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Original question:

MSP432P401R: MSP432 ADC input resistance

MSP432P401R: MSP432P401R

user5724612
Intellectual 340 points

Part Number: MSP432P401R

Hi, 

I have found this:

Acording to that, the input resistance is very low.

  • 0
    TI__Mastermind 22640 points

    Hello,

    I apologize but I don't understand the question! Could you explain what you are looking for?

    Thanks,

    Sai

  • 0 in reply to Sai Reddy
    Intellectual 340 points

    My mistake, I wrote my question too quikly.

    We are developing some devices with the MSP432P4111 MCU. Everytime we use the ADC14 er get weird data. After some research we think we have discovered that the problem is the input impedance (is too low). Looking at the documentation we have found this:
     
    You can find that table in this document: http://www.ti.com/lit/ds/symlink/msp432p4111.pdf table 3_36. Does that mean that the input impedance of the ADC14 is just 2.000 ohms?
     
    If that if the case we would have to implement an AO or something to garatnee that our measuraments are right.
     
    Thank you very much.
  • 0 in reply to user5724612
    TI__Guru 74691 points

    Hello,

        The table you show with the 2Kohms is for the comparator and not the ADC.  Please refer to 5.26.7, Table 5-27 and the parameter Ri which can typically be about 135 ohms.  Also refer to Table 5-28 and the parameter tsample.  Using the equation found in note 4 you can determine is the sample and hold time is adequate for the impedance in your setup.  This includes the impedance of the ADC as well as the source impedance of what is being measured.  If an acceptable sample time cannot be achieved with the impedances of the system, then it is recommended to add a simple voltage follower to reduce the source impedance.

    Regards,

    Chris

  • 0 in reply to Chris Sterzik
    Intellectual 340 points

    We will do the maths and add a voltage follower to see what works better.

    Thank you very much.

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