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參數資料
| 型號： | ADR421BR-REEL7 |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | 10/100-ST SM PLUS |
| 中文描述： | 1-OUTPUT THREE TERM VOLTAGE REFERENCE, 2.5 V, PDSO8 |
| 封裝： | MS-012AA, SOIC-8 |
| 文件頁數： | 14/16頁 |
| 文件大小： | 223K |
| 代理商： | ADR421BR-REEL7 |
REV. B
–14–
A
DR420/ADR421/ADR423/ADR425
Dual Polarity References
V
IN
V
OUT
GND
4
6
2
ADR425
U1
5
TRIM
V
IN
1 F
0.1 F
R1
10k
+10V
–
10V
OP1177
U2
V
–
V+
–
5V
R2
10k
+5V
R3
5k
Figure 8. +5 V and –5 V Reference Using ADR425
V
IN
V
OUT
GND
4
6
2
ADR425
U1
5
TRIM
+10V
R1
5.6k
+2.5V
R2
5.6k
–
2.5V
–
10V
OP1177
U2
V+
V
–
Figure 9. +2.5 V and
–
2.5 V Reference Using ADR425
Dual polarity references can easily be made with an op amp and
a pair of resistors. In order not to defeat the accuracy obtained
by ADR42x, it is imperative to match the resistance tolerance as
well as the temperature coefficient of all the components.
Programmable Current Source
AD5232
U2
DIGITAL POT
A
B
W
U2
R1
50k
C2
10pF
R2
A
1k
R2
B
10
R2
’
1k
C1
10pF
R1
’
50k
V
IN
GND
4
2
V
DD
V
OUT
6
ADR425
U1
5
TRIM
LOAD
IL
VL
V
SS
V
DD
OP2177
A1
V
–
V+
V
SS
V
DD
OP2177
A2
V
–
V+
Figure 10. Programmable Current Source
Together with a digital potentiometer and a Howland current
pump, ADR425 forms the reference source for a programmable
current as
I
R
R
R
2
R
V
L
A
B
B
W
=
+
×
2
2
1
(3)
and
V
D
N
2
V
W
REF
=
×
(4)
where
D
= Decimal Equivalent of the Input Code
N
= Number of Bits
In addition, R1' and R2' must be equal to R1 and R2
A
+ R2
B
,
respectively. R2
B
in theory can be made as small as needed to
achieve the current needed within A
2
output current
driving
capability. In this example, OP2177 is able to deliver a maxi-
mum of 10 mA. Since the current pump employs both
positive
and
negative feedback, capacitors C1 and C2 are needed to
ensure the
negative feedback prevails and, therefore, avoids oscillation.
This circuit also allows bidirectional current flow if the inputs
V
A
and V
B
of the digital potentiometer are supplied with the
dual polarity references as shown previously.
Programmable DAC Reference Voltage
With a multichannel DAC such as a Quad 12-bit voltage output
DAC AD7398, one of its internal DACs and an ADR42x voltage
reference can be served as a common programmable V
REFX
for the
rest of the DACs. The circuit configuration is shown in Figure 11.
The relationship of V
REFX
to V
REF
depends upon the digital code
and the ratio of R1 and R2 and is given by:
V
V
R
R
R
R
D
N
2
REFX
REF
=
×
+
+
×
1
2
1
2
1
1
where
D
= Decimal Equivalent of Input Code and
N
= Number of Bits
V
REF
= Applied External Reference
V
REFX
= Reference Voltage for DAC A to D
(5)
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相關代理商/技術參數 |
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