Problem of AD7908.

Hi ,

I use the AD7908 and the current sensor IC "MAX4073T" without any OP between current sensor output and Vin of AD7908.

In some case, the output of current sensor will be 0.4V, but there is a 3.6V rising due to the reverse current of ADC.

I put an 1M ohm resistor between two IC's to reduce the reverse current temporarily.

Is there any possible error that may happen in my circuit?

Thanks a lot,
Stan

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  • 0
    •  Analog Employees 
    on Dec 9, 2011 7:19 PM

    Hi Stan,

    Appologies for delayed response to your questions.

    I think what you have experienced is the transient kick back from the converter itself which may have a strong implication on accuracy of the system. To verify whether or not this kick back has an effect on the accuracy of the AD7908 device I would need to know MAX40731 output impedance, selected througput rate of the AD7908 and external componet configuration between these two devices.

    1 M ohm resistor is probably not ideal to be present on the input of the SAR converter as it significantly affects source ability to charge/discharge internal sampling capacitor to required accuracy level within converter acquisition time.

    Regards,
    Jakub.

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  • 0
    •  Analog Employees 
    on Dec 9, 2011 7:19 PM

    Hi Stan,

    Appologies for delayed response to your questions.

    I think what you have experienced is the transient kick back from the converter itself which may have a strong implication on accuracy of the system. To verify whether or not this kick back has an effect on the accuracy of the AD7908 device I would need to know MAX40731 output impedance, selected througput rate of the AD7908 and external componet configuration between these two devices.

    1 M ohm resistor is probably not ideal to be present on the input of the SAR converter as it significantly affects source ability to charge/discharge internal sampling capacitor to required accuracy level within converter acquisition time.

    Regards,
    Jakub.

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