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Using a single power supply for dual supply "Sample and Hold"

Discussion in 'Electronic Basics' started by aman, Oct 24, 2005.

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  1. aman

    aman Guest

    Sample and hold IC LF198 operates from +-5V to +-18V. I am assuming
    that if I bias it using +5V and GND single supply, the only difference
    will be that it would just be able to handle rail to rail voltages(that
    is, only positive voltages from 0V to 5V).

    Is my assumption correct ?

    -Aman
     
  2. Sorry, no. The device needs between 10 and 30 volts across its supply
    pins in order to function correctly. Where ground is between these
    voltages is just a matter of input and output signal swing capability.

    This detail is hidden in a cryptic comment on the data sheet:
    http://www.ee.washington.edu/stores/DataSheets/linear/lf398.pdf

    On page 2, directly under the section title "Electrical
    Characteristics" it says, "The following specifcations apply for -VS +
    3.5 <= VIN +VS -3.5..."

    I think that means that all the specifications apply only if the
    signal voltage (Vin) is 3.5 or more volts more positive than the
    negative supply rail voltage (-VS) and also 3.5 or more volts more
    negative than the positive supply rail voltage (+VS).

    So the device might have a very small signal range with a positive and
    negative 3.5 volt supply (or some combination that adds up to 7 volts,
    but they don't actually say it works for any supply total less than 10
    volts, total.
     
  3. Jasen Betts

    Jasen Betts Guest

    according to the above it wants atleast 10V between it's VSS and VDD

    +12 (or +10) and 0 could probably work - unless it needs a ground too.

    Bye.
    Jasen
     
  4. aman

    aman Guest

    Ok now these make sense. So if I have to use input of 0 to 5V, I would
    probably have to use power supply like -3.5 and +8.5 atleast. Correct ?
     
  5. Yes. That would be the minimum that is covered by the spec sheet.
    Selected individual units may do a bit better than that, but it is not
    guaranteed.
     
  6. aman

    aman Guest

    Thanks
     
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