Problems interfacing AD623 with AD8561 comparator.

I ran into an issue when interfacing the AD623 with the AD8561 comparator.

Pin 3 of the comparator (negative input) is 'feeding' or is biased at ~1.4V. This seems to cause problems with the AD623 driving the input of the comparator.

The AD623 can drive loads of 10kohm or greater.

The AD8561 has a PNP differential stage input.

Does this means that the AD623 output is incompatible with the AD8561 input and an extra buffer is needed between the two?

Thank you in advance.

Christian

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  • 0
    •  Analog Employees 
    on Sep 22, 2011 8:27 PM

    Hi Christian,

    A few questions for you:

    - What are the supply voltages for the AD623 and AD8561?

    - What is the AD623 reference voltage?

    - What is the gain of the AD623?

    - Can you elaborate on "this seems to cause problems with the AD623".  Is it railing, oscillating, giving a wrong DC value, etc?

    - If you run the same signal into the AD623 when it is not connected to the AD8561 everything looks good, but as soon as you connect it ot the AD8561 you have issues?  Is this correct?

    Thanks,

    Matt

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  • 0
    •  Analog Employees 
    on Sep 22, 2011 8:27 PM

    Hi Christian,

    A few questions for you:

    - What are the supply voltages for the AD623 and AD8561?

    - What is the AD623 reference voltage?

    - What is the gain of the AD623?

    - Can you elaborate on "this seems to cause problems with the AD623".  Is it railing, oscillating, giving a wrong DC value, etc?

    - If you run the same signal into the AD623 when it is not connected to the AD8561 everything looks good, but as soon as you connect it ot the AD8561 you have issues?  Is this correct?

    Thanks,

    Matt

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