REV. 0
ADG3249
–9–
BUS SWITCH APPLICATIONS
Mixed Voltage Operation, Level Translation
Bus switches can provide an ideal solution for interfacing
between mixed voltage systems. The ADG3249 is suitable for
applications 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
microprocessor. The microprocessor may not have 3.3 V toler-
ant inputs, therefore placing the ADG3249 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
ADG3249
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 V
CC
is 3.3 V (SEL = 3.3 V) and the input signal range is
0 V to V
CC
, the maximum output signal will be clamped to
within a voltage threshold below the V
CC
supply. 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.
ADG3249
2.5V
2.5V
3.3V
2.5V
3.3V
Figure 5. 3.3 V to 2.5 V Voltage Translation,
SEL
= V
CC
V
IN
2.5V
V
OUT
0V
3.3V
SWITCH
INPUT
SWITCH
OUTPUT
3.3V SUPPLY
SEL = 3.3V
Figure 6. 3.3 V to 2.5 V Voltage Translation,
SEL
= V
CC
2.5 V to 1.8 V Translation
When V
CC
is 2.5 V (SEL = 2.5 V) and the input signal range is
0 V to V
CC
, the maximum output signal will, as before, be clamped
to within a voltage threshold below the V
CC
supply. In this case,
the output will be limited to approximately 1.8 V, as shown
in Figure 8.
ADG3249
1.8V
2.5V
2.5V
Figure 7. 2.5 V to 1.8 V Voltage Translation,
SEL
= 2.5 V
CC
V
IN
1.8V
V
OUT
0V
2.5V
SWITCH
INPUT
SWITCH
OUTPUT
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 ADG3249 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. The SEL pin is an active low control pin. SEL acti-
vates internal circuitry in the ADG3242 that allows voltage
translation between 3.3 V devices and 1.8 V devices.
When V
CC
is 3.3 V and the input signal range is 0 V to V
CC
, 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
.
ADG3249
1.8V
3.3V
3.3V
Figure 9. 3.3 V to 1.8 V Voltage Translation,
SEL
= 0 V
V
IN
1.8V
V
OUT
0V
3.3V
SWITCH
INPUT
SWITCH
OUTPUT
3.3V SUPPLY
SEL = 0V
Figure 10. 3.3 V to 1.8 V Voltage Translation,
SEL
= 0 V
