Datasheet

ADG3248
Rev. A | Page 10 of 12
BUS SWITCH APPLICATIONS
MIXED VOLTAGE OPERATION, LEVEL
TRANSLATION
Bus switches can provide an ideal solution for interfacing between
mixed voltage systems. The ADG3248 is suitable for applications
in which 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 20 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
tolerant inputs; therefore, placing the ADG3248 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.
2.5
V
3.3
V
3.3
V
ADG3248
3.3V ADC
2.5V
MICROPROCESSOR
04404-020
Figure 20. 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 and the input signal range is 0 V to V
CC
, the
maximum output signal is clamped to within a voltage threshold
below the V
CC
supply.
In this case, the output is limited to 2.5 V, as shown in
Figure 22.
This device can be used for translation from 2.5 V to 3.3 V
devices and also between two 3.3 V devices.
ADG3248
2.5V
2.5V
3.3
V
3.3V
2.5V
04404-021
Figure 21. 3.3 V to 2.5 V Voltage Translation
2.5V
0V 3.3V
3.3V SUPPLY
V
OUT
V
IN
SWITCH
INPUT
SWITCH
OUTPUT
04404-022
Figure 22. 3.3 V to 2.5 V Voltage Translation
2.5 V to 1.8 V Translation
When V
CC
is 2.5 V and the input signal range is 0 V to V
CC
, the
maximum output signal is, as before, clamped to within a voltage
threshold below the V
CC
supply. In this case, the output is limited
to approximately 1.8 V, as shown in
Figure 24.
ADG3248
1.8V
2.5
V
2.5V
04404-023
Figure 23. 2.5 V to 1.8 V Voltage Translation
1.8V
0V 2.5V
2.5V SUPPLY
V
OUT
V
IN
SWITCH
INPUT
SWITCH
OUTPUT
04404-024
Figure 24. 2.5 V to 1.8 V Voltage Translation
ANALOG SWITCHING
Bus switches can be used in many analog switching applica-
tions, for example, video graphics. Bus switches can have lower
on resistance, smaller on and off channel capacitance, and thus
better frequency performance than their analog counterparts.
The bus switch channel itself, consisting solely of an NMOS
switch, limits the operating voltage (see
Figure 3 for a typical
plot) but, in many cases, this does not present an issue.