AD5112 AD [Analog Devices], AD5112 Datasheet - Page 20

• Manufacturer Part Number: AD5112
• Manufacturer: AD [Analog Devices]

AD5111/AD5113/AD5115
Similar to the mechanical potentiometer, the resistance of
the RDAC between the W terminal and the A terminal also
produces a digitally controlled complementary resistance, R
R
data loaded into the latch increases. The general equations for
this operation are
AD5111:
AD5113:
AD5115:
where:
D is the decimal equivalent of the binary code in the 5-/6-/7-bit
RDAC register; 128, 64, and 32 refer to top scale step.
R
R
R
Regardless of which setting the part is operating in, take care
to limit the current between A to B, W to A, and W to B, to
the maximum continuous current of ±6 mA (5 kΩ and 10 kΩ)
or ±1.5 mA (80 kΩ), or pulse current specified in Table 6.
Otherwise, degradation or possible destruction of the internal
switch contact can occur.
WA
AB
W
TS
is the wiper resistance.
is the wiper resistance at top scale.
is the end-to-end resistance.
starts at the maximum resistance value and decreases as the
R
R
R
R
R
R
R
R
R
AW
AW
AW
AW
AW
AW
AW
AW
AW
(
(
(
=
=
=
=
=
=
D
D
D
R
R
R
R
R
R
)
)
)
=
TS
=
TS
TS
AB
AB
AB
=
128
64
32
+
+
+
128
64
32
R
R
R
−
−
−
W
W
W
D
D
D
×
×
×
R
R
R
AB
AB
AB
+
+
+
R
R
R
W
W
W
From 0 to 127 (8)
Bottom scale (10)
From 0 to 63 (11)
Bottom scale (13)
From 0 to 31 (14)
Bottom scale (7)
Top scale (12)
Top scale (15)
Top scale (9)
WA
Rev. 0 | Page 20 of 24
.
PROGRAMMING THE POTENTIOMETER DIVIDER
Voltage Output Operation
The digital potentiometer easily generates a voltage divider at
W-to-B and W-to-A that is proportional to the input voltage at
A-to-B, as shown in Figure 44. Unlike the polarity of V
GND, which must be positive, current across A-to-B, W-to-A,
and W-to-B can be in either direction.
If ignoring the effect of the wiper resistance for simplicity,
connecting Terminal A to 5 V and Terminal B to ground
produces an output voltage at W to B ranging from 0 V to 5 V.
The general equation defining the output voltage at V
respect to ground for any valid input voltage applied to
Terminal A and Terminal B, is
where:
R
R
Operation of the digital potentiometer in the divider mode
results in a more accurate operation over temperature. Unlike
the rheostat mode, the output voltage is dependent mainly
on the ratio of the internal resistors, R
absolute values. Therefore, the temperature drift reduces to
5 ppm/°C.
TERMINAL VOLTAGE OPERATING RANGE
The
ESD diodes for protection. These diodes also set the voltage
boundary of the terminal operating voltages. Positive signals
present on the A, B, or W terminals that exceed V
clamped by the forward-biased diode. There is no polarity
constraint between V
than V
WB
AW
(D) can be obtained from Equation 1 to Equation 6.
(D) can be obtained from Equation 7 to Equation 14.
AD5111/AD5113/AD5115
V
W
DD
(
D
or lower than GND.
)
=
Figure 44. Potentiometer Mode Configuration
R
WB
R
AB
(
D
)
A
V
, V
I
×
V
W
A
, and V
+
A
B
R
AW
R
W
are designed with internal
AB
(
B
D
, but they cannot be higher
)
V
WA
×
O
V
and R
B
Data Sheet
WB
, and not the
DD
are
W
DD
with
to
(16)