AD5243 AD [Analog Devices], AD5243 Datasheet - Page 15

• Manufacturer Part Number: AD5243
• Description: Dual 256-Position I2C Compatible Digital Potentiometer
• Manufacturer: AD [Analog Devices]

CONSTANT BIAS TO RETAIN RESISTANCE SETTING
For users who desire nonvolatility but cannot justify the addi-
tional cost for the EEMEM, the AD5243/AD5248 may be
considered as low cost alternatives by maintaining a constant
bias to retain the wiper setting. The AD5243/AD5248 are
designed specifically with low power in mind, which allows low
power consumption even in battery-operated systems. The
graph in Figure 43 demonstrates the power consumption from a
3.4 V 450 mAhr Li-Ion cell phone battery, which is connected to
the AD5243/AD5248. The measurement over time shows that
the device draws approximately 1.3 µA and consumes negligible
power. Over a course of 30 days, the battery is depleted by less
than 2%, the majority of which is due to the intrinsic leakage
current of the battery itself.
100%
104%
102%
110%
108%
106%
98%
96%
94%
92%
90%
0
V
DD
Figure 43. Battery Operating Life Depletion
10µF
5
Figure 42. Power Supply Bypassing
C3
+
0.1µF
C1
10
DAYS
15
V
DD
AD5243
20
T
GND
A
= 25 °C
25
30
Rev. 0 | Page 15 of 20
This demonstrates that constantly biasing the potentiometer is
not an impractical approach. Most portable devices do not
require the removal of batteries for the purpose of charging.
Although the resistance setting of the AD5243/AD5248 is lost
when the battery needs replacement, such events occur rather
infrequently such that this inconvenience is justified by the
lower cost and smaller size offered by the AD5243/AD5248. If
and when total power is lost, the user should be provided with a
means to adjust the setting accordingly.
EVALUATION BOARD
An evaluation board, along with all necessary software, is avail-
able to program the AD5243/AD5248 from any PC running
Windows 98/2000/XP. The graphical user interface, as shown in
Figure 44, is straightforward and easy to use. More detailed
information is available in the user manual, which comes with
the board.
The AD5243/AD5248 start at midscale upon power-up. To
increment or decrement the resistance, the user may simply
move the scrollbars on the left. To write any specific value, the
user should use the bit pattern in the upper screen and press the
Run button. The format of writing data to the device is shown
in Table 9. To read the data out from the device, the user can
simply press the Read button. The format of the read bits is
shown in Table 10.
Figure 44. AD5243 Evaluation Board Software
AD5243/AD5248