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参数资料
| 型号： | AD5260BRU200-REEL7 |
| 厂商： | ANALOG DEVICES INC |
| 元件分类： | 数字电位计 |
| 英文描述： | 32-Tap. Nonvolatile. Linear-Taper Digital Potentiometers in SOT23 |
| 中文描述： | 200K DIGITAL POTENTIOMETER, 3-WIRE SERIAL CONTROL INTERFACE, 256 POSITIONS, PDSO14 |
| 封装： | TSSOP-14 |
| 文件页数： | 14/20页 |
| 文件大小： | 859K |
| 代理商： | AD5260BRU200-REEL7 |
REV. 0
–14–
AD5260/AD5262
TEST CIRCUITS (continued)
SDI
CLK
CS
V
LOGIC
I
LOGIC
DIGITAL INPUT
VOLTAGE
Test Circuit 8. V
LOGIC
Current vs. Digital Input Voltage
W
B
V
CM
I
CM
A
NC
GND
NC
V
SS
V
DD
DUT
Test Circuit 9. Analog Crosstalk
PROGRAMMING THE POTENTIOMETER DIVIDER
Voltage Output Operation
The digital potentiometer easily generates output voltages at wiper-
to-B and wiper-to-A to be proportional to the input voltage at
A-to-B. Ignore the effect of the wiper resistance at the moment.
For example, connecting A-terminal to 5 V and B-terminal to
ground produces an output voltage at the wiper-to-B starting at
zero volts up to 1 LSB less than 5 V. Each LSB of voltage is equal
to the voltage applied across terminal AB divided by the 256 posi-
tion of the potentiometer divider. Since the AD5260/AD5262
operates from dual supplies, the general equation defining the
output voltage at V
W
with respect to ground for any given input
voltage applied to terminals AB is:
D
V
V
W
AB
B
( )
=
256
Operation of the digital potentiometer in the divider mode results
in more accurate operation over temperature. Unlike the rheostat
mode, the output voltage is dependent on the ratio of the internal
resistors R
WA
and R
WB
and not the absolute values; therefore, the
drift reduces to 5 ppm/
∞
C.
V
D
￥
+
(3)
APPLICATIONS
Bipolar DC or AC Operation from Dual Supplies
The AD5260/AD5262 can be operated from dual supplies enabling
control of ground referenced AC signals or bipolar operation.
The AC signal, as high as V
DD
/V
SS
, can be applied directly across
terminals A–B with output taken from terminal W. See Figure 13
for a typical circuit connection.
V
SS
+5.0V
CLK
CS
GND
V
DD
SDI
GND
V
DD
–5.0V
SCLK
MOSI
C
SS
5V p-p
2.5V p-p
D = 80
H
Figure 13. Bipolar Operation from Dual Supplies
Gain Control Compensation
Digital potentiometers are commonly used in gain control as in
the noninverting gain amplifier shown in Figure 14.
U1
V
O
W
B
A
R2
200k
C2
4.7pF
V
i
R1
47k
C1
25pF
Figure 14. Typical Noninverting Gain Amplifier
Notice that when the RDAC B terminal parasitic capacitance is
connected to the op amp noninverting node, it introduces a zero
for the 1/
b
O
term with +20 dB/dec, whereas a typical op amp GBP
has –20 dB/dec characteristics. A large R2 and finite C1 can cause
this Zero’s frequency to fall well below the crossover frequency.
Hence the rate of closure becomes 40 dB/dec and the system has
0
∞
phase margin at the crossover frequency. The output may 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 prob-
lem. A better approach, however, is to include a compensation
capacitor C2 to cancel the effect caused by C1. Optimum compen-
sation occurs when R1 C1 = R2 C2. This is not an option
because of the variation of R2. As a result, one may use the relation-
ship above 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 will avoid the ringing or
oscillation at 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 avoided in most cases.
Programmable Voltage Reference
For voltage divider mode operation, Figure 15, it is common
to buffer the output of the digital potentiometer unless the load is
much larger than R
WB
. Not only does the buffer serve the pur-
pose of impedance conversion, but it also allows a heavier load
to be driven.
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