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BQ25890H: Bug or feature? Dropping Vbatt does not lower charge current

Eric Steimle
Expert 2290 points
Part Number: BQ25890H

According to the datasheet the pre-charge current of the BQ25890H should be 128mA when the battery voltage is between 2V - 3V.  If I apply 3.1V I see the charge current is about 2.05A.  If I then lower the battery voltage, even all the way down to 2.5V, the charge current continues to be 2.05A.  

Now if I disconnect and reconnect the USB input source the charge current comes up as less than 128mA.  It's only when I go down in voltage that I see this issue.  I feel like you could hit this condition in real life if you were supplementing Vsys with the battery and the battery was slowly draining.

Is this a bug or expected behavior? 

Thank you

  • 0
    TI__Guru 57541 points
    Did you test on the official bq25890H EVM? Where do you measure the battery voltage? Thanks!
  • 0 in reply to Ning T
    Expert 2290 points

    No this our board, but the schematics at least were checked and blessed by TI.  For the most part charging seems to be working, it’s just this corner case.  The voltage was checked at the bat1/bat2 pins.  If I remove and then reapply USB power it goes back to < 128mA so it’s reading the voltage OK.  It’s just when you lower the voltage that it appears the internal state machine does not switch to the lower current.

  • 0 in reply to Eric Steimle
    TI__Guru**** 166176 points
    Hi Eric,

    I just tested a bq25890H on the bench and found that if I lower the battery simulator voltage so that V(BAT pins) < ~2.8V, the charge current transitions from fast charge (~2A) to precharge. Because my connection from the battery simulator to battery was a bit resistive, I had to lower the voltage from the battery simulator to 2.4V in order for the voltage at BAT pin to drop below 2.8V.
  • 0 in reply to Jeff F
    Expert 2290 points

    Interesting, okay I'm also using a battery simulator (keysight).  I'll re-run the experiment tomorrow and make sure to check the voltage right at the pins.