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ADS8685: mux to change input gain

Giorgia Navarra
Intellectual 1301 points
Part Number: ADS8685
Other Parts Discussed in Thread: ADS8688

Dear e2e team,

Is it possible to use a mux before the ADS8685 in order to change the input gain to have different signal levels?

Thanks,

Giorgia

  • 0
    TI__Mastermind 40135 points

    Hi Giorgia,

    I guess you are trying to use an external mux for different level signals, then switch the mux to sample different level signals, yes, you can do that. You can configure the input range of ADS8685 to get the full scale range according to your specific signal level. However you have to wait for a certain time for settling after you switch the channels.

    Another solution is, you can use ADS8688 or ADS8686858A which is an 8-ch input ADC with mux and has a similar front-end structure as the ADS8685, this solution does not need to wait for settling.

    Regards,

    Dale

  • 0 in reply to Dale Li
    TI__Intellectual 1301 points

    Hi Dale,

    thanks for your answer.

    It is clear to me that after activating the mux channel I have to wait for some time to stabilize the signal.

    When the converter gain is changed, is it immediately available Or do I have to wait some time before starting the conversion?

    Thanks,

    Giorgia

  • +1 in reply to Giorgia Navarra
    TI__Mastermind 40135 points

    Hi Giorgia,

    You have to wait for around 120us because of internal LPF filter. Otherwise, you will not be able to get an accurate conversion result.

    Best regards,

    Dale