Connect with us

Current monitor max "vout" = ?

Discussion in 'General Electronics Discussion' started by eem2am, Sep 11, 2013.

  1. eem2am

    eem2am

    414
    0
    Aug 3, 2009
    Hello,
    This concerns single supply operation of LT1787 as in figure 8, page 12 of the datasheet.
    The LT1787 current monitor, on page 3 of its datasheet quotes "vout" as "v(bias) + 1.024V" if "Vs+ > 3.3V".

    Why does "Vs+" have to be greater than 3.3V?

    Surley LT1787 can produce vout = v(bias) + 1.204V if "VS+" = 2.5v?
    (assuming v(bias) = 0V.

    Further down the page on page 3, "VOmax" is stated as VS+ -0.75v.

    So why are they saying that "vs+" has to be greater than 3.3V for "vout" to be 1.024V?
    Surely if "Vs+" is just 2.5v, then "vout" could be 1.024V ?

    LT1787 DATASHEET:
    http://cds.linear.com/docs/en/datasheet/1787fc.pdf
     
  2. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,178
    2,690
    Jan 21, 2010
    I can't say why, but they are telling you that.

    Perhaps the generation of the internal reference voltage requires a little over 2V of headroom?

    Perhaps you could do your own tests to see if it works at a lower voltage.
     
  3. eem2am

    eem2am

    414
    0
    Aug 3, 2009
    I am wondering if its actually possible for "vout" to be 1.024V if "vs+" is just 2.5V.

    I see your point, but even if I order one and it does give vout=1.024v at vs+=2.5v, -if the datasheet doesn't corroborate this, then i'll be worrying if the next batch of LT1787 will behave so well?
     
  4. (*steve*)

    (*steve*) ¡sǝpodᴉʇuɐ ǝɥʇ ɹɐǝɥd Moderator

    25,178
    2,690
    Jan 21, 2010
    Exactly.

    And that's why you stay within specified limits. You have a far higher degree of certainty that what works will work next time.
     
  5. eem2am

    eem2am

    414
    0
    Aug 3, 2009
    I am just wondering what is the guaranteed maximum achievable value of "Vout" if "vs+" is just 2.5v?
     
Ask a Question
Want to reply to this thread or ask your own question?
You'll need to choose a username for the site, which only take a couple of moments (here). After that, you can post your question and our members will help you out.
Electronics Point Logo
Continue to site
Quote of the day

-