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ADR441BRZ-REEL7 데이터 시트보기 (PDF) - Analog Devices

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ADR441BRZ-REEL7 Ultralow Noise, LDO XFET Voltage References with Current Sink and Source ADI
Analog Devices ADI
ADR441BRZ-REEL7 Datasheet PDF : 20 Pages
First Prev 11 12 13 14 15 16 17 18 19 20
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 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
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.
+VDD
2
VIN
ADR440/
ADR441/
ADR443/
ADR444/
ADR445
VOUT 6
GND
4
R1
R2
10k10k
ADJ VREF
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 I2
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
Part No.
AD5251
No. of
No. of
Channels Positions ITF R (kΩ)
VDD1
2.00
64.00
I2C 1, 10, 50, 100 5.5
AD5207 2.00
AD5242 2.00
256.00
256.00
SPI 10, 50, 100
5.5
I2C 10, 100, 1M
5.5
AD5262 2.00
AD5282 2.00
AD5252 2.00
256.00
256.00
256.00
SPI 20, 50, 200
15
I2C 20, 50, 100
15
I2C 1, 10, 50, 100 5.5
AD5232 2.00
256.00
SPI 10, 50, 100
5.5
AD5235 2.00
1024.00
SPI 25, 250
5.5
ADN2850 2.00
1024.00
SPI 25, 250
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.
VCC
0.1µF
2
VIN
ADR440/
ADR441/
ADR443/
ADR444/
ADR445
VOUT 6
RSENSE
GND
4
0.1µF
AD5259
ILOAD
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.
+VS
SST111
VISHAY
2
VIN
ADR440/
ADR441/
ADR443/
ADR444/
ADR445
VOUT 6
GND
4
OP90
2N3904
–VS
Figure 40. Floating Current Source
Rev. A | Page 16 of 20
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