ADR121/ADR125/ADR127

Rev. B | Page 17 of 20

APPLICATIONS INFORMATION

BASIC VOLTAGE REFERENCE CONNECTION

The circuit in Figure 49 illustrates the basic configuration for

the ADR12x family voltage reference.

NC

NC

ADR12x

1

2

3

6

5

4

NC

GND

0.1µF

0.1µF

OUTPUT

INPUT

+

+

Figure 49. Basic Configuration for the ADR12x Family

STACKING REFERENCE ICs FOR ARBITRARY

OUTPUTS

Some applications may require two reference voltage sources

that are a combined sum of the standard outputs. Figure 50

shows how this stacked output reference can be implemented.

NC

NC

ADR12x

1

2

3

6

5

4

NC

GND

NC

NC

ADR12x

1

2

3

6

5

4

NC

GND

0.1µF

0.1µF

0.1µF

0.1µF

U2

U1

Figure 50. Stacking References with the ADR12x

Two reference ICs are used and fed from an unregulated input,

voltage and the terminal of U2. U1 and U2 are chosen for the

two voltages that supply the required outputs (see Table 6). For

Table 6. Required Outputs

U1/U2

ADR127/ADR121

1.25 V

3.75 V

ADR127/ADR125

1.25 V

6.25 V

ADR121/ADR125

2.5 V

7.5 V

NEGATIVE PRECISION REFERENCE WITHOUT

PRECISION RESISTORS

A negative reference is easily generated by adding an op

amp, for example, the AD8603, and is configured as shown in

reference can be taken directly from the output of the op amp.

The op amp must be dual-supply, low offset, and rail-to-rail if

the negative supply voltage is close to the reference output.

NC

NC

ADR127

AD8603

1

2

3

6

5

4

NC

GND

–

V+

V–

3

2

+

0.1µF

1kΩ

Figure 51. Negative Reference

GENERAL-PURPOSE CURRENT SOURCE

In low power applications, the need can arise for a precision

current source that can operate on low supply voltages. The

ADR12x can be configured as a precision current source (see

Figure 52). The circuit configuration shown is a floating current

source with a grounded load. The reference’s output voltage is

load. With this configuration, circuit precision is maintained for

load currents ranging from the reference’s supply current, typi-

cally 85 μA, to approximately 5 mA.

NC

NC

ADR12x

1

2

3

6

5

4

NC

GND

P1

Figure 52. ADR12x Trim Configuration