ADG3242

Rev. A | Page 13 of 16

BUS ISOLATION

A common requirement of bus architectures is low capacitance

loading of the bus. Such systems require bus bridge devices that

extend the number of loads on the bus without exceeding the spec-

ifications. Because the ADG3242 is designed specifically for

applications that do not need drive, yet require simple logic func-

tions, it solves this requirement. The device isolates access to

the bus, thus minimizing capacitance loading.

BUS/

BACKPLANE

LOAD A

LOAD C

LOAD B

LOAD D

BUS SWITCH

LOCATION

Figure 35. Location of Bus Switched in a Bus Isolation Application

HOT PLUG AND HOT SWAP ISOLATION

The ADG3242 is suitable for hot swap and hot plug applications.

The output signal of the ADG3242 is limited to a voltage that

Figure 34. Thus, the switch acts like a buffer to take the impact

from the hot insertion, protecting vital and expensive chipsets

from damage.

In hot plug applications, the system cannot be shut down when

new hardware is being added. To overcome this, a bus switch can

be positioned on the backplane between the bus devices and the

hot plug connectors. The bus switch is turned off during hot plug.

Figure 36 shows a typical example of this type of application.

PLUG-IN

CARD (1)

CARD I/O

CARD I/O

RAM

BUS

CPU

PLUG-IN

CARD (2)

Figure 36. ADG3242 in a Hot Plug Application

There are many systems, such as docking stations, PCI boards for

servers, and line cards for telecommunications switches, that

require the ability to handle hot swapping. If the bus can be isolated

prior to insertion or removal, there is more control over the hot

swap event. This isolation can be achieved using bus switches. The

bus switches are positioned on the hot swap card between the con-

nector and the devices. During hot swap, the ground pin of the

hot swap card must connect to the ground pin of the backplane

before connecting to any other signal or power pins.

ANALOG SWITCHING

Bus switches are used in many analog switching applications,

for example, video graphics. Bus switches can have lower on

resistance, smaller on and off channel capacitance, and better

frequency performance than their analog counterparts. The

bus switch channel itself, consisting solely of an NMOS switch,

limits the operating voltage (see Figure 4 for a typical plot), but

in many cases, this does not present an issue.

HIGH IMPEDANCE DURING POWER-UP/POWER-

DOWN

To ensure the high impedance state during power-up or power-

minimum value of the resistor is determined by the current sink-

ing capability of the driver.