EVAL-AD5263EBZ Analog Devices Inc, EVAL-AD5263EBZ Datasheet - Page 24

• Manufacturer Part Number: EVAL-AD5263EBZ
• Description: EVALUATION BOARD I.C.
• Manufacturer: Analog Devices Inc

Specifications of EVAL-AD5263EBZ

• 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: Lead free / RoHS Compliant

AD5263
8-BIT BIPOLAR DAC
Figure 60 shows a low cost, 8-bit, bipolar DAC. It offers the
same number of adjustable steps, but not the precision as
compared to conventional DACs. The linearity and temperature
coefficient, especially at low values codes, are skewed by the
effects of the digital potentiometer wiper resistance. The output
of this circuit is
BIPOLAR PROGRAMMABLE GAIN AMPLIFIER
For applications requiring bipolar gain, Figure 61 shows one
implementation similar to the previous circuit. The digital
potentiometer U1 sets the adjustment range. The wiper voltage
at W2 can therefore be programmed between V
given U2 setting. Configuring A2 in the noninverting mode
allows linear gain and attenuation. The transfer function is
where K is the ratio of R
V
GND
I
V
1
ADR425
VIN
V
V
V
O
I
U1
O
I
=
VOUT
TRIM
=
AD5263
⎛
⎜
⎝
⎛ +
⎜
⎝
Figure 61. Bipolar Programmable Gain Amplifier
AD5263
256
1
2
D
+5VREF
U1
R2
U2
R1
A2
A1
−
1
⎞
× ⎟
⎠
⎞
× ⎟
⎠
Figure 60. 8-Bit Bipolar DAC
W2
W1
B2
B1
V
⎛
⎜
⎝
A1
OP2177
256
REF
D2
WB1
W
B
V+
V–
/R
V
V
×
AD5263
DD
SS
A
(
WA1
OP2177
A1
1
+
V+
V–
+15V
set by U1.
K
)
−
–KV
K
A2
⎞
⎟
⎠
OP2177
I
V
–5VREF
V+
V–
DD
OP2177
V
A2
SS
C1
+15V
V+
V–
–15V
I
and –KV
R2
R1
V
V
I
O
O
at a
Rev. B | Page 24 of 28
(5)
(6)
Similar to the previous example, in the simpler (and much more
usual) case where K = 1, a single channel is used and U1 is
replaced by a matched pair of resistors to apply V
the ends of the digital potentiometer. The relationship becomes
If R2 is large, a compensation capacitor of a few pF may be
needed to avoid any gain peaking.
Table 8 shows the result of adjusting D, with A2 configured with
unity gain, gain of 2, and gain of 10. The result is a bipolar amplifier
with linearly programmable gain and 256-step resolution.
Table 8. Result of Bipolar Gain Amplifier
D
0
64
128
192
255
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 62.
In this circuit, the inverting input of the op amp forces the V
to be equal to the wiper voltage set by the digital potentiometer.
The load current is then delivered by the supply via the
N-channel FET, N1. N1 power handling must be adequate to
dissipate power equal to (V
source a maximum of 100 mA with a 5 V supply. For precision
applications, a voltage reference such as ADR421, ADR03, or
ADR370 can be applied at the A terminal of the digital
potentiometer.
V
O
AD5263
=
U1
⎛ +
⎜
⎝
Figure 62. Programmable Booster Voltage Source
1
R1 = ∞, R2 = 0
–1
–0.5
0
0.5
0.968
V
IN
R2
A
B
R1
⎞
× ⎟
⎠
W
⎛
⎜
⎝
AD8601
2
256
×
D2
+V
U2
–V
IN
− V
U3 2N7002
−
1
1.937
R1 = R2
–2
–1
0
1
⎞
× ⎟
⎠
OUT
V
) × I
I
SIGNAL
L
. This circuit can
LD
C
C
R2 = 9 × R1
–10
–5
0
5
9.680
R
I
V
BIAS
and –V
OUT
I
L
I
at
OUT
(7)