AD7766

Rev. C | Page 20 of 24

DRIVING THE AD7766/AD7766-1/AD7766-2

R1 and R2 set the attenuation ratio between the input range and

the desired input resistance, signal bandwidth, antialiasing, and

noise contribution. The ratio of R2 to R1 should be equal to the

ratio of REF to the peak-to-peak input voltage. For example, for

the ±10 V range with a 4 kΩ impedance, R2 = 1 kΩ and R1 = 4 kΩ.

The AD7766/AD7766-1/AD7766-2 must be driven with fully

differential inputs. The common-mode voltage of the differential

inputs to the AD7766/AD7766-1/AD7766-2 devices, and therefore

the limits on the differential inputs, is set by the reference voltage

ADR435, or ADR425), the common mode is at 2.5 V, meaning

that the maximum inputs that can be applied on the AD7766/

AD7766-1/AD7766-2 differential inputs are a 5 V p-p input

around 2.5 V.

0V

2

0V

2

ADA4841-1

15Ω

3.3nF

1kΩ

ADA4841-1

15Ω

3.3nF

1kΩ

4

5

1

2

AD7766

2.2nF

2.2nF

*

ADR4xx

ADP3330-2.5

2.5V

2.5V TO 5V

REFERENCE

VOLTAGE

1kΩ

1kΩ

1kΩ

1kΩ

AIN+

AIN–

Figure 39. Maximum Differential Inputs to the AD7766

An analog voltage of 2.5 V supplies the AD7766/AD7766-1/

allow the user to apply a reference voltage of up to 5 V. This

provides the user with an increased full-scale range, offering the

user the option of using the AD7766/AD7766-1/AD7766-2 with

a greater LSB voltage. Figure 39 shows the maximum inputs to

the AD7766.

Figure 40. Driving the AD7766 from a Fully Differential Source

15Ω

15Ω

100µF

R1

100nF

100nF

2.5V

VOUT = 5V REF

5.2V

–0.2V

R4

R2

R6

R3

R5

AGND

AD7766

2.2nF

2.2nF

ADA4941-1

IN

FB

OUTP

OUTN

REF

ADR425

ADR445

ADP3330-2.5

LDO

DGND

0.1µF

0.1µF

DIFFERENTIAL SIGNAL SOURCE

An example of recommended driving circuitry that can be used

in conjunction with the AD7766 is shown in Figure 40. Figure 40

shows how the ADA4841-1 device can be used to drive an input

to the AD7766 from a differential source. Each of the differential

paths is driven by an ADA4841-1 device.

SINGLE-ENDED SIGNAL SOURCE

For applications using a single-ended analog signal, either

bipolar or unipolar, the ADA4941-1 single-ended-to-differential

driver creates a fully differential input to the AD7766. The

schematic is shown in Figure 41.

Figure 41. Driving the AD7766 from a Single-Ended Source

Table 8. Resistor Values Required When Using the Differential-to-Single-Ended Circuit with ADA4941 (See Figure 41)

OUT+ (V)

OUT− (V)

R1 (kΩ)

R2 (kΩ)

R4 (kΩ)

R3 = R5 = R6 (kΩ)

+20, −20

2.5

2.203

−0.01, +4.96

5.01, 0.04

8.06

1

12.7

10

+10, −10

2.5

2.000

0.01, 4.99

4.99, 0.01

4.02

1

15

10

+5, −5

2.5

1.667

0.00, 5.00

5.00, 0.00

2

1

20

10