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ADC128S102: ADC128S102QML

Rajan Bedi
Expert 1465 points
Part Number: ADC128S102

Hello,

For the ADC128S102, what is the input resistance/impedance of the analog inputs? I may want to measure some currents which I will convert to a voltage and want to ensure the ADC's has an input impedance which will not affect current measurements.

Thank you and kind regards,

Rajan

  • 0
    TI__Mastermind 38260 points

    Hello Rajan,

    The input of ADC128S102 is a switched capacitor, with value of 38pF.  When the capacitor is connected to the inputs, you will have a charging current that depends on the internal switch resistance and the external source impedance.  After the sampling capacitor is fully charged, there will be a leakage current that is rated 10nA typical.

    If operating at higher sample rates, you will typically need an input amplifier to properly charge the sampling capacitor within the acquisition time period.  At lower data rates (longer acquisition times) you may be able to directly drive the ADC/MUX input without an external amplifier, provide the source resistance is low.

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    TI__Guru 62665 points

    Hi Rajan,

    I wanted to add to Keith's nice response that we have a video which explains these effects in detail and also a tool in our analog engineer calculator which can be used to help with your designs. 

    https://www.ti.com/tool/ANALOG-ENGINEER-CALC

    https://training.ti.com/ti-precision-labs-driving-sar-without-amplifiers

    Lastly, we've recently released the ADC128S102-SEP, a Space Enhanced Plastic, product to add to our current ADC128S102QML-SP offering.  The -SEP product may be interesting for your LEO applications requiring lower radiation performance versus a standard QMLV product.