AD588(RevD) Просмотр технического описания (PDF) - Analog Devices
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AD588 Datasheet PDF : 16 Pages
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AD588
RB
A1
R1
R2
R3
A2
R4
R5
R6
RC
VISHAY S102C
OR SIMILAR
A3
A4
AD588
RC = 10k⍀
1.0mA
0.01%
+
100⍀
+VS
VOUT
–
–VS
–15V
OR
GROUND
RTD = OMEGA K4515
0.24؇C/mW SELF-HEATING
Figure 24. Precision Current Source for RTD
BOOSTED PRECISION CURRENT SOURCE
In the RTD current-source application, the load current is
limited to ± 10 mA by the output drive capability of amplifier
A3. In the event that more drive current is needed, a series-pass
transistor can be inserted inside the feedback loop to provide
higher current. Accuracy and drift performance are unaffected
by the pass transistor.
VCC
220⍀
A3
Q1
RB
A1
AD588
R1
R4
R2
R3
A2
R5
R6
A4
+VS
IL
=
10V
RC
–VS
LIMITED BY
Q1 AND RC
POWER
DISSIPATION
LOAD
Figure 25. Boosted Precision Current Source
BRIDGE DRIVER CIRCUITS
The Wheatstone bridge is a common transducer. In its simplest
form, a bridge consists of four, two-terminal elements connected
to form a quadrilateral, a source of excitation connected along
one of the diagonals and a detector comprising the other diago-
nal. Figure 26a shows a simple bridge driven from a unipolar
excitation supply. EO, a differential voltage, is proportional to
the deviation of the element from the initial bridge values. Unfor-
tunately, this bridge output voltage is riding on a common-mode
voltage equal to approximately VIN/2. Further processing of this
signal may necessarily be limited to high common-mode rejec-
tion techniques such as instrumentation or isolation amplifiers.
Figure 26b shows the same bridge transducer, this time driven
from a pair of bipolar supplies. This configuration ideally elimi-
nates the common-mode voltage and relaxes the restrictions on
any processing elements that follow.
+
VIN
–
R4
R3
–+
EO
R1
R2
Figure 26a. Bridge Transducer Excitation—
Unipolar Drive
+
V1
–
+
V2 –
R4
R3
–+
EO
R1
R2
Figure 26b. Bridge Transducer Excitation—
Bipolar Drive
+15V
220⍀
Q1 =
2N3904
A3
RB
A1
AD588
R1
R4
R2
A4
R5
R3
R6
A2
–+
EO
220⍀
Q2 =
2N3904
–15V
+VS
–VS
Figure 27. Bipolar Bridge Drive
As shown in Figure 27, the AD588 is an excellent choice for the
control element in a bipolar bridge driver scheme. Transistors
Q1 and Q2 serve as series-pass elements to boost the current
drive capability to the 28 mA required by a typical 350 Ω bridge.
A differential gain stage may still be required if the bridge balance
is not perfect. Such gain stages can be expensive.
REV. D
–13–
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