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參數(shù)資料
| 型號： | AD7376AN1M |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 數(shù)字電位計 |
| 英文描述： | +-15 V Operation Digital Potentiometer |
| 中文描述： | 1000K DIGITAL POTENTIOMETER, 3-WIRE SERIAL CONTROL INTERFACE, 128 POSITIONS, PDIP14 |
| 封裝： | PLASTIC, DIP-14 |
| 文件頁數(shù)： | 8/12頁 |
| 文件大?。?/td> | 335K |
| 代理商： | AD7376AN1M |
AD7376
–8–
REV. 0
0.1V
CODE = OO
H
I
SW
V
SS
TO V
DD
W
B
DUT
0.1V
I
SW
R
SW
=
Figure 38. Incremental ON Resistance Test Circuit
I
CM
V
CM
W
B
DUT
V
V
SS
NC
A
NC
GND
Figure 39. Common-Mode Leakage Current Test Circuit
OPE RAT ION
T he AD7376 provides a 128-position digitally-controlled vari-
able resistor (VR) device. Changing the programmed VR set-
tings is accomplished by clocking in a 7-bit serial data word into
the SDI (Serial Data Input) pin, while
CS
is active low. When
CS
returns high the last seven bits are transferred into the RDAC
latch setting the new wiper position. T he exact timing require-
ments are shown in Figure 1.
T he AD7376 resets to a midscale by asserting the
RS
pin, sim-
plifying initial conditions at power-up. Both parts have a power
shutdown
SHDN
pin which places the RDAC in a zero power
consumption state where terminal A is open circuited and the
wiper W is connected to 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 opera-
tional mode from power shutdown, the VR settings return to
their previous resistance values.
D6
D5
D4
D3
D2
D1
D0
RDAC
LATCH
&
DECODER
R
S
R
S
R
S
R
S
SHDN
A
W
B
R
S
= R
NOMINAL
/128
Figure 40. AD7376 Equivalent RDAC Circuit
PROGRAMMING T HE VARIABLE RE SIST OR
Rheostat Operation
T he nominal resistance of the RDAC between terminals A and
B are available with values of 10 k
, 50 k
, 100 k
and 1 M
.
T he final three characters of the part number determine the
nominal resistance value, e.g., 10 k
= 10; 50 k
= 50; 100 k
= 100; 1 M
= 1M. T he nominal resistance (R
AB
) of the VR
has 128 contact points accessed by the wiper terminal, plus the
B terminal contact. T he 7-bit data word in the RDAC latch is
decoded to select one of the 128 possible settings. T he wiper’s first
connection starts at the B terminal for data 00
H
. T his B–termi-
nal connection has a wiper contact resistance of 120
. T he
second connection (10 k
part) is the first tap point located
at 198
(= R
BA
[nominal resistance]/128 + R
W
= 78
+ 120
)
for data 01
H
. T he third connection is the next tap point repre-
senting 156 + 120 = 276
for data 02
H
. Each LSB data value
increase moves the wiper up the resistor ladder until the last tap
point is reached at 10041
. T he wiper does not directly con-
nect to the B terminal. See Figure 40 for a simplified diagram of
the equivalent RDAC circuit.
T he general transfer equation that determines the digitally pro-
grammed output resistance between W and B is:
R
WB
(D) = (D)/128
×
R
BA
+ R
W
where
D
is the data contained in the 7-bit VR latch, and
R
BA
is
the nominal end-to-end resistance.
For example, when V
B
= 0 V and A–terminal is open circuit, the
following output resistance values will be set for the following
VR latch codes (applies to the 10 k
potentiometer).
(1)
T able I.
D
(DE C)
R
WB
(
V
)
Output State
127
64
1
0
10041
5120
276
198
Full-Scale
Midscale (
RS
= 0 Condition)
1 LSB
Zero-Scale (Wiper Contact Resistance)
Note that in the zero-scale condition a finite wiper resistance of
120
is present. Care should be taken to limit the current flow
between W and B in this state to a maximum value of 5 mA to
avoid degradation or possible destruction of the internal switch
contact.
Like the mechanical potentiometer the RDAC replaces, it is
totally symmetrical. T he resistance 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 tied to
the wiper. Setting the resistance value for R
WA
starts at a maxi-
mum value of resistance and decreases as the data loaded in the
latch is increased in value. T he general transfer equation for this
operation is:
R
WA
(
D
) = (128-
D
)/128
×
R
BA
+
R
W
where
D
is the data contained in the 7-bit RDAC latch, and
R
BA
is the nominal end-to-end resistance. For example, when V
A
= 0 V
and B–terminal is tied to the wiper W the following output
resistance values will be set for the following RDAC latch codes.
(2)
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