REV. 0
ADG3246
–9–
BUS SWITCH APPLICATIONS
Mixed Voltage Operation, Level Translation
Bus switches can be used to provide an ideal solution for interfac-
ing between mixed voltage systems. The ADG3246 is suitable
for applications where voltage translation from 3.3 V technology to
a lower voltage technology is needed. This device can translate
from 3.3 V to 1.8 V, 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 ADG3246 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
ADG3246
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 (SEL = VCC) 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.
ADG3246
2.5V
3.3V
2.5V
3.3V
Figure 5. 3.3 V to 2.5 V Voltage Translation,
SEL = V
CC
In this case, the output will be limited to 2.5 V, as shown in
Figure 6.
VIN
2.5V
VOUT
0V
3.3V
SWITCH
INPUT
S
WITCH
OU
TPUT
3.3V SUPPLY
SEL = 3.3V
Figure 6. 3.3 V to 2.5 V Voltage Translation,
SEL = V
CC
This device can be used for translation from 2.5 V to 3.3 V
devices and also between two 3.3 V devices.
2.5 V to 1.8 V Translation
When VCC is 2.5 V (SEL = VCC) 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.
ADG3246
1.8V
2.5V
Figure 7. 2.5 V to 1.8 V Voltage Translation,
SEL = V
CC
In this case, the output will be limited to approximately 1.8 V,
as shown in Figure 7.
VIN
1.8V
VOUT
0V
2.5V
SWITCH
INPUT
S
WITCH
OU
TPUT
2.5V SUPPLY
SEL = 2.5V
Figure 8. 2.5 V to 1.8 V Voltage Translation,
SEL = V
CC
3.3 V to 1.8 V Translation
The ADG3246 offers the option of interfacing between a 3.3 V
device and a 1.8 V device. This is possible through use of the
SEL pin.
SEL pin: An active low control pin. SEL activates internal cir-
cuitry in the ADG3246 that allows voltage translation between
3.3 V devices and 1.8 V devices.
ADG3246
1.8V
3.3V
Figure 9. 3.3 V to 1.8 V Voltage Translation,
SEL = 0 V
When VCC is 3.3 V and the input signal range is 0 V to VCC, the
maximum output signal will be clamped to 1.8 V, as shown in
Figure 9. To do this, the
SEL pin must be tied to Logic 0. If
SEL is unused, it should be tied directly to V
CC.