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Re: [Electronics_101] MAX712/713 charger

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  • paul thomas
    Hi Stefan, I know you are an, ‘elder member’ on this group, so pardon me in advance for the stupid comments. Concerning PCB layout, as this is a switcher
    Message 1 of 184 , Sep 4, 2004
      Hi Stefan,
      I know you are an, �elder member� on this group, so
      pardon me in advance for the stupid comments.
      Concerning PCB layout, as this is a switcher you must
      have a full ground plane for the board, the power
      rails should be low impedance at 6A, and should also
      be a plane. Concerning parts, the caps C5, and
      possibly C4, C1 should be low ESR type, and the 100uH
      coil should have self-resonance in terms of MHz as the
      switcher IC is in terms of 100KHz. The diodes
      (1N5820�s) should be mounted as close to the coil as
      possible.
      Lastly, most switchers will not work without a load,
      maybe adding a 10 Ohm 1w across the load will help
      debug the circuit.
      Hope this helps,
      Paul Thomas


      --- Stefan Trethan <stefan_trethan@...> wrote:

      >
      > hi everyone...
      >
      > I'm trying to build that charger using a max712 or
      > 713.
      > the datasheet is here:
      >
      <http://www.maxim-ic.com/quick_view2.cfm/qv_pk/1666>.
      >
      > I wanted to make
      >
      <http://www.maxim-ic.com/appnotes.cfm/appnote_number/86>
      > and made a pcb for exactly the shown circuit.
      > It didn't work and i tried to troubleshoot, but it
      > didn't work out.
      > Stupid really, assuming i can just build a appnote
      > circuit and take
      > operation for granted.
      >
      >
      > I decided to breadboard the "linear" mode then,
      > because it is simpler.
      > The circuit on page 1 of the datasheet is EXACTLY
      > what i built and checked
      > three times. it does not reach the current set by
      > the resistor.
      > The DRV (open souce) stays relatively high (10V @12V
      > supply).
      > The device is in fastarge mode.
      > i checked the voltage "sensed" over the resistor, it
      > is way lower than it
      > should be.
      >
      > I programmed the device for 1 cell and charge 1
      > cell.
      >
      > Any ideas what i can try? i have read others have
      > built the same circuit,
      > working.
      > I have tried other ICs but the same, none has had
      > any reason to get damged.
      > The V+ and REF regulators work fine.
      > What reasons could there be for it not reaching the
      > expected charge
      > current?
      >
      >
      > thanks
      >
      > ST
      >
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    • Stefan Trethan
      On Sat, 4 Sep 2004 12:44:57 -0700 (PDT), paul thomas ... I have put the power parts close together with very short tracks, but i have no
      Message 184 of 184 , Sep 4, 2004
        On Sat, 4 Sep 2004 12:44:57 -0700 (PDT), paul thomas <pbt1668@...>
        wrote:

        > Hi Stefan,
        > I know you are an, ‘elder member’ on this group, so
        > pardon me in advance for the stupid comments.
        > Concerning PCB layout, as this is a switcher you must
        > have a full ground plane for the board, the power
        > rails should be low impedance at 6A, and should also
        > be a plane. Concerning parts, the caps C5, and
        > possibly C4, C1 should be low ESR type, and the 100uH
        > coil should have self-resonance in terms of MHz as the
        > switcher IC is in terms of 100KHz. The diodes
        > (1N5820’s) should be mounted as close to the coil as
        > possible.
        > Lastly, most switchers will not work without a load,
        > maybe adding a 10 Ohm 1w across the load will help
        > debug the circuit.
        > Hope this helps,
        > Paul Thomas

        I have put the power parts close together with very short tracks, but i
        have no ground
        plane. I used power diodes out of other switching supplys.
        The switcher alone would work, but the max713 causes trouble.
        In the linear mode tried i finally got it to regulate the current.
        There was still a small 1Mhz oscillation but it seemed to work.
        As i would prefer a switcher i next tried the "switching mode" schematic
        on the last page of the datasheet. I thought if i can't stop the
        oscillations
        i will use it in a mode where the oscillations are wanted.
        It does not regulate well, and i don't know why so far.

        I must admit i'm a bit tired of it all, and i think maybe i should
        just make it linear and forget the switcher.
        I mean i can make a nice big heatsink in much less time than all this has
        taken
        already, and it isn't that much power....

        i'm building this charger because i want _reliable_ delta-u shutoff, and
        so far
        i can see none of that. If the charger isn't reliable then i can just as
        well continue
        to charge with constant current.

        thanks

        ST
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