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AM335x Input Impedance

JasonHaedt
Genius 3320 points

Team,

Has the ADC input been characterized to understand what the maxim ADC input impedance can be? Thanks for the help.

-Jason 

 

  • 0
    Genius 3320 points

    Team,

    Any comments on this post?

  • 0
    TI__Mastermind 28125 points

    Jason

    The ADC has not been characterized but I talked to the designer of the module and he provided the following comments:

    up to 1K  guaranteed to meet the spec
    1K to 5K Should be ok
    5K to10K not guaranteed
    >10K not recommended.

    The values listed are for the source impedence.

      Paul

     

     

  • 0 in reply to PaulM
    TI__Guru 63145 points

    The previous answer was describing the expected source impedance required to minimize error.

    The minimum input impedance for the AM335x ADC would be about [1/(65.97 x10-12 * f)], where f is the frequency if the input signal.

    For example, the minimum input impedance for a 50 KHz input signal would be about 303K ohms.

    Regards,
    Paul

  • 0 in reply to peaves
    Intellectual 950 points
    Hi,
    What about if we have DC Signal on the AIN? For example , we want to measure 4-20mA output from pressure sensor whose response time is around 1ms. I want to make this without opamp buffer and I use external reference on VREF+ of the Sitara. According the limitations from AM335x datasheet this can be max, 1.8V. In that case current sensing resistor is max. 90R.

    Circuit concept would be as like as on this link:
    e2e.ti.com/.../381911

    Br,
    Josko