EVAL-AD5262EBZ Analog Devices Inc, EVAL-AD5262EBZ Datasheet - Page 21

• Manufacturer Part Number: EVAL-AD5262EBZ
• Description: EVALUATION BOARD
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD5262EBZ

• Main Purpose: Digital Potentiometer
• Utilized Ic / Part: AD5262
• Primary Attributes: Dual Channel, 256 Positions
• Secondary Attributes: SPI Interface
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Embedded: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The circuit is simple, but be aware that dual-supply op amps are
ideal because the ground potential of REF191 can swing from
−2.048 V at zero scale to V
setting. Although the circuit works under single supply, the
programmable resolution of the system is reduced.
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 65). If the resistors are matched, the load
current is
PROGRAMMABLE LOW-PASS FILTER
Digital Potentiometer AD5262 can be used to construct a
second-order, Sallen-Key low-pass filter (see Figure 66). The
design equations are
AD5260
ω
I
V
V
3
L
O
O
i
–5V
2
4
V
SLEEP
GND
A
B
+5V
=
+5V
S
=
Figure 65. Programmable Bidirectional Current Source
=
REF191
Figure 64. Programmable 4-to-20 mA Current Source
–2.048 TO V
(
W
OUTPUT
R
S
U1
2
2
R1R2C1C2
A
+
+
R
ω
Q
A1
ω
1
R
2
OP2177
O
6
B
+15V
–15V
L
2
O
S
B
2
1µF
C1
+
0V TO (2.048V + V
)
ω
R1
O
L
2
×
AD5260
at full scale of the potentiometer
V
W
150kΩ
150kΩ
10pF
C2
R1
R1'
U2
OP1177
L
)
+5V
–5V
B W
A
–
+
10pF
C1
AD8016
14.95kΩ
+15V
–15V
15kΩ
R2A
R2'
R
102Ω
R
100Ω
A2
S
L
R
50Ω
R
500Ω
V
L
L
L
I
L
V
I
L
(10)
Rev. A | Page 21 of 24
L
(8)
(9)
Users can first select any convenient value for the capacitors. To
achieve maximally flat bandwidth where Q = 0.707, let C1 be
twice the size of C2 and let R1 = R2. As a result, users can adjust
R1 and R2 to the same settings to achieve the desirable bandwidth.
PROGRAMMABLE OSCILLATOR
In a classic Wien-bridge oscillator (see Figure 67), the Wien
network (R, R’ , C, C’) provides positive feedback, whereas R1
and R2 provide negative feedback. At the resonant frequency, f
the overall phase shift is zero, and the positive feedback causes
the circuit to oscillate. With R = R’ , C = C’ , and R2 = R2A//(R2B +
R
where R is equal to R
At resonance, setting
balances the bridge. In practice, R2/R1 should be set slightly
larger than 2 to ensure the oscillation can start. However, the
alternate turn-on of the diodes, D1 and D2, ensures R2/R1 to
be smaller than 2 momentarily and therefore stabilizes the
oscillation.
When the frequency is set, the oscillation amplitude can be
tuned by R2B because
V
selection of R2B, an equilibrium is reached such that V
converges. R2B can be in series with a discrete resistor to
increase the amplitude, but the total resistance cannot be too
large to saturate the output.
In both circuits in Figure 66 and Figure 67, the frequency tuning
requires that both RDACs be adjusted to the same settings.
Because the two channels are adjusted one at a time, an intermedi-
DIODE
O
, I
D
Q
ω
R
2
3
V
R2
R1
, and V
), the oscillation frequency is
i
O
V
=
=
O
=
=
256 −
R1C1
2
=
RC
256
1
SAME SETTINGS
1
A
ADJUSTED TO
I
D
R
D
R1
are interdependent variables. With proper
D
R
+
or
W
B
Figure 66. Sallen Key Low-Pass Filter
2
R2C2
R
B
f
AB
1
+
O
WA
A
V
R
=
R2
such that
D
2
W
C2
B
π
1
RC
C1
AD5260/AD5262
AD8601
+2.5V
–2.5V
V
O
O
(11)
(12)
(13)
(14)
(15)
o
,