problem with Negative supply for ADC

Discussion in 'General Electronics Chat' started by omarcillo, Mar 2, 2009.

  1. omarcillo

    Thread Starter New Member

    Mar 2, 2009
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    0
    Hi:
    I have a problem using the output of a TC7660 as floating ground fro a voltage reference, so the output of the TC7660 (-2.5V) is the ground for the LT1021 (5 V) reference, I think I need a resistor between this 2 elements but I do no know how to connect that..

    Any suggestion is appreciated..
     
  2. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,343
    Hello,

    What is the voltage of V+ in your drawing ?
    What is the reference voltage you expect on the output of the LT1021 ?
    (When the ground pin is at - 2.5 Volts, the reference output pin will be + 2.5 Volt).

    Greetings,
    Bertus
     
  3. omarcillo

    Thread Starter New Member

    Mar 2, 2009
    3
    0
    Hi,
    V+ is 2.5V that comes from a regulator, and the idea is that output of the LT1021 is +2.5 measured from GND or 5V measured form -2.5V
    The output of the LT1021 is very stable 5V, that is why I am using that......
    regards
     
  4. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,343
    Hello,

    If the - 2.5 Volts is not stable the + 2.5 volts from the LT1021 is also not stable as it is references to the - 2.5 Volts of the ICL7660.

    Greetings,
    Bertus
     
  5. omarcillo

    Thread Starter New Member

    Mar 2, 2009
    3
    0
    Hello,
    Yeah the 2.5 will no be stable measured from GND but it will be the difference between -2.5 and 2.5, but the reference for my ADC is the difference between the -2.5V and 2.5V....
    Regards
     
  6. bertus

    Administrator

    Apr 5, 2008
    15,638
    2,343
    Hello,

    What is your problem then ?
    I see you have used 1 μF caps at the ICL7660.
    In the datasheet they always use 10 μF caps.
    Perhaps this makes it a little bit more stable.

    Greetings,
    Bertus
     
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