Regulating from 4v to 3.3v

Discussion in 'The Projects Forum' started by solexious, Jul 3, 2012.

  1. solexious

    Thread Starter Active Member

    Nov 20, 2007
    55
    0
    Hello all,

    Tried searching with no luck, think I may be using the wrong terms.

    I'm going to be using a li-ion battery rated at 3.7v (Initial charge starts out closer to 4v if I have done my research correctly) and I want to regulate it for use with 3.3v ICs.

    Whats the best type of regulator to use and what specs should I look out for?

    This is the most fitting one I could find so far from my research http://uk.mouser.com/ProductDetail/...=wjXTWlTR2QzFFANo/9rKi3OTSRNxBq/AD8RsPCd74hg= is that a good choice?

    It doesn't need to be super cheap, but not wanting to break the bank one one component.

    Thanks

    Sol
     
  2. #12

    Expert

    Nov 30, 2010
    16,338
    6,824
    The datasheet on page 5 shows that the dropout voltage is .35 volts at maximum current and temperature.

    3.3 + .35 = 3.65
     
  3. solexious

    Thread Starter Active Member

    Nov 20, 2007
    55
    0
    Great, thanks.

    Is an LDO the correct component for the job? What happens if the input falls below 3.65, does it cutout or do strange things?

    Sol
     
  4. #12

    Expert

    Nov 30, 2010
    16,338
    6,824
    If the input voltage falls below the needed voltage, the output voltage will decrease by exactly as much as you fail to meet the need.

    As far as I know, a low drop out voltage regulator is the way to do this, especially compared to a high drop out voltage regulator.
     
  5. wayneh

    Expert

    Sep 9, 2010
    12,151
    3,058
    I'd consider just putting a diode in series. It'll drop 0.7V or so, less if you choose a Schottky. Cheap and easy, although not exactly a regulator.
     
  6. bountyhunter

    Well-Known Member

    Sep 7, 2009
    2,498
    507
    You'll get more for your money choosing an LDO which is made via CMOS and has a maximum voltage rating of about 6V, since your max supply is less than 4.5V. A 16V device is payng extra for something you don't need. Nat Semi had a bunch of these, Linear Tech and Maxim do as well. You want to get the lowest dropout for the $ at the load current you desire (which you did not list).

    One example:

    http://www.ti.com/lit/ds/symlink/lp3961.pdf
     
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