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ADS5500 input polar circuit

Thomas Chang15933
Expert 4770 points
Other Parts Discussed in Thread: ADS5500, THS4513, THS4509

Hi All:

In our ADS5500 (figure44)or THS4513(figure84) datasheet showed the circuit with input polar opposite always.

I think the circuit  should be workable, but it still has phase issue in some applications.

Or I am wrong, the ADC should be connect opposite polar to amplify, right?

  • 0
    TI__Expert 3855 points

    Thomas,

    I believe you are correct. The fully differential amplifiers invert the outputs compared to the inputs so it should be connected the other way around as you suggest. I'll take a note for the next time we update the data sheet. I saw it is also backwards in the THS4509 data sheet.

    In AC coupled applications it doesn't make a difference as it's equal to a phase shift by 180deg. The phase will also shift simply by the trace length on the pcb.

    However in DC coupled applications (e.g. when the input is a pulse) the polarity does make a difference.

    Tommy