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LMC7660 + 16f877 Ref Problem

Discussion in 'Electronic Basics' started by Chris, May 19, 2004.

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  1. Chris

    Chris Guest

    Ok i have a lmc7660 hooked up supplying -4.8 volts to a pair of 1na116pa
    instrumentation amps, i'm also bleeding off that line to the -ref on the
    pic, problem is if i measure the voltage on the output of the lmc7660 i
    get .8 volts if i disconnect only the pic end i get -4.8 volts, whats
    up? is the pig draining too much? how can i get around this???

  2. dont know

    dont know Guest

    you answered your own question. Why are you connecting a negative
    voltage to a PIC?
  3. Chris

    Chris Guest

    Connecting the neg voltage from the lmc7660 to vref- on the pic isn't
    this were i should be grabbing the neg reference???
  4. dont know

    dont know Guest

    I will let any "pic" expert answer that
  5. The PIC reference inputs are constrained to be at or between the
    supply rails. If you apply a voltage outside the rails, protective
    diodes between the input and the supply rails become forward biased.
    This limitation also applies to all the analog inputs and logic inputs
    to the PIC. You can have an analog section that deals with voltages
    outside this range, but you will have to convert any signals that are
    to go to the PIC so that they remain between its rails.
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