ADR391/ADR392/ADR395

Rev. H | Page 16 of 20

General-Purpose Current Source

Many times in low power applications, the need arises for a

precision current source that can operate on low supply voltages.

The ADR391/ADR392/ADR395 can be configured as a precision

current source. As shown in Figure 37, the circuit configuration

is a floating current source with a grounded load. The reference

current into the load. With this configuration, circuit precision

is maintained for load currents in the range from the reference

supply current, typically 90 μA to approximately 5 mA.

ADR39x

GND

R1

P1

R1

0.1µF

SHDN

ADJUST

Figure 37. A General-Purpose Current Source

High Power Performance with Current Limit

In some cases, the user may want higher output current delivered

to a load and still achieve better than 0.5% accuracy out of the

ADR39x. The accuracy for a reference is normally specified on

the data sheet with no load. However, the output voltage changes

with load current.

The circuit shown in Figure 38 provides high current without

compromising the accuracy of the ADR39x. The series pass

transistor, Q1, provides up to 1 A load current. The ADR39x

delivers only the base drive to Q1 through the force pin. The

sense pin of the ADR39x is a regulated output and is connected

to the load.

The Transistor Q2 protects Q1 during short-circuit limit faults

by robbing its base drive. The maximum current is

(6)

SHDN

GND

U1

ADR39x

Q2

Q2N2222

R1

4.7k

Ω

Q1

Q2N4921

Figure 38. ADR39x for High Power Performance with Current Limit

A similar circuit function can also be achieved with the

Darlington transistor configuration, as shown in Figure 39.

ADR39x

GND

U1

SHDN

Q1

Q2N2222

R1

4.7k

Ω

Q2

Q2N4921

Figure 39. ADR39x for High Output Current

with Darlington Drive Configuration