AD5247

LAYOUT AND POWER SUPPLY BYPASSING

It is a good practice to employ a compact, minimum lead-length

layout design. The leads to the inputs should be as direct as

possible with a minimum conductor length. Ground paths

should have low resistance and low inductance.

Similarly, it is a good practice to bypass the power supplies with

quality capacitors for optimum stability. Supply leads to the

device should be bypassed with 0.01 µF to 0.1 µF disc or chip

ceramic capacitors. Low ESR 1 µF to 10 µF tantalum or electro-

lytic capacitors should also be applied at the supplies to

minimize any transient disturbance and low frequency ripple

(see

). Note that the digital ground should also be

joined remotely to the analog ground at one point to minimize

the ground bounce.

Figure 40

Figure 40. Power Supply Bypassing

AD5247

C1

C3

GND

10

µF

0.1

µF

+

CONSTANT BIAS TO RETAIN RESISTANCE SETTING

For users who desire nonvolatility but cannot justify the

additional cost for the EEMEM, the AD5247 may be considered

as a low cost alternative by maintaining a constant bias to retain

the wiper setting. The AD5247 was designed specifically with

low power in mind, which allows low power consumption even

in battery-operated systems. The graph in

demonstrates the power consumption from a 3.4 V 450 mAhr

Li-ion cell phone battery, which is connected to the AD5247.

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 was depleted by less than 2%, the

majority of which is due to the intrinsic leakage current of the

battery itself.

Figure 41

Figure 41. Battery Operating Life Depletion

DAYS

0

90%

92%

94%

96%

510

15

98%

100%

102%

104%

106%

108%

110%

20

25

30

This demonstrates that constantly biasing the pot 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 AD5247 will be 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 AD5247. 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

available to program the AD5247 from any PC running

Windows® 98, Windows 2000®, or Windows XP®. The graphical

user interface, as shown in

, is straightforward and

easy to use. More detailed information is available in the user

manual, which comes with the board.

Figure 42

Figure 42. AD5247 Evaluation Board Software

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