ADR390/ADR391/ADR392/ADR395

Rev. F | Page 18 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 vol-

tages. ADR390/ADR391/ADR392/ADR395 can be configured

as a precision current source. As shown in Figure 45, the circuit

configuration is a floating current source with a grounded load.

which sets the output current into the load. With this

configuration, circuit precision is maintained for load currents

in the range from the reference’s supply current, typically 90 µA

to approximately 5 mA.

ADR39x

GND

R1

ADJUST

P1

R1

0.1

µF

SHDN

Figure 44. 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 45 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

R1

4.7k

Ω

Q2

Q2N2222

Q2N4921

Q1

SHDN

GND

U1

ADR39x

Figure 45. 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 46.

ADR39x

R1

4.7k

Ω

Q2

Q2N2222

Q2N4921

GND

Q1

U1

SHDN

Figure 46. ADR39x for High Output Current

with Darlington Drive Configuration