ADG3242BRJ-R2 datasheet(12/16 Pages) AD

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ADG3242

Rev. A | Page 12 of 16

BUS SWITCH APPLICATIONS

MIXED VOLTAGE OPERATION, LEVEL

TRANSLATION

Bus switches provide an ideal solution for interfacing between

mixed voltage systems. The ADG3242 is suitable for applications

where voltage translation from 3.3 V technology to a lower voltage

technology is needed. This device translates from 3.3 V to 1.8 V,

from 2.5 V to 1.8 V, or from a bidirectional 3.3 V directly to 2.5 V.

Figure 28 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 does not have 3.3 V tolerant inputs,

therefore, placing the ADG3242 between the two devices allows

the devices to communicate easily. The bus switch directly connects

the two blocks, therefore introducing minimal propagation delay,

timing skew, or noise.

3.3V ADC

2.5V

3.3V

2.5V

MICROPROCESSOR

3.3V

Figure 28. Level Translation Between a 3.3 V ADC and a 2.5 V Microprocessor

3.3 V TO 2.5 V TRANSLATION

When VCC is 3.3 V (SEL = 3.3 V) and the input signal range is

0 V to VCC, the maximum output signal is clamped to within a

voltage threshold below the VCC supply. In this case, the output

is limited to 2.5 V, as shown in Figure 30. This device can be used

for translation from 2.5 V to 3.3 V devices and also between two

3.3 V devices.

ADG3242

2.5V

3.3V

2.5V

3.3V

Figure 29. 3.3 V to 2.5 V Voltage Translation, SEL = VCC

VIN

2.5V

VOUT

3.3V

SWITCH

INPUT

3.3V SUPPLY

SEL = 3.3V

Figure 30. 3.3 V to 2.5 V Voltage Translation, SEL = VCC

2.5 V TO 1.8 V TRANSLATION

When VCC is 2.5 V (SEL = 2.5 V) and the input signal range is

0 V to VCC, the maximum output signal is also clamped within

a voltage threshold below the VCC supply. In this case, the output

is limited to approximately 1.8 V, as shown in Figure 32.

ADG3242

1.8V

2.5V

Figure 31. 2.5 V to 1.8 V Voltage Translation, SEL = 2.5 VCC

VIN

1.8V

VOUT

2.5V

SWITCH

INPUT

2.5V SUPPLY

SEL = 2.5V

Figure 32. 2.5 V to 1.8 V Voltage Translation, SEL = VCC

3.3 V TO 1.8 V TRANSLATION

The ADG3242 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 activates inter-

nal circuitry in the ADG3242 that allows voltage translation

between 3.3 V devices and 1.8 V devices.

When VCC is 3.3 V and the input signal range is 0 V to VCC, the

maximum output signal is clamped to 1.8 V, as shown in Figure 34.

To do this, the SEL pin must be tied to Logic 0. If SEL is unused,

it can be tied directly to VCC.

ADG3242

1.8V

3.3V

Figure 33. 3.3 V to 1.8 V Voltage Translation, SEL = 0 V

VIN

1.8V

VOUT

3.3V

SWITCH

INPUT

3.3V SUPPLY

SEL = 0V

Figure 34. 3.3 V to 1.8 V Voltage Translation, SEL = 0 V

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