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参数资料
| 型号： | AD5254EVAL |
| 厂商： | Analog Devices, Inc. |
| 元件分类： | 通用总线功能 |
| 英文描述： | Dual, 256-Tap, Nonvolatile, I2C-Interface, Digital Potentiometers |
| 中文描述： | 双路、256抽头、非易失、I2C接口、数字电位器 |
| 文件页数： | 23/28页 |
| 文件大小： | 834K |
| 代理商： | AD5254EVAL |
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AD5253/AD5254
DIGITAL POTENTIOMETER OPERATION
The structure of the RDAC is designed to emulate the
performance of a mechanical potentiometer. The RDAC
contains a string of resistor segments, with an array of analog
switches acting as the wiper connection to the resistor array.
The number of points is the resolution of the device. For
example, the AD5253/AD5254 emulates 64/256 connection
points with 64/256 equal resistance, R
S
, allowing it to provide
better than 1.5%/0.4% settability resolution. Figure 41 provides
an equivalent diagram of the connections between the three
terminals that make up one channel of the RDAC. Switches
SWA and SWB are always ON, while one of switches SW(0) to
SW(2
N–1
) is ON one at a time, depending on the setting decoded
from the data bit. Since the switches are nonideal, there is a
75 wiper resistance, R
W
. Wiper resistance is a function of
supply voltage and temperature; lower supply voltages and
higher temperatures result in higher wiper resistances.
Consideration of wiper resistance dynamics is important in
applications where accurate prediction of output resistance is
required.
Rev. 0 | Page 23 of 28
0
SW
A
A
X
SW (2
N
– 1)
SW (2
N
– 2)
SW(1)
DIGITAL
CIRCUITRY
OMIITTED FOR
CLARITY
RDAC
WIPER
REGISTER
AND
DECODER
SW(0)
SW
B
R
S
= R
AB
/2
N
B
X
W
X
R
S
R
S
R
S
Figure 41. Equivalent RDAC Structure
PROGRAMMABLE RHEOSTAT OPERATION
If either the W-to-B or W-to-A terminal is used as a variable
resistor, the unused terminal can be opened or shorted with W;
such operation is called rheostat mode (see Figure 42). The
resistance tolerance can range ±20%.
0
A
B
W
A
B
W
A
B
W
Figure 42. Rheostat Mode Configuration
The nominal resistance of the AD5253/AD5254 has 64/256
contact points accessed by the wiper terminal, plus the B
terminal contact. The 6-/8-bit data-word in the RDAC register
is decoded to select one of the 64/256 settings. The wiper’s first
connection starts at the B terminal for data 0x00. This B termi-
nal connection has a wiper contact resistance, R
W
, of 75 ,
regardless of the nominal resistance. The second connection
(AD5253 10 k part) is the first tap point where R
WB
= 231
[R
WB
=R
AB
/64 + R
W
= 156 + 75 ] for data 0x01, and so on.
Each LSB data value increase moves the wiper up the resistor
ladder until the last tap point is reached at R
WB
= 9893 . See
Figure 41 for a simplified diagram of the equivalent RDAC
circuit.
The general equation that determines the digitally programmed
output resistance between W and B, is
R
WB
(
D
) = (
D
/64) ×
R
AB
+ 75 (
AD5253
) (1)
R
WB
(
D
) = (
D
/256) ×
R
AB
+ 75 (
AD5254
) (2)
Where
D
is the decimal equivalent data contained in the RDAC
latch, and
R
AB
is the nominal end-to-end resistance.
(
D (Code in Decimal)
0
0
25
50
75
100
0
10
32
48
63
R
WA
R
WB
Figure 43. AD5253 R
WA
(D) and R
WB
(D) vs. Decimal Code
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