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BQ25898: bq25898 / Behavior at system shorted during charging operation

S.Satoshi
Guru 21685 points
Part Number: BQ25898

Hi,

Please let me ask the behavior at system shorted during charging operation. Is my following understanding correct?

  1. System short condition is happened during charging
  2. Input current is increased and trip to input current limit
  3. Operation move from charging to supplement mode, and then discharge battery current reach to IBAT(FET_OCP)
  4. System Overcurrent Protection is worked and the device latches off BATFET

Best Regards,

Satoshi / Japan Disty

  • 0
    TI__Guru**** 167086 points
    Satoshi-san,

    There is another action if the battery drops below 2.0V.

    The battery is charged with IBATSHORT (typically 100 mA) current when the VBAT < VSHORT (2.0Vtypical), or precharge current as set in IPRECHG register when the battery voltage is between VSHORT and VBATLOWV.

    The feedback loops, like input current limit, are much slower than comparators like VSHORT so input current limit may not respond.
  • 0 in reply to Jeff F
    Guru 21685 points
    Hi Jeff,

    Thank you for your comment. But now I'm asking about the case of Vsys short, not battery short condition. You commented that the the input current limit may not respond, then the converter stop the switching due to over current protection? Does bq25898 has over current protection by monitoring HS or LS FET?

    Best Regards,
    Satoshi / Japan Disty
  • 0 in reply to S.Satoshi
    TI__Guru**** 167086 points
    If battery is attached during a fast short on SYS, then the IC may enter supplement mode faster than the input current loop can respond and so it becomes a BAT short event. All of the bq25898 have cycle by cycle current limit protection using the LS FET.
  • 0 in reply to Jeff F
    Guru 21685 points
    Hi Jeff,

    Thank you. I understood.
    Regarding cycle by cycle current limit, I can't find its threshold in datasheet. Which parameter is threshold of cycle by cycle current limit?

    Best Regards,
    Satoshi
  • 0 in reply to S.Satoshi
    TI__Expert 8230 points
    Hello Satoshi-san,

    On the bq25898, the HSFET cycle by cycle protection is typically around 8.5A with a minimum of around 6.4A. Please note this is a not part of the datasheet spec.

    Thank you,
    Fernando
  • 0 in reply to Fernando Lopez
    Guru 21685 points

    Hi Fernando,

    Thank you for your response.

    1. Regarding current monitoring point, which is correct LSFET or HSFET? Because Jeff commented LSFET. Please let me know correct information.
    2. I think the cycle by cycle current protection is the important feature however why you don't describe it in datasheet? I can't read if bq25898 has cycle by cycle current limit protecton.

    Best Regards,

    Satoshi

  • 0 in reply to S.Satoshi
    TI__Expert 8230 points

    Hello Satoshi-san,

    The LSFET cycle by cycle spec is for OTG mode, this one is shown on the datasheet. The HSFET cycle-by-cycle I mentioned is used in buck mode, but we don't have a specification for it. The value I provided is based on experimental data hence why we don't show it on the datasheet.

    Thanks,