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参数资料
| 型号： | AD5280BRU20 |
| 厂商： | ANALOG DEVICES INC |
| 元件分类： | 数字电位计 |
| 英文描述： | Low Power, 8 Channel, 10-bit, 40MSPS ADC, 1.8V 257-BGA MICROSTAR -40 to 85 |
| 中文描述： | 20K DIGITAL POTENTIOMETER, 2-WIRE SERIAL CONTROL INTERFACE, 256 POSITIONS, PDSO14 |
| 封装： | MO-153AB-1, TSSOP-14 |
| 文件页数： | 6/10页 |
| 文件大小： | 156K |
| 代理商： | AD5280BRU20 |
PRELIMINARY TECHNICAL DATA
AD5280/AD5282
6
REV PrE 12 MAR 02
Information contained in this Product Concept Data Sheet describes a product in the early definition stage. There is no guarantee that the information contained here will become a final
product in its present form. For latest information contact Walt Heinzer/Analog Devices, Santa Clara, CA. TEL 408 382-3107; FAX 408 382-2721; email; walt.heinzer@analog.com
SCL
SDA
1
9
1
0
1
1
0
AD0
AD1
R/
W
ACK. BY
AD5280
1
9
D7
D6
D5
D3
D4
D0
D1
D2
NO ACK.
BY MASTER
FRAME 1
Slave Address Byte
MASTER
DataFRAME 2
RDAC Register
STOP BY
Figure 3. Reading Data from a Previously Selected RDAC Register
OPERATION
The AD5280/AD5282 provides a single/dual channel, 256-
position digitally-controlled variable resistor (VR) device. The
terms VR and RDAC are used interchangeably throughout this
documentation. To program the VR settings, refer to the Digital
Interface section. Both parts have an internal power ON preset
that places the wiper in mid scale during power on, which
simplifies the fault condition recovery at power up. In addition,
the shutdown
SHDN
pin of AD5280/AD5282 places the RDAC
in a zero power consumption state where terminal A is open
circuited and the wiper W is connected to terminal B, resulting
in only leakage currents being consumed in the VR structure. In
shutdown mode the VR latch settings are maintained, so that,
returning to operational mode from power shutdown, the VR
settings return to their previous resistance values.
RS
D5
D4
D3
D2
D1
D0
RDAC
LA&
DECODER
SHDN
Ax
Bx
Wx
RS
RS
RS
D6
D7
Figure 4. AD5280/AD5282 Equivalent RDAC Circuit
PROGRAMMING THE VARIABLE RESISTOR
Rheostat Operation
The nominal resistance of the RDAC between terminals A and B
are available in 20K
, 50K
, and 200K
. The final three
digits of the part number determine the nominal resistance
value, e.g. 20K
= 20; 50K
= 50; 200K
= 200. The
nominal resistance (R
AB
) of the VR has 256 contact points
accessed by the wiper terminal, plus the B terminal contact. The
eight bit data in the RDAC latch is decoded to select one of the
256 possible settings. Assume a 20K
part is used, the wiper's
first connection starts at the B terminal for data 00
H
. Since there
is a 60
wiper contact resistance, such connection yields a
minimum of 60
resistance between terminals W and B. The
second connection
is the first tap point corresponds to 138
(R
WB
= R
AB
/256 + R
W
= 78
+60
) for data 01
H
. The third
connection is the next tap point representing 216
(78x2+60)
for data 02
H
and so on. Each LSB data value increase moves the
wiper up the resistor ladder until the last tap point is reached at
19982
[R
AB
–1LSB+R
W
]. The wiper does not directly connect
to the B terminal. See Figure 4 for a simplified diagram of the
equivalent RDAC circuit.
The general equation determining the digitally programmed
output resistance between W and B is:
1
eqn.
256
)
(
W
AB
WB
R
R
D
D
R
+
=
where D is the decimal equivalent of the binary code which is
loaded in the 8-bit RDAC register, and R
AB
is the nominal end-
to-end resistance.
For example, R
AB
=20K
, when V
B
= 0V and A–terminal is open
circuit, the following output resistance values R
WB
will be set for
the following RDAC latch codes. Result will be the same if
terminal A is tied to W:
D
(DEC)
R
WB
(
)
Output State
256
128
1
0
19982
Full-Scale (R
AB
- 1LSB + R
W
)
10060
Mid-Scale
138
1 LSB
60
Zero-Scale (Wiper contact resistance)
Note
that in the zero-scale condition a finite wiper resistance of
60
is present. Care should be taken to limit the current flow
between W and B in this state to a maximum current of no more
than 5mA. Otherwise, degradation or possible destruction of the
internal switch contact can occur.
Similar to the mechanical potentiometer, the resistance of the
RDAC between the wiper W and terminal A also produces a
digitally controlled resistance R
WA
. When these terminals are
used the B–terminal should be let open or tied to the wiper
terminal. Setting the resistance value for R
WA
starts at a
maximum value of resistance and decreases as the data loaded in
the latch is increased in value. The general equation for this
operation is:
2
eqn.
256
256
)
(
W
AB
WA
R
R
R
D
D
+
=
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