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AD7766

Preliminary Technical Data

Rev. PrD | Page 16 of 18

DRIVING THE AD7766

The AD7766 must be driven with fully differential inputs. The

common mode voltage of the differential inputs to the AD7766

device and thus the limits on the differential inputs are set by

the reference voltage VREF applied to the device. The common

mode voltage of the AD7766 is VREF/2. Where the AD7766 VREF

pin is supplied with a 5V supply (the ADR435 is

reccommended) the common mode is at 2.5V. This means that

the max inputs that can be applied on the AD7766 differential

inputs are a 5V pk-pk input around 2.5V.

VREF

VIN+

VIN–

VREF

Figure 16 Maximum differential inputs to the AD7766

An analog voltage of 2.5V supplies the AD7766 AVDD pin.

However, the AD7766 allows the user to apply a reference

voltage of up to 5V. This provides the user with an increased

full-scale range, offering the user the option of using the

AD7766 with a larger LSB voltage size Figure 16 shows the

maximum and minimum inputs to the AD7766.

DIFFERENTIAL SIGNAL SOURCE

An example of some recommended driving circuitry that can be

employed in conjunction with the AD7766 is shown in Figure

17. Figure 17 shows how the ADA4841 device can be used to

drive an input to the AD7766 from a differential source. Each of

the differential is driven by an ADA4841 device.

AIN+

ADA4841

499R

VIN-

VIN+

AD7766

10nF

3R3

499R

3.3nF

AIN-

ADA4841

499R

2x VCM

3R3

499R

3.3nF

REF+

ADR425

2.5V

Figure 17. Driving the AD7766 from a fully differential source

SINGLE-ENDED SIGNAL SOURCE

In the case where the AD7766 is being supplied from a single-

ended source the following application circuit can be used to

drive the AD7766 device. Figure 18 shows how the ADA4941

single to differential amplifier can be used to create a fully

differential input to the AD7766. The single-ended signal input

is applied to the positive input of the ADA4941 device

ADA4941

DIS

V-

OUT-

REF

V+

OUT+

Vss -

Vss +

2 xV

VIN-

VIN+

AD7766

REF+

ADR425

2.5V

Ain +

offset

Figure 18. Driving the AD7766 from a single- ended source.

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