How to OR together 3 li-poly batteries and protect batteries fromundervoltage

Discussion in 'Electronic Design' started by Michael, Jul 16, 2008.

  1. Michael

    Michael Guest

    Hi there - I need to combine together 3 lithium polymer battery packs.
    Each battery pack is a 4 cell (in series) pack, so the voltage of each
    pack could be as high as say around 18V, and I can't let it fall below
    12V otherwise damage to the pack could occur. Once the battery pack is
    shut off I need drain on the pack to be brought to a minimum - I'd
    like it to be well under a milli-amp.

    Further, Each battery will be connecting to a separate (but identical)
    PCB. the PCBs will have 3 connections going between all of them - a
    power ground (the battery ground), ORed power high, and a low current
    switch connection (to turn off all batteries, regardless of voltage
    level).

    I need to do the switching on the high side of the batteries,
    unfortunately. I need to protect the batteries from charging each
    other as that would (clearly) be less than good. So my first
    inclination is to have the positive side of my batter packs connected
    to the anode of a schottky, with the schottky's cathode connected to
    the source of a N-FET, and the drain connected to the ORed power
    supply. An unvervoltage protection circuit would be ORed with the
    switch line, and with some sort of charge pump that would drive the
    FET.

    This would work. This is also a lot of parts - and I'm very space
    constrained.

    I stated looking around and have found such a thing as an "N+1 and
    ORing Power Rail Controller". For example, the TI TPS2413:
    http://focus.ti.com/lit/ds/symlink/tps2413.pdf

    This part won't work due to the 16.5V max bus voltage limitation, but
    otherwise, it looks like it handles... everything.

    Does this sort of part sound like the right solution for me? Does
    anybody know of a similar part that can handle my bus voltage?

    Thanks!

    -Michael
    Michael, Jul 16, 2008
    #1
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  2. Re: How to OR together 3 li-poly batteries and protect batteries from undervoltage

    On Wed, 16 Jul 2008 08:18:27 -0700 (PDT), in sci.electronics.design
    Michael <> wrote:

    >Hi there - I need to combine together 3 lithium polymer battery packs.
    >Each battery pack is a 4 cell (in series) pack, so the voltage of each
    >pack could be as high as say around 18V, and I can't let it fall below
    >12V otherwise damage to the pack could occur. Once the battery pack is
    >shut off I need drain on the pack to be brought to a minimum - I'd
    >like it to be well under a milli-amp.
    >
    >Further, Each battery will be connecting to a separate (but identical)
    >PCB. the PCBs will have 3 connections going between all of them - a
    >power ground (the battery ground), ORed power high, and a low current
    >switch connection (to turn off all batteries, regardless of voltage
    >level).
    >
    >I need to do the switching on the high side of the batteries,
    >unfortunately. I need to protect the batteries from charging each
    >other as that would (clearly) be less than good. So my first
    >inclination is to have the positive side of my batter packs connected
    >to the anode of a schottky, with the schottky's cathode connected to
    >the source of a N-FET, and the drain connected to the ORed power
    >supply. An unvervoltage protection circuit would be ORed with the
    >switch line, and with some sort of charge pump that would drive the
    >FET.
    >
    >This would work. This is also a lot of parts - and I'm very space
    >constrained.
    >
    >I stated looking around and have found such a thing as an "N+1 and
    >ORing Power Rail Controller". For example, the TI TPS2413:
    >http://focus.ti.com/lit/ds/symlink/tps2413.pdf
    >
    >This part won't work due to the 16.5V max bus voltage limitation, but
    >otherwise, it looks like it handles... everything.
    >
    >Does this sort of part sound like the right solution for me? Does
    >anybody know of a similar part that can handle my bus voltage?
    >
    >Thanks!
    >
    >-Michael

    The Linear LTC1473 works up to 30V, but is a dual, the ltc1479 is
    triplle, but is a larger package

    HTH


    martin
    Martin Griffith, Jul 16, 2008
    #2
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  3. Michael

    Michael Guest

    On Jul 16, 11:31 am, Martin Griffith <> wrote:
    > On Wed, 16 Jul 2008 08:18:27 -0700 (PDT), in sci.electronics.design
    >
    >
    >
    >
    >
    > Michael <> wrote:
    > >Hi there - I need to combine together 3 lithium polymer battery packs.
    > >Each battery pack is a 4 cell (in series) pack, so the voltage of each
    > >pack could be as high as say around 18V, and I can't let it fall below
    > >12V otherwise damage to the pack could occur. Once the battery pack is
    > >shut off I need drain on the pack to be brought to a minimum - I'd
    > >like it to be well under a milli-amp.

    >
    > >Further, Each battery will be connecting to a separate (but identical)
    > >PCB. the PCBs will have 3 connections going between all of them - a
    > >power ground (the battery ground), ORed power high, and a low current
    > >switch connection (to turn off all batteries, regardless of voltage
    > >level).

    >
    > >I need to do the switching on the high side of the batteries,
    > >unfortunately. I need to protect the batteries from charging each
    > >other as that would (clearly) be less than good. So my first
    > >inclination is to have the positive side of my batter packs connected
    > >to the anode of a schottky, with the schottky's cathode connected to
    > >the source of a N-FET, and the drain connected to the ORed power
    > >supply. An unvervoltage protection circuit would be ORed with the
    > >switch line, and with some sort of charge pump that would drive the
    > >FET.

    >
    > >This would work. This is also a lot of parts - and I'm very space
    > >constrained.

    >
    > >I stated looking around and have found such a thing as an "N+1 and
    > >ORing Power Rail Controller". For example, the TI TPS2413:
    > >http://focus.ti.com/lit/ds/symlink/tps2413.pdf

    >
    > >This part won't work due to the 16.5V max bus voltage limitation, but
    > >otherwise, it looks like it handles... everything.

    >
    > >Does this sort of part sound like the right solution for me? Does
    > >anybody know of a similar part that can handle my bus voltage?

    >
    > >Thanks!

    >
    > >-Michael

    >
    > The Linear LTC1473 works up to 30V, but is a dual, the ltc1479 is
    > triplle, but is a larger package
    >
    > HTH
    >
    > martin


    Hi Martin - I'm looking for a single controller - since I need one
    controller per board. Looking at some parts in the same family as
    those two Linear parts I stumbled across the LT4351 (http://
    www.linear.com/pc/downloadDocument.do?navId=H0,C1,C1003,C1142,C1079,P2173,D2942).
    It looks pretty good - though it doesn't have an enable. It looks like
    I could use the overvoltage pin as an enable however, as I'm not
    worried about an overvoltage condition occuring.

    -Michael
    Michael, Jul 16, 2008
    #3
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