ADR440/ADR441/ADR443/ADR444/ADR445
PROGRAMMABLE VOLTAGE SOURCE
PROGRAMMABLE CURRENT SOURCE
To obtain different voltages than those offered by the ADR44x,
some extra components are needed. In Figure 38, two
potentiometers are used to set the desired voltage, while the
buffering amplifier provides current drive. The potentiometer
connected between VOUT and GND, with its wiper connected to
the noninverting input of the operational amplifier, takes care of
coarse trim. The second potentiometer, with its wiper
It is possible to build a programmable current source using a
setup similar to the programmable voltage source, as shown in
Figure 39. The constant voltage on the gate of the transistor sets
the current through the load. Varying the voltage on the gate
changes the current. This circuit does not require a dual digital
potentiometer.
V
CC
connected to the trim terminal of the ADR44x, is used for fine
adjustment. Resolution depends on the end-to-end resistance
value and the resolution of the selected potentiometer.
2
0.1µF
V
IN
R
SENSE
ADR440/
ADR441/
ADR443/
ADR444/
ADR445
+V
DD
2
V
OUT
6
V
IN
ADR440/
ADR441/
ADR443/
ADR444/
ADR445
GND
4
0.1µF
ADJ V
REF
AD5259
6
V
OUT
I
LOAD
R1
R2
GND
4
10kΩ 10kΩ
Figure 39. Programmable Current Source
HIGH VOLTAGE FLOATING CURRENT SOURCE
Figure 38. Programmable Voltage Source
Use the circuit in Figure 40 to generate a floating current source
with minimal self heating. This particular configuration can
operate on high supply voltages, determined by the breakdown
voltage of the N-channel JFET.
For a completely programmable solution, replace the two
potentiometers in Figure 38 with one Analog Devices dual
digital potentiometer, offered with either an SPI® or an I2C®
interface. These interfaces set the position of the wiper on both
potentiometers and allow the output voltage to be set. Table 9
lists compatible Analog Devices digital potentiometers.
+V
S
SST111
VISHAY
Table 9. Digital Potentiometer Parts
2
V
IN
No. of
No. of
1
Part No.
AD5251
AD5207
AD5242
AD5262
AD5282
AD5252
AD5232
AD5235
ADN2850
Channels
Positions
ITF
I2C
SPI
I2C
SPI
I2C
I2C
SPI
SPI
SPI
R (kΩ)
VDD
5.5
5.5
5.5
15
ADR440/
ADR441/
ADR443/
ADR444/
ADR445
2.00
2.00
2.00
2.00
2.00
2.00
2.00
2.00
2.00
64.00
1, 10, 50, 100
10, 50, 100
10, 100, 1M
20, 50, 200
20, 50, 100
1, 10, 50, 100
10, 50, 100
25, 250
256.00
256.00
256.00
256.00
256.00
256.00
1024.00
1024.00
V
OUT
6
2N3904
OP90
15
GND
4
5.5
5.5
5.5
5.5
25, 250
–V
S
1 Can also use a negative supply.
Figure 40. Floating Current Source
Adding a negative supply to the operational amplifier allows
the user also to produce a negative programmable reference,
by connecting the reference output to the inverting terminal
of the operational amplifier. Choose feedback resistors to
minimize errors over temperature.
Rev. A | Page 16 of 20
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