Micro input current

Discussion in 'Homework Help' started by wuz, Aug 3, 2011.

  1. wuz

    Thread Starter New Member

    Oct 4, 2010
    8
    0
    Hi I'm new to electronics and this is a very basic question hope you guys can help me with.

    In the attached circuit, how do you calculate the current flowing into the micro pin? What value do you generally use for R3?


    Thanks!
     
  2. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    The current required by the input (can be into or out of the pin) is stated in the datasheet. It is in the range of uA.

    What are you trying to do.
     
  3. ErnieM

    AAC Fanatic!

    Apr 24, 2011
    7,388
    1,605
    Generally, I don't do that. You're making 2.5V on a device that's probably running off 5V, and if that is a digital input pin you could blow the device. Only if it's an analog pin then it is OK.

    We would need more information as to where this came from to give any definite answer.
     
  4. wuz

    Thread Starter New Member

    Oct 4, 2010
    8
    0
    Hi the micro input is an ADC. What's the typical input impedance of an ADC, and what's the typical input impedance of a digital pin? I can't seem to find this type of information on the micro controller datasheets.
    Thanks!
     
  5. mik3

    Senior Member

    Feb 4, 2008
    4,846
    63
    Have a look at the Electrical Specifications section of the datasheet.
     
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