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BQ25890H: BQ25890H without battery attached

Lawrence May
Prodigy 130 points
Part Number: BQ25890H

Hi, I'm using the BQ25890H in a system with a replaceable battery.  I observe that Vsys seems to have a slow, high magnitude ripple when the charger is powered from USB, but the battery is disconnected.  I'm just starting to dig into it, but right now it seems like the NVDC charger is hunting from the minimium VSYS up to 4.2 + the dropout over a 10s of ms period.  Is this known/typical?  Are there settings I can modify in the BQ25890H to reduce/eliminate this?  Is operating the BQ25890H without a battery a supported mode of operation?

Thanks!

  • 0
    TI__Guru**** 165766 points
    Lawrence,

    The ripple is caused by the charger charging up the capacitor on BAT, thinking it is a battery, then letting that capacitor discharge to the recharge threshold then recharging. If you disable charging with either the /CE pin or bit, the ripple will go away and the output will regulate to MINSYS.
  • 0 in reply to Jeff F
    Prodigy 130 points
    Hi Jeff,

    That makes sense, I assumed it would be something similar but getting the answer from you like this was much more direct. Thanks for your reply, it was very helpful.