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Original question:

BQ25886: Standalone 2 Li Ion Battery Charging through USB

BQ25886: Can I simply not use the SYS pin?

Chris Davidoff
Prodigy 220 points
Part Number: BQ25886
Other Parts Discussed in Thread: BQ40Z80,

Hello,

I have the schematic below..  I want to use the BQ25886 to simply charge my 2 cell Li-Ion battery pack.  I don't want it for anything else, I am already using a BQ40Z80 for a fuel gauge.

So my question is, can I ignore using the SYS pin?  I don't want my power path to run through the BQ25886 chip as I sometimes pull more current than it can handle.  The BQ40Z80 also handles turning off a CHG FET when it detects a full charge, so I don't even need the BQ25886 to stop the charging process because the BQ40Z80 will do that.  I'll attach the STAT pin, to a pin on my micro-controller in order to turn the rest of the system off while the device charges.

So, can I just leave the SYS pin floating?

Thank you for your time!!  It is much appreciated

  • 0
    TI__Mastermind 40845 points

    Dear Chris,

    You can leave the SYS pin floating, however the minimum capacitance of 44 uF is required. Please however note that SYS will have a voltage. Its voltage will follow the description in section 8.3.6 of the datasheet.

    In summary, when the battery is below the minimum system voltage, SYS will be 200 mV above SYSMIN. As the battery comes above MINSYS, the SYS voltage tracks slightly above the BAT voltage.

    Thanks,

    Mike Emanuel

    Please click "This resolved my issue" button if this post answers your question.

  • 0 in reply to Michael Emanuel35
    Prodigy 220 points

    Awesome!  This is exactly what I was hoping for.  Thank you very much!!