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參數資料
| 型號： | ADR444A |
| 廠商： | Analog Devices, Inc. |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | Ultralow Noise, LDO XFET Voltage References with Current Sink and Source |
| 中文描述： | 超低噪聲，LDO的XFET電壓與電流吸入和源引用 |
| 文件頁數： | 16/20頁 |
| 文件大小： | 417K |
| 代理商： | ADR444A |
ADR440/ADR441/ADR443/ADR444/ADR445
PROGRAMMABLE VOLTAGE 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 V
OUT
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
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.
Rev. A | Page 16 of 20
ADR440/
ADR441/
ADR443/
ADR444/
ADR445
6
2
4
V
IN
V
OUT
GND
R2
10k
ADJ V
REF
0
+V
DD
R1
10k
Figure 38. Programmable Voltage Source
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 I
2
C
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.
Table 9. Digital Potentiometer Parts
No. of
Channels
AD5251
2.00
AD5207
2.00
AD5242
2.00
AD5262
2.00
AD5282
2.00
AD5252
2.00
AD5232
2.00
AD5235
2.00
ADN2850
2.00
Part No.
No. of
Positions
64.00
256.00
256.00
256.00
256.00
256.00
256.00
1024.00
1024.00
ITF
I
2
C
SPI
I
2
C
SPI
I
2
C
I
2
C
SPI
SPI
SPI
R (kΩ)
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
25, 250
V
DD1
5.5
5.5
5.5
15
15
5.5
5.5
5.5
5.5
1
Can also use a negative supply.
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.
PROGRAMMABLE CURRENT SOURCE
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.
ADR440/
ADR441/
ADR443/
ADR444/
ADR445
V
IN
V
OUT
GND
4
I
LOAD
V
CC
R
SENSE
AD5259
2
6
0.1μF
0.1μF
0
Figure 39. Programmable Current Source
HIGH VOLTAGE FLOATING CURRENT 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.
ADR440/
ADR441/
ADR443/
ADR444/
ADR445
V
IN
V
OUT
GND
4
OP90
+V
S
SST111
VISHAY
2N3904
–V
S
0
2
6
Figure 40. Floating Current Source
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