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BQ25618:BQ25618 VSYS_OVP

Part Number: BQ25618
Other Parts Discussed in Thread: BQ25619

Hi TI team,

About the SYSOVP trigger threshold for different battery voltage conditions is as below:

1)In VSYSMIN regulation (VBAT<VSYSMIN), SYSOVP triggers typically at VSYSMIN+350mV.
2)Not in VSYSMIN regulation (VBAT>VSYSMIN), SYSOVP triggers typically at VBAT+350mV.

I have some question about the SYSOVP:

1).After trigger the SYSOVP, what is the recover SYS threshold for the different battery voltage conditions?

2).During CC/CV charge status, the BAFTET is fully-on.

(1) When the ISYS drops largely, and the SYS voltage will increase, and it will generate the large charge current flowing to battery. It has the damage risk for the battery. Right?

(2)Also due to the BATFET fully-on, the SYS voltage will be clamped to VBAT+ICHG*Rdson_BAT. So it will not trigger the SYSOVP. Right?

3). The SYSOVP could happen in which charge status? Pre-charge? CC? CV? Termination?

Thanks very much!

BR

Eleven

  • Hi Eleven:

    During SYSOVP, converter stops switching until the SYS voltage is below the threshold.

    If VBAT is higher than VSYS_MIN, BATFET is fully on but the current is monitored.

    (1) When the ISYS drops largely, and the SYS voltage will increase, and it will generate the large charge current flowing to battery. It has the damage risk for the battery. Right?

    No, the maximum current goes to battery is charge current.

    (2)Also due to the BATFET fully-on, the SYS voltage will be clamped to VBAT+ICHG*Rdson_BAT. So it will not trigger the SYSOVP. Right?

    SYSOVP will not be triggered in normal operation.

    3). The SYSOVP could happen in which charge status? Pre-charge? CC? CV? Termination?

     SYSOVP is for any case that SYS is running.

  • Hi Hong,

    Thanks very much for your reply.

    (1) What is the VSYS falling threshold to recover from the SYSOVP?

    (2) When VSYS increase, the BATFET will regulate ICHG by VGS_BATFET, right?

    If so, the BATFET will bear the high power loss(Big VDS). How to ensure the safety of the BATFET?

    (3) You say IC will regulate the battery charge current to ICHG, so VSYS should increase and possibly trigger SYSOVP.

     You mention that "SYSOVP will not be triggered in normal operation." How to understand?

    Thanks very much!

    BR

    Cheng

  • Please see my further comments below:

    (1) What is the VSYS falling threshold to recover from the SYSOVP?

    350mV + 350mV, no hysteresis

    (2) When VSYS increase, the BATFET will regulate ICHG by VGS_BATFET, right?

    If so, the BATFET will bear the high power loss(Big VDS). How to ensure the safety of the BATFET?

    System overshoot occurs only during transient.

    (3) You say IC will regulate the battery charge current to ICHG, so VSYS should increase and possibly trigger SYSOVP.

    In normal operation, VSYS follows battery voltage, so no SYSOVP.

     You mention that "SYSOVP will not be triggered in normal operation." How to understand?

    Please see datasheet application curves of Figure 10-5 to 10-8.

    Thanks very much!

  • Hi Hong,

    1). I don't think there is no hystersis. Please help confirm again.

    2). Yes, the VSYS overshoot only during transient. Bu it still should ensure the safety of the BATFET, right?

    3). I could understand there is no SYSOVP without SYS transient.

    My question is: During CC fast charge, the BATFET is fully-on. When SYS transients to trigger SYSOVP, the SYS voltage will be clamped to VBAT+ICHG*Rdson_BAT. So it will not trigger the SYSOVP. So there will no SYSOVP during CC fast charge even SYS transients. Please confirm this understanding is right or not?

    BR

    Eleven

  • 1. The hysterias is about 150mV.

    2). Yes, the VSYS overshoot only during transient. Bu it still should ensure the safety of the BATFET, right?

        Upon SYSOVP, converter stops switching immediately to clamp the overshoot. The charger provides 30 mA discharge current to bring down the system voltage. With the SYSOVP, BATFET is safe and devices on SYS are safe. Please refer to the application curves in the datasheet I indicated earlier.

    3) My question is: During CC fast charge, the BATFET is fully-on. When SYS transients to trigger SYSOVP, the SYS voltage will be clamped to VBAT+ICHG*Rdson_BAT. So it will not trigger the SYSOVP. So there will no SYSOVP during CC fast charge even SYS transients. Please confirm this understanding is right or not?

    Yes, correct.

  • Hi, do you have further questions?

  • Hi Hong,

    Thanks very much!

    I have another question: During supplement mode, the battery will discharge to system through BATFET. If the charger is always in supplement mode, and the battery voltage is lower than the battery depletion voltage threshold, what is the reation of the charger?

    Thanks very much!

    BR

    Cheng

  • Cheng:

    When battery voltage falls below the depletion voltage threshold, BATFET shuts off. However, battery pack circuit may have shut off the battery pack first.

  • Hi Hong,

    After the battery voltage falls below the depletion threshold, the BATFET will be disabled. At the same time, VBUS is still present.

    How to re-charge the battery again?

    Thanks!

    BR

  • Eleven:

    Once the load on SYS is removed, the battery will be charged. Supplement mode is allowed during transient, but if it is ruing for extended time, the battery will be over discharged.

  • Hi Hong,

    Due to the VBAT<VBAT_DPL_FALL, BATFET will latch-off. To recover from over-discharge latch-off, an input source plug-in is required at VAC/VBUS.(Refer page 28 in BQ25618/9 datasheet.)

    If based on the description, the charger will not chage the battery even if the VBUS is present.

    It should remove VBUS and plug-in again to recover, right?

    Thanks!

    BR

    Eleven

  • Eleven:

    You asked the same questions in different threads. To avoid duplicated work from support, I suggest you ask the same question in one place.

    When VBAT<VBAT_DPL, BATFET turns off, not latch off. However, once over load at SYS is removed, then charger will recover charge.

  • Hi Hong,

    8.3.9.4.2
    Battery Over-Discharge Protection
    When battery is discharged below VBAT_DPL_FALL, the BATFET will latch off to protect battery from over discharge.
    To recover from over-discharge latch-off, an input source plug-in is required at VAC/VBUS.

    Please refer to the description in BQ25619 datasheet: When battery is discharged below VBAT_DPL_FALL, the BATFET will latch off to protect battery from over discharge.

    So the description in datasheet is wrong?

    Thanks!

    BR

    Eleven

  • Hi Eleven,

    I believe the datasheet is talking about no VBUS case. With VBUS presents, the charge is always in charge mode.

    The battery is charged with ISHORT  when the VBAT < VSHORT, or precharge current as set in IPRECHG

    register when the battery voltage is between VSHORTZ and VBAT_LOWV.