EVAL-AD5273DBZ Analog Devices, EVAL-AD5273DBZ Datasheet - Page 14

• Manufacturer Part Number: EVAL-AD5273DBZ
• Description: Digital Potentiometer Development Tools EVALUATION BOARD I.C.
• Manufacturer: Analog Devices
• Series: AD5273r

Specifications of EVAL-AD5273DBZ

• Rohs: yes
• Product: Evaluation Boards
• Tool Is For Evaluation Of: AD5273
• Resistance: 1 kOhms/10 kOhms/50 kOhms/100 kOhms
• Operating Supply Voltage: 5.5 V
• Interface Type: I2C
• Maximum Operating Temperature: + 105 C
• Factory Pack Quantity: 1
• For Use With: Sim DAC Web Tool

AD5273
VARIABLE RESISTANCE AND VOLTAGE FOR
RHEOSTAT MODE
If only the W-to-B or W-to-A terminals are used as variable
resistors, the unused A or B terminal can be opened or shorted
with W. This operation is called rheostat mode (see Figure 33).
The nominal resistance, R
accessed by the wiper terminal, plus the B terminal contact if
R
to select one of the 64 settings. Assuming that a 10 kΩ part is
used, the wiper’s first connection starts at Terminal B for Data
Register 0x00. This connection yields a minimum of 60 Ω
resistance between Terminal W and Terminal B because of the
60 Ω wiper contact resistance. The second connection is the
first tap point, which corresponds to 219 Ω (R
R
increase moves the wiper up the resistor ladder until the last
tap point is reached at 10,060 Ω (63 × R
shows a simplified diagram of the equivalent RDAC circuit.
The general equation determining R
where:
D is the decimal equivalent of the 6-bit binary code.
R
R
the internal switch.
Table 4. R
D (Dec)
63
32
1
0
Because a finite wiper resistance of 60 Ω is present in the zero-
scale condition, care should be taken to limit the current flow
between W and B in this state to a maximum pulse current of
20 mA. 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
complementary resistance, R
Terminal B can be opened or shorted to W. Setting the resistance
value for R
decreases as the data loaded in the latch increases in value.
WB
W
AB
W
) for Data Register 0x01, and so on. Each LSB data value
is the wiper resistance contributed by the on resistance of
is the end-to-end resistance.
is considered. The 6-bit data in the RDAC latch is decoded
R
WB
( )
D
WB
WA
R
10,060
5139
219
60
A
B
WB
vs. Codes; R
=
starts at a maximum value of resistance and
Figure 33. Rheostat Mode Configuration
63
(Ω)
D
W
×
R
AB
Output State
Full scale (R
Midscale
1 LSB
Zero scale (wiper contact resistance)
+
A
B
AB
AB
R
, of the RDAC has 64 contact points
W
= 10 kΩ; Terminal A Opened
WA
. When these terminals are used,
W
AB
WB
+ R
is
A
B
AB
W
)
/63 + R
W
W
= 1 × R
W
). Figure 34
AB
/63 +
Rev. H | Page 14 of 24
(1)
The general equation for this operation is
Table 5. R
D (Dec)
63
32
1
0
The typical distribution of the resistance tolerance from device
to device is process-lot dependent, and it is possible to have
±30% tolerance.
VARIABLE RESISTANCE AND VOLTAGE FOR
POTENTIOMETER MODE
If all three terminals are used, the operation is called the
potentiometer mode. The most common configuration is
the voltage divider operation (see Figure 35).
Ignoring the effect of the wiper resistance, the transfer function
is simply
A more accurate calculation, which includes the wiper
resistance effect, yields
V
V
R
WA
W
W
( )
( )
D
D
( )
D
WA
=
=
Figure 35. Potentiometer Mode Configuration
vs. Codes; R
=
Figure 34. AD5273 Equivalent RDAC Circuit
63
D
63
D
63
R
AB
V
DECODER
63
D5
D4
D3
D2
D1
D0
R
−
R
60
4980
9901
10,060
LATCH
A
RDAC
AB
WA
AND
+
D
2
+
(Ω)
V
×
R
I
R
W
R
W
AB
AB
V
=10 kΩ; Terminal B Opened
+
A
A
B
R
R
R
R
S
S
S
W
W
Output State
Full scale
Midscale
1 LSB
Zero scale
V
O
A
W
B
(2)
(3)
(4)