AD5247BKSZ100-R2 datasheet(17/20 Pages) AD

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Data Sheet

AD5247

Rev. F | Page 17 of 20

LAYOUT AND POWER SUPPLY BYPASSING

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

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

sible with minimum conductor length. Ground paths should

have low resistance and low inductance.

Similarly, it is 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 electrolytic capaci-

tors should also be applied at the supplies to minimize any transient

disturbance and low frequency ripple (see Figure 40). Note that the

digital ground should also be joined remotely to the analog ground

at one point to minimize the ground bounce.

AD5247

VDD

0.1µF

10µF

GND

VDD

Figure 40. Power Supply Bypassing

CONSTANT BIAS TO RETAIN RESISTANCE SETTING

For users who desire nonvolatility but cannot justify the additional

cost for the EEMEM, the AD5247 can be considered a low cost

alternative because it maintains a constant bias to retain the

wiper setting. The AD5247 is specifically designed with low

power in mind, which allows low power consumption even in

battery-operated systems.

Figure 41 demonstrates the power consumption from a 3.4 V

450 mA/hr 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 was due to the intrinsic leakage

current of the battery itself.

DAYS

90%

92%

94%

96%

98%

100%

102%

104%

106%

108%

110%

TA = 25°C

Figure 41. Battery Operating Life Depletion

This demonstrates that constantly biasing the potentiometer

is a practical approach. Most portable devices do not require

the removal of batteries for charging. Although the resistance

setting of the AD5247 is lost when the battery needs replace-

ment, such events occur rather infrequently. As a result, this

inconvenience is justified by the lower cost and smaller size

offered by the AD5247. If total power is lost, the user should

be provided with a means to adjust the setting accordingly.

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