then precautions

must be implemented to prohibit the current and voltage at

the logic pin and signal pins from exceeding the maximum

ratings of the switch. The following two methods can be used

to provide additional protection to limit the current in the

event that the voltage at a signal pin or logic pin goes below

ground or above the V+ rail.

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

series with the logic 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 acceptable for the signal path inputs.

Adding a series resistor to the switch input defeats the

purpose of using a low RON switch. Connecting Schottky

diodes to the signal pins (as shown in Figure 8) 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+

INH

ADDX

VNX

VCOM

OPTIONAL

SCHOTTKY

DIODE

GND

FIGURE 8. OVERVOLTAGE PROTECTION

FN6042 Rev 3.00

February 24, 2012

Power-Supply Considerations

The ISL8452X construction is typical of most CMOS analog

switches, except that they have 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

maximum supply voltage, the ISL8452X 15V maximum

supply voltage provides plenty of room for the 10% tolerance

of 12V supplies, as well as room for overshoot and noise

spikes.

The minimum recommended supply voltage is 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 (starting on page 3) and

Typical Performance Curves (starting on page 10) for details.

V+ and GND also power the internal logic and level shifters.

The level shifters convert 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 TTL compatible (0.8V and 2.4V) over a

supply range of 2V to 11V. At 12V the VIH level is about 2.5V.

This is still below the TTL guaranteed high output minimum

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

with a 12V supply, use a logic family that provides a VOH

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 50 systems, signal response is reasonably flat even past

100MHz (see Figure 13). Figure 13 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 14 details the high Off Isolation and Crosstalk

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

about 55dB 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.

Page 9 of 13

Share Link: