AD8275

Rev. 0 | Page 12 of 16

POWER SUPPLIES

Use a stable dc voltage to power the AD8275. Noise on the

supply pins can adversely affect performance. Place a bypass

capacitor of 0.1 μF between each supply pin and ground, as

close to each pin as possible. A tantalum capacitor of 10 μF

should also be used between each supply and ground. It can

be farther away from the AD8275 and typically can be shared

by other precision integrated circuits.

REFERENCE

The reference terminals are used to provide a bias level for the

output. For example, in a single-supply 5 V operation, the

reference terminals can be set so that the output is biased at

2.5 V. This ensures that the output can swing positive or

negative around a 2.5 V level.

Figure 33 and Figure 34 illustrate two different ways to set the

reference voltage. See the Basic Connection section for the

differences between the two settings.

The allowable reference voltage range is a function of the

common-mode input and supply voltages. The REF1 and REF2

The REFx terminals should be driven by low source impedance

because parasitic resistance in series with REF1 and REF2 can

adversely affect CMRR and gain accuracy.

20kΩ

20kΩ REF2

REF1

50kΩ

–IN

INCORRECT

CORRECT

7

4

5

6

8

1

2

50kΩ

50kΩ

20kΩ

20kΩ

10kΩ

3

–IN

+IN

REF2

REF1

OUT

SENSE

3

AD8275

7

4

5

6

8

2

50kΩ

10kΩ

3

+IN

OUT

SENSE

AD8275

1

20kΩ

20kΩ REF2

REF1

50kΩ

–IN

7

4

5

6

8

1

2

50kΩ

50kΩ

20kΩ

20kΩ

10kΩ

3

–IN

+IN

REF2

REF1

OUT

SENSE

AD8275

4

5

6

8

2

50kΩ

10kΩ

3

+IN

OUT

SENSE

AD8275

1

–IN

2

50

0kΩ R

REF1

1

0kΩ

5

+IN

NSE

–IN

2

50

0kΩ R

REF1

1

0kΩ

5

+IN

O

NSE

7

Figure 35. REF1 and REF2 Pin Guidelines

COMMON-MODE INPUT VOLTAGE RANGE

The common-mode voltage range is a function of the input

voltage range of the internal op amp, the supply voltage, and

the reference voltage.

Equation 1 expresses the maximum positive common-mode

voltage range.

Equation 2 expresses the minimum common-mode voltage

range.

(2)

The voltage range of the internal op amp varies depending on

temperature. The equations reflect a typical input voltage range

expected common-mode ranges for typical configurations.

Table 5. Expected Common-Mode Voltage Range for Typical

Configurations

5

5

0

23.5

−12.6

5

2.5

0

29.8

−6.4

5

4.096

0

25.8

−10.4

3.3

3.3

0

5.4

−8.4

3.3

2.5

0

7.4

−6.4

5

5

5

11.0

−25.1

5

4.096

4.096

15.5

−20.6

5

3

3

21.0

−15.1

5

2.5

2.5

23.5

−12.6

5

2.048

2.048

25.8

−10.4

5

1.25

1.25

29.8

−6.4

5

0

0

36.0

−0.1

INPUT PROTECTION

The inputs of the AD8275, +IN and −IN, are protected by ESD

operating on a single +5 V supply, the ESD diode conducts at

input voltages less than −35 V and greater than +40 V.

If the input voltage is expected to exceed the maximum ratings

of the AD8275, use external transorbs. Adding series resistors to

the inputs of the AD8275 is not recommended because the

internal resistor ratios are matched to provide optimal CMRR

and gain accuracy. Adding external series resistors to the input

degrades the performance of the AD8275.

All other pins are protected by ESD diodes that clamp 0.5 V

beyond either supply rail. For example, the voltage range of the

REF1 and REF2 pins on a 5 V supply is −0.5 V to +5.5 V.