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Does AD680 have high impedance mode?

We designed to connect AD680 to four AD7741 at 2.5V.

When the pull down resistor was 20kΩ, the voltage of AD680 drops from 2.5V to 2.35V. And when the pull down resistor was changed to 500Ω, the voltage drop was eliminated.

Why is the problem solved?

Is this because the AD680 has a high impedance mode?

Please tell me m(-_-)m

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  • Hi tamatama55,

    Thank you for sharing block diagram. Now to debug/understanding the issue please try the following:

    1) With the configuration as shown in block diagram measure supply current of only AD680 with 20k Ohm pull down resistor. you can use amp meter.

    2) Repeat number 1 but now measure supply current of only AD680 with 500 Ohm pull down resistor.

    Repeat steps 1 and 2 but now connect pull down resistor after turning on power supply (5V). 

    Following these steps will help us understand if there is any power sequence problem.