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Pull down from 0.8V to 0V

Discussion in 'Electronic Basics' started by Dummy, Aug 3, 2004.

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  1. Dummy

    Dummy Guest

    IC1 is controlled by a microcontroller. Let's say when micocontroller
    issues a command to IC1, pin 28 supposed to be pulled down to 0V. If
    mesaured voltage at pin 28 of IC1 was 0.8V, what kind of additional
    circuit that can be placed at pin 28 to make sure that the pin is
    always 0V at certain condition?
     
  2. Andrew

    Andrew Guest

    You say that 'pin 28 is supposed to be pulled down to 0V'. That will never
    be the case with any digital device. It will always output a small positive
    voltage, usually ~0.5-0.8V when outputting a logic 0. Look at you
    microcontroller's data sheet for VOL (Voltage Output Low)

    For example, for the 16F877, VOL = 0.6V with IOL=8.5ma, VDD=4.5V.

    What are you driving? Any logic device will expect such a voltage for a
    logic 0.
     
  3. Norm Dresner

    Norm Dresner Guest

    Well, a resistor to ground would pull it down to 0V. An NPN transistor as
    an emitter-follower could provide high output. It all depends on the
    impedences [current requirements] of the remaining circuits.

    Norm
     
  4. Rok Sitar

    Rok Sitar Guest

    Diode and resistor should do the trick.

     
  5. Tam/WB2TT

    Tam/WB2TT Guest

    You are probably overloading the pin. Put a noninverting CMOS buffer between
    the pin and the load. Make sure the buffer can supply the desired load
    current. If you have a pullup resistor on it, try a whole lot higher
    value.Also, make sure the VCC and ground pins on IC1 are what you think they
    are.

    Tam

    Tam
     
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