ADR390/ADR391/ADR392/ADR395

Rev. F | Page 17 of 20

APPLICATIONS

BASIC VOLTAGE REFERENCE CONNECTION

The circuit shown in Figure 41 illustrates the basic configuration

for the ADR39x family. Decoupling capacitors are not required

for circuit stability. The ADR39x family is capable of driving

capacitive loads from 0 µF to 10 µF. However, a 0.1 µF ceramic

output capacitor is recommended to absorb and deliver the

charge, as required by a dynamic load.

SHUTDOWN

INPUT

0.1

µF

0.1

µF

*

*

OUTPUT

*NOT REQUIRED

ADR39x

SHDN

GND

Figure 41. Basic Configuration for the ADR39x Family

Stacking Reference ICs for Arbitrary Outputs

Some applications may require two reference voltage sources,

which are a combined sum of standard outputs. Figure 42 shows

how this stacked output reference can be implemented.

GND

U2

1

2

3

4

5

U1

C2

0.1

µF

3

4

1

2

C2

0.1

µF

GND

5

OUTPUT TABLE

U1/U2

ADR390/ADR390

ADR391/ADR391

ADR392/ADR392

ADR395/ADR395

2.048

2.5

4.096

5

4.096

5.0

8.192

10

SHDN

SHDN

Figure 42. Stacking Voltage References with the

ADR390/ADR391/ADR392/ADR395

The outputs of the individual ICs are simply connected in

this voltage and the terminal voltage of U2. U1 and U2 are

simply chosen for the two voltages that supply the required

outputs (see the Output Table in Figure 42). For example, if

While this concept is simple, a precaution is required. Since the

lower reference circuit must sink a small bias current from U2

plus the base current from the series PNP output transistor in

U2, either the external load of U1 or R1 must provide a path for

this current. If the U1 minimum load is not well defined, the R1

resistor should be used and set to a value that will conservatively

that the two U1 and U2 reference circuits are treated locally as

macrocells; each has its own bypasses at input and output for

best stability. Both U1 and U2 in this circuit can source dc

currents up to their full rating. The minimum input voltage,

dropout voltage of U2.

A Negative Precision Reference without Precision

Resistors

A negative reference can be easily generated by adding an A1 op

are at virtual ground and, therefore, the negative 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.

GND

A1

2

4

3

5

1

SHDN

Figure 43. Negative Reference