REV. 0

ADG3248

–7–

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 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 1 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 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.

3.3V ADC

2.5V

3.3V

2.5V

MICROPROCESSOR

3.3V

Figure 1. 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

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

Figure 3. 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

3.3V

2.5V

3.3V

Figure 2. 3.3 V to 2.5 V Voltage Translation

2.5V

0V

3.3V

SWITCH

INPUT

3.3V SUPPLY

Figure 3. 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 5.

ADG3248

1.8V

2.5V

2.5V

Figure 4. 2.5 V to 1.8 V Voltage Translation

1.8V

0V

2.5V

SWITCH

INPUT

2.5V SUPPLY

Figure 5. 2.5 V to 1.8 V Voltage Translation

Analog Switching

Bus switches can be used in many analog switching applications,

for example, video graphics. Bus switches can have lower on

resistance, smaller ON and OFF channel capacitance, and thus

improved frequency performance than their analog counterparts.

The bus switch channel itself, consisting solely of an NMOS

switch, limits the operating voltage (see TPC 1 for a typical

plot), but in many cases, this does not present an issue.