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

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

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

2.5V

0V

3.3V

SWITCH

INPUT

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

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

1.8V

0V

2.5V

SWITCH

INPUT

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.

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

ADG3249

1.8V

3.3V

3.3V

Figure 9. 3.3 V to 1.8 V Voltage Translation,

SEL = 0 V

1.8V

0V

3.3V

SWITCH

INPUT

3.3V SUPPLY

SEL = 0V

Figure 10. 3.3 V to 1.8 V Voltage Translation,

SEL = 0 V