EVAL-AD5235EBZ Analog Devices Inc, EVAL-AD5235EBZ Datasheet - Page 25

• Manufacturer Part Number: EVAL-AD5235EBZ
• Description: BOARD EVALUATION FOR AD5235
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD5235EBZ

• Main Purpose: Digital Potentiometer
• Utilized Ic / Part: AD5235
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Secondary Attributes: -
• Embedded: -
• Primary Attributes: -

BIPOLAR PROGRAMMABLE GAIN AMPLIFIER
For applications requiring bipolar gain, Figure 51 shows one
implementation. Digital Potentiometer U1 sets the adjustment
range; the wiper voltage (V
between V
(A2) as a noninverting amplifier that yields a transfer function of
where K is the ratio of R
In the simpler (and much more usual) case where K = 1, V
simplified to
Table 21 shows the result of adjusting D2, with OP2177 (A2)
configured as a unity gain, a gain of 2, and a gain of 10. The
result is a bipolar amplifier with linearly programmable gain
and 1024-step resolution.
Table 21. Result of Bipolar Gain Amplifier
D2
0
256
512
768
1023
10-BIT BIPOLAR DAC
If the circuit in Figure 51 is changed with the input taken from a
precision reference, U1 is set to midscale, and
configured as a buffer, a 10-bit bipolar DAC can be realized (as
shown in Figure 52). Compared to the conventional DAC, this
circuit offers comparable resolution but not the precision because
of the wiper resistance effects. Degradation of the nonlinearity
and temperature coefficient is prominent near the low values
of the adjustment range. Alternatively, this circuit offers a unique
nonvolatile memory feature that, in some cases, outweighs any
shortfalls in precision.
V
V
V
V
I
O
O
I
AD5235
=
AD5235
=
I
U2
⎛ +
⎜
⎝
and −KV
⎛ +
⎜
⎝
1
Figure 51. Bipolar Programmable Gain Amplifier
1
U1
R1 = ∞, R2 = 0
−1
−0.5
0
0.5
0.992
A2
A1
R2
R1
R2
R1
⎞
⎟
⎠
⎞
× ⎟
⎠
W1
I
W1
B2
B1
⎛
⎜
⎝
at a given U2 setting. Configure
OP2177
A1
1024
⎛
⎜
⎝
2
1024
D
V+
V–
WB1
D2
V
V
2
DD
SS
W2
/R
−
×
1
) can, therefore, be programmed
WA1
⎞
× ⎟
⎠
1 (
+
V
set by U1.
K
I
–KV
R1 = R2
−2
−1
0
1
1.984
)
−
I
A2
OP2177
K
⎞
⎟
⎠
V+
V–
V
V
DD
SS
AD8552
R2
R1
R2 = 9 × R1
−10
−5
0
5
9.92
OP2177
C
(A2) is
V
O
O
is
Rev. D | Page 25 of 32
(4)
(5)
Without consideration of the wiper resistance, the output of this
circuit is approximately
PROGRAMMABLE VOLTAGE SOURCE WITH
BOOSTED OUTPUT
For applications that require high current adjustment, such as a
laser diode driver or tunable laser, a boosted voltage source can
be considered (see Figure 53).
In this circuit, the inverting input of the op amp forces V
equal to the wiper voltage set by the digital potentiometer. The
load current is then delivered by the supply via the N-Ch FET N
(see Figure 53). N
(V
with a 5 V supply.
For precision applications, a voltage reference, such as ADR421,
ADR03, or ADR370, can be applied at Terminal A of the digital
potentiometer.
2
V
GND
I
V
IN
− V
I
U3
V
V
TRIM
ADR421
U1 = MIDSCALE
O
OUT
V
O
I
) × I
=
6
5
⎛
⎜
⎝
Figure 53. Programmable Booster Voltage Source
1024
A
B
2
+2.5V
L
D
AD5235
W
power. This circuit can source a 100 mA maximum
2
REF
−
1
AD8601
power handling must be adequate to dissipate
1
U2
Figure 52. 10-Bit Bipolar DAC
⎞
⎟
⎠
×
W2
B2
A1
U2
W1
U1
V
V+
V–
REF
A2
B1
A1
AD8552
2N7002
V+
V–
+2.5V
–2.5V
–2.5V
SIGNAL C
U1 = U2 = AD5235
REF
AD8552
LD
A2
C
V+
V–
+2.5V
–2.5V
R
BIAS
AD5235
V
I
L
O
O
to be
V
O
1
(6)