ADR391/ADR392/ADR395

Rev. H | Page 15 of 20

APPLICATIONS INFORMATION

BASIC VOLTAGE REFERENCE CONNECTION

The circuit shown in Figure 34 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

0.1µF

0.1µF

*

*

OUTPUT

*NOT REQUIRED

ADR39x

SHDN

GND

Figure 34. 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 35 shows

how this stacked output reference can be implemented.

GND

U2

U1

C2

0.1µF

C2

0.1µF

OUTPUT TABLE

U1/U2

SHDN

ADR391/ADR391

ADR392/ADR392

ADR395/ADR395

2.5

4.096

5

5.0

8.192

10

GND

SHDN

Figure 35. Stacking Voltage References with the ADR391/ADR392/ADR395

The outputs of the individual ICs are connected in series, which

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

two voltages that supply the required outputs (see the Output

Table in Figure 35). For example, if both U1 and U2 are ADR391s,

While this concept is simple, a precaution is required. Because

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 an external resistor must

provide a path for this current. If the U1 minimum load is not

well defined, the external resistor should be used and set to a

value that conservatively passes 600 μA of current with the

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.

A Negative Precision Reference without Precision Resistors

A negative reference can be easily generated by adding an A1

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

SHDN

Figure 36. Negative Reference