REV. 0
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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
ADG3243
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
When VCC is 3.3 V and the input signal range is 0 V to VCC, the
maximum output signal will be clamped to within a voltage
threshold below the VCC supply.
ADG3243
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.
VIN
2.5V
VOUT
0V
3.3V
SWITCH
INPUT
S
WITCH
OU
TPUT
3.3V SUPPLY
Figure 6. 3.3 V to 2.5 V Voltage Translation
2.5 V to 1.8 V Translation
When VCC is 2.5 V and the input signal range is 0 V to VCC, the
maximum output signal will, as before, be clamped to within a
voltage threshold below the VCC supply. In this case, the output
will be limited to approximately 1.8 V, as shown in Figure 8.
ADG3243
1.8V
2.5V
Figure 7. 2.5 V to 1.8 V Voltage Translation
VIN
1.8V
VOUT
0V
2.5V
SWITCH
INPUT
S
WITCH
OU
TPUT
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
below the VCC supply, as shown in Figures 6 and 8. Therefore
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.