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ADG3243

BUS SWITCH APPLICATIONS

Mixed Voltage Operation, Level Translation

Bus switches can provide an ideal solution for interfacing between

mixed voltage systems. The ADG3243 is suitable for applica-

tions where voltage translation from 3.3 V technology to a lower

voltage technology is needed. This device can translate from

2.5 V to 1.8 V or bidirectionally from 3.3 V directly to 2.5 V.

Figure 4 shows a block diagram of a typical application in which a

user needs to interface between a 3.3 V ADC and a 2.5 V micro-

processor. The microprocessor may not have 3.3 V tolerant inputs,

therefore placing the ADG3243 between the two devices allows

the devices to communicate easily. The bus switch directly

connects the two blocks, thus introducing minimal propagation

delay, timing skew, or noise.

3.3V ADC

2.5V

3.3V

2.5V

MICROPROCESSOR

3.3V

Figure 4. Level Translation between a 3.3 V ADC

and a 2.5 V Microprocessor

3.3 V to 2.5 V Translation

maximum output signal will be clamped to within a voltage

ADG3243

2.5V

2.5V

3.3V

2.5V

3.3V

Figure 5. 3.3 V to 2.5 V Voltage Translation

In this case, the output will be limited to 2.5 V, as shown in

Figure 6. This device can be used for translation from 2.5 V to

3.3 V devices and also between two 3.3 V devices.

2.5V

0V

3.3V

SWITCH

INPUT

3.3V SUPPLY

Figure 6. 3.3 V to 2.5 V Voltage Translation

2.5 V to 1.8 V Translation

maximum output signal will, as before, be clamped to within a

will be limited to approximately 1.8 V, as shown in Figure 8.

ADG3243

1.8V

2.5V

2.5V

Figure 7. 2.5 V to 1.8 V Voltage Translation

1.8V

0V

2.5V

SWITCH

INPUT

2.5V SUPPLY

Figure 8. 2.5 V to 1.8 V Voltage Translation

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

specifications. Because the ADG3243 is designed specifically for

applications that do not need drive yet require simple logic

functions, 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 9. Location of Bus Switched in a Bus

Isolation Application

Hot Plug and Hot Swap Isolation

The ADG3243 is suitable for hot swap and hot plug applications.

The output signal of the ADG3243 is limited to a voltage that is

the switch acts like a buffer to take the impact from 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 10 shows a typical example of this type of application.