AD5235BRU250-RL7 Analog Devices Inc, AD5235BRU250-RL7 Datasheet - Page 24

• Manufacturer Part Number: AD5235BRU250-RL7
• Manufacturer: Analog Devices Inc

Specifications of AD5235BRU250-RL7

• Number Of Elements: 2
• # Of Taps: 1024
• Resistance (max): 250KOhm
• Power Supply Requirement: Single/Dual
• Interface Type: Serial (4-Wire/SPI)
• Single Supply Voltage (typ): 3.3/5V
• Dual Supply Voltage (typ): ±2.5V
• Single Supply Voltage (min): 3V
• Single Supply Voltage (max): 5.5V
• Dual Supply Voltage (min): ±2.25V
• Dual Supply Voltage (max): ±2.75V
• Operating Temp Range: -40C to 85C
• Operating Temperature Classification: Industrial
• Mounting: Surface Mount
• Pin Count: 16
• Lead Free Status / RoHS Status: Not Compliant

AD5235
PROGRAMMABLE CURRENT SOURCE
A programmable current source can be implemented with the
circuit shown in Figure 52.
The
handling precision reference that can deliver 20 mA at 2.048 V.
The load current is simply the voltage across Terminal W to
Terminal B of the digital potentiometer divided by R
The circuit is simple but be aware that there are two issues.
First, dual-supply op amps are ideal because the ground potential
of REF191 can swing from −2.048 V at zero scale to V
scale of the potentiometer setting. Although the circuit works
under single supply, the programmable resolution of the system
is reduced by half. Second, the voltage compliance at V
limited to 2.5 V, or equivalently, a 125 Ω load. When higher
voltage compliance is needed, consider digital potentiometers,
such as, AD5260, AD5280, and AD7376. Figure 53 shows an
alternate circuit for high voltage compliance.
To achieve higher current, such as when driving a high power
LED, replace U1 with an LDO, reduce R
series with the A terminal of the digital potentiometer. This
limits the current of the potentiometer and increases the current
adjustment resolution.
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 53). If the resistors are matched, the load
current is
REF191
I
I
L
L
=
3
=
–2.048V TO V
R
V
+5V
SLEEP
GND
R2A
2
V
4
S
S
REF
is a unique low supply headroom and high current
×
R2B
1024
R1
Figure 52. Programmable Current Source
×
+
U1
AD5235
REF191
D
OUTPUT
R2B
L
×
V
6
W
C1
0V TO (2.048V + V
V+
V–
OP1177
1µF
+5V
–5V
U2
B
A
–
+
W
S
, and add a resistor in
100Ω
L
)
R
L
R
102Ω
S
V
L
S
I
.
L
L
L
at full
is
Rev. C | Page 24 of 28
(7)
(8)
AD5235
R2B, in theory, can be made as small as necessary to achieve the
current needed within the A2 output current driving capability.
In this circuit,
the voltage compliance approaches 15 V. Without the additions
of C1 and C2, the output impedance (looking into V
Z
R1 and R2A + R2B, respectively, which is desirable. On the other
hand, if the resistors do not match, Z
oscillation. As a result, C1, in the range of a few picofarad, is
needed to prevent oscillation from the negative impedance.
PROGRAMMABLE LOW-PASS FILTER
In analog-to-digital conversions (ADCs), it is common to
include an antialiasing filter to band limit the sampling signal.
Therefore, the dual-channel AD5235 can be used to construct a
second-order Sallen-Key low-pass filter, as shown in Figure 54.
The design equations are
O
can be infinite, if Resistors R1
Z
Q =
ω
V
V
O
V
O
O
I
I
=
+2.5V
–2.5V
A
B
=
=
Figure 53. Programmable Bidirectional Current Source
R1
R1
S
1
2
R1
CONCURRENTLY
C1
W
A
R1'
R2'
+
R
OP2177
R1
ADJUSTED
R2
A1
ω
+
Q
+
–
W
Figure 54. Sallen-Key Low-Pass Filter
ω
OP2177
R2B
B
−
–15V
f
+15V
1
R2
V+
V–
C1
f
R1'
S
2
1
+
C2
C2
(
A
R1
R
ω
delivers ±5 mA in either direction, and
(
R2
R2A
f
2
+
W
C2
B
R2A
+
150kΩ
R2B
R1
)
150kΩ
'
and R2
R1
C1
)
O
can be negative and cause
AD8601
+2.5V
–2.5V
'
–
+
OP2177
match precisely with
–15V
+15V
V+
V–
V+
V–
15k
14.95kΩ
U1
R2
R2A
Ω
A2
10pF
C1
L
) can be
R2B
50Ω
R
500Ω
L
V
O
V
L
(10)
(11)
(12)
I
L
(9)