CN0359: Float of signal from Instrumentation Amplifier

We have set up EVAL-CN0359 and have the following problem. 
We are measuring the voltage from J5 pins 2 or 3.
These feed AD8253.
We see the expected distorted square wave on the scope but it is floating up and down between the rails.
Page 18 of the datasheet for AD8253 possibly implies that the inputs are not stabilized by a bias current path to ground in the CN0359 layout.
See also fig. 6 of your article by Kitchin concerning "Common Problems When Designing Amplifier Circuits".

Any advice here? T
hanks--Fritz
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  • 0
    •  Analog Employees 
    on Jul 10, 2019 8:49 AM

    Hello EZ,

    Just an update on this in case someone encounters this problem: further discussion on this topic has been done directly through email. If you are using the IST LFS1505 sensor and are encountering this drift issue, please connect a 10 µF capacitor in series with pin 1 of J5 and 1 µF capacitors in series with pins 2 and 3. In addition, place 1 MΩ resistors on pins 2 and 3 of J5 to ground. The below diagram shows the connections for this:

    This should stabilize the output signal of the U15 in-amp as shown below:

    Please note that we are still working with Fritz on this; an update may be posted at a later date. Thank you.

Reply
  • 0
    •  Analog Employees 
    on Jul 10, 2019 8:49 AM

    Hello EZ,

    Just an update on this in case someone encounters this problem: further discussion on this topic has been done directly through email. If you are using the IST LFS1505 sensor and are encountering this drift issue, please connect a 10 µF capacitor in series with pin 1 of J5 and 1 µF capacitors in series with pins 2 and 3. In addition, place 1 MΩ resistors on pins 2 and 3 of J5 to ground. The below diagram shows the connections for this:

    This should stabilize the output signal of the U15 in-amp as shown below:

    Please note that we are still working with Fritz on this; an update may be posted at a later date. Thank you.

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