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BQ25886: Max current from SYS pin and behavior when one or both batteries are reversed

Todd Cottle
Prodigy 20 points
Part Number: BQ25886

I'm evaluating the BQ25886 for one of our applications.  A couple of questions

1.  What is the max current that I can draw from the sys pin?  I couldn't find this value on the datasheet

2.  My application will use 2 18650 batteries in series.  The batteries will be customer serviceable so there is a chance that one or both batteries will be inserted backwards.  How does the charger handle this condition?  

Thanks!

Todd

  • 0
    TI__Guru**** 165886 points

    Hi Todd,

    Regarding 1, as with any boost converter, max output current is a function of input power. It is best estimated using an efficiency power balance: eff=Pout/Pin = VSYS*(ISYS+IBAT)/(VBUS*IBUS).  The worst case efficiency from the datasheet efficiency is about 89% and maximum IBUS=3.0A if D+/D- pins detect DCP and ICO doesn't reduce the input current limit.  If a battery is present, the battery can supplement the system load up to 5A continuous and 9A for a 1us pulse.

    Regarding 2, the charger has no protection against batteries installed in reverse and will be damaged if that happens.

    Regards,

    Jeff

     

  • 0 in reply to Jeff F
    Prodigy 20 points

    Hi Jeff

    Thanks for the quick reply!  The 5A continuous (with disclaimers about the source) answer is what I was looking for

    Having the charger be damaged if one or more cells are reversed is a deal breaker on what otherwise looks like a perfect part.  Is there anything else in the TI catalog that can charge 2 batteries in series from a 5V USB adapter and can tolerate a reversed battery?

    Todd

  • 0 in reply to Todd Cottle
    TI__Guru**** 165886 points

    Hi Todd,

    Unfortunately, none of our chargers have integrated reverse battery connection.  I am not aware of a competitor who does either. 

    Regards,

    Jeff