AD5263EVAL Analog Devices Inc, AD5263EVAL Datasheet - Page 25

• Manufacturer Part Number: AD5263EVAL
• Description: BOARD EVAL FOR AD5263
• Manufacturer: Analog Devices Inc

Specifications of AD5263EVAL

• Rohs Status: RoHS non-compliant
• Main Purpose: Digital Potentiometer
• Embedded: No
• Utilized Ic / Part: AD5263
• Primary Attributes: 4 Channel, 256 Position
• Secondary Attributes: I²C & SPI Interfaces
• Lead Free Status / Rohs Status: Not Compliant

PROGRAMMABLE 4 TO 20 MA CURRENT SOURCE
A programmable 4–20 mA current source can be implemented
with the circuit shown in Figure 63. The REF191 is a unique low
supply headroom and high current handling precision reference
that can deliver 20 mA at +2.048 V. The load current is simply
the voltage across Terminal B to Terminal W of the digital
potentiometer divided by R
The circuit is simple, but beware of two things. First, dual-supply
op amps are ideal because the ground potential of the REF191
can swing from −2.048 V at zero scale to V
potentiometer setting. Although the circuit works with a single
supply, the programmable resolution of the system is reduced.
For applications that demand higher current capabilities, a few
changes to the circuit in Figure 63 produce an adjustable
current in the range of hundreds of mA. First, the voltage
reference needs to be replaced with a high current, low dropout
regulator, such as the ADP3333, and the op amp needs to be
swapped with a high current, dual-supply model, such as the
AD8532. Depending on the desired range of current, an
appropriate value for R
current flowing to the load, the user must pay attention to the
load impedance so as not to drive the op amp past the
positive rail.
I
L
=
–2.048V TO V
3
V
SLEEP
GND
4
Figure 63. Programmable 4–20 mA Current Source
R
REF191
REF
S
+5V
VIN
2
VOUT
×
U1
2
×
N
D
L
6
0 TO (2.048V + V
C1
1µF
S
must be calculated. Because of the high
OP8510
U2
S
AD5263
–5V
:
+5V
V+
V–
L
)
A
B
W
L
at full scale of the
R
102Ω
R
100Ω
S
L
V
L
I
L
Rev. B | Page 25 of 28
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PROGRAMMABLE BIDIRECTIONAL CURRENT
SOURCE
For applications that require bidirectional current control or
higher voltage compliance, a Howland current pump can be a
solution (see Figure 64). If the resistors are matched, the load
current is
AD5263
R2B, in theory, can be made as small as needed to achieve the
current needed within the A2 output current driving capability.
In this circuit, OP2177 can deliver ±5 mA in either direction,
and the voltage compliance approaches +15 V. It can be shown
that the output impedance is
This output impedance can be infinite if resistors R1′ and R2′
match precisely with R1 and R2A + R2B, respectively. On the
other hand, it can be negative if the resistors are not matched.
As a result, C1 in the range of 1 pF to 10 pF is needed to prevent
oscillation.
I
Z
L
o
–5V
A
+5V
=
=
Figure 64. Programmable Bidirectional Current Source
W
(
R1
R2A
R
×
1
R
OP2177
× ′
+
+15V
–15V
R2B
2
R2B
V+
V–
− ′
R
2
A1
R
B
)
1
(
′
R1
(
R1
R2A
+
×
V
R2A
150kΩ
10pF
+
W
R1
C2
150kΩ
R2B
R1
)
)
OP2177
+15V
–15V
15kΩ
R2
V+
V–
14.95kΩ
R2
A
C1
10pF
A
2
AD5263
R2
50Ω
R
500Ω
L
B
V
L
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|
L
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