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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  • 0
    •  Analog Employees 
    on May 29, 2019 10:59 PM over 1 year ago

    Hi tamatama55,

    To understand the pull down resistor, can you please share more details and schematic? 

    Can you please provide more details regarding what you mean by high impedance mode?

    How are you measuring output voltage of AD680 ? DMM, ADC or etc.

    Regards,

    Anshul

  • Hi Anshul,

    Thank you for your replying.

    The schematic is below. It also describes the measurement method.

    When AD680 supply 2.35V(when it is used 20kΩ), the current of measurement spot is almost zero.

    That's why, I think that this is high impedance mode. Thank you for your cooperation.

  • 0
    •  Analog Employees 
    on May 30, 2019 9:18 PM over 1 year ago in reply to tamatama55

    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.

    Regards,

    Anshul 

Reply
  • 0
    •  Analog Employees 
    on May 30, 2019 9:18 PM over 1 year ago in reply to tamatama55

    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.

    Regards,

    Anshul 

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