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advref-pin-current-draw-sa

Discussion in 'ARM' started by Flyback, Jun 18, 2013.

  1. Flyback

    Flyback Well-Known Member

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    Hello ,

    We are using an MCP9700 temperature monitor IC and feeding its output into the ADC pin (AD4) of the SAM3N00B microcontroller.
    The MCP9700 only provides a maximum of 100uA output current, so is that enough to supply the current drawn by the ADC pin, or do i need to buffer the temperature monitor IC's output voltage?

    MCP9700 Temperture monitor IC
    http://www.electro-tech-online.com/custompdfs/2013/06/21942e-1.pdf

    SAM3N00B datasheet:
    http://www.electro-tech-online.com/custompdfs/2013/06/doc11011-2.pdf
     
  2. alec_t

    alec_t Well-Known Member Most Helpful Member

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    The datasheet section dealing with the ADC should tell you the maximum source impedance of the analogue input and give you some idea of the ADC's input impedance or current.
     
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  3. Flyback

    Flyback Well-Known Member

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    datasheet doesnt tell this, it just tells a "TRACKTIM" calculation which gives you the maximum sample rate.
    We are only sampling once every few secs and its not relevant.
    Datasheet only tells the overall current draw of the ADC module.
     
  4. dave

    Dave New Member

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  5. dougy83

    dougy83 Well-Known Member

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    Datasheet does specify ADC leakage current, table 35-34
     
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  6. Flyback

    Flyback Well-Known Member

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    i think "leakage" current is not the current that flows when a conversion is taking place. Leakage current, by definition , is like the leakage current that you get into an opamp input....its "leakage"......that current that "leaks" all the time
     
  7. dougy83

    dougy83 Well-Known Member

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    Oh, is that what you're after? You can work that out from the formula for TRACKTIM. This will give you Ron and Csample. From there you can work out the current required to charge the cap if you so desire.

    You can just increase Zsource though if you're worried about peak current. Alternately you can add a capacitor in addition to a Zsource resistor. Personally I wouldn't bother, but you can test the performance with and without the series resistor.
     
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