PRELIMINARY TECHNICAL DATA

REV. PrD

ADG3247

–9–

BUS SWITCH APPLICATIONS

Mixed Voltage Operation, Level Translation

Bus switches can be used to provide an ideal solution for inter-

facing between mixed voltage systems. The ADG3247 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 ADG3247 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

ADG3247

2.5V

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.

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

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

ADG3247

1.8V

2.5V

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.

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 ADG3247 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

circuitry in the ADG3247 that allows voltage translation between

3.3 V devices and 1.8 V devices.

ADG3247

1.8V

3.3V

3.3V

Figure 9. 3.3 V to 1.8 V Voltage Translation,

SEL = 0 V

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