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Simple Li-Ion monitoring circuit

Discussion in 'Electronic Design' started by arybinsky, Apr 2, 2007.

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  1. arybinsky

    arybinsky Guest


    I have a 7.4V Li-ion battery (or rather a battery pack). It is
    connected to the 3.3V DC-DC converter which runs the rest of my
    the battery voltage drops below 6V.
    The DC-DC converter has enable pin, so I've figured out I just need to
    connect the monitoring circuit to this pin.

    What kind of monitoring circuit would you recommend? I really need
    something simple, it may be an integrated circuit.

    Or maybe it is possible to put this circuit between the battery and
    the DC-DC converter? So it blocks any current passing, when the
    battery is low?
  2. check out Texas Inst. TL7702
    or google for voltage supervisors

  3. AJ

    AJ Guest

    I have used the MAX8212 in the past, you can get them from Digikey


  4. Anywhere between 5.8 and 6.6 should be fine, and there's almost no
    energy to be had between those voltages (very steep slope). This means
    you can use cheap, high-tolerance parts to set your cutoff with very
    little loss of usable energy.

    All you need, then, are two resistors, a voltage reference, and a
    comparator. The voltage supervisory chips suggested by others combine
    the reference and the comparator without costing much more, although
    they may be more complicated than what you need and I haven't looked at
    their power consumption.

    I would recommend looking at the quiescent current of whatever you pick
    - you don't want your cutoff circuit itself drawing the battery down
    below 2v per cell and ruining it even after the main circuit has been
    shut down.
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