ADR431B AD [Analog Devices], ADR431B Datasheet - Page 17

• Manufacturer Part Number: ADR431B
• Description: Ultralow Noise XFET Voltage References with Current Sink and Source Capability
• Manufacturer: AD [Analog Devices]

HIGH VOLTAGE FLOATING CURRENT SOURCE
The circuit in Figure 34 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.
KELVIN CONNECTIONS
In many portable instrumentation applications where PC board
cost and area go hand-in-hand, circuit interconnects are very
often of dimensionally minimum width. 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 flowing through wiring resistance produce
an error (V
connection of Figure 35 overcomes the problem by including
the wiring resistance within the forcing loop of the op amp.
Because the op amp senses the load voltage, the op amp loop
control forces the output to compensate for the wiring error and
to produce the correct voltage at the load.
ERROR
Figure 34. High Voltage Floating Current Source
ADR43x
GND
= R × I
– V
V
A1
IN
DD
V
OUT
Figure 33. Negative Reference
L
) at the load. However, the Kelvin
6
A1 = OP777, OP193
V
OP90
OUT
ADR43x
+V
GND
V
2
4
DD
IN
+V
S
–V
2N3904
– V
VISHAY
SST111
S
R
2.1kΩ
REF
L
ADR430/ADR431/ADR433/ADR434/ADR435/ADR439
Rev. B | Page 17 of 24
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 ADR43x, it is imperative to match the resistance tolerance as
well as the temperature coefficient of all the components.
V
IN
1 µ F
+10V
Figure 37. +2.5 V and −2.5 V References Using ADR435
Figure 36. +5 V and −5 V References Using ADR435
ADR43x
Figure 35. Advantage of Kelvin Connection
0.1 µ F
GND
V
2
4
GND
IN
V
V
2
IN
4
OUT
ADR435
GND
V
2
U1
4
6
ADR435
IN
TRIM
V
OUT
U1
V
TRIM
A1 = OP191
+
OUT
5
6
A1
V
5.6kΩ
5.6kΩ
IN
6
5
R
R2
+2.5V
R1
–2.5V
LW
10k Ω
5k Ω
R3
R
R1
LW
OP1177
OP1177
+10V
V
SENSE
V
FORCE
R
– 10V
V+
V–
U2
–10V
U2
OUT
OUT
L
V+
V–
10k Ω
R2
+5V
–5V