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ADR425BR View Datasheet(PDF) - Analog Devices

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ADR425BR Datasheet PDF : 24 Pages
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ADR420/ADR421/ADR423/ADR425
HIGH VOLTAGE FLOATING CURRENT SOURCE
The circuit in Figure 43 can be used 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
ADR420/
ADR421/
ADR423/
ADR425
VOUT 6
GND
4
OP09
2N3904
RL
2.10k
–VS
Figure 43. High Voltage Floating Current Source
KELVIN CONNECTIONS
In many portable instrumentation applications where PC board
cost and area are important considerations, circuit intercon-
nects are often narrow. These narrow lines can cause large
voltage drops if the voltage reference is required to provide load
currents to various functions. In fact, a circuit’s interconnects
can exhibit a typical line resistance of 0.45 mΩ/square (1 oz. Cu,
for example). Force and sense connections, also referred to as
Kelvin connections, offer a convenient method of eliminating
the effects of voltage drops in circuit wires. Load currents flow-
ing through wiring resistance produce an error (VERROR = R × IL)
at the load. However, the Kelvin connection in Figure 44
overcomes the problem by including the wiring resistance
within the forcing loop of the op amp. Because the op amp
senses the load voltage, op amp loop control forces the output to
compensate for the wiring error and to produce the correct
voltage at the load.
VIN
2
ADR420/
ADR421/
ADR423/
ADR425
VOUT 6
GND
4
RLW
VIN
RLW
A1
A1 = OP191
VOUT
SENSE
VOUT
FORCE
RL
Figure 44. Advantage of Kelvin Connection
DUAL-POLARITY REFERENCES
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 the ADR42x, it is imperative to match the resistance toler-
ance and the temperature coefficient of all components.
VIN
1µF 0.1µF 2
VIN
VOUT 6
+5V
R1
U1
10k
R2
10k
ADR425
+10V
GND TRIM 5
V+
4
U2
OP1177
–5V
V–
R3
5k
–10V
Figure 45. +5 V and −5 V Reference Using ADR425
+2.5V
+10V
2
VIN
VOUT 6
U1
ADR425
R1
5.6k
GND
4
TRIM 5
R2
5.6k
–2.5V
V+
U2
OP1177
V–
–10V
Figure 46. +2.5 V and −2.5 V Reference Using ADR425
Rev. H | Page 18 of 24
 

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