AD8276/AD8277

Rev. A | Page 17 of 20

The differential output voltage and common-mode voltage of

the AD8226 is shown in the following equations:

Refer to the AD8226 data sheet for additional information.

2

12

3

14

13

11

40kΩ

40kΩ

40kΩ

+VS

–IN

+IN

+OUT

40kΩ

AD8277

6

10

5

8

9

4

40kΩ

40kΩ

40kΩ

–VS

40kΩ

–OUT

Figure 48. AD8277 Differential Output Configuration

The two difference amplifiers of the AD8277 can be configured

to provide a differential output, as shown in Figure 48. This

differential output configuration is suitable for various applications,

such as strain gage excitation and single-ended-to-differential

conversion. The differential output voltage has a gain of 2 as

shown in the following equation:

CURRENT SOURCE

The AD8276 difference amplifier can be implemented as part

of a voltage-to-current converter or a precision constant current

source as shown in Figure 49. Using an integrated precision

solution such as the AD8276 provides several advantages over

a discrete solution, including space-saving, improved gain accuracy,

and temperature drift. The internal resistors are tightly matched

to minimize error and temperature drift. If the external resistors,

R1 and R2, are not well-matched, they become a significant

source of error in the system, so precision resistors are recom-

mended to maintain performance. The ADR821 provides a

precision voltage reference and integrated op amp that also

reduces error in the signal chain.

The AD8276 has rail-to-rail output capability that allows higher

current outputs.

REF

1

2

3

4

5

10

9

8

7

6

V–

V+

ADR821

40kΩ

40kΩ

R1

R2

2N3904

40kΩ

40kΩ

V+

7

4

5

6

2

3

1

AD8276

–2.5V

R1 = R2

Figure 49. Constant Current Source

VOLTAGE AND CURRENT MONITORING

Voltage and current monitoring is critical in the following

applications: power line metering, power line protection, motor

control applications, and battery monitoring. The AD8276/

AD8277 can be used to monitor voltages and currents in a

system, as shown in Figure 50. As the signals monitored by the

AD8276/AD8277 rise above or drop below critical levels, a

circuit event can be triggered to correct the situation or raise

a warning.

OP1177

R

AD8276

R

AD8276

R

AD8276

R

AD8276

R

AD8276

8:1

ADC

Figure 50.Voltage and Current Monitoring in 3-Phase Power Line Protection

Using the AD8276

Figure 50 shows an example of how the AD8276 can be used to

the common or zero lines. Couplers or transformers interface

the power lines to the front-end circuitry and provide

attenuation, isolation, and protection.

On the current monitoring side, current transformers (CTs)

step down the power-line current and isolate the front-end

circuitry from the high voltage and high current lines. Across

the inputs of each difference amplifier is a shunt resistor that

converts the coupled current into a voltage. The value of the