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ADR435ARZ 데이터 시트보기 (PDF) - Analog Devices

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ADR435ARZ Ultralow Noise XFET Voltage References with Current Sink and Source Capability ADI
Analog Devices ADI
ADR435ARZ Datasheet PDF : 24 Pages
First Prev 11 12 13 14 15 16 17 18 19 20 Next Last
ADR430/ADR431/ADR433/ADR434/ADR435/ADR439
VIN
2
ADR43x
VOUT 6
GND
4
RLW
VIN
A1
OP191
+
RLW
VOUT
SENSE
VOUT
FORCE
RL
Figure 37. Advantage of Kelvin Connection
DUAL POLARITY REFERENCES
Dual polarity references can easily be made with an operational
amplifier and a pair of resistors. To avoid defeating the accuracy
obtained by the ADR43x, it is imperative to match the resistance
tolerance as well as the temperature coefficient of all the components.
VIN
1µF 0.1µF 2
VIN
VOUT 6
+5V
ADR435
U1
R1
10k
R2
10k
+10V
GND TRIM 5
4
V+
OP1177
–5V
U2
V–
R3
5k
10V
Figure 38. +5 V and −5 V References Using ADR435
+2.5V
+10V
2
VIN
VOUT 6
ADR435
U1
R1
5.6k
GND
4
TRIM 5
R2
5.6k
–2.5V
V+
OP1177
U2
V–
–10V
Figure 39. +2.5 V and −2.5 V References Using ADR435
PROGRAMMABLE CURRENT SOURCE
Together with a digital potentiometer and a Howland current
pump, the ADR435 forms the reference source for a programmable
current as
⎜⎛ R2A + R2 B ⎟⎞
IL
=
⎜⎝
R1
R2 B
×
VW
⎟⎠
(4)
and
VW
=
D
2N
×VREF
(5)
where:
D is the decimal equivalent of the input code.
N is the number of bits.
In addition, R1' and R2' must be equal to R1 and (R2A + R2B),
respectively. In theory, R2B can be made as small as needed to
achieve the necessary current within the A2 output current
driving capability. In this example, the OP2177 can deliver a
maximum output current of 10 mA. Because the current pump
employs both positive and negative feedback, C1 and C2
capacitors are needed to ensure that the negative feedback
prevails and, therefore, avoids oscillation. This circuit also
allows bidirectional current flow if the VA and VB inputs of
the digital potentiometer are supplied with the dual polarity
references, as shown in Figure 40.
C1
10pF
VDD
2
VIN TRIM 5
ADR435
U1
GND VOUT 6
4
U2
AD5232
A
BW
VDD
V+
OP2177
A1
V–
VSS
R1'
50k
C2
10pF
R1
50k
R2'
1k
VDD
V+
OP2177
A2
V–
VSS
R2A
1k
+
VL
Figure 40. Programmable Current Source
R2B
10
IL
IL
Rev. J | Page 19 of 24
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