EVAL-AD5263EBZ Analog Devices Inc, EVAL-AD5263EBZ Datasheet - Page 23

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EVAL-AD5263EBZ

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

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
APPLICATIONS
BIPOLAR DC OR AC OPERATION FROM DUAL
SUPPLIES
The AD5263 can be operated from dual supplies, enabling
control of ground referenced ac signals or bipolar operation.
The ac signal, as high as V
Terminal A to Terminal B, with the output taken from Terminal W.
GAIN CONTROL COMPENSATION
A digital potentiometer is commonly used in gain control such
as the noninverting gain amplifier shown in Figure 58.
Notice the RDAC B terminal parasitic capacitance is connected
to the op amp noninverting node. It introduces a zero for the
1/β
–20 dB/dec characteristics. A large R2 and finite C1 can cause
this zero’s frequency to fall well below the crossover frequency.
Thus, the rate of closure becomes 40 dB/dec and the system has
µC
o
term with +20 dB/dec, whereas a typical op amp GBP has
GND
V
DD
SCLK
MCSI
Figure 57. Bipolar Operation from Dual Supplies
Figure 58. Typical Noninverting Gain Amplifier
47kΩ
R1
C1
25pF
DD
SCL
SDA
GND
AD5263
/V
VI
SS
, can be applied directly across
B
200kΩ
U1
4.7pF
W
C2
R2
V
A
V
DD
SS
A1
W1
B1
A2
W2
B2
±2.5V p-p
V
D = 0x90
O
_
+5.0V
±5V p-p
5.0V
Rev. B | Page 23 of 28
0
ring or oscillate if the input is a rectangular pulse or step
function. Similarly, it is also likely to ring when switching
between two gain values, because this is equivalent to a step
change at the input.
Depending on the op amp GBP, reducing the feedback resistor
may extend the zero’s frequency far enough to overcome the
problem. A better approach is to include a compensation
capacitor C2 to cancel the effect caused by C1. Optimum
compensation occurs when R1 × C1 = R2 × C2. This is not
an option, because of the variation of R2. As a result, one
may use the relationship described and scale C2 as if R2 is
at its maximum value. Doing so may overcompensate and
compromise the performance slightly when R2 is set at low
values. However, it avoids the gain peaking, ringing, or
oscillation in the worst case. For critical applications, C2 should
be found empirically to suit the need. In general, C2 in the
range of a few pF to no more than a few tenths of pF is usually
adequate for the compensation.
Similarly, there are W and A terminal capacitances connected to
the output (not shown); fortunately, their effect at this node is
less significant and the compensation can be disregarded in
most cases.
PROGRAMMABLE VOLTAGE REFERENCE
For voltage divider mode operation (Figure 59), it is common to
buffer the output of the digital potentiometer unless the load is
much larger than R
purpose of impedance conversion, but it also allows a heavier
load to be driven.
°
phase margin at the crossover frequency. The output may
GND
1
VIN
Figure 59. Programmable Voltage Reference
AD1582
5V
U1
VOUT
WB
. Not only does the buffer serve the
3
AD5263
A
B
W
A1
AD8601
5V
V
O
AD5263

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