EVAL-AD5243SDZ Analog Devices, EVAL-AD5243SDZ Datasheet - Page 13

• Manufacturer Part Number: EVAL-AD5243SDZ
• Description: Digital Potentiometer Development Tools EVALUATION BOARD
• Manufacturer: Analog Devices
• Series: AD5243r

Specifications of EVAL-AD5243SDZ

• Rohs: yes
• Product: Evaluation Boards
• Tool Is For Evaluation Of: AD5243
• Resistance: 2.5 kOhms/10 kOhms/50 kOhms/100 kOhms
• Operating Supply Voltage: 5.5 V
• Interface Type: I2C
• Maximum Operating Temperature: + 125 C
• Factory Pack Quantity: 1
• For Use With: Sim DAC Web Tool

Data Sheet
THEORY OF OPERATION
The AD5243/AD5248 are 256-position, digitally controlled
variable resistor (VR) devices.
An internal power-on preset places the wiper at midscale
during power-on, which simplifies the fault condition recovery
at power-up.
PROGRAMMING THE VARIABLE RESISTOR AND
VOLTAGE
Rheostat Operation
The nominal resistance of the RDAC between Terminal A and
Terminal B is available in 2.5 kΩ, 10 kΩ, 50 kΩ, and 100 kΩ.
The nominal resistance (R
accessed by the wiper terminal and the B terminal contact. The
8-bit data in the RDAC latch is decoded to select one of the 256
possible settings.
Assuming that a 10 kΩ part is used, the first connection of the
wiper starts at the B terminal for Data 0x00. Because there is
a 160 Ω wiper contact resistance, such a connection yields a
minimum of 320 Ω (2 × 160 Ω) resistance between Terminal W
and Terminal B. The second connection is the first tap point,
which corresponds to 359 Ω (R
2 × 160 Ω) for Data 0x01. The third connection is the next tap
point, representing 398 Ω (2 × 39 Ω + 2 × 160 Ω) for Data 0x02,
and so on. Each LSB data value increase moves the wiper up the
resistor ladder until the last tap point is reached at 10,281 Ω
(R
AB
+ 2 × R
A
B
W
).
Figure 38. AD5243 Equivalent RDAC Circuit
W
Figure 37. Rheostat Mode Configuration
D7
D6
D5
D4
D3
D2
D1
D0
DECODER
LATCH
RDAC
AND
A
B
AB
) of the VR has 256 contact points
R
R
R
R
S
S
S
S
WB
W
= R
AB
/256 + 2 × R
A
B
A
W
B
W
W
= 39 Ω +
Rev. B | Page 13 of 20
The general equation determining the digitally programmed
output resistance between W and B is
where:
D is the decimal equivalent of the binary code loaded in the
8-bit RDAC register.
R
R
the internal switch.
In summary, if R
the following output resistance, R
RDAC latch codes.
Table 7. Codes and Corresponding R
D (Dec)
255
128
1
0
Note that in the zero-scale condition, a finite wiper resistance of
320 Ω is present. Care should be taken to limit the current flow
between W and B in this state to a maximum pulse current of no
more than 20 mA. Otherwise, degradation or possible destruction
of the internal switch contact may occur.
Similar to the mechanical potentiometer, the resistance of the
RDAC between Wiper W and Terminal A also produces a
digitally controlled complementary resistance, R
terminals are used, the B terminal can be opened. Setting the
resistance value for R
and decreases as the data loaded in the latch increases in value.
The general equation for this operation is
When R
output resistance, R
codes, as listed in Table 8.
Table 8. Codes and Corresponding R
D (Dec)
255
128
1
0
Typical device-to-device matching is process-lot dependent and
may vary by up to ±30%. Because the resistance element is pro-
cessed in thin-film technology, the change in R
has a very low temperature coefficient of 35 ppm/°C.
AB
W
is the wiper resistance contributed by the on resistance of
is the end-to-end resistance.
R
R
WB
WA
AB
(
(
D
D
is 10 kΩ and the B terminal is open circuited, the
)
R
10,281
5380
359
320
)
R
359
5320
10,280
10,320

WB

WA
256
256
AB
(Ω)
(Ω)
D
256
is 10 kΩ and the A terminal is open circuited,
WA


WA
R
D
, is set according to the RDAC latch
AB
Output State
Full scale (R
Midscale
1 LSB + 2 × R
Zero scale (wiper contact resistance)
starts at a maximum value of resistance

Output State
Full scale
Midscale
1 LSB + 2 × R
Zero scale

R
AB
2


R
2
W
WB

R
AB
, is set for the indicated
W
W
W
− 1 LSB + 2 × R
AD5243/AD5248
WB
WA
Resistance
Resistance
AB
with temperature
WA
. When these
W
)
(1)
(2)