REV. A

–8–

ADR370

12-Bit Precision Programmable Current Source

By replacing the potentiometer in Figure 6 with a 12-bit precision

DAC like the AD5322, a higher precision programmable current

source can be achieved. Figure 7 illustrates the implementation

of this circuit. The load current can be determined with the

following equation.

I

VD

R

L

REF

SET

=

−

()

×

1

4096

(6)

The compliance voltage should be kept low so that the supply

U1

U2

+5V

V+

V–

1

11

U3

2

3

VREF (1 – D2/N)

+5V

OP1177

AD5322

–5V

ADR370

GND

+5V

TOL

±0.05%

GND

Figure 7. 12-Bit Programmable Current Source

Precision Boosted Output Regulator

A precision voltage output with boosted current can be realized

by the ADR370 at 2.048 V.

The ADR370 sources a maximum of 5 mA if the load current,

R1

10k

ADR370

GND

Q1

2N3906

4V TO 12V

Figure 8. Precision Boosted Output Regulator

Q1 will be turned on to regulate current as needed. R1 is required

to bias the base of Q1 and must be large enough to comply with

the supply current requirements of the ADR370. The supply

voltage can be as low as 4 V.

The maximum current output of this circuit is limited by the

power dissipation of the bipolar transistor, Q1.

PV

I

DISS

DD

L

=−

2 048

.

(7)

Using the 2N3906 PNP transistor shown in Figure 8 and a 4 V

is drawn from the circuit, which limits the power dissipation of

Q1 to ~200 mW.